Around 12.1% of US energy comes from renewable sources, but its grid only has the ability to store a pitiful 1%. As renewables such as wind and solar increasingly enter the mix, the need for the more storage will certainly need to grow considerably, too. So what technologies would be most energy efficient, if a whopping 80% of the country’s requirements were to be from renewables? Stanford University researchers Charles Barnhart and Sally Benson decided to find out.
They made a comparison of pumped hydroelectric storage, compressed air energy storage, and lead-acid, lithium-ion, sodium-sulphur, vanadium-redox and zinc-bromine batteries. The criteria in each case was looking at how much energy it would take to produce the technology, compared with the amount of energy it could store during a 30-year lifespan. The greater the ratio of energy stored to energy expended, the better the option the technology would be, over the longer term.
The report found that pumped hydro gave by far the best return in terms of energy stored to energy expended, with a ratio of 210. The best lithium-ion batteries, by comparison, only managed a score of 10, while the worst batteries, lead-acid, only score two. The reason for such small ratios is the relatively small number of recharge cycles. Lithium-ion batteries can handle at most around 6,000 cycles and lead-acid batteries only 700, compared to more than 25,000 cycles for a pumped hydro project.