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Comment by nephanth | Hacker News Reader

> In Europe, up to 60 per cent of renewable energy capacity goes unused on sunny and windy days. This results in the reliance on fossil-based energy resources such as coal or gas to meet electricity demands when renewable sources are unavailable.

I am really curious as to what hides behind this number. Afaik solar and wind aren't dispachable. You cannot just tell your solar panel or wind farm to stop producing energy if you have too much.

So if 60% of the capacity goes unused, it must be dispatchable hydraulic, in which case, isn't that kind of a good thing?

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> You cannot just tell your solar panel or wind farm to stop producing energy if you have too much

You absolutely can, this is called "curtailment". The turbine is disconnected from the generator and the generator from the grid, while the blades can be turned to not generate lift ("feathering"). Meanwhile in a solar panel the electron-hole pairs made at the junction just harmlessly recombine.

The issue is that often the subsidy payment structure is set up such that, if the renewables are curtailed, they still have to be paid for.

See "California duck curve": using batteries to bridge mid-day energy into the evening.

I didn't know that, thanks for the info

Wind energy is dispatchable. "Redispatch". Around here the wind turbines are turned off all the time when there's too much energy. The wind farm operators are compensated for that.

Solar is not as trivial which is why batteries and other storage mechanisms are important. Or Power to X things where power can be dumped if needed.

Huh? Solar panels can certainly be ‘turned off when there’s too much energy’ generation. In fact that’s their default state, they don’t generate any power until you pull current from them. They just sit there with a voltage difference across them.

Yes, that is true. I should have been more clear, sorry. At least in Germany most private solar systems cannot be remote controlled yet so it's harder to actively steer the generation. That is different with wind turbines.

Any source can be disconnected from the bulk electric system. If there is too much power and a generator is told to disconnect it is called a curtailment. Some contracts allow the generator to get paid for the power they could have produced but weren’t allowed to deliver due to too much supply / not enough load, so it isn’t really a good thing as the ratepayers still end up paying for the power not generated.

Dispatchable generally means you can tell the source when to generate as opposed to when not to.

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