Comment by rgmerk
11 hours ago
It's not clear (yet) what a 100% clean energy powered world would use to cover the last couple of percent of demand when loads peak and/or variable generation troughs for extended periods.
It'll be some combination of demand management (which isn't nearly as horrifying as people make it out to be), pumped hydro, long-duration batteries like iron-air, but also possibly burning hydrogen or hydrogen-derived synthetic fuels (produced by electrolysis when hydrogen is abundant) and/or biofuels in turbines.
Or very long term thermal storage, as from standardthermal.com
This would also need some sort of turbine to convert back to electrical energy.
Somebody calculated that a home in UK needs 1 Megawatt-Hour battery to backup solar energy during the winter. I suspect in 10 years that may cost below 25K, a small fraction of the property cost.
But is it really 1 MWh of _electricity_, or could you replace a good chunk of that with a huge tank of boiling water? In the winter, about half of my electricity consumption goes to my heat pump, to produce 45-50C water for heating and tap water. But if we could increase the reservoir temperature to 95C (or even go superheated to 160C at 6 bar), then it could supply the 45-50C flow temperature much longer without needing to recharge.
There is a time- honored, straightforward way to deal with the last two percent problem, which is to overbuild by a couple of percent or so.
That’s not how the maths works unfortunately.
Basically, you end up having to overbuild to crazy levels, or build insane amounts of battery storage, which only gets used a few days a year.
That is right (if rather exaggerated, and I will note that it was you who originally picked the figure of two percent), and in practice, we accept a certain risk that we will not always have all the capacity we want, even though (or because) we cannot precisely predict how big or often these events will be. There is no particular reason to think this specific case is any different.
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