Pumped hydro is a simple and effective way to store energy — you just pump water back up over the dam — but building new dams isn’t easy. All the good spots have already been taken, and the regulatory hurdles keep growing. There are other ways to apply the same simple principles though:
Instead of trying to build new pumped hydro facilities, the founders of ARES — William Peitzke, Matt Brown and John Robinson — asked themselves, “How can we do pumped storage hydro-electric, but without any water?” The answer they found was basically the opposite of water: rocks. Or more specifically, rocks on trains.
“We realized the solution was right in front of us,” said Kelly. “The railroad industry had developed an incredibly efficient way to move mass.” One ARES engineer determined that the coefficient friction of steel wheels on railroad track is lower than the coefficient friction of ice skates on ice.
The ARES system uses excess energy from the grid to pull 140-ton railcars up hills (total train weight: 1,350 tons). When the grid needs that power back, they simply let gravity take the weighted cars back down. Regenerative braking — similar to what you find in a Toyota Prius, or in Japanese subways — captures the energy the trains produce along the way
ARES built a test facility in California to prove the concept, and now they’re in the final stages of building a 50 megawatt facility in Nevada, which will come online in 2016. For comparison, this facility alone will add more energy storage than was built across the entire US in 2013 (44.2 megawatts), according to a recent recent report by US Energy Storage Monitor. The same report suggests that 220 megawatts will be deployed in 2015, twice the capacity of the previous two years combined.
I don’t think “Megawatts” is a very good metric for an energy storage system: it just indicates the rate at which energy can be delivered, saying nothing about how long it can be delivered for. Megawatt-hours would be a much more meaningful number.
I’m so used to pop-science writing that I (correctly?) assumed they meant megawatt-hours.
Yeah, it seems impossible for most journalists to grasp the difference. But if it’s really 50 megawatts, that seems unimpressive…it could store the output of a 500MW plant for all of 6 minutes.
Here’s a pumped storage hydro project that says it will be able to store 17,000 MWH.
Environmentalists successfully killed off pumped storage. It remains to be seen whether this is acceptable to them.
Aside from their low capacity factors (which require 1 kW of fossil fuel backup for each kW of installed solar or wind), solar and wind often produce excess power when it is not needed. This raises havoc in distribution systems, and the solar or wind systems have to be shut down. People are desperately looking for energy storage systems to capture this lost power. Chemical batteries can’t do it for reasons of cost, energy density and recharge time. This scheme might work if the costs are reasonable.
Of course, the environmentally correct solution is to shut down all solar or wind systems.
According to this article and this followup article the California Public Energy Commission (CPUC) has required utilities in that state to purchase an amount of energy storage denominated in megawatts and that storage could be as little as 15 minutes capacity (or less) if that is “enough to bring value in this context”.
So, they used the wrong unit, but it was on purpose?
Yeah, that’s how I read it. They may have been worried that the utilities would build just a few small facilities with excessive storage to game the requirement, e.g. pumped hydro with a small generator and a very large reservoir.