The price is signaling that additional solar power production during the day isn't very useful; and additonal solar power production in the early evening when demand is high and the sun isn't shining and you need a battery system to have already been accumulating energy during the day is useful, albeit more expensive and complicated to build and run.

With falling battery prices this should be an addressable problem. Soak up the locally generated excess energy and sell it later in the day when the need is there. Electrical arbitrage seems like a win/win solution for the utilities their customers.