So much for " Cheap Green " SA Power, page-38

Acorn and I have crossed posts in the mail. But what I've written largely complements what he's said.

Take a system that is supplied on average by a 17% solar, 17% wind, 17% renewables biofuels, 17% interconnections to other systems, 17% battery storage, and 17% hydro/pumped storage.

Loose your wind for a few weeks and you are down just 17%. The rest of your system just needs to produce 20% more than it does on average through the year. No sweat.
Even if you put the make-up generation entirely on the hydro part of the system, all it needs to do is double it's average output for a few weeks. That would be easy stuff for any hydro scheme.

Knock out all your wind AND solar for a few weeks. If that was all put on your hydro it would need to treble it's output compared average. That too isn't at all unlikely for a well designed hydro system. They are typically designed to handle lots of rain/water inflows when they are already near full storage, because the electrical generating plant is usually a small part of an overall hydro scheme capital costs.

Then remember that fossil fuel generators have around 10% downtime a year for routine and unplanned maintenance. So a fossil fuel based system also has to have considerable redundancy to allow for that.

Then remember that a system needs to be capable of meeting peak demands that are typically double or more the average demand. And that every existing power system carries sufficient redundant capacity to be able to do that.

It should be pretty easy to see, when you break it down this way, that a system coping with loosing it's wind and/or solar for a few weeks isn't actually that big a deal.


As Amory Lovins and others have shown, it's pretty straightforward and economic to have a 100% renewables system. We haven't built one yet because we are just getting to the point where solar and wind plus battery are cheaper than coal and gas. To date we've just added cheap wind and had existing fossil fuel back up. But from here on solar + wind + batteries plus other renewables is where we are heading.