New Energy World™
New Energy World™ embraces the whole energy industry as it connects and converges to address the decarbonisation challenge. It covers progress being made across the industry, from the dynamics under way to reduce emissions in oil and gas, through improvements to the efficiency of energy conversion and use, to cutting-edge initiatives in renewable and low-carbon technologies.
Energy storage – long and short-term
19/11/2025
8 min read
Feature
Lithium-ion batteries sometimes seem to have taken over the world, as they are nearly universal in consumer electronic devices. One of their most obvious benefits is that they retain charge for a substantial length of time, writes Toby Clark.
But not all applications need that ability to remain on standby, and this opens up the possibility of using various types of battery chemistry and even completely different types of energy storage. They range from capacitors used with tiny indoor photovoltaic (PV) cells to power tiny Internet of Things devices, to giant thermal ‘sand batteries’ which retain the heat from large-scale industrial processes, and iron-air batteries which harness ‘reversible rusting’ to give energy output duration of several days.
A clear application for short-to-medium-term storage – for a matter of hours – is ‘load levelling’ (sometimes called ‘peak shaving’) where power is stored during low demand (or high supply) to be released in periods of high demand (or low supply). A more sophisticated use is ‘grid forming’ to stabilise the power output and AC frequency of the network – particularly relevant when intermittent energy sources such as wind and solar are part of the mix.
Round-trip efficiency is the measure of how much energy is returned from the storage system compared with the energy put in. It is usually expressed as a percentage: some lithium-ion batteries can achieve 95% (although 85% is typical) while lead-acid batteries struggle to reach 80%. Pumped hydroelectric is around 75% efficient, while ‘green’ hydrogen manages only around 40%. Perhaps surprisingly, large thermal batteries can have a round-trip efficiency of 90%+, and flywheel-based kinetic batteries can reach 98%.