What happens when the wind stops blowing / the sun goes in?
This is called intermittency and of course depends on which renewable source you use. Renewables that use fuel, such as biomass and biogas, can be treated as non-intermittent (or ‘on demand’) generators, just like a fossil fuel station. Others are intermittent to a greater or lesser extent. Wind turbines, for example have an output related to wind speed, and may need to shut down in very high winds. Solar generation stops at night, so is also intermittent, but more predictable. Tidal energy is intermittent but thoroughly predictable. The effects of such intermittency are moderated by the use of the grid network, where many generators feed in together and the variations in any one are therefore made up by the output of the others. The National Grid Company has estimated that intermittency would be a minor issue up to about a 15% contribution from wind power, for example. The effects are further mitigated by having a broad geographic spread of projects (the sun is usually shining somewhe
