by Emil Morhardt
Why would you want to store electricity generated at home when you have a perfectly good connection to the grid and the power company buys back all the electricity your solar panels generate at the cost you pay for electricity? You wouldn’t. But what if the power company started paying much less for the electricity you are shipping back than you could have purchased it from them—as they have been doing recently in Australia (Muenzel et al. 2014)—or decided to charge so much for transmission of electricity back to the grid that there was little point in selling it to them in the first place (as it appears they are contemplating doing in California from the radio spots I hear recently.) Now you might want a battery large enough to prevent any of the electricity you generate getting back to the grid, and ideally meeting all of your routine electricity demands. A cost-effective solution might be about to arrive just in time to offset these likely policy changes; used electric vehicle batteries.
New electric vehicle batteries store something on the order of 24 k Wh—the Nisan Leaf, for example (Lacey et al. 2013). Around 2019 many of these will have degraded by 20% and need replacing. According to these Lacey et al., they ought to be perfectly usable for non-vehicular energy storage applications even when degraded to 50% of their original capacity, and according to Muenzel et al. all you would need in a typical home is 6–7 k Wh to obviate the need of using utility-provided electricity, so they would work fine in most cases with a payback period of 10 years, about the same as the solar panels feeding them. Thus, combining such a battery pack with existing or new residential photovoltaic installations is likely to make good sense about the time they become available.
By the way, doesn’t it seem a little shocking that the amount of energy stored in a Nissan Leaf battery, which is good for something on the order of 40 miles, is enough electricity to run your house for three days? That makes it rather clear that improving gas mileage of cars ought to be far more effective at decreasing CO2 releases than increasing household energy efficiency.
Muenzel, V., de Hoog, J., Mareels, I., Vishwanath, A., Kalyanaraman, S., Gort, A., PV Generation and Demand Mismatch: Evaluating the Potential of Residential Storage. http://www.juliandehoog.com/publications/2015_ISGT_PotentialStorage.pdf
Lacey, G., Putrus, G., Salim, A., 2013. The use of second life electric vehicle batteries for grid support, EUROCON, 2013 IEEE. IEEE, pp. 1255-1261.