And? I'm still connected to the grid.

I think you are talking about off-grid vs. grid, but the others are not. The cost of solar applies also to utility companies, and I think that’s what GP was alluding to.

The grid will switch to solar + battery if it becomes cheaper than alternatives (gas, coal, nuclear, etc.)

Unless battery/storage tech gets wildly better, you're still going to have to have the natural gas turbine plants that we're currently using for peak demand power to smooth out the inevitable spikes and troughs in supply from solar/wind renewables.

It's such a damned shame that so many decades of potential progress in nuclear power were stymied by misguided FUD.

You're replying to a comment about the true cost of solar being the battery + the panels, asking why anyone would think of buying a battery.

That's why.

That still doesn't answer their question. Why does the sun going down at night matter for people who are still tied to the grid?

If I move into a house with a grid connection only, I budget on power costs = cost of grid connection + grid power price.

If I move to a house with solar panels, I budget on power costs = cost of grid connection + X * grid power price + (1-X) * solar price (which is the capital cost of the panels smoothed out over their useful life).

The issue here is that I can't maneuver into a situation where my power price = solar price without sacrificing my ability to do anything after sundown without candles. Clearly, the true cost of power in a solar-enabled house is going to be higher than the cost of the solar panels.