Very little until the SolarCity facility comes online, and the battery storage at the Port Allen solar array has been disappointing and expensive, with batteries that died unexpectedly early.
Also, Hawaii gets its electricity from oil and gas shipped in by tanker and residents pay $.30/kWh; the utility there managed to negotiate $.15/kWh from SolarCity, which is almost certainly below their cost of production right now; they couldn't meet the utility's original tender and reapplied several times. I'm guessing that SolarCity is betting that over the life of their 20 year (!!!) contract they can bring their costs down and eventually turn a profit. I wonder about that bet, though, given that SolarCity isn't in great financial shape.
Anyways, I'm very much in favor of subsidized and incentivized solar power; what grates on me are people who assume that there's a great deal of unrealized value in clean technologies ("new industrial revolution!"). Converting to clean technologies will destroy value because oil and gas, especially when untaxed, are cheaper and easier to exploit. But of course we must convert because, well, 400ppm.
I'm confident that battery cost reductions will be substantial when Tesla's Gigafactory is at full production (they've already signed yet another utility scale battery storage deal in the last 10 days), cost reductions that will further increase uptake in energy storage contracts.
Cumulative global installed solar photovoltaic capacity will surpass 310 GW this year, compared with just 40 GW at the end of 2010. Polysilicon module prices continue to plummet; even if storage costs have not caught up, we can continue to drive out fossil fuel generation with more solar and wind, not to mention shifting loads to renewable generation hours whenever possible.
100% nuclear would work too but is politically unviable. Waste and the risk of accidents are a big problem, but at this point I believe they would be preferable to breathing in fossil fuel emissions all day.
Every existing light water reactor in the world could melt down like Fukushima and it won't come close the human disaster that will happen if much of the world's climate exceeds a wet bulb temperature of 35C for any part of the year.
The cost of solar will continue to crater; it is not a matter of "if" we will run entirely on solar, but only "when" at this point.