If solar is used instead of nonrenewables, regardless of whether load has peaked, you decrease carbon output for each watt generated. In the chart on wikipedia,

If solar is used instead of nonrenewables, regardless of whether load has peaked, you decrease carbon output for each watt generated. In the chart on wikipedia, it looks like you could double California solar output without adding storage. If you want to provide 100% of your energy with solar, you'd need storage. But we're not at that point yet.