Three reasons, and most solar homes have all three at once.

Feed-in tariffs have been falling for years, so the power you export earns less than it used to. The electricity you import has gone the other way and risen sharply, so any gap in your solar coverage costs more to fill. Then there’s timing. If your household uses power in the evening after the sun goes down, you’re buying from the grid at higher time-of-use rates.

This is why solar alone only gets you halfway. A battery addresses all three by letting you store your own solar and use it later rather than depending on the grid.