But you also need your night-time base load, so maybe there is a pumped hydro station somewhere, or a wind turbine farm. The energy has to flow into the hydro plant, or from far distant turbines, so it's not so much a reduction in the grid requirements, as a change.

Domestic solar does have  big impact on the generating environment, because you fundamentally need less centralized generation. But then if you have more electrified trains or electric cars, then you're potentially increasing again the need for electricity generation to compensate for the reduction in diesel or gasoline. And then the grid topology changes yet again.

The way to think of the future energy system is not as a reduction or an increase but as a change and, hopefully, improvement.