There is no such thing as a free lunch, and there is no such thing as “free” electricity. What is true is that there are going to be days in summer when supply exceeds demands and hence the value of electricity generated will be zero. Surpluses arise because a renewables-based system needs far more total generating capacity to guarantee supply at all times, including when the sun is not shining and the wind is not blowing. Using the UK as an example, meeting a peak demand of around 45GW may require roughly double the capacity compared with the “bad old days” of fossil-fuel-based generation, as well as twice the grid system and lots of batteries and storage. There are bound to be times when lots of that 120GW is generating but demand is low.

But excess electricity does not reduce the costs. These don’t magically go away. Investors will build wind, solar and nuclear plants only if they are paid through mechanisms such as fixed-price contracts, and households also need to fund the expanded grid, balancing and storage required to handle the extra capacity. As a result, “free” electricity during certain periods will still be paid for elsewhere – ultimately by consumers and taxpayers. Renewables are a good thing, but they need to be accompanied by an honest public discussion about the real system costs of decarbonisation rather than the promise of free energy.