Wind and solar complementary

In my previous post I calculated the costs of wind and solar with various kinds of storage or "firming" added.  In practice, though, wind and solar are complementary, day-by-day and over the seasons: there is more wind when solar is reduced.  So the amounts of storage I included will be more than is needed, and will provide substantial redundancy.

These charts come from a presentation by Ramez Naam in South Africa. Because they are screendumps from the video, they're not as clear as I'd like.

The first chart shows renewables output in California on an average day.  Note how wind is strong during the night and solar during the day, just like it is in Queensland.  Typically, demand peaks during the day and into the evening, so storage would only be needed from 5 pm to say 10 pm.  5 hours, compared with the 10 to 12 hours I calculated.

In Germany, there's more wind in winter, compensating for less sunlight.  It's not perfect compensation: the total for wind and solar still fluctuates from month to month, so some storage, probably power-to-gas will be needed.  An alternative is HVDC (high voltage DC) lines to Denmark and the North Sea (windier) and Italy (sunnier) to cover any shortfalls.  To provide redundancy (i.e., over capacity) prolly both should be used.

Even with the substantial storage I added in to the costs of renewables, they are still cheaper than coal.  And with diversified supply, both by type and geographically, even less storage may be needed than the 10 to 12 hours I used.  This means the costs of renewables are even lower, and their advantage over coal greater.   Over the next 5 years, the only thing stopping the rapid transition of coal-based grids to renewables will be vested interests, not economics nor technology.