Researchers at Stanford University's Global Climate and Energy Project have published the results of a study of the energy efficiency of different ways of storing energy on the electricity grid.

The study found that compressed air and pumped hydro storage are by far the most energy-efficient techniques.

Over its lifetime, compressed air storage can store 240 times more energy than is needed in its construction. Pumped hydro can store 210 times more energy than is needed to build it.

Of the five battery technologies tested, lithium-ion batteries were the best performers, storing 10 times as much energy as is required to manufacture them.

Sodium-sulfur batteries store 6 times, vanadium-redox batteries store 3 times and zinc-bromine batteries store 3 times as much energy as is used in their manufacture.

The least efficient technology was lead-acid batteries which, over their lifetime, can store just twice as much energy as is needed to manufacture them.