This. Normal solar relies on the grid as it's "storage". The economics of solar become very different if you have to provide local storage. This is also why

This. Normal solar relies on the grid as it's "storage". The economics of solar become very different if you have to provide local storage. This is also why there is an ongoing fight over net metering and in some places solar connections aren't even allowed. So long as solar is a small fraction of the total power it has basically zero effect on the grid. Now, however, there are a lot of solar setups. Look what happens to the grid: The total delivered power drops, but the peak power (when the cloud passes in front of the sun and all those panels quit working) stays the same. They need to spend just as much on generators as before but they aren't selling as much power. Historically, the cost of being able to produce the power has simply been folded into the cost of the power but with the two going out of sync this model no longer applies. Solar gets a substantial hidden subsidy from this, without this subsidy solar is almost never economic. Second, look at what happens when *lots* of homes go solar. Lets say the local substation is delivering 1000A of power to it's area. Lots of panels go up, the combined power is 1500A. Now the substation transformer is being asked to push 500A back up to the distribution wires--and it's probably not built to survive that. Either those substations must be upgraded or the power company simply prohibits the situation from arising the in the first place by not allowing too much solar on any given segment.