In the last piece on this website I argued that the most effective means of completely decarbonising electricity supply in the UK and elsewhere is to hugely expand the capacity of wind and solar power. This will mean frequent substantial surpluses of electricity when the unneeded power will be converted to hydrogen via electrolysis. This hydrogen can then be used an energy source for use in combined cycle gas turbine plants during periods of electricity deficit.

I suggested that the UK needed approximately 4.5 times its existing resources of wind and solar power to carry out this strategy. These resources would provide enough electricity to cover all electricity needs, including in periods of deficit. The assumptions behind this number are overly simply but gave a good indication of how much new wind and solar would be needed. I also said that the country would have needed about 75 GW of electrolysers to ensure that all electricity generated would be used.

This brief article now looks in a little more detail at the requirements for electrolysers. In particular, I ask the question ‘how much more electricity generating capacity would be needed if we restricted the availability of electrolysers to much lower levels?’. The logic is this: 75 GW would only be needed for a few half hour periods a year so if we had less capacity, we would lose relatively small amounts of hydrogen. We would have to make up this loss by installing more wind and solar but this might be less costly than installing huge amounts of electrolyser plant.

I also made one important change to the spreadsheet. I previously assumed that wind and solar would produce all the the electricity needed in each of the 17,520 half periods of the year to 30th June 2021. This ignored other low carbon sources. So for the exercise covered in this article I included nuclear power, biomass and hydro as low carbon sources. In each period I therefore took the total demand figure and deducted the amounts of power provided by these three types of generator. This reduces the electricity required from wind and solar.

The change substantially cuts the additional capacity required from these sources of power. Instead of needed 4.5 times as much solar and wind as today, the UK will only need a 3.4 times multiple. As a consequence, the maximum demand for electrolyser capacity falls from 75 GW to around 55 GW. To be clear, a 55 GW need arises because in at least one half hour period in the year under analysis, a 3.4 times multiple of wind and solar capacity would have resulted in 55 GW of unneeded electricity that would have been available for conversion into hydrogen.

But is it worth investing in as much electrolyser plant? If much of the capacity is only used a few hours a year, would it be better to install a smaller capacity for making hydrogen? This would mean that some electricity would be wasted at times of high production. However this could be compensated for by increases in solar and wind capacity that would produce more power in periods of lower surpluses.

The chart below shows how what multiple of current wind and solar power would be needed to compensate for reduced electrolyser capacity. This exercise shows that partially restricting electrolyser availability has little impact because the number of hours of very substantial electricity surpluses were few in number across the year under study The addition requirements for renewables are very small indeed until electrolyser installations fall to less than half the maximum 55 GW total.

I then compared the costs of installing 55 GW of electrolyser and a 3.4 times multiple of current wind and solar with an alternative of 20 GW electrolyser capacity and 3.59 times these renewables.

I think the approximate number suggest that the reduction in required electrolyser capacity reduces costs by about twice as much as the increased need for investment in renewables.

The conclusion seems clear. It would be much better for the UK to go for 20 GW of electrolysers (or perhaps less) and a 3.59 times multiple of wind and solar. In addition, there is further smaller advantage. A 3.59 multiple, rather than 3.4, means that in periods of deficit the requirement for combined cycle gas turbine capacity to turn the hydrogen back into power would be slightly less.

In addition, it is worth pointing out that the total amount of electricity generation necessary to cover the UK’s needs in the year to June 2021 would have been about 1.25 times eventual demand, after taking into account the energy losses from the conversion into hydrogen and back again. Let’s mention one of the implications of this. If new renewables can now be commissioned by commercial developers at prices of £40 or less, the full electricity cost of 1.25 times means an underlying wholesale price of electricity of £50 (before the costs of electrolysers and CCGT). ‘Renewables plus hydrogen’ can work effectively as the key decarbonisation weapon, and the cost is less than any alternative.