When the wind dies down or the sun stops shining at night or during cloudy days, the solar collectors and wind turbines stop working. There is just no cost effective way of storing energy from these sources.
Not anymore.
A recent development of energy storage using vanadium electrochemical cells is now about to break into the commercial realm.
In a solar installation photovoltaic solar panels catch the sun’s energy and convert it into electricity. This is then stored into the vanadium battery so that the energy can be used at a later time or pumped into the grid.
A vanadium battery, which works similarly as the familiar battery used in toys and flashlights, has distinct advantages over the other battery cells in the target application. The main advantage is it uses the same elements in both half-cells which eliminates cross-contamination of the two half-cell electrolytes during prolonged use. The positive and the negative half-cells are separated by a proton exchange membrane.
It has high efficiencies of 80 – 90 % in large installations. Furthermore, the costs rapidly goes down as the installation is scaled up. And maintenance is easy.
The battery can also be fully charged or discharged. In cases where time is the essence, the electrolyte solutions can simply be replaced rather than waiting for recharging.
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Sidebar:
The electrochemistry involved is not too difficult to understand even by undergraduate students of chemistry. The schematic is shown below (courtesy of the University of New South Wales):
The half-reactions are:
At the positive electrode:
VO2+ + 2H+ + e = VO2+ + H2O E° = 1.00V
At the negative electrode:
V3+ + e- = V2+ E° = -0.26 V
The standard cell potential E° (cell) is 1.26 Volts at concentrations of 1 mole per litre and at 25°C, but under actual cell conditions, the open circuit cell voltage is 1.4 Volts at 50% state-of-charge and 1.6 Volts at 100% SOC (Skyllas-Kazacos, 2002, p. 2).
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Early demonstration projects include a solar-powered housed in Thailand, an electric golf cart, and a back-up power system for a nuclear submarine.
In the United States, which is playing catch up with the technology, a 15-kW photovoltaic installation has just been put up at the Lowry Park Zoo in Tampa, Florida jointly by Tampa Electric and the University of South Florida’s (USF) Power Center for Utility Explorations (PCUE) at a cost of approximately $ 575,000 (Tampa Electric, 2008).
Earlier in June, two similar 5 kWx4hr systems have been installed at the downtown St. Peteresburg campus of USF and at Albert Whitted Park in the same city by the university and Progress Energy of Florida (VRB, 2008).
The vanadium redox battery has been developed and its use pioneered at the University of New South Wales. An engaging historical and scientific account of its development has been presented by Skyllas-Kazacos (2002).
With the technology now available what remains is the development of policy initiatives as embodied in the renewable energy bill still pending in Congress for the solar and wind power to take off in the Philippines.
References
Skyllas-Kazacos, M. (2002, July). An historical overview of the vanadium redox flow battery development at the University of New South Wales, Australia, 13. Retrieved August 19, 2008, from http://www.vrb.unsw.edu.au/overview.htm
Tampa Electric (2008, August 4 news release). Tampa Electric, USF partner with Tampa’s Lowry Park Zoo to develop new renewable energy project. Retrieved August 19, 2008 from http://www.tampaelectric.com/news/article/index.cfm?article=466.
VRB Power Systems Inc. (2008, June 9 press release). Progress Energy and University of South Florida’s Power Center for Utility Explorations unveil two 5kW x 4hr VRB Energy Storage Systems as part of SEEDS project . Retrieved August 19, 2008 from http://www.vrbpower.com/docs/news/2008/news_20080609.pdf
VRB Power also have an soon to be installed battery at the Sorne Hill wind farm in Ireland.
ReplyDeleteFor this project, Sustainable Energy Ireland (SEI) studied 17 storage installations. SEI concluded that with wind + storage gave a better than 98% firmness -- equivalent to good base load generating assets (and better than such assets as gas-fired turbines).
The most important conclusion within the SEI report is the level of return generated with storage. When the proposed 2 MW/12 MWh VRB-ESS batteries were internally financed by wind farm owner Tapbury, the project would have a 11.7% internal rate of return. Generally acceptable given the hurdle rates in the wind industry are typically 8-9% range.
However, if appropriate gearing is applied, the IRR jumps to 17.5 – an unheard of figure for any component of a windfarm.
However there’s a lot more to the storage story than just the boost it gives wind.
Storage protects against mistakes in forecasting, removes barriers in connecting renewable sources to a variety of grids, shifts demand peaks by storing off-peak energy to sell back to the grid during peak times, provides frequency regulation and deters expensive grid upgrades.
In short, storage provides the basis for a complete change in the thinking surrounding power generation and use.
I read in a recent Scientific American Dec 2007 ("A Solar Grand Plan") article that another storage mechanism they are looking at is to make compressed air while the solar PV cells are pumping electricity, and then store the compressed air in caverns in the ground and use it to run turbines during the evening. According to the Sci-Am article, they already have this in places like Huntorf, Germany and McIntosh, Alabama. It also mentioned that studies by the Electric Power Research Institute in Palo Alto, CA said that the cost is about half that of lead acid batteries. It also said that the infrastructure is similar to the natural gas storage system that the US uses. Another technology described by the article is to store the heat in molten salt, which stores heat efficiently. The heat can be used to make steam in the evening, again to drive a turbine. Of course it doesn't mean that battery storage is already out of the equation; these are merely alternative technologies.
ReplyDeletethat is really impressive!!! now we are going to charge the batteries no using electric energy but using solar energy and wins energy too. that is amazing.
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