First let me say that this most suitable at the small community level and larger quantity of energy storage. If it proves out (and it looks like that is a given since the fundamental technology is the same as home heat pumps) its low cost will accelerate the removal of carbon from our energy system. The first piece is a news article in the Gardian highlighting the device, and the second is a piece that places it in the role we need it to serve in a renewable energy grid.
Giant gravel batteries could make renewable energy more reliable
Wind and solar power are often criticised for being too intermittent, but Cambridge researchers could change that
Newly designed giant gravel batteries could be the solution to the on-off nature of wind turbines and solar panels. By storing energy when the wind stops blowing or the sun stops shining, it is hoped the new technology will boost to renewable energy and blunt a persistent criticism of the technology - that the power from it is intermittent.
Electricity cannot be stored easily, but a new technique may hold the answer, so that energy from renewables doesn't switch off when nature stops playing ball. A team of engineers from Cambridge think they have a potential solution: a giant battery that can store energy using gravel.
"If you bolt this to a wind farm, you could store the intermittent and relatively erratic energy and give it back in a reliable and controlled manner," says Jonathan Howe, founder of Isentropic and previously an engineer at the Civil Aviation Authority.
The Labour government committed to cutting the country's carbon emissions by 34% by 2020 and 80% by 2050, both relative to 1990 levels. To achieve this, ministers outlined plans to build thousands of wind turbines by 2020. The only economically viable way of storing large amounts of energy is through pumped hydro – where excess electricity is used to pump water up a hill. The water is held back by a dam until the energy is needed, when it is released down the hill, turning turbines and generating electricity on the way.
Isentopic claims its gravel-based battery would be able to store equivalent amounts of energy but use less space and be cheaper to set up....
http://www.guardian.co.uk/environment/2010/apr/26/gravel-batteries-renewable-energy-storageDoes Wind Need Storage?
The fact that “the wind doesn’t always blow” is often used to suggest the need for dedicated energy storage to handle fluctuations in the generation of wind power. Such viewpoints, however, ignore the realities of both grid operation and the performance of a large, spatially diverse wind-generation resource. Historically, all other variation (for example, that due to system loads, generation-commitment and dispatch changes, and network topology changes) has been handled systemically. This is because the diversity of need leads to much lower costs when variability is aggregated before being balanced.
Storage is almost never “coupled” with any single energy source—it is most economic when operated to maximize the economic benefit to an entire system. Storage is nearly always beneficial to the grid, but this benefit must be weighed against its cost. With more than 26 GW of wind power currently operating in the United States and more than 65 GW of wind energy operating in Europe (as of the date of this writing), no additional storage has been added to the systems to balance wind. Storage has value in a system without wind, which is the reason why about 20 GW of pumped hydro storage was built in the United States and 100 GW was built worldwide, decades before wind and solar energy were considered as viable electricity generation technologies. Additional wind could increase the value of energy storage in the grid as a whole, but storage would continue to provide its services to the grid—storing energy from a mix of sources and responding to variations in the net demand, not just wind.
As an example, consider Figure 7 below, which is based on a simplified example of a dispatch model that approximates the western United States. All numerical values are illustrative only, and the storage analysis is based on a hypothetical storage facility that is limited to 10% of the peak load and 168 hours of energy. The ability of the system to integrate large penetrations of wind depends heavily on the mix of other generation resources. Storage is an example of a flexible resource, and storage has economic value to the system even without any wind energy. As wind is added to the system in increasing amounts, the value of storage will increase. With no wind, storage has a value of more than US$1,000/kW, indicating that a storage device that costs less would provide economic value to the system. As wind penetration increases, so does the value of storage, eventually reaching approximately US$1,600/kW. In this example system, the generation mix is similar to what is found today in many parts of the United States. In such a system with high wind penetration, the value of storage is somewhat greater because the economic dispatch will result in putting low-variable-cost units (e.g., coal or nuclear) on the margin (and setting the market-clearing price) much more often than it would have without the wind. More frequent periods with lower prices offers a bigger price spread and more opportunities for arbitrage, increasing the value of storage.
In a system with less base load and more flexible generation, the value of storage is relatively insensitive to the wind penetration. Figure 8 shows that storage still has value with no wind on the system, but there is a very slight increase in the value of storage even at a wind-penetration rate of 40% (energy). An across-the-board decrease in market prices reduces the incentives for a unit with high fixed costs and low variable costs (e.g., coal or nuclear) to be built in the first place. This means that in a high-wind future, fewer low-variable-cost units will be built. This reduces the amount of time that low-variable-cost units are on the margin and also reduces the value of storage relative to the “near-term” value with the same amount of wind.
The question of whether wind needs storage ultimately comes down to economic costs and benefits. More than a dozen studies analyzing the costs of large-scale grid integration of wind come to varying conclusions, but the most significant is that integration costs are moderate, even with up to 20% wind-energy penetration, and that no additional storage is necessary to integrate up to 20% wind energy in large balancing areas. Overall, these studies imply that the added cost of integrating wind over the next decade is far less than the cost of dedicated energy storage, and that the cost can potentially be reduced by the use of advanced wind-forecasting techniques.
You can download the full document by clicking the pdf link below and you'll be able to see figures 7 & 8.
Wind Power Myths Debunked
november/december 2009 IEEE power & energy magazine
Digital Object Identifier 10.1109/MPE.2009.934268
1540-7977/09/$26.00©2009 IEEE
By Michael Milligan, Kevin Porter, Edgar DeMeo, Paul Denholm, Hannele Holttinen, Brendan Kirby, Nicholas Miller, Andrew Mills, Mark O’Malley, Matthew Schuerger, and Lennart Soder
http://www.ieee-pes.org/images/pdf/open-access-milligan.pdf
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