We recently had photoelectric panels installed. We have 8 kw. In Germany this is subsidised and we reckon to break even in about 9 years, just by selling it and by own use during the daytime.
Anyway, the point is not to make a profit, but to make our own electricity, to at least feel a bit self-sufficient. So we need a method of storing our nice power until we need it, e.g. to charge an electric car or to heat water.
There are many ways to do this; batteries seemed to me to be the obvious solution but they are extremely expensive, and some of them are fire-risks. Then the solar man suggested compressed air, although this is apparently noisy. Then there's turning water into hydrogen and back again – which sounds like a fire risk to me.
In this erudite circle there is certainly someone who can point me in the right direction; I'm fine with new technology but it has to be
- practical
- economical
- maintenance-friendly
edit: Hmm, environmental impact. I gather our solar panels will now generate more power in their official 20-year lifespan than were used in their manufacture. But this is a different question. But really it's about self-sufficiency – a suspicion that if Germany gets any greener they will start rationing electricity (this has been mentioned, in passing, by the Greens). Also, turning off the nuclear power stations and iffy gas deliverers may well mean the power just goes off on dark nights with no wind.
Best Answer
We're still living in complicated times when it comes to figuring what's best in terms of energy usage and storage.
If the goal is to become purely fiscally self-sufficient, I think ben's answer is really good. Sell your excess for cash. Then use said cash to exchange it for 'cheap' (relatively speaking) storable energy sources like a propane tank + generator.
Whether we like it or not, fossil fuels are still the cheapest way to store energy for extended use.
If the goal is to help the environment, then ideally you are never drawing power from the grid at all if the grid is powered by fossil fuels. On the other hand, if the grid is powered by wind or solar (or, arguably, nuclear) then it actually may be better for you to draw from the grid rather than storing it yourself.
If the grid is fossil fuel based, then you're back to finding a device to store energy with.
Options:
and plenty more options: http://en.wikipedia.org/wiki/Energy_storage
Based purely on your 3 bullet point needs, I'd say the propane tank + generator are your best bet.