In reply to Hugh Bantin’s query about wind energy (8 May, page 32), yes, it is fickle and average output is about 30% of maximum

The biggest potential renewable energy sources with which we are blessed are wind, wave and tidal, but all are fickle, so other ways of generating energy will be needed for back-up. These need to be able to change output quickly according to changes in demand. The two best renewable sources in this respect are hydro and concentrated solar power (CSP), both of which lend themselves, crucially, to relatively cheap energy storage. Hydro has worked successfully in north Wales and Scotland, but the potential capacity is limited. A worldwide boom is occurring with CSP, but it is not viable until one goes south to areas like southern Spain or Greece. However, by using high-voltage direct current cables (HVDC) we could import such energy, losing as little as 3% per 1,000km. CSP with storage can enable close to 24-hours-a-day energy generation, and heat storage is only about a 20th of the cost of electrical storage.

HVDC grid links would also enable complementary energy trading. We could export our wind and wave energy southwards when this exceeds our needs (mainly in the winter), and import from the Mediterranean and even north Africa when those sources are strongest. The barriers are mainly political, vested interests, and lack of joined-up thinking, but readers can help by writing to their MP and asking them to sign early day motion 123 on this issue.

David Weight, Davis Langdon