Expensive compared to what? CO2 emissions? You already get a 30% federal tax credit as well as CA state and local utility incentives, what more is necessary? A free system?

I agree a carbon tax would be ideal. It seems politically impossible though, so you achieve what you can.

That was a response to your statement that the relevant research has been done.

I don't think it has. We still have to figure out ways to lower the cost of storage.

You're saying it is cheap enough that we can now mandate it?

It should be cheap enough when purely green energy is superior to any other source. Solar alone is cheap, but not solar + storage.

"Cheap enough" should take into account the expected future costs of climate change. That's the major reason for subsidies and regulations to encourage renewable energy usage. There is a huge externality to account for.