Alternative batteries solve renewable energy’s biggest problem

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Many of the cheapest and cleanest sources of energy depend on environmental conditions – turbines can’t spin if the wind isn’t blowing and solar panels can’t harvest power if the sun isn’t shining (usually ).

Fossil fuels don’t have this consistency problem – you can burn coal or natural gas anytime to generate electricity – so we rely on them when renewables aren’t available.

Storage Renewable energy when supply is high can accelerate the transition to a world powered by clean energy, but traditional lithium-ion batteries, like those in your smartphone, aren’t perfect for this use.

Many of the cheapest and cleanest sources of energy are dependent on environmental conditions.

This is because these batteries are self-discharging, which means they are constantly losing some of their stored energy. Therefore, we can only store energy in it for a a few days or weeks – we cannot store the energy captured in the windy spring and use it in the relatively calm autumn.

However, lithium-ion is not the only type of battery.

Around the world, groups are using other types of batteries — some well-established, some brand new — for renewable energy storage. Here are some of the alternative batteries that are helping the world decarbonise and transition to a more sustainable future – one grid at a time.

Water batteries

People have been using gravity to store energy for over 100 years with pumped hydroelectric storage systems, or “water batteries.”

These systems require two lakes or reservoirs, one located at a higher elevation than the other.

When the network has excess energy, it is used to pump water from the lower reservoir to the upper reservoir. When more power is needed, the water in the upper reservoir comes down again, which drives hydroelectric turbines.

An infographic showing how excess energy is stored in Nant de Drance’s “water battery”. Credit: Nant de Drance

Benefits: Water batteries are among the cheapest ways to store energy in terms of kWh, and we know they work – there are over 150 already in service and accounted for around 95% of the world’s energy storage capacity in 2020.

That means we don’t have to worry about developing new technologies to use for renewable energy storage, and the United States has enough technically feasible sites to double the amount of energy they store in water batteries.

The inconvenients : Building water batteries is expensive and time-consuming, and building one in a location with little elevation change or no natural reservoirs is particularly expensive.

Massive water batteries also face issues common to many megaprojects: delays and cost overruns. The largest pumped hydroelectric project in the world, Snowy 2.0 in Australiais six years behind schedule and will cost three times as much as originally projected (not including network upgrades to accommodate it).

Efficiency is also a concern: you lose 15-30% of your energy in the up and down cycle of water, and certain types of reservoirs (river dams, for example) can disrupt natural ecosystems.

The last: The Nant de Drance pumped storage power plant in the Swiss Alps became operational in July 2022. With a storage capacity of 20 million kWh – up to 400,000 EV batteries – it’s one of the most powerful water batteries in Europe (albeit a fraction of the size of Snowy 2.0).

The developers dug more than 10 miles of tunnels to connect the Emosson and Vieux Emosson reservoirs for the water battery – in total the construction process took 14 years and cost $2.1 billion.

sand batteries

Another way to store excess renewable energy is to trap it as heat in certain materials, such as water, volcanic rockor — the last medium to explore — the sandin a well-insulated container.

When electricity is needed, the heat from a sand battery can be used to boil water, creating steam that spins turbines. Heat can also be distributed directly as heat, keeping buildings warm during the winter months and supplied with hot water throughout the year.

For some forms of clean energy, such as wind power, storing sand first requires converting electricity to heat, but solar and geothermal energy can be captured directly as heat — no conversion required.

renewable energy storage

Polar Night Energy’s sand battery helps heat homes in Finland. Credit: Polar Night Energy

Benefits: Sand is cheap, widely available and easy to store. It can also be heated to higher temperatures than other battery media, such as water – with the right insulation, it can exceed 980 degrees Celsius (1,800 degrees Fahrenheit).

Sand batteries could be built virtually anywhere – they can even be built underground to save land.

The inconvenients: Energy is lost when it is converted from one medium to another, so a thermal battery is not as efficient at generating electricity as it is for direct heating.

New technology could change that, however – MIT recently unveiled a heat engine that converts heat into electricity more efficiently than a traditional turbine.

When the stored heat from the sand battery is used directly as heat, it is 99% energy efficient.

The last: The world’s first commercial-scale sand battery is now operational in Finland. The battery looks like a silo, but instead of wheat, it’s filled with 100 tons of sand that can be heated to 500 C (932 F) using excess solar and wind power.

The sand battery has a capacity of 8 MWh (roughly equal to 160 electric vehicle batteries), but unlike lithium-ion batteries for electric vehicles, it can store this heat for months, with little loss. When the heat it stores is used directly as heat — what it is actually — it is 99% energy efficient, according to its manufacturer, Polar Night Energy.

Flow batteries

Compared to water and sand batteries, flow batteries are a technically more complicated renewable energy storage solution.

They consist of two liquid reservoirs electrolyte solution. In one tank the solution is positively charged and in the other it is negatively charged. These solutions are pumped into a cell, where they remain separated by a membrane.

In this cell, the chemical energy of solutions can be converted into electricity and discharged, or vice versa, by a process involving electrodes and the movement of electrons and ions.

renewable energy storage

This diagram illustrates what happens inside a flow battery. Credit: VRB Energy

Benefits: Compared to their lithium-ion cousins, flow batteries are less likely to catch fire and lose little storage capacity, even after thousands of cycles. Their self-discharge is lowand when the flow battery is not in use, it does not waste any energy.

Flow batteries are easier to scale than lithium-ion batteries – instead of building more batteries, all you have to do is increase the size of your tanks – and because they don’t Not dependent on geography, they can be installed in more places than water stacks.

The inconvenients : Flow batteries are relatively new in terms of renewable energy storage – as of September 2021, global installed capacity was barely 1.1 million kWh (~22,000 EV batteries) – so they are not as proven as water batteries.

Flow batteries also have a lower energy density than lithium-ion batteries – you need large reservoirs to store a lot of energy in them – and most of them require vanadium, a metal which should increase in demand and cost.

renewable energy storage

A sample of the semi-solid substance used in MIT’s flow battery. Credit: MIT / Annelisa Leinbach

The last: In November 2021, researchers at MIT published a paper detailing their creation of a new flow battery that replaces the traditional liquid electrolyte with a thicker, jet-black substance that resembles molasses.

The recipe for this electrically conductive blend does not include vanadium, and in testing it has outperformed traditional vanadium flow batteries in performance and cost – ironically suggesting that the future of energy may rest on a black mud, just like the past.

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