Renewable energies such as wind and solar power produce intermittent power and have been known to produce more power than is actually needed at that time. Researchers from the University of Stanford have released studies as to whether it is more energetically sound to switch off the power sources at that point or attempt to use fossil fuelled batteries to store the energy for use when needed.
The Stanford Global Climate and Energy Project (GCEP) researchers tested pair solar and wind farms with five different types of batteries – lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine. The study looks into how much energy it takes to produce these batteries from mining the raw materials to make them all the way through their life cycle to maintenance of the finished product in use. The idea is that when pairing products like batteries that have a high (dirty) energy cost with something like clean wind power, the overall result is still positive clean energy production. This value is known as energy return on investment or EROI. Simply put, it costs energy to make energy – this study is to make sure that we are spending less energy than we are creating.
The results show that it would be “energetically favourable” to produce grid scale batteries with solar farms but not necessarily with wind farms. In wind farms it reduced the EROI by 20% (for lithium-ion batteries) to 50% (for lead-acid batteries) whereas curtailing only reduced the return by 10%.
“You wouldn’t spend a $100 on a safe to store a $10 watch,” said GCEP postdoctoral scholar Michael Dale, a co-author of the study. “Likewise, it’s not sensible to build energetically expensive batteries for an energetically cheap resource like wind, but it does make sense for photovoltaic systems, which require lots of energy to produce.”
However there are other options for wind power grid storage such as pumped hydro or using the excess power for other applications including charging a fleet of electric vehicles. The authors also say that increasing or doubling the life cycle of the batteries tested would be the easier way to come up with a positive result.
“Energy return on investment is one of those metrics that sheds light on potential roadblocks,” said co-author Sally Benson, the director of GCEP. “Hopefully this study will provide a performance target to guide future research on grid-scale energy storage.”