While the intermittent nature of wind and solar has long been the bane of renewables, it has been the potential boon of many fledgling storage technologies. Fly wheels, fuel cells, batteries and even electric vehicles all offer the possibility of storing power generated from renewables and delivering it when it is needed.


Now, we can add another novel concept to that growing list of storage technologies: electric rails or, more simply, trains.


Advanced Rail Energy Storage (ARES), based in Santa Barbara, Calif., was formed in 2010. The company has patented a unique method that harnesses gravity and repurposes rail cars to store grid-scale power generated by renewables.


The process is fairly simple. Electric locomotives haul a string of cars filled with concrete uphill to store the power. The trains wait until the power is needed. Then they roll back down the hill using gravity and their heavy loads to create inertia. The motors capture the energy and generate power as the trains speed back down. That power is then delivered to the grid.


According to ARES, with enough track space and slope, projects could be built with up to 3 gigawatts of capacity and 24 gigawatt-hours of storage.


At least one utility has taken notice. ARES boasts that the Valley Electric Association, a co-op based in Pahrump, Nev., has contracted for a $40 million rail energy-storage plant in Nevada, which will tie into the California ISO. The project will have a generating capacity of 50 megawatts and 12.5 megawatt-hours of storage. It is expected to be completed and operational by 2016.