Solar batteries are the best way to store unused power for use after the sun goes down, rather than sending some of the solar power back into the grid.
T3Sol has the most financially effective battery system, while most Solar batteries are not financially effective right now(with the high feed-in tariffs for putting unused energy back into the grid)
With a solar panel battery you can reduce your electricity use from the grid (which is predominantly coal and gas generated) and even go off-grid by installing a solar panel battery.