As the consequences of climate change become ever more apparent, investments in renewable energy are seen as crucial to safeguarding the future of the planet.
Renewable sources, including wind, solar and hydroelectric, currently account for about a quarter of global electricity generation – a proportion that is set to increase as part of efforts to decarbonise.
However, the sector still suffers from constraints. The most common criticism of renewables is reliability because output fluctuates according to, for example, the time of day, the weather and, in the case of hydroelectric power, seasonal river flows.
Making renewables more reliable
This is where energy storage comes into play. Grid-scale storage involves technologies that are linked to the grid and can send power back into it when necessary.
Pumped-storage-hydropower, where water is pumped into a reservoir and released at another time to generate power, is currently the biggest form of grid-scale storage.
UAE leading the charge
Demand for battery storage is also growing, as scientists are working to devise devices that are more efficient and – crucially – affordable.
Some of that research is taking place in the UAE, as evidenced by a recent announcement by Dubai Water and Electricity Authority (Dewa).
The organisation revealed that it had filed a patent for a chemical liquid said to make energy systems more efficient. The liquid could, Dewa said, be suitable for lithium-ion batteries and fuel cells.
Lithium-ion batteries are among the most important methods of short-term energy storage. They typically last up to a few hours, and can level out demand on the power grid.
As renewable energy ramps up and electric cars (which typically use lithium-ion batteries) are manufactured in ever-greater numbers, demand for lithium is on an upwards trajectory – so what is getting in the way of producing enough?
“From the point of view of technology, there’s actually no reason nowadays to not implement 100 per cent renewable,” Prof Fabio La Mantia, who works on energy storage and conversion at the University of Bremen in Germany, said.
“The limitation is how much do you need? Where will we find all the materials? And how much do we have to pay for 100 per cent renewable instead of fossil fuels?”
He added: “So the research, the new technology, is to find materials that are more abundant, less problematic, more safe and cheaper systems – new technologies that are simply cheaper.”
Is zinc the answer?
A few alternatives are being looked at which use materials that don't break the bank.
These include batteries using what are sometimes called post-lithium-ion technologies, including lithium-sulphur and lithium-air, and post-lithium technologies, which include zinc-ion, potassium-ion, sodium-ion and magnesium.
“They’re following similar principles in the way the system works, the battery works, however using different materials that are cheaper,” Prof La Mantia said.
“Zinc is nowadays getting a lot of attention; magnesium a little bit less. Zinc is really more abundant than lithium – four to five times more, but less than sodium. From a safety point of view, the industry is interested in zinc products, they’re cheap to assemble and to produce.”
What does the future have in store?
Renewables will require serious progress around medium-term and long-term energy storage.
The global demand will be “huge”, according to Prof Yulong Ding, director of the Birmingham Centre for Energy Storage at the University of Birmingham in the UK.
He said that in the UK alone – which has less than one per cent of the world’s population – the demand for energy storage by 2050 will be as great as the current total global capacity.
“Different countries have different [demands],” he said. “For example, the UAE is very hot, so their need for heating is minimal but their need for cooling is high. But broadly, the needs for storage will be similar, namely short-term, medium-term and long-term storage.”
There are several technologies that could be used for medium-term storage, ranging from a few hours up to several weeks and even months.
Some of these involve what are called phase transitions, including systems that use energy to compress, cool and liquefy air. This liquefied air releases the energy stored within it when required.
Mechanical forms include compressed storage, which uses energy to compress and store the air, often underground, before it is released when needed to generate energy.
Hydrogen, Prof Ding said, can be used for long-term storage. “This could store energy for years,” he said.
With investments expected to be up to trillions of dollars by 2040, when some analysis suggests energy systems should have decarbonised in order to hit climate goals, energy storage is set to be big business – and an essential one.