Renewables cannot be stored economically on a well-run power system

WREN and Visiting Prof, Kingston University, Woking, Surrey GU21 4XX United Kingdom

email: donald@swift-hook.com

Abstract

Economic storage on a power system must rely on arbitrage, buying electrical power when it is cheap and selling when it is dear. In practice, this means a store must buy power at night and sell it during the day.

There is no solar power at night [by definition], so solar power cannot be stored economically on a well-run power system. Also renewables [and nuclear] are installed commercially to save fuel but fuel costs the same at night as it does during the day, so there is no arbitrage on fuel-saving to justify storage.

Pumped water storage has always been widely used on power systems and is still the only method that is economic today, although many others have been tried, including fuels cells, compressed air and batteries. Devices for power correction and balancing [e.g. capacitor banks and batteries] may physically involve the storage of energy [just as a mobile phone does] but it is misleading to describe them as methods of power system storage, [just as it would be misleading to call a School bus a fuel transportation system, even though it does transport fuel].

When a power system has different sorts of plant generating - coal, gas, nuclear, wind etc - any power being put into storage is from the plant that would need to be switched off [because less power was needed] if storage ceased [e.g. because the store became full or failed]. On a well-run power system, that always has the highest fuel/running cost, but the wind blows free and has zero fuel/running cost, so wind is never [normally] stored unless there is no other plant on line i.e. wind power is the last to be stored.