Neither storage nor interconnectors can provide a viable solution to the problem of intermittency, and wind and solar output are not complementary as some have claimed.
“With the energy storage technology available for the foreseeable future, no combination of wind and solar energy with backup storage would be suitable to supply a significant proportion of grid electricity without full conventional backup being available,” the report said.
The conclusions are based on a model solar fleet with a capacity of 8.4GW. The report said it was necessary to model a fictional fleet because all solar generation is currently connected to the distribution grid and therefore only reports summary data over extended periods, rather than the half hourly data available for all other generation. Ten years of historic weather data was used to estimate production levels, variability and intermittency.
The report found that the average annual load factor for the model fleet – the ratio between the maximum possible output and the actual energy produced – would be just 9 per cent when the panels were newly installed. The efficiency of solar panels reduces over time and so it could average as little as 8 per cent over the fleet’s lifetime, falling to just 7 per cent after 25 years.
It would produce “hardly any power” when demand is highest over the winter. The average load factor would fall to 4.8 per cent over the season and reach a nadir of 3.6 per cent in December. “No generation occurs overnight and solar generation can make little or no contribution to meeting the UK maximum demand period which occurs in the winter months between 4pm and 8pm each weekday,” the report said.
Output would also be “severely intermittent”, dropping below 10 per cent of installed capacity for nearly 5,800 hours – or 35 weeks – each year and exceeding 60 per cent for only seven hours.
Output from the model solar fleet
Source: The Adam Smith Institute
The report said the entire fleet would have the same delivery capabilities as 882MW combined cycle gas turbine, which would cost a fraction of the price to build. The lifetime production of the present solar fleet in the UK could be matched within seven years by a 2.5GW nuclear plant which would occupy far less space.
Combining the modelled solar fleet with the current wind fleet does little to improve things. Output would fall below 10 per cent of their combined 18.4GW capacity for around 16 weeks each year and would surpass 60 per cent for just 30 hours. Daily output could fall to as little 5.6 per cent on some winter days: “The level of dependable power output seems negligible – perhaps a few hundred megawatts at best.”
Storage and interconnectors could do little to solve this problem. Pumped storage would be the “best and most cost-effective” solution for large-scale storage but would be “enormously expensive” and have a “severe environmental impact” when deployed on such a huge scale. Batteries would be “even more expensive” and would require frequent replacement.
“Interconnectors to a northern European renewable-energy grid would be ineffective, because both solar and wind resources vary with time across the region in much the same way as for the UK,” it added.
Despite its findings, the report said solar panels could still have a “useful role” to play as a source of space and water heating – “an option which has been successfully implemented in New Zealand in the past”.
It conclusions contrast with those of a recent report by Aurora Energy Research, which found that the cost of integrating the UK’s current solar fleet will be “negligible” by 2030. It said tripling the fleet to 40GW would incur an integration cost of just £6.80/MWh by the end of the next decade.