Depends on what back-up you have got. In Sweden with 40% of electricity from hydro everything is handled by adjusting the flow in the dams. So barring exceptional circumstances (lots of nuclear down, cold winter, low water levels at the same time (which has happened too much lately)) the total amount of variation should be the important factor. And as I have presented elsewhere on ET, wind, hydro and nuclear in Sweden has about the same yearly variations.

I would like to see numbers from day-to-day variation for a country with decent amounts of wind and nuclear (and other types as well if possible) so that we could crunch the numbers once and for all.

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