Glossary / Batteries and storage
Round-trip efficiency
The share of the electricity put into a battery or other store that can later be taken back out.
Charge with 100 units and get 80 back, and the round-trip efficiency is 80%. Lithium-ion batteries reach around 90%, pumped hydro 70–80%, and iron-air can fall below 50%.
Low efficiency costs little if the charging electricity is nearly free, and a cheap store can come out cheaper overall. A 2019 study by Oliver Schmidt and colleagues compared efficiency, capital cost, lifetime and duty together and showed that which storage technology is cheapest depends on the application[1].
Related terms
- Iron-air batteryA battery that draws electricity as iron rusts in air and turns the rust back into iron when charged. Its materials are extremely cheap, suiting it to storing energy for days.
- Lithium iron phosphateA type of lithium-ion battery with an iron-phosphate positive electrode. It uses no cobalt or nickel and is cheap, hard to ignite and long-lived.
- CurtailmentSwitching off or reducing solar or wind output that could have been generated, because demand or grid capacity is insufficient.