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The amount of years it takes for solar to pay for itself is not set in stone. The ten year prognosis is extremely conservative and frequently untrue, especially if you start to load most of your power-heavy operations (washing, dishes, etc) into the daytime when the generated power is sufficient to support those things.

Given that there is not yet (as far as I'm aware) a tax on kWh used entirely from solar panels (ie not coming from or going into the net, but taken directly from panel generation) it should not matter very much whether or not the government decides to subsidise you. Do not count on a solar panel installation company to make such complicated calculations for you, they are most busy with either sowing unrest about government regulations or (more likely) giving you a fair-weather calculation that involves subsidies forever.

You are correct that if you use your energy before it gets on the grid you are fine.

But that is quite hard for most people to accomplish, most people are not at home during daytime when the panels generate most. The time my washing machine actually consumes energy warming up the water is relatively short.

The largest part of the power consumption of my home owners association is spent on lighting, the other part on the elevator which is most of the time just idling and peaks when someone uses it.

Batteries are inefficient and still expensive. You could warm up a boiler for hot water during day but I think that is done more efficiently with a heat collector instead of pv->electricity->heat. You can warm up your house, but you have to have very good insulation otherwise most energy is lost by the time you get home.

Anyway, in practice the change in policy can have a huge effect in return on investment time.

Silicon Valley is coincidentally a place where home-time and solar-peak kind of coincide. My brother's solar panels peak in the late afternoon all summer, when he's programmed the air conditioning to come on.

As European I wonder if you really need a/c in Silicon Valley? I've never been there but from weather averages it seems that the climate is comparable with Paris where a/c's are absolutely not common. Even in more southern cities like Barcelona many people don't use a/c.

If you want to get very technical it is questionable whether or not you really need air conditioning anywhere. It's a luxury item and if you view it as such it's not surprising that people in SV have it - it's already a super high CoL place, might as well install some extra perks.

Agreed. For environments with A/C, solar is very well correlated with demand.

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