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.

> I’m pretty sure everyone was quite aware the sun doesn’t shine at night whenever the previous rules and regulations were written.

And because they knew, the regulations I've heard of set some sort of statutory price that consumers get. This is because it's been fairly likely from the start that if the price is set by the market with reference to the value of the electricity, consumers won't get anything. Because their contribution is largely worthless and occasionally value-destructive.