If a customer is permitted to buy as much electricity as they want at a fixed price while also being able to sell as much as they can at a different time at a fixed price, it seems like there's an obvious subsidy happening anytime they sell electricity at other than when the wholesale price is the highest or buy other than when the wholesale price is lowest. (In areas with an excess of solar generation capacity, these distortions become quite large.)

(I'm still all for these subsidies on the balance of factors; we just shouldn't pretend that they're not subsidies.)