European power traders have had a trying time over the past few years, as an onslaught of generation from renewable sources has fundamentally changed the continent's energy mix. While natural gas, coal and nuclear power were once the preferred means of electricity generation in Europe, heavy subsidies have caused renewables – including solar, wind and hydropower – to account for a rapidly growing share.

Renewable energy is intermittent – in other words, it cannot be turned on all the time – and