With the complaints of people highjacking wk057s thread I thought I'd take the initiative and start one specifically about the general objective that batteries are meant to accomplish; storing energy when it's available and making stored energy available when the sun ain't shining. IMO there's a bit of tunnel vision in regards to this... similar to the way PV gets more attention than cheaper, although admittedly less sexy, energy saving regimes. The lowest hanging fruit on the energy 'storage' tree is hot water heaters. One of my friends lives in Texas and doesn't benefit from net-metering so he saves $0.05/kWh if he self-consumes instead of exporting. So he bought a $20 timer for his hot water heater. Now he mostly uses energy from his PV array to heat his water... he effectively bought a 4kWh battery for $20... that's kinda hard to beat. To take this idea a step further; if you swap out your old resistance water heater for a heat pump instead of tossing out the old one put it in series with the new one as extra insulated volume. Install a small pump connected to a timer that sends heated water to the old water heater during the day when you should be exporting. Again that's ~4kWh+ storage for <$100 without the small risk of running out of hot water during the night.