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L’énergie dans le développement de la Nouvelle-Calédonie

 | 
Yves Le Bars
, 
Elsa Faugère
, 
Philippe Menanteau
, 
et al.

New energy production and storage technology

New technologies for consideration in New Caledonia

Texte intégral

TRADITIONAL AND ALTERNATIVE FUELS

1Chemically converting a fuel to produce electricity for the industry, housing, and service sectors requires two choices: the type of fuel and the combustion process itself. To adapt to changes in the market, the best systems must be flexible enough to use either traditional (gas, liquid or solid fossil hydrocarbons) or alternative fuels, while continuing to operate at full capacity (a change in demand for electricity must not impair the system’s energy efficiency). Note that the best use for liquid fuels is in the transport sector where they provide unmatched performance in terms of mass and volume.

The potential of traditional fossil fuels for New Caledonia

2For any given use, a fuel is selected based on its suitability, its price, its safety of use and in more recent years, its ability to produce the least amount of CO2 per converted kWh.

Natural gas is not feasible for use in New Caledonia

3Natural gas is composed primarily of methane (generally 95 %, but its content can vary between 70 and 100 %) and has an average low net calorific value (NCV) of 38.1 MJ/kg; i.e. 10.6 kWh/kg, depending on its composition and its origin. In 2005, it represented 23 % of the energy consumed worldwide. Of all the hydrocarbons, it emits the least amount of CO2 per kWh due to its emission factor (EF) of 201 g CO2/kWhth. The world has abundant reserves of natural gas, and it is widely used in industrialized countries.

4Natural gas is transported from producer countries to the end user by gas pipelines or in liquid form by boats (liquid natural gas tankers). However, for most islands, building a methane tanker terminal is costly and disrupts the ecosystem. In addition, we feel that the small quantities of gas likely to be imported would not be of sufficient benefit to New Caledonia. Floating systems, although probably better suited to New Caledonia, would have to operate in cyclone areas; therefore, we feel that they would be no more feasible.

Liquid hydrocarbons have a potentially higher price subject to fluctuations

5Liquid hydrocarbons represent 37 % of the energy consumed worldwide in 2005 and are used by the industrial, housing, service and transport sec-tors, which depend on it for 95 % of their needs. Their NCVs are the highest (39.9 MJ/kg for heavy fuel oil, i.e. 11.1 kWh/kg) and have an emission factor of 282 gCO2/kWhth for heavy fuel and 267 gCO2/kWh for kerosene. The transport sector will undoubtedly continue to use liquid fossil hydrocarbons as their primary source of fuel for a very long time, even with the introduction of biofuels. For industry, the high, fluctuating cost of liquid fuels and the competition for its use with the transport sector will gradually make it less economically attractive for long-term use.

Coal is the most available fuel

6Peat and lignite are brown coal; flaming coal, fat coal, (bituminous) and anthracite are hard coal. The heating value increases from browncoal to hardcoal, and the moisture, volatile materials, and ash content decreases. Coal’s NCV ranges between 15 and 27 MJ/kg (i.e. 4.16 to 7.5 kWh/kg) values according to its carbon, sulphur, hydrogen and moisture percentages. Lignite contains very little sulphur, but has a high moisture content. Coal has an emission factor of 364 gCO2/kWhth for lignite and 347 gCO2/kWhth for anthracite: it is the worst fuel in terms of GHG emissions, yet represents 24 % of the world’s primary energy. Its cost and ample reserves continue to make it the most competitive primary fuel for generating electricity.

Are alternative fuels right for New Caledonia?

Hydrogen

  • 1 Nm3 = standard metric cube, i.e. the volume occupied by gas in “normal temperature and pressure co (...)

7Hydrogen is the most abundant element in the universe and is found in large quantities in the stars and planets. On Earth, hydrogen is the main component of all living matter due to the fact that it is present and combined with carbon in all organic compounds. Its NCV is 10.7 MJ/Nm31 (i.e. 2.98 kWh/Nm3) and its EF is zero since combustion products consist primarily of water with 0 % CO2. During its combustion, precautions must be taken to limit the formation of pollutants such as thermal nitrogen oxides, and the oxidation of substances remaining from its manufacturing process.

8However, to produce hydrogen, several procedures are used that require more energy than can ever be recovered from its final conversion. The most widely used method today is methane, methanol, or ethanol reforming (or bio-methanol or bio-ethanol reforming); a procedure based on transforming fossil hydrocarbons while simultaneously producing CO2.

9The energy supply needed to produce hydrogen is lost when it is converted into another type of energy, which is why hydrogen is considered to be an energy vector and not a source. Using hydrolysis to produce hydrogen during periods of excess electrical power production can be seen as a form of energy storage.

10The traditional method is to store and transport this gas in bottles under a pressure of 700 bars. The danger of a collision, at least in the medium term, prevents the use of gaseous hydrogen in automobiles. For now, there are only experimental prototypes of vehicles with combustible batteries or a hydrogen engine, which are still being tested. Other technologies involve hydrogen adsorption on metal hydrides (magnesium hydride) or in carbon nanotubes; however, these technologies did not yield the expected results. Finally, research still continues on hybrid reservoirs, high pressure, and hydrogen-absorbing barriers to reduce leaks.

11The development of a hydrogen system (including production, distribution, and storage) does not seem suited to conditions in New Caledonia.

Landfill gas and treatment plant sludge

12Biogas consists primarily of methane (between 50 and 90 %) and carbon dioxide (10 to 40 %), with variable quantities of water, and hydrogen sulphide (H2S) from 0 to 0.1 %. Its NCV (9.42 x 0.7 = 6.59 kWh/m3 for biogas with 70 % methane, at 15 °C in atmospheric pressure) only comes from methane and is based on the dilution rate in CO2. Its productivity is estimated between 0.15 to 0.30 m3 of biogas per m3 of digester and per day.

13Thus, biogas is the renewable form of natural gas. Recovering biogas produced by landfills is particularly beneficial given that methane is a powerful greenhouse gas (recovering it forms a greenhouse gas sink, it should be mandatory). To use biogas in an engine or boiler, the gas must first be dehydrated to curb corrosion caused by the halogenated compounds that it contains.

14In New Caledonia, several thousand m3/h of methane could undoubtedly be recovered and used from large landfills (1 m3 of methane equals 1 litre of gas!) because a waste burial site recovers an average of 100 m3 of methane per ton of treated waste. Improved waste energy management would give New Caledonia an eco-friendly image and provide it with an improved energy supply.

15Which waste can be methanised? Animal and plant waste – crop and silage residue, dairy runoff, food waste, lawn clippings, and so on. Also note that pooling all livestock waste into one cattle waste digester in New Caledonia seems difficult because the cattle are raised on ranches. Waste from the agri-food industry can also be methanised, as well as the bottom of lakes and ponds.

16Methanising urban or industrial sludge from treatment plants can eliminate liquid organic compounds and make the plant relatively energy-independent. An average facility produces approximately 40 g more of dry matter per day and per inhabitant. Their quantity is reduced 35 % and one ton of this waste generates up to 175 m3 of biogas; i.e. the energy equivalent of 190 litres of gas. Sludge is usually put into a landfill or recycled through manuring or composting, when it is authorized; however, it could also be digested by anaerobic bacteria to produce biogas and the digestor’s sludge then spread over soil (after being composted).

17Biogas provides an eco-friendly energy solution to the problem of treating organic waste. It is also a biofuel with numerous advantages for reducing greenhouse gas emissions and replacing other exogenic energy sources (fossil and nuclear). After CO2 is separated from biogas, its uses are identical to those of methane. The combustion of biogas from methanisation reduces the emission of GHG twenty times more than gas from fermentation.

First and second-generation biofuels

18Over the last few years there has been extensive growth in the biofuel market throughout the world. To strengthen this trend, the European Council has set a 10 % binding minimum target for biofuels in the total consumption of gas and diesel fuel in the European Union from now until 2020. A first generation of biofuels is already being used, but their energy efficiencies are controversial and they are competing with food uses. A second generation based on energy from wood waste is being studied for future generations.

19The January 2008 publication of the ENR [renewable energy] directive maintains the objective of incorporating 10 % biofuels into the fuel pool between now and 2020. It introduces several criteria for qualifying the sustainability of biofuels. They must reduce greenhouse gas emissions by at least 35 % compared to the equivalent fossil fuels and not be produced from land with high biodiversity value or land with high carbon stock (in other words, wetlands or continuously forested areas).

20These relatively strict criteria demonstrate the need for sustainable biofuel development before considering the substantial cost reduction provided by fossil fuels and CO2 emissions. However, before beginning their production, a continuous biomass supply system must be established including planting, cultivation, harvesting, conditioning, transporting and preparing the biomass resource, knowing that all of this involves large volumes of biomass.

21Environmental impact indicators must also be taken into account. The agricultural phase of biofuels can produce nitrate leaks and phytosanitary products in the soil, and nitrogen oxide emissions in the air; the industrial phase produces hexane emissions during seed crushing; and finally, combustion emits nitrogen oxide, CO, particles, and unburnt hydrocarbons. Other studies show that, overall, using biofuel can increase NOx emissions, but reduce CO and particle emissions. Numerous studies are currently being conducted to quantify the energy, ecological, and economic returns of bio-fuels through the use of life cycle analyses (LCA).

22Finally, we must consider the competing uses between farm land used for food production and land used to produce biofuel: the energy demand of industrialized countries must not deprive the other half of the planet of food.

First-generation biofuels

23Already on the market and produced through mature technology, firstgeneration biofuels use only a portion of a plant by recycling either its starch or its seed oil. Two traditional systems are currently being used: the ethanol system that produces biogasoline (ethyl tert-butyl ether, ETBE) and the diesel fuel system that produces diesel engine fuel from vegetable oil (vegetable oil ethyl ester, VOEE).

24Producing bioethanol from cereal or starch crops to make biofuels (ETBE) is technically feasible in New Caledonia as long as there are enough agricultural resources available. Bioethanol production units with a volume of 6 m3 are available on the market at modest prices (scale of a large agricultural operation or a town). The bioethanol that is produced can be mixed directly with gasoline in proportions up to 20 % without having to adjust engine settings. For an ethanol percentage of 85 % (called E85 in Europe) the vehicle must be equipped with a FlexFioul-Ethanol system and the country must deploy a distribution system for this biofuel. Also note that there are processes for recycling effluents and coproducts from ethanol production.

25After purification, straight vegetable oils (SVO) are sometimes used as fuel for diesel engines; however; they cannot meet the technology and performance requirements of new engines. Today, straight vegetable oils are converted through transesterification with alcohol (generally methanol) to produce methyl ester (vegetable oil methyl esters, VOME). This can then be used in all diesel engines by either mixing it with diesel fuel in any concentration or in its pure form, which can reduce the consumption of fossil fuels.

26Soybean oil is the most widely produced vegetable oil in the world, followed by palm oil; next comes rapeseed oil, sunflower, peanut, coconut (copra) and olive. There are three steps to producing straight vegetable oils (SVO): crushing, extracting and refining. This produces edible oil. The amount of energy consumed to reach the refining stage is 150 MJ in steam and 10kWh of electricity.

27When used in an engine, the high viscosity of these SVOs affects atomization, their low volatility increases combustion time and carbon build up on the engine walls, and they freeze in the cold – all which can damage a diesel engine. It must also be pointed out that they are diluted in lubricating oil, which wears out the engine quicker. If such oils were able to be used directly in tractors or generator sets, their use in modern engines would become increasingly essential.

28Using VOEEs (vegetable oil ethyl esters) directly in diesel engines does not have the same drawbacks as using SVOs. These esters even provide better lubrication to diesel fuels with low sulphur content. They can be mixed with diesel fuel, but their heating value is slightly low leading to 7 % more consumption. Their environmental impact is positive with an overall drop in CO and HC emissions, but an increase in NOx.

29These results show the potential for the production and use of biofuels in New Caledonia. Although there are several farmable crops on the island, copra may be the best choice because it has already been used; however, the system would need to be boosted. This system includes planting, cultivating (water, supplies), harvesting, converting the harvest into VOMEs, and using it locally. There is equipment for pre-processing oil and transesterification available on the market, its cost is reasonable (several thousand Euros), and it is easy to use.

30In conclusion, from a technical point of view, both ETBE and VOME systems could be easily used in New Caledonia. The equipment needed for both of them is affordable and easily suited to small productions.

Second-generation biofuels

31This type of fuel is still in the study phase with several objectives: to recycle the entire plant (seeds and stalks), to use wood and wood waste, and to evaluate their competition with food crops.

32Lignocellulosic biomass is derived from agricultural waste, forest residues, and wood processing by-products, as well as dedicated energy crops (woody or herbaceous plants). Converting wood generates a large quantity of residues that can be recycled as energy or raw material for pulping. The same goes for dry agricultural waste and forest residues, which also provide large amounts of lignocellulosic biomass. Dedicated energy crops provide a pool of lignocellulose that can be recycled for energy.

33Like first-generation fuels, there are two systems that can recycle these lignocellulosic resources: a thermochemical process (dry) and a biological process (wet).

34The thermochemical conversion of lignocellulosic biomass, called Biomass to Liquid (BTL), holds real challenges for the world by the year 2020. There are two main processes for producing energy renewable products: pyrolysis and gasification. Pyrolysis is a step in the homogenisation process and therefore, a step in pretreating biomass. It offers the double advantage of separating the production of biomass from its use (the production unit is installed near the resource) and directing the reaction towards liquid, solid or gas so that unwanted fractions can be recovered or concentrated into one of its phases.

35The technology is mature, but currently lacks markets. Oils produced by pyrolysis can only be used in a few engines specially designed for generator sets and cannot be used in a gas turbine or automobile engine.

36The most promising process is the gasification of oils and/or vegetable carbon to produce synthetic gas, which is then converted into methanol or hydrocarbons by Fischer Tropsh synthesis. Gasification is a thermochemical process that converts solid fuel (coal, biomass) by reacting it with a gaseous reagent (oxygen, steam, hydrogen). Its objective is to convert the solid mate-rial into a gas mixture called a synthetic gas or “syngas”. This syngas can be used for different applications such as engine combustion, electricity/heat cogeneration with improved efficiency due to direct biomass combustion, and biofuel synthesis.

37Biofuel synthesis is the most beneficial because it recycles all of the components in lignocellulosic biomass into biofuels such as methanol, dimethyl ether (DME) or hydrocarbons produced by the Fischer Tropsch process (synthetic diesel or kerosene). However, this gasification process is still in the pilot stage and is benefited by scale effects, which is not to New Caledonia’s advantage.

38This leaves the biochemical process: while producing ethanol from the sucrose of sugar plants or starch from starchy plants is a mature process, the process for producing ethanol from lignocellulosic materials faces two hurdles – the hydrolysis of cellulose into fermentable sugars and converting pentose from hemicellulose into ethanol. Lignin cannot be fermented into ethanol; therefore, the lignocellulosic matrix must be pre-treated to make the cellulose and hemicellulose hydrolysable in order to produce potential sources of fermentable sugars. Finally, raw material processed in this fashion can be separated from the ethanol fermentation to produce ethanol that can be mixed with gas up to significant proportions of 85 %.

39Using lignocellulosic biomass to produce fuel ethanol provides a multitude of environmental advantages. Its CO2 footprint is better than sugar or starch crops and recycling waste from the entire plant does not compete with food crops. Processes have been designed, but a number of obstacles exist that require progress to be made in cellulose enzymology and yeast physiology. The future of this process depends primarily on the development of biotechnologies with the underlying development of genetically modified crops.

Transforming algae into energy

40During their evolution, photosynthetic microorganisms adapted to diverse environmental conditions. They are found almost everywhere in the world, in the oceans, in both fresh and salt water, and in every temperature, including extreme cold and heat. This acclimation to a wide variety of surroundings explains the broad taxonomic range of this group of photosynthetic organisms, which currently contains estimates of between 20,000 and 40,000 different species, and that is for microalgae and cyanobacteria (bluegreen algae) alone. However, this bio-resource remains largely underused, due in particular to the relatively recent interest of the scientific community in these microorganisms.

41Algae have the double advantage of being able to form CO2 sinks and be a source of fuel. While bacteria belong to the animal kingdom, microalgae and cyanobacteria are plant cells and thus based on the same concept of photosynthesis as higher plants. Consequently, they have the ability to grow in an entirely mineral or water-based medium. Light helps them grow by absorbing needed minerals and surrounding inorganic carbon.

Algae cultivation processes: photobioreactors (PBR)

42A photobioreactor refers to systems dedicated to photosynthetic microorganisms, and thus to microalgae. These systems are unique in that they require light energy as well normal cultivation conditions. Unlike the usual substrates added to a culture medium, these light sources are always outside of the culture. Photosynthetic (or phototrophic) microorganisms require large amounts of light energy; thus, the efficiency of reactors is severely limited because light is absorbed by the surface algae and cannot penetrate to cultivate algae in deeper water.

43The easiest design is to cultivate phototrophic microorganisms in an open basin (lagoons, raceways, curved canals, etc.). Today, a large portion of production comes from these extensive systems (5,000 to 6,000 tons per year of dry material). By using the right designs, it is possible to obtain optimal photosynthetic conversion of light energy into biomass. In addition, 100 tons/ ha/year of dry material can be produced with a system that directly captures solar energy.

44Compared to higher plants, microalgae have intrinsic capabilities that make them highly useful in a number of applications. Their primary advantages are their fast growth rate (doubling a population in a few hours), their broad diversity (due to their long evolutions: 3.7 billion years), and their metabolic plasticity. This plasticity makes it possible, under the right conditions, to force the microorganism to produce a given metabolite.

45Microalgae and cyanobacteria can synthesize most basic organic elements such as proteins, sugars, and lipids, and have a more varied biochemistry than other microorganisms. Moreover, the identification of particular metabolites strongly encouraged research, particularly on indus-trial molecules such as pigments, polysaccharides, and various biologically active components. This research uncovered possible applications in areas as diverse as food, pharmacology, and cosmetology. Selecting the right strain and culturing them in the appropriate systems should help meet major challenges in agri-food, energy production, waste cleanup, and water recycling.

46Depending on space and applied conditions, hydrogen can be produced through biophotolysis of water, plant biomass rich in lipids for energy (biodiesel) or sugars used to produce methane. Hydrogen can also be produced by gasification or fermentation. In addition, photosynthetic growth requires a supply of inorganic carbon (CO2 sinks), and working with a waterbased culture improves control over mineral salt intakes. Because of all these advantages, photosynthetic microorganisms are often considered to be the renewable and eco-friendly bioenergy source of the future.

Algae as carbon sinks

47To reach optimal efficiency, algae need CO2 in large quantities in basins or bioreactors. Bioreactors must be coupled with traditional thermal power plants that produce electricity and release CO2 with an average concentration of 13 %. The CO2 is put into basins to bubble and is assimilated by the algae. This technology can increase photosynthesis efficiency and treat wastewater. In this sense, it is an advance in the environment field.

48For example, the Prony plant includes two 40-MWelectric units, i.e. 240MWthermal, and releases 4,500 tons of CO2/day. Assuming that we could have the current, solar PBRs, a surface of 2.5*4500 = 11250ha and a volume of 11.106 m3, would be needed to absorb the CO2 produced; i.e. an algae mass produced from 5,625 tons for an incident flux of 100 W/m2. If research can develop PBRs with internal light distribution to achieve maximum thermodynamic efficiency, the algae mass formed would remain at approximately 5,400 tons/day. To reach this optimal efficiency, you would still have to provide enough energy to filter 360,000 m3 of water per day!

49You can also refer to the paragraph titled “Biological separation of CO2 by algae and enzymes” in “Emissions and the reduction of greenhouse gas emissions in New Caledonia.”

Algae source of triglycerides

50These microorganisms also have advantages over land-based oilseed species: They can accumulate up to 50 % of their dry weight in fatty acids, which can produce 30 times the efficiency per hectare than land-based oilseed species. Large-scale greenhouse algae cultivation does not require phytosanitary products and can help manage the nitrogen and phosphorus cycle by controlling nutrient recycling.

51Using the Prony plant example: capturing two units could produce 6,300 tons of dry material per day; i.e. 4,400 tons/fatty acids per day (~70 % triglyceride). Transesterification of these oils would provide approximately 4,400 tons of biodiesel / day. In other words, ten days of production per day would be enough to cover diesel consumption in New Caledonia! Do not forget that this would require an optimized reactor (currently theoretical), power for pumping, validated processes on test models, etc. This involves research and, a fortiori, a very long-term deployment (algae are sometimes referred to as third-generation biofuels).

Algae for producing biohydrogen

52From a renewable energy perspective, there is no doubt that hydrogen should be promoted as a new energy vector. New applications will be found in the residential and transportation sectors via the transformation of hydrogen into electricity and heat in combustible batteries or combined cycle gas turbines.

53Green single-cell algae, microalgae, and bacteria are able to produce hydrogen from solar and energy and water because they all contain the enzyme, hydrogenase, which is the catalyst for these processes. Thus, natural hydrogen production processes can be harnessed to create hydrogen photo-bioproduction processes that do not generate greenhouse gases. Here again however, the processes are not mature and require significant improvements before being implemented.

ELECTRICITY PRODUCTION TECHNOLOGY

54Electricity is a form of energy that is very easy to convert and control, but often costs more both economically and environmentally. This is why, as we point out again, managing its consumption takes priority over developing new production methods.

55Note that if we take a look at the recent changes in the development of new power plants, those that use renewable resources (primarily photovoltaic and wind) have related growth records.

Combustion and conversion processes

56There are several technologies that can produce electricity: for example, the photoelectric effect that converts photons from light, the thermoelectric effect that converts heat, and conversion by electron transfer during a chemical or mechanical reaction through a generator or alternator. Electron transfer is currently the most widely-used process by thermal and nuclear power plants.

57A thermal power plant produces electricity using heat from the combustion of a gas or liquid hydrocarbon, coal, biomass, or industrial or household waste. The heat released during combustion heats up a fluid, generally water, which then turns from liquid into steam. This runs a turbine coupled to an alternator on a thermodynamic cycle, which in turn transforms mechanical energy into electric power. To power the steam turbine, the pressure is dropped between its inlet and exhaust by using a cold source to condense the fluid downstream into a gas. The condensed fluid is usually reused as a steam source (Rankine cycle).

Gas turbines (GT) or combustion turbines

58A gas turbine, (GT) (or combustion turbine) is a thermodynamic rotating machine belonging to the internal combustion engine family. Its role is to produce mechanical energy from energy contained in hydrocarbon and to transfer it to a generator or alternator.

59The theoretical efficiency of a GT increases with the compression rate and combustion temperature. Low efficiency (25 to 35 %) is due to the fact that energy supplied by the fuel is diverted by the compressor or lost as heat in the exhaust gas. Efficiency is improved by increasing the temperature in the combustion chamber (above 1,200 °C); however, problems occur in maintaining the temperature of the materials used to make the turbine part. Cooling systems with multiple perforations are set up in the chamber’s walls along with blades made from nickel-based heat resistant alloys.

Combined cycle gas turbines (GT)

60The expression “combined cycle” describes an energy production process or power plant that uses more than a thermodynamic cycle. Gas turbines convert part of the energy provided by combustion into effective work, which is then converted into electricity through a generator or alternator. Efficiency is usually from 25 to 30 %. Recovering the heat from exhaust gas can increase the machine’s overall efficiency by more than 50 %. To do this, exhaust gas heat (more than 600 degrees) is used to produce steam in a boiler that feeds a steam turbine, which in turn powers a second electric generator. Turbine efficiency can also be increased by reheating the gas at the end of the compression phase (before the combustion chambers) by running it through a heat exchanger located in the heat exhaust system.

Conventional thermal power plants

61Conventional thermal power plants stabilize combustion in a boiler using yellow flame burners. Gas, liquid, or solid fuel jets are injected into the burner tip near the air or oxygen jets. Combustion is stabilized in the fuel/oxidizer mixing zone. This process is safe because no reagent mixtures are formed before the combustion chamber; however, it does not provide enough control over the reaction zone or formation of pollutants. In any case, this type of power plant is the most popular throughout the world and provides high-power units.

Fixed-bed, fluidized-bed and circulating fixed bed (CFB) boilers

62Fixed-bed boilers establish combustion within a layer of combustible particles that remain stationary when fluid (oxidizing agent: air, oxygen) flows through it and reacts within the bed. Fluidized-bed reactors are made up of a group of solid particles (coal or biomass) that are passed upward through a fluid whose force on the solids is enough to balance their weight. Once a certain flow rate is surpassed the bed moves. The solid can be separated from the fluid in the column head by cyclone and recycled in the base: the circulating fluidized bed (CFB) remains relatively dense with many gas-solid interactions.

63This is the type of boiler that the SLN plans to use for the new plant in Doniambo (see in “Energy management: a major challenge to the sustainable development of New Caledonia and its energy security”, paragraph on “Key advantages of energy efficiency on the SLN site”, in which we describe the advantages of a circulating fluidized bed).

Super and heavy duty boilers

64To improve the efficiency of a system’s thermodynamic cycle, which can increase from approximately 35 % to nearly 50 %, the steam must be brought to a high temperature and high pressure in the boiler. This will mean working with water in supercritical conditions (Tc=376 °C and Pc=221 bar) or even hypercritical conditions (Tc=700-720 °C and Pc=350 bar). To do this, the piping and steam turbine must be made with a nickel-based alloy. The cost of such facilities is therefore very high and is only suited to power units higher than 400 MWelectric.

Cogeneration and trigeneration

65To increase the overall energy efficiency of electricity production, byproduct heat from the boiler or GT is recycled by distributing steam or heat through industrial or domestic systems: this is called electricity/heat cogeneration or even electricity/heat/cold trigeneration.

IGCC plants (Integrated Gasification Combined Cycle)

66An integrated gasification combined cycle – or IGCC - unit is a thermal power plant that operates on synthetic gas, or syngas. This gas is often used to operate a gas turbine, and the effluent heat from the gas turbine is then recycled by a steam turbine (combined cycle GT). IGCC technology uses a gasification process to convert coal or biomass into synthetic gas made up of a mixture of CO and hydrogen. Fuel impurities are thus removed before the combustion phase, which results in lower emissions of pollutants such as sulphur dioxide, particles and metals. Overall efficiency is also improved compared to a traditional, pulverized coal unit.

67This type of IGCC process is called “integrated” because the synthetic gases are produced by a gasification unit that is optimized by a combined cycle. To improve the overall efficiency of the process, the heat coming from the exhaust gas of the GT and gasification reactor are reused by a boiler and a steam turbine, which in turn produce additional electricity. Gasification and hydrogen combustion turn this system into a process with a small ecological footprint and optimized energy efficiency through the use of a combined cycle.

Internal combustion engines

68Electricity can also be produced on a remote site or with generator sets if the system is down. These generators consist of an engine similar to a car engine, coupled to a generator or alternator. The overall efficiency is rather low. However, this system performs better with the combustion of biogas from fermenters or landfills (moreover, this use can earn CO2 credits).

Conclusion: The potential application of these technologies in New Caledonia

69In principle, all of the industrial techniques for producing electricity by chemically converting energy are possible for New Caledonia. The selection criteria, as well as the technical restrictions for using these techniques include the power sought, fuel, biomass recycling, and combustion processes.

70Technological analysis indicates the best economic choices to use for New Caledonia:

  • A coal-fired power plant, cheapest to buy. However, this process releases SOx and NOx if it is not equipped with pollution control units. Using lignite reduces SOx emissions, but tCO2/kWh emissions are higher and it does not work as well. This was the process chosen by the Prony plant.
  • A circulating fluidized-bed boiler system offers the best potential for New Caledonia. This system was selected for future plants in Doniambo and Koniambo.

Hydroelectric stations

71The technologies for producing electricity from hydraulic resources are relatively mature, and although we cannot describe them as new, we propose a brief overview, particularly to highlight recent developments. In France, stations that generate between 2 and 10 MW of electricity are referred to as small hydroelectric stations, stations generating between 500 kW to 2 MW are mini-stations, stations generating 20 to 500 kW are micro-stations, and stations producing less than 20 kW are pico-stations. For factories along rivers and other waterways, the productivity of hydroelectric stations depends directly on the water flow rate; the same is true, but to a lesser extent, when there is a retaining dam providing enough storage capacity to better meet demand and stabilize the system. The Yaté dam, which uses an artificial lake, provides storage capacity of more than 300 million m3 and a large quantity of stored energy (approximately 100 GWh, i.e 5 % of the annual consumption in 2008). It has 68 MW (4 groups) of electrical power with an annual productivity of approximately 5,000 hours (+/-20 % based on the years) at full power. Let us also point out that a hydroelectric system can power a micro-network (isolated site), usually without using electrochemical energy storage, if the water flow is sufficiently steady. There are different control systems for stabilizing voltage and frequency in order to provide good service quality and reliability.

72Pelton, Francis and Kaplan turbines are used for a wide range of heads and flows. For smaller plants there are a few special technologies such as the Banki turbine (paddle wheels). Conversion efficiencies are very high (generally higher than 90 %), particularly since the nominal wattages are high. High-power electric generators (more than a few MW) are almost exclusively synchronous type generators with excitation coils that control the field current, which in turn controls voltage. Cage induction generators are used for grid-connected units with powers lower than a few megawatts; these generators can help control costs, but cannot control voltage. The more compact, permanent magnet generators can reduce civil engineering costs, but still cannot control voltage. The introduction of variable speed, which can increase productivity with variable flow rates and head heights, as well as control voltage, is slow to be developed, but the technology exists.

Wind turbines

73Vergnet, SA is the only company that makes wind turbines designed for cyclone regions and difficult to access areas. Its turbines are collapsible and include a system of stays and an automatic winch that help protect them from being destroyed in case of a cyclone. In addition, they are light and easy to carry into remote areas, and do not require a crane.

74More than a hundred turbines like this are currently in use in New Caledonia, and each unit produces approximately 250 kW of power. The latest generation is significantly different; it has a nacelle that can go down the entire length of the tower: This is the model selected for the Yaté farm, which should begin operating between 2010 and 2012 with 35 units for an annual production of 60 GWh.

75The cost for installing these turbines is high, approximately 2.3 to 2.5 €/W; in other words, nearly double the cost of European installations. This additional cost is explained by the unique technology, the remote location of New Caledonia, and possibly the lack of competition. The only other manufacturer is Vestas, which from 1996 to 1999 installed twenty 225 kW turbines in Negandi. They were destroyed by Cyclone Erica in March 2003, and fifteen of them were replaced; however, it seems that Vestas no longer wants to be involved in building new wind farms in New Caledonia.

76The productivity of Vergnet turbines suffered a few setback seemingly related to insufficient maintenance. The creation of Vergnet Pacific and new pricing methods should resolve these temporary problems. With normal operation, the Vergnet turbines should produce approximately 1,600 to 1,900 hours per year depending on the sites and years; this means that a 1 MW wind turbine produces 1.6 and 1.9 GWh per year.

77Finally, note that there is definitely potential in offshore wind power; however, current technologies are not yet suited for cyclone areas. Nonetheless, keep in mind that testing has begun on off shore floating technologies, and in a few years, they could be useful because of their resilience in strong winds.

Wave-powered generators

78Generated by the wind blowing over the surface of the ocean, wave energy is an abundant resource that could satisfy a certain percentage of the world’s electricity consumption within a few decades. Gross wave power is measured in kilowatts per meter of wave front, with rough estimates between 10 and 100 kW/m (Cape Horn). However, the conversion efficiency of current recovery systems is low, with averages of approximately 10 % annually.

79Ocean floor depths also play an important role in the sense that more energy is lost in shallow depths. Thus, by the time a wave reaches the shore, it has usually lost a large amount of its energy potential.

80A wave field consists of multiple waves propagating in different directions. Random waves can be easily characterized with two measurements: crest-to-trough height (Hs) and a Tp period. These two parameters represent a random sea state based on a standard model of spectral energy distribution (Tp is thus the spectral peak period).

81Apart from the fact that waves undulate at low frequency and cause instant fluctuations in power, average wave power fluctuates considerably based on the state of the sea. Thus, recoverable power depends on the width of the captured wave and the efficiency of the conversion device. Wave-powered generators often have a behaviour relatively suited for one given type of wave, and even if an advanced control can optimize the extraction of power in various conditions, their output power characteristics are not really in proportion with Hs2.Tp (gross power from theoretical law).

82Wave-powered generators can be located on the shoreline, nearshore with depths less than 50 m for anchorage, or offshore.

83The cost of investing in wave-powered generators near maturity is currently estimated at a range of 1 to 3 €/W. Production costs, depending of course on technology and local conditions, could go from ten to thirty c€/kWh to a few c€/kWh within a few decades. They could also benefit from the development of offshore wind turbines, and in particular, infrastructures for transporting electricity on the ground.

84Below is a simple summary of the many devices that have been designed, patented and/or tested since the 1970s:

  • Wave-powered generators with wave breaking ramps: generators in this family were initially designed to harness the characteristics of coastal sites. One of these generators is the Wave Dragon floating system, which has a floating height that can be adjusted according to the wave’s characteristics. Seawater breaks over a ramp and is collected in a reservoir located behind it, where it is sent through a low-head turbine back into the sea. These systems offer the advantage of smoothing the power and providing relatively steady production that does not fluctuate with the rhythm of the waves.
  • Wave-powered generators with oscillating water columns: this is possibly the most widely used design; moreover, it mimics the natural “blowholes” found in rocky coasts where the air trapped in a cavity ebbs and flows with the waves. The systems are placed on coasts or on floating devices. Waves enter a submerged cavity and the free surface inside oscillates like a liquid piston. Air comes in and out of the hole through an output duct into the atmosphere. A turbine turning in the same direction, regardless of airflow direction, is placed in the duct. The turbine powers an alternator, which produces continual energy. Among non-floating systems are the Kvaerner column (Norway) and the European Pico pilot project, named after the Aççores Island in Portugal. There are also floating oscillating water column projects that can be used in a wider variety of sites, such as the Sperboy (UK).
  • Wave-motion generators This category groups together a broad range of concepts and systems, including Power Buoy (Ocean Power Technologies, Inc., United States), Searev (a wave energy converter project conducted by the École Centrale de Nantes), Ceto Cylindrical Energy Transfer Oscillator (Australian project from the Carnegie Corp. in which France’s EDF new energies is involved) and the Anaconda system from the English company, Checkmate. The most well-known device is the Pelamis, which resembles a long, curvy snake, and is currently one of the most mature wave-powered devices in the industrial sector.

85Its overall shape allows it to support a variety of waves and use their energy. It has the advantage of being able to smooth a naturally fluctuating energy. Its lifespan is approximately 20 years and its maximum electric power is 750 kW. Three P750 units were installed in 2008 5 km off the coasts of Portugal to form a 2.2 MW experimental wave-powered generator farm for a total of €8 M. In principle, a surface area of 1 km2 can pro-vide a production capacity of 8 to 30 MW. Just like off-shore wind farms, the units are organized into clusters and spaced approximately 150 m apart.

Photovoltaic (solar) generators

86Photovoltaic (PV) electricity is produced through the direct conversion of light into electricity. Because no mechanical movement is needed to generate solar power, highly reliable and quiet technologies can be developed, which are well-suited for use in buildings. Today, the market for producing PV through direct energy conversion (connected directly to systems without storage) is booming with high growth rates (more than 50 % annually).

87The most mature photovoltaic technologies are based on polycrystalline silicon and monocrystalline silicon (slightly better efficiency: approximately 17 %), as well as amorphous silicon (low cost and lower efficiency). More marginal technologies exist that can increase efficiency through multi-spectral cells, which broaden the sensitivity spectrum. The theoretical limits are approximately 86 % and the best current experiment results come within 37 % with a triple InGaP/GaAs/Ge structure. Thin-layer technologies, such as copper indium selenide (CIS)-based technology and organic materials, can provide better cost performances, but they are slow to emerge and/or still have insufficient life spans (in the case of organic materials). Finally, there are concentration structures whose performances are improved with high intensity radiation, but they require concentrating systems that are high in cost and low in reliability (soiling).

88Photovoltaic electricity production is significantly proportional to solar radiation intensity and is sensitive to temperature; this is why it is best to provide naturally ventilated panels, particularly on the back surface. PV production fluctuates directly with the natural variations in sunlight. Mass production of grid-tied PV systems would face the same difficulties as wind power, requiring new grid management methods, as well as the development of storage systems.

89In New Caledonia, annual PV productivity is approximately 1,500 hours at full power, which reduces production costs for this electricity compared to less sunny regions, such as Northern Europe.

Concentrated solar power plants (CSP)

90Concentrated solar power plants use direct sunlight; thus, it is important to make sure that there is enough sunlight to make these processes economically feasible. The accepted feasibility threshold is 800 kWh/m2/year. There are different concentrated solar power technologies:

  • Solar towers: two-way adjustable mirrors focus sunlight towards a tower where it heats up a heat transfer medium (molten salts) to produce steam. The steam is then put through a turbine and produces electricity with a classic alternator. Being able to store heat makes it possible to smooth the effects of cloudy intervals, as well as day/night alternations, and to better optimize the steam turbine’s design.
  • Parabolic troughs This technology uses mirrors shaped like troughs with one axis of rotation. The troughs direct the sunlight into a tube containing a heat transfer fluid positioned along the focal line of the trough. It then operates just like a solar tower. This technology has been in use since the 1980s in California (Mojave Desert) and other projects are planned throughout the world.
  • Linear Fresnel systems: this shares the same concept as the previous systems, but has flat mirrors positioned to reflect sunlight into a tube at a lower cost and slightly lower efficiency (needs more space).
  • Parabolic mirror units direct sunlight to the heat source of a Stirling engine (operates without combustion). This technology, which is apparently more expensive than the previous technology described, was already evaluated and proposed for New Caledonia in 2002 by the Australian company Solar Systems Corp2.

Ocean Thermal Energy Converters (OTEC)

91Oceans and seas are a large collector of solar radiation that stores and transfers huge quantities of heat, significantly affecting the planet’s thermal balance. It is likely that a part of this energy reservoir could be harnessed in areas where the difference in temperatures is significant enough to operate thermodynamic engines at the best cost. Sufficient thermal gradients are near the equator or in the tropics, and although the conditions are not exceptional, New Caledonia’s thermal gradient is adequate.

92The gross solar energy power captured annually by the oceans is enormous, approximately 400,000 TWh, yet only a small portion is accessible. However, it is of vital importance that we do not overuse this natural cycle, which plays a crucial role in climate stability. Given the overall flow rate of all deep, cold water currents, along with the fact that the envisioned thermodynamic engines require a very high cold water flow, and the weak conversion efficiency (mainly due to the small temperature difference between warm and cold sources), we expect a maximum global renewable energy potential of 80,000 TWh.

93Among the projects proposed are the OTEC (Ocean Thermal Energy Converter) in Hawaii, which has been in operation since 1979 and produces 18 kW of electricity for 8,000 hours per year, based on maintenance stops. OTEC systems work on the following principle: warm seawater (surface water temperature: 26 to 30°) is used to evaporate the working fluid; the expanding fluid turns the turbine; the vapour is then condensed by cold water pumped into the machine from the deep sea. Therefore, water needs to be pumped from depths of approximately 800 to 1,000 m to get the largest temperature difference possible without pending an excessive amount of energy for pumping.

94In addition, there must be ample flows of warm and cold water of approximately 2 to 3 m3/s par MWe. Related pumping losses (both warm and cold water) are even lower than head losses because there is less runoff in the pipes. Therefore, it is important to have a large enough pipe diameter, particularly for the long cold water pipelines. The result of all of this is a net electricity production efficiency of approximately 2.5 % to 3 %. Until now, one of the major drawbacks in developing OTEC technologies, apart from their lack of maturity and technical difficulties (such as the resistance of long pipes), is the cost of investment, which remains very high (4 to 12 €/W for 100-MW units, based on the distance from the coast).

95OTEC systems can be built on the coast; this would make it easier to transport electricity, but increase the cost of pumping because it would require longer pipelines, particularly cold water pipes. This proves to be technically impossible if the depth does not decrease fast enough near the coast. In other cases, the conversion facility must be built on a barge.

Extracting kinetic tidal energy

96Tidal energy can be extracted from the variation in sea level height and can be exploited via a barrage or by directly harnessing currents through turbines placed in tidal streams, like underwater wind turbines (also called underwater generators). One of the advantages of tides is their predictability, which makes it easier to plan and add such production systems to power grids. With dam systems, the storage effect in upstream and downstream basins can be used to store energy by pumping in the advantageous phases of the cycle.

97The method for capturing tidal flows is similar to that of a wind generator, except that the direction of the current is steady, their direction alternates (tidal effect) or is continuous, and the turbines are found in salt water (this technology has already been proven in fresh water, particularly in Amazon Rivers). Thus there are two major turbine families, vertical and horizontal axis crossflow, as well as other more original technologies such as systems that use oscillating hydrofoils (Stingray System from Engineering Business Ltd), and “paddle wheel” type floating systems (French Hydrogen project).

98With the exception of a few Gulf Stream energy extraction projects, most current projects involve tidal currents. Low-power submerged generators can be floating and placed beneath a barge. This makes it easier to manage changes in water level due to the tides themselves and see to it that the generators always remain near the surface. Generators can also be suspended from a floating buoy, like those offered by the SMD Hydrovision company or Ponte de Archimede with its vertical-axis Kobold turbine. This method is already used in rivers. Hydrogenerators can also be placed on the seabed using a gravity foundation or mounted on a metal monopile. The type of supporting structure selected is dictated by the depth and nature of the seabed. Finally, prototypes and systems in the pre-industrial stage can generate anywhere from a few dozen to a few hundred kW.

Electronuclear production3

  • 3 With the support of Franck Carre (CEA/DEN/DDIN), from the department of nuclear innovation and dev (...)

99In an electrical network, it is strongly suggested that the maximum unit power supply remains 10 % lower than the total power installed in order to be able to compensate for a malfunctioning unit when the voltage and frequency are stable. Based on a total power capacity of approximately 500 MWe (maybe slightly more from now until 2015 if new factories are built, like in Koniambo), this would provide a maximum power capacity of approximately 50 MWe, which is significantly below what exists today on the reactor market and probably even below what will be developed in the years to come. Note that “small” units of this type would solve the problem of production interruption through metal production processes that must not be interrupted.

100Moreover, Areva does not have a reactor project with power less than 1,000 MWe and resorting to a Russian offer (in the range of 40 to 300 MWe) would raise certification problems. The same goes for an American-Japanese or Chinese offer in the range of 300 MWe, if this power level could be considered.

101Given new Caledonia’s modest electricity requirements, as well as its need to invest in specific industrial infrastructures, the cost of a nuclear option cannot compete with the cost of gas, goal, or fuel oil plants, regardless of New Caledonia’s remote location (probably > 5,000 €/kWe for the investment only).

102In addition, supplying fuel for the reactor and recovering spent fuel for reprocessing in France, (or even Japan if there is an agreement) would require secure transportation over long distances.

103In summary, the unfavourable technical and economic considerations, complicated further by the demand for a cumbersome administrative procedure for creating a nuclear site, leads us to believe that given the current information – and without even addressing the political and social aspects – we can exclude the nuclear option as a way to provide energy to New Caledonia in the decades to come.

Fuel cells and hydrogen

104Fuel cells are electric power converters that can convert the hydrogen / oxygen oxidation-reduction reaction into electricity and water with excellent efficiency, unrestricted by the second principle of thermodynamics (Carnot efficiency). Typical efficiency for a fuel cell is approximately 50 % at nominal wattage; it can be higher, but it would be over-dimensioned and overpriced. Thus, a fuel cell produces electricity, heat, and water.

105Hydrogen, which is the fuel for this reaction, is not easily available in nature; just like electricity, it must be converted from a primary resource. If this primary resource is a fossil fuel, the overall conversion rate is generally poor; therefore, from the perspective of both life cycle efficiency and green-house gas emissions, hydrogen must be produced from renewable resources.

106Certain fuel cells, called direct fuel cells, can directly convert a carbon fuel such as methanol or methane, but the conversion produces greenhouse gas emissions. Therefore, it must be determined that the overall result, including fuel production, is advantageous, which is not always the case, for example, when the fuel is from non-renewable resources (natural gas for example) or certain biofuels.

107When using an electrolyser for production, electrolyis efficiencies are between 70 and 85 % Industrial electrolysers generally consume 4 to 6 kWh/Nm3 of electricity, and approximately 1 litre per Nm3 of water (the purest possible).

108Electrolyzing steam at very high temperatures can significantly reduce electrical power consumption. Finally, some thermochemical processes can be used to extract hydrogen from water through a high-temperature heat source such as concentrated solar radiation.

109Even if commercial or semi-commercial products exist, their lifespan, restrictions for use and cost are still currently incompatible with stationary applications and ground transportation. This is why intense research programs are being conducted at all levels. The same applies for an electronuclear system. We do not think that New Caledonia should pursue the use of fuel cells as a way to convert energy in the medium term, particularly because there are other more promising and less risky alternatives.

Aluminium-air system4

  • 4 This paragraph answers a special request from the DIMENC and its content was written with the scie (...)

110If we think of aluminium as an energy carrier used for “consumption” in aluminium-air fuel cells, then we need to think about its lifecycle by calculating in particular the overall amount of primary energy needed to produce 1 kWh of electricity.

111With current manufacturing processes, producing aluminium itself consumes approximately 32 kWh of primary energy per kilogram of material for production from ore (because a part of aluminium cannot be recycled after consumption, we preferred to base our numbers on the primary resource and include recycling options). In an Al-air fuel cell (FC), 1 kg of aluminium can produce approximately 3 kWh of electricity, knowing that the maximum theoretical value is 4.8 kWh.

112The aluminium recycling procedure (aluminium trioxide) needs to eliminate traces of potassium and uses approximately 3 kW of electricity plus 5 to 6 kWh of thermal energy; i.e. approximately 15 kWh of primary energy based on current methods for producing electricity. Assuming that approximately 8 % of raw materials are lost during each recycling operation, the energy spent to produce to 1 kWh of electricity (0.3 kg of aluminium) can be estimated, excluding transportation costs, at approximately 17 kWh. The transportation of aluminium and alumina back and forth between the producing country should also be taken into account given that aluminium combustion cannot supply all of the energy needed for recycling.

113Without going too far, and even if a potential for improvement undoubtedly exists, these figures clearly do not support aluminium as an energy carrier for producing electricity. An energy efficiency of 1/17th will result in a prohibitive cost for this electricity compared to all of the other currently familiar production methods.

Power generating buildings

114A building (residential, service, and industrial) receives a significant amount of solar radiation, and even wind, and can satisfy, at least on an annual average, more than its own needs. This type of building is referred to as a positive energy building. Electricity is produced, which is then sent to the grid to which the building is tied. These aspects have already been laid out in the first part of the report. Rough estimates for potential solar energy production depend on the direction of the surfaces equipped with photovoltaic generators; the average rough estimate is 100 kWh/m2/year (see “Energy management: a major challenge to the sustainable development of New Caledonia and its energy security”, in which aspects related to producing energy in a building were discussed).

ENERGY STORAGE TECHNOLOGIES

Storing electricity

115Storing electrical energy can now be widely done on numerous portable electronic devices (computers, phones) and stationary devices (uninterruptable power systems (UPS): inverters, power supplies for remote sites produced by photovoltaic or wind power). Electrical energy storage is also used in the ground transportation sector to supply automobiles and electric two-wheelers.

116The best technologies for meeting these needs are almost exclusively electrochemical: these are batteries. Their essential quality is their mass, high-volume performances, which are better than any other existing electricity storage system, even if they sometimes still seem insufficient to us. The most common are:

  • Acid lead: Used in particular for stationary applications because they are heavy-duty (approximately 20 to 30 Wh/kg).
  • Nickel cadmium (NiCd): not long ago it was being used for mobile applications for the general public. It was banned because of the toxicity of non-recycled cadmium, but is still widely used for industrial trucks and trolleys in a professional, supervised sector. Its performances are higher than lead, approximately 40 Wh/kg, and can be charged and discharged more quickly without damage or significant energy loss.
  • Nickel-metal-hydride (NiMH): Performances are better than NiCd batteries: they are the essential component in the standard “rechargeable batteries” market and are used in ground transportation (Toyota Prius hybrid, two-wheelers, etc.).
  • Lithium: there are several families of lithium batteries that provide the highest mass performance (from 80 to 200 Wh/kg based on power features). This technology is widely used in high-performance mobile applications (mobile phones, portable PCs) and will probably branch out into ground propulsion and stationary applications soon.

117Overall, all of these technologies offer potentially high charge/discharge efficiency, as long as the required power remains relatively low. However, one of the weak points of electrochemical technologies is their rapid aging during service life. This is why economic, as well as environmental analyses must be conducted on the entire life cycle of the overall system considered.

118For stationary applications, mass constraints are less important than in mobile applications, and there is a wide range of electrical energy storage solutions. Among the mass storage systems tailored to grids and long “time constants” are: the following:

  • Pumped storage hydroelectric plant, also called pumped storage power station, or pumped storage plant. This technology is currently used most in high-power plants with approximately 80 % efficiency. The major drawback is the need for appropriate geography for these sites. Despite their high power, these systems can now operate at variable speed, making it possible to fine tune the power level and stabilize the grid. This option could be studied by New Caledonia where condition seems favourable. It is conceivable that pumped storage hydroelectric plants built next to the ocean with a large slope over the coast would transfer seawater to an upper reservoir without having to build an even higher one. Of course, leak tightness should be checked to prevent seawater from seeping into the floors, particularly when considering seismic risks. In addition, technologies would be available at acceptable costs.
  • Compressed Air Energy Storage (CAES) is already a relatively mature technology with several high-power operations. Building CAES systems requires suitable geography with large cavities such as old salt mines. There is a specific definition of efficiency here because natural gas is burnt in a combustion chamber to heat the air, before compressing it in a turbine. There are very few facilities, mainly because it has strict requirements for use (connecting to natural uses, suitable sites, etc.). More streamlined systems (Advanced CAES) can improve the energy balance, but always in combination with a gas turbine.
  • Redox flow batteries are able to bypass the limitation of traditional electrochemical accumulators in which electrochemical reactions create solid compounds that are stored directly on the electrodes where they were formed. The amount of solid material it can accumulate locally is significantly limited, which sets a capacity maximum. In so-called redox flow batteries, the chemical compounds responsible for storing energy are liquid and remain in solution in the electrolyte. Three technologies are under development with ZnBr- (Zinc-bromine), NaBr- (Sodium-bromine) and VBr(Vanadium-bromine) based electrolytes. The electrolyte is pumped to external reservoirs whose volume represents stored energy. High-capacity systems (qq 100 kWh to qq 10 MWh) are being tested.
  • High-temperature heat turbine storage: this system is still in the planning stages, but deserves a look. Concept: refractory materials are heated by resistance during storage. To recover the accumulated energy, warm air is fed into a combined-cycle turbine and efficiency should be expected to be approximately 60 %. There are no geological restrictions for creating these reservoirs of heat, and self-discharge losses are relatively few, especially if it is a large-scale system. It has among the lowest investments costs, but its feasibility and performances remain to be seen.

119Among medium-and small-scale storage systems are the following:

  • Electrochemical accumulators already mentioned above. Sodium sulphur (NaS) can be added to the technologies presented, and is used for electrical network applications. It functions at high-temperature (approximately 300 °C) with commercial products that are both reliable and nearly standardized (this must be mentioned because it is rare at this level of power and energy) at several MWh, for several MW of power (typically 1 MW – 10 MWh modules).
  • Supercapacitors are very high energy storage (volume and mass), high power capacitors with a long service life. Unlike electrochemical devices, electrical energy is accumulated in the electric field; there is no chemical reaction, which could significantly improve cyclability. The concept is similar to a capacitor, but the insulator that separates the electrodes is replaced by an ionic conductor electrolyte in which ions move up and down the length of a special large surface area conductor electrode.
  • Superconducting Magnetic Energy Storage (SMES) are superconducting coils, without ferromagnetic circuits, functioning at cryogenic temperatures; generally with helium liquid for low-temperature technologies, or liquid nitrogen for high-temperature technologies. The coil is a direct current source; this varies based on the charge status and must be converted to be used as continuous or alternating voltage. Like supercapicators, SMES are well suited to low time constants.
  • Flywheel Energy Storage (FES) systems include a large or composite flywheel combined with an engine-generator and special bearings (often magnetic) housed in a vacuum enclosure in order to minimize self-discharge losses. Thus, self-discharge rates of a few % / hour can be achieved. They have long lifetimes determined by fatigue dimensioning. Simply put, the wheel is dimensioned in energy and the engine-generator is dimensioned in power, making it easy to uncouple energy and power. Normally, we think of flywheel accumulators as being a part of low time constant systems, which is where they were first used commercially. However, they can also create slower systems and broaden their use.
  • Compressed air energy storage: An electric compressor fills bottles with high pressure air. There are losses during compression and the electrical efficiency is often mediocre. However, advanced technologies use an interface fluid to produce better efficiency. The air is compressed through an adiabatic process with fluid; this fluid itself is compressed by a reversible compressor/hydraulic engine connected to an electrical machine. The system is more complex and cumbersome than the compressed-air only solution for mobile applications, and for this reason, it is for stationary applications. There are no commercial products yet, but they are under development.
  • Electrolyser-hydrogen-fuel cell (or reversible heat pump) systems use hydrogen as the intermediate fuel stored under low pressure, which can be converted by electricity and pure water. Their overall efficiency during the charge/discharge cycle is low and their lifespan is insufficient for applications tied to power grids. In addition, the costs for investing in and operating an electrolysis-storage-fuel cell chain are high. However, many research projects are being conducted on these systems throughout the world, and improved efficiency and lower costs for this type of system is conceivable. However, it is difficult to imagine a direct market for such a system. In contrast, producing hydrogen by itself from surplus electricity production could be advantageous for hydrogen systems because it could recycle them through direct use. Finally, it must be noted that the efficiency and lifespan of electroylsers are affected by fluctuations in the power supply, which happens with intermittent photovoltaic and wind resources.

120In conclusion, there is a wide range of electricity storage solutions suited to many different situations, but their cost is often an obstacle. Stronger environmental restrictions will speed up the penetration of energy storage in electrical conversion chains. To optimize its dimensioning, its inclusion in systems, and its management, it is essential to consider its life cycle from both an economic and environmental perspective, taking into account service life, particularly during cycling, and operating costs (energy losses in particular).

Storing hydrogen

121Stationary applications generally use gas storage under low pressure in steel cylindrical tanks. In Europe, these tanks typically store 115 to 400 kg of hydrogen under 50 bars at a volume between 100 and 350 m3.

122For onboard applications where high mass energy is needed, hydrogen has an intrinsically high calorific value (34 kWh/kg, i.e. approximately 3 times more than liquid hydrocarbons), which is very attractive at first glance. However, storing it creates serious difficulties and is one of the downsides of using hydrogen in the transportation sector. In high-pressure tanks, 700 bars for example, the tank’s mass is approximately 20 times heavier than the mass of the hydrogen it contains. This severely reduces the mass energy of the tank/fuel unit (i.e. 1.6 kWh/kg) without even counting the amount of energy expended in compression, which further diminishes performances.

123If hydrogen is stored as cryogenic fluid (-253 °C at 5 to 10 bars), mass performances are similar, and the energy expended during liquefaction is still high. In this case, the thermal insulation has a continuous leak that loses an estimated thousand per hour, which is considered acceptable (this provides a loss of approximately 18 % in a week). Finally, metal hydride storage, which pro-vides better volume and safety performances in theory, is still being researched with mass performances that are lower or equal to previous storage systems.

Cold storage

124Cold storage accumulates cooling energy during low-use periods and then discharges it during periods when there is a higher need and it is more expensive to produce. In addition to the economic savings, cold storage can reduce the power of refrigerated units, as well as the environmental impacts of installations. Potential applications include air-conditioning and refrigeration in the service industry and industrial processes requiring refrigeration (refrigerated warehouses, central kitchens, meat-packing plants, etc.).

Storage technologies

125There are two techniques available for meeting storage needs:

  • Dynamic storage: characterized by the fact that water used for storage is distributed directly to users. This technique has three different processes on the market: ice on external-melting tubes, harvested ice, and slush.
  • Static storage: the water or storage material remains inside the tank. This system is commonly used in air-conditioning with numerous processes (ice on internal-melting tubes, encapsulated ice or eutectic mixture).

Potential for use in New Caledonia

126Several storage strategies can be envisioned based on the price signal (in New Caledonia, there must be a differentiation between warm season and cold season), to eliminate or limit demand during the busiest hours of the electrical grid.

Current offer on the market

127For large, new buildings, builders propose ad hoc installation that is dimensioned and built to order. Recent package-type offers for small and medium-sized service buildings make it possible to gradually expand latent cold storage reserved for large projects (>100 kW) through mini cold storage systems, which were first sold in Japan, but are now available throughout the world. This could be a good solution for developing a system in New Caledonia where the market potential consists of small and medium-size buildings. However, it is essential that local engineering departments, installers and users become familiar with cold storage techniques through training, support and follow-up.

Comparing technologies based on their maturity

128In the section of the summary titled “What framework for an energy and climate policy promoting the development of New Caledonia”, figure 14 summarizes the main technologies described here and indicates their level of technological maturity. They can then be ranked on the following scale from 1 to 4: (1) R&D stage or initial demonstration operations, (2) Commercial applications in niche markets (3) Technology becomes more competitive and quickly becomes widespread (4) Technology stabilizes and gradually loses market shares (4).

Managing electrical grids with integration of intermittent production

129The potential increase in the production of electricity by wind power poses stability problems for traditional power grids that count on an instant balance of production/consumption in order to run smoothly. This balance depends on the right plan of production methods placed in order based on cost criteria. It is generally estimated that a 20 % penetration rate of lower power does not cause any major disturbances for the grid; however, these figures usually involve interconnected continental grids with fewer stability problems.

130Under these conditions, without storage methods as is the case in New Caledonia, and for a penetration rate of approximately 10 %, intermittent electricity production can be treated as negative consumption. Just as human activity and weather forecasts are drawn up for consumption profiles, reliable forecasts must also be provided for intermittent production profiles. However, we must note a trend in significantly increasing penetration rates as shown in the by-law of 23 April 2008 “related to the design and operation guidelines for connecting a public electricity distribution network to a low or medium voltage public power grid”. For weak grids in island areas (article 22), a maximum rate of 30 % is given. If the rate goes beyond this percentage, the person in charge of maintaining consumption/production balance has the right to disconnect wind or solar generators. Currently, it is highly likely that this 30 % will be exceeded by adding storage devices.

131If we consider current methods (including both Prony units), the peak production power for the New Caledonia grid is approximately 470 MW (including hydraulic and wind production) and the installed wind power (or in the process of being installed with the Touango farm) is approximately 36 MW. Because photovoltaic power remains insignificant, the amount of power from intermittent production systems can be considered to be 7 % of the power used for planning.

132By improving planning quality, encouraging better communication between operators, and controlling current production methods as much as possible, it is certainly technically possible to reach a penetration rate of approximately 25 to 30 %. A balance between wind and photovoltaic power installations would probably improve the expansion of intermittent production, but that remains to be proven. Studies could be conducted on this issued based on productivity data measured for at least one year in different geographical locations.

133Next, incentives for using consumption files, including for example the option of offloading (through special contracts) during peak periods, could push the penetration rate even further.

134Finally, implementing storage methods would provide much more flexibility in managing the grid. A penetration rate reaching 100 % power is definitely possible if the appropriate storage methods are available. Pumped storage is probably the best technology for meeting Grande Terre’s specifications; in addition, it is by far the most widely used technology in the world. To obtain faster storage, other storage technology can be envisioned (sodium sulphur for example) as currently planned by Reunion Island.

135In regards to small islands, hybrid photovoltaic-type micro-grids (with generator set and electrochemical storage) are definitely the best technical and economic solutions. The production cost for these small systems is evidently higher than that of Grande Terre (main island), but the cost of an offshore connection would not be recovered and would undoubtedly be a source of increased default risks. Such hybrid systems can be dimensioned for low fuel consumption for power plants that are only used in special circumstances (abnormally weak sunlight during an unforeseen period or unplanned over-consumption or breakdown), unless there are enough local biofuels available.

Notes

1 Nm3 = standard metric cube, i.e. the volume occupied by gas in “normal temperature and pressure conditions”.

2 http://www.solarsystems.com.au/

3 With the support of Franck Carre (CEA/DEN/DDIN), from the department of nuclear innovation and development.

4 This paragraph answers a special request from the DIMENC and its content was written with the scientific support of Professor Jean-Franççois Fauvarque, electrochemica chair of CNAM.

© IRD Éditions, 2010

Conditions d’utilisation : http://www.openedition.org/6540