[AnthonyMouse]

Demand for electricity is higher during the day. The previous rules were written when solar was a smaller part of the grid and "generates during the day" was an advantage.

As the amount of solar increases, the supply during the day goes up, so the daytime price starts going down. Meanwhile the highest demand period is just after sunset, so that's going to be when the price is highest because not only is that the highest demand, that's when solar generation is zero. And it's when people selling solar during the day are trying to buy power back. But now they're selling low and buying high.