Energy Storage: The Ultimate Challenge for Renewables
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August 11th, 2010 - Energy storage is a major challenge in developing renewable power sources – wind, solar, geothermal and hydroelectric power alike. We look at what can be done to store surplus electricity produced by these systems, the procedures that need to be put in place and how much they will cost. If renewable energy sources are to take hold on a wide scale, power-storage techniques need to be fully harnessed.
Over the past few years, energy experts and industry professionals have been looking at a number of options to meet the challenge of wind and solar power storage. “Technological solutions already exist today, the stumbling block is the economic side of the equation. On a purely technical level, power storage means that we can stabilise the grid, adjust output, and ensure current and voltage continuity,” explains Stéphane Biscaglia, of the renewable energy department at France’s Environment and Energy Management Agency (Ademe).
With total installed solar and wind power wattage of around 372 GW worldwide (204 GW for solar thermal energy, 15 GW for photovoltaic energy and 152 GW for wind power), storage is still the crux of the matter for many market players. “Storage also has an economic function, too, and can lead to deferred investments. In the medium term, it also has a financial function. Liberalizing the energy market has brought with it price fluctuations – and will continue to do so – and looks to be paving the way for energy trading,” he adds. A variety of storage technologies could therefore be developed in the light of these factors.
“With intelligent interfaces we will also be able to aggregate output”
Storage is an essential factor in attracting new investors, offering customers efficient solutions, and controlling electricity flows and the power grid. “This has major implications, in that it ensures that a balance is maintained between energy supply and demand,” says Eric Dyèvre, the French Energy Regulatory Commission (CRE) commissioner and chairman of the working party on covering line losses on the public electricity grids. “Diffuse” individual storage trials have been conducted over the past few years, accordingly, with consumers managing their energy reserves on an individual basis, using purpose-built equipment. Private customers connected to the national grid can also sell their surplus energy on and buy in from others in the event of a shortfall.
Batteries are used to store from five to 15 kWh of unused electricity production. Smart grids unquestionably come into their own here, on a worldwide scale. “Intelligent grids will be crucial if the system is to operate smoothly and sustainably,” comments Sandrine Pincemin, studies and research engineer at the Scientific and Technical Centre for Building (CSTB). “With intelligent interfaces we will also be able to aggregate output,” deems Stéphane Biscaglia.
Searching for the ideal batteryBatteries are a key component of the endeavour, with most experts favoring the lithium variety. “They should become the norm because of their long-life operation,” remarks Biscaglia. Although nickel and metal hydride batteries had originally been considered on account of their low cost, “lithium finally won out because of its high yield. Ultimately, despite the cost, lithium provides better damping and a higher kWh return.”
The second option considered is using power storage plants. “Other, more industrial battery technologies would need to be developed here. Dedicated buildings and specific logistics would also be required. This would allow greater energy volumes to be stored,” Biscaglia states. The experts suggest using sodium/sulphur and nickel batteries in this case, but not exclusively.
Other technologies are under test for larger volumes
One of the most widespread technologies being researched for large volume energy storage is gravity hydraulics. InGoldisthal, Germany, a 1 GW pumped storage plant is now up and running. On Reunion Island, renewable-energy supplier Aérowatt has received backing from Oséo, the French government new enterprise funding scheme, for its hydraulic energy-storage project. The power company’s Onergie plant is due to come on stream at the end of 2009. In Denmark, scientific center Riso-DTU, local energy operator Kema and an architecture firm are looking at tapping into the country’s giant water reserves to store intermittent renewable energies.
Hydroelectricity is the most effective way to store energy on a large scale, without undue wastage. The technique involves producing photovoltaic solar electricity to feed hydraulic pumps throughout the day. The water is stored high up in reservoirs, dams or water-retention zones, then released, yielding its potential energy by means of hydroelectric turbines, as required.
Hydroelectricity is a clean, sustainable energy source, but its use is questioned by a number of researchers, some of whom advocate compressed-air or hydrogen-based techniques. “Hydrogen and compressed air look great on paper, but there’s huge energy wastage in reality,” explains Biscaglia.
“In France, there are no plans to install these systems in the medium term”
When it comes to deciding who will actually pay for the various storage methods to be put in place, the possible leads are even less specific than the choice of technology. “No decision has been taken as yet,” remarks Biscaglia. Under the aegis of the research demonstration fund, set up by the French government in 2008 to encourage experimental schemes and boost technological innovations, a “win-win” economic model is currently under test. But, for the time being, “it isn’t workable for private customers”.
To give electricity producers a nudge in the right direction in developing and installing storage plants, they could be required to adopt the constant flow principle. This would give them responsibility for the upkeep of their networks.
“Storage isn’t an issue in France in the medium term, except in island areas. On Reunion Island, for instance, we have launched invitations to tender with the requirement for operators to store their output, but on the mainland this type of set-up is not under consideration for the time being,” states Jacques Lengyel, head of renewable energies, Directorate General for Energy and Climate at the Ministry of the Environment. In the US, inertial force is under consideration for kick-starting storage development programmes. Currently, apart from Desertec, there are no other projects in the offing to set up large-scale energy storage systems.
Storage is nonetheless a key factor in developing and sustaining green energy sources. Wind and solar power is well-placed to replace fossil fuels by 2050. However, although this objective is entirely feasible on paper, it can only be achieved through the use of optimum storage systems.
Graphic: A domestic energy storage system for photovoltaics (© Saft)
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