Building a 100% renewable – and affordable - energy system is challenging for any country, but for the UK it is particularly difficult. Solar power is likely to be the biggest contributor to low carbon energy worldwide in the coming decades, but it is most suited to hot countries that require most energy in the summer months to power air-conditioning. The UK, where our energy demand is highest in winter, is just not that suited to solar power.
So what about wind? Britain is a windy island with a long coastline that makes it a prime location for fleets of wind turbines dotted around the country. Recent cost reductions achieved in the wind industry have made this an even more attractive proposition - but the wind does not always blow. An energy system highly reliant on a weather-dependent technology will always be vulnerable to extreme weather events or even just a cold snap in winter.
This concern is particularly relevant this month. In a new report I’ve written for Policy Exchange, I plotted the combined solar and wind output for January 2017 for the UK. Solar output, as expected, was almost negligible in a dark winter month compared to summertime. Wind output was high but extremely variable. In the second week of the month, British windfarms generated around six gigawatts of electricity almost continuously (about 10% of total peak electricity demand), but in the following week this fell by a factor of six. If the UK decides to pursue 100% renewable energy it will need a strategy to meet demand in a cold week in January.
There are a number of storage options, none of them ideal. Battery technology gets the most attention when in comes to electricity storage, but batteries are most suited to providing fast bursts of energy to meet short spikes in demand or for storing solar energy during the day for use at night. They are not suitable for long-term large-scale storage. For example, we would need 200 million Tesla Powerwalls to provide 20 gigawatts (about 50% of average winter demand) continuously for five days. At current prices this would cost £1 trillion, an unacceptable burden for energy bill payers. Large centralised battery facilities could bring down the cost a bit and individual battery prices will decline over time as the technology improves and manufacturers become more efficient. But there is still a long, long way to go before using batteries for large-scale long-term energy storage can be considered a good idea. It is not even an environmentally friendly option at present as the greenhouse gas emissions involved in mining the metal components of batteries are significant.
There are other technologies that are more suitable for large-scale energy storage and the Government should assess their viability in a UK context. Pumped storage hydro, compressed air, and ‘hot rock’ storage all have potential, but they are typically geographically dependent. The UK has used up most of its suitable sites for hydroelectricity and flooding valleys around the country would not be a popular strategy to create the hundreds of new facilities that might be required to provide the backup power we need.
That leaves the option of conventional power stations. We could, in theory, have hundred of gas turbines dotted around the country sitting idle for most of the year and only being used a few days per year when wind and solar output is low, but this would make for an inefficient energy system.
In order to assess the system cost of any new energy technology it is always a good idea to take into account system costs. To do this academics in the field of energy policy create computer models of our whole energy system and calculate the likely cost of different energy mixes. There is disagreement over the exact system integration costs of intermittent technologies like solar and wind, but there is general agreement that these balancing costs increase steeply as you begin to get over 50% solar plus wind and they are extremely high as you approach 100%. This is because the more solar and wind you have, the more inefficient unused storage you need.
Having nuclear energy as part of the system is still a good option. Given the spiralling costs of large nuclear reactors in the West, we should investigate whether small modular reactors (SMRs) are a technology worth pursuing. SMRs can be built in factories, so could be cheaper and faster to install than plants like Hinkley Point, and they could offer additional benefits in the future in the decarbonisation of heat and hydrogen production.
The late Sir David MacKay, ex-Chief Scientist to the Department for Energy and Climate Change, said in his last interview that the idea that the UK could power itself on 100% renewable energy is an ‘appalling delusion’, that we still need some nuclear power and we need to get on with developing carbon capture and storage. The astonishing progress of solar and wind is something to be celebrated, but the laws of physics do not change. We need huge amounts of low carbon energy in order to completely decarbonise electricity, heat, transport and industry. This mammoth task will be a lot more achievable if we accept that renewable energy cannot do it all.