It means some other infrastructure (fossil fuels?) needs to take up the slack, and people underestimate actual costs at larger scales.

It’s the big issue in Germany for instance - it’s all fun and games until Winter.

Germany has more wind in winter, so traditionally has more production of renewables in winter months.

Which is fine, since you're still reducing your reliance on the grid.

However, when you're off grid, underestimating capacity means your SOL and need to buy a generator and burn fuel on-site.

And? Any coal not used in summer is coal not dug up.