Dave Elliott: As the capital cost of wind and solar photovoltaics (PV) falls, some say it makes sense to oversize their installed capacity, to ensure that a greater proportion of energy demand can be met during lower wind or PV-availability periods. Even if it means that, at other times, there would be too much power output and a need to dump, or curtail, it. As I noted previously, the UK Energy Research Centre (UKERC) made that point years ago — curtailment of excess output is not necessarily economically irrational. “Some level of curtailment may be both economically rational and sensible from a system operation perspective — so, in isolation, a degree of curtailment is not necessarily an indicator of the unsuitability of any particular form of variable renewable generation,” the centre said. However, curtailment is still a waste of potentially valuable green power, even if it is only valuable if it can be used at some other time. Hence the attraction of storage, and, in particular, “Power to Gas” (P2G) conversion of surpluses to hydrogen, which can be stored if necessary over long periods and later be converted back to power to meet demand peaks and/or long lulls in wind and solar output. The bottom line? Overcapacity may be sensible, especially if the resultant surpluses are converted to hydrogen to help with balancing and/or for heating, vehicle and industrial applications. If the cost of P2G electrolysis is low, overcapacity and P2G combined would limit the need to have fossil backup plants to deal with renewable variations, and also reduce the economic problem faced by renewables — that they cannot always generate power at peak demand times, when prices are high, and may generate at times when demand and prices are low. Instead, with P2G, they may be able to expand even more, while providing their own balancing and finding a range of new markets, so helping to cut emissions even more. Sounds too good to be true? In my next post I look at some of the problems with P2G and hydrogen gas distribution.
Physics World 24th July 2019 read more »