Axion Power International recently announced that its PowerCubeTM has been selected to provide energy storage and frequency regulation for the Coatesville Solar Initiative 9.1 megawatt solar farm in Pennsylvania. When completed, that solar farm will be the largest in the state, and will provide power to the Coatesville Area School District through a power purchase agreement. Under the 25 year agreement, the school district will pay about $0.03/kWh less than the grid rate. My ballpark calculations say that they’ll save about $200,000 a year in electricity costs. At a time when public schools are easy targets for budget-cutting legislators, an extra $200k per year may not seem like much, but it softens the blow at least a little. Other school districts, and even entire municipalities, are taking advantage of power purchase agreements to save money on their energy bills while making no initial investment.
The storage technology for this project is Axion’s PowerCube, which can be used for grid-level storage, behind the meter energy management, and off-grid energy storage. Each PowerCube includes forty 12-Volt Lead Carbon (PbC) batteries connected in series to produce 480VDC. Multiple strings are connected in parallel to provide the required current and power for a given application. The PowerCubes are scalable, providing as much capacity as needed. When the PbC batteries reach the end of their useful lives, they’re 99% recyclable.
Image: Axion Power International
The PowerCube includes sophisticated electronics, including an inverter, charge controller, battery monitoring system, and communications that allow it to send status information and be controlled remotely via the internet.
Lead-acid batteries often suffer from stratification and unequal cell voltages. Periodic “equalizing charging,” which charges the batteries with a voltage higher than the nominal value and brings each cell to a full state of charge, will alleviate that problem. Axion’s battery packs have a self-equalizing feature that equalizes the cells even at a partial state of charge.
Several battery technologies are trying to become the standard for grid-level storage. Flow batteries (zinc and vanadium), lithium-ion, dual carbon, and hybrid battery/supercap combinations all show promise in labs and limited field testing, and that’s not even considering mechanical storage systems like flywheels, pumped hydro, and compressed air. It’ll be years, if not decades, before a clear winner emerges. Meanwhile I’m going to grab some popcorn, watch the competition, and keep reporting what I see. Enjoy the show!