These Technologies Show That The Future Of Energy Storage Isn’t (Only) Batteries

Energy storage


If you were to crown a king of storage technologies, batteries make a strong case. Battery storage is dominating the news and showing strong funding and M&A figures. However, many other energy storage technologies are currently in play.

The graphic below shows some of those storage technologies. It also illustrates a significant reason why batteries are not going to have it all their own way.

Energy storage

The energy output capacity is on the x-axis, while the y-axis shows how long a given energy storage technology is generally capable of delivering power for (without being recharged).

While it may be a bit oversimplified, the graph highlights a couple of points that I believe are crucial when talking about the future of energy storage. One is that while batteries are great for many use cases, they would struggle in some scenarios. Secondly, the future of energy storage is one of complementary, overlapping systems and technologies; if the capacity of the different energy storage technologies stays relatively stable in relation to each other, of course.

That is why the future of energy storage belongs to not one but a series of technologies. Something also illustrated by both funding and M&A figures. Below are ten of the technologies that I believe could play a role in the future of energy storage.  

Flywheel storage

Flywheels can deliver energy almost instantaneously. When demand is low, electricity is used to accelerate a cylinder spinning in a case, which is vacuum-sealed to reduce friction. When electricity demand is high, the resulting kinetic energy is converted back into electricity.

While somewhat smaller than the market for batteries, there is some funding and M&A activity – one of the latest being Convergent’s acquisition of 40 MW of flywheel energy storage.

Pumped Hydro

Quiet but efficient would be a fair way of describing the stored hydro market and technology. The basic principle is that whenever there is a surplus of energy, water is pumped up into a dam or similar holding area (for example a lake). When the energy need increases, it is run through a hydroelectric power station and turned into electricity.

Hydro-related M&A activity is high, in part because it provides up to 95% of current installed energy storage capacity. Data from the BDO deal database show that hydro is seeing a lot more M&A activity than any other energy storage technology. Something I hope to explore in detail in a later article.

ETES (thermo-electric)

Thermo-electric storage involves storing surplus electric energy as heat – or in rare cases cold. The usual storage medium is air. When the energy is needed, it is converted back into electricity.

This is a relatively simple technology with a potentially very large storage capacity. It is also amongst the cheapest ways of storing energy. Recently, Siemens began building a ETES wind to storage facility in Hamburg, and on the funding side, Axiom Energy raised funds from companies including Shell and Meson Capital to develop its technology.

Flow batteries

Flow batteries are similar to their regular cousins. However, instead of solid electrolytes, you have two tanks filled with liquid solutions. The solutions are pumped through two chambers, separated by a membrane, where an electrochemical reaction takes place (charge or discharge of the battery’s energy storage). The biggest advantages of flow batteries are that they can be recharged many times and can store large amounts of energy. However, they tend to be mechanically complex and require a lot of space. Increasing capacity you need to increase the tanks volume.

Flow battery companies have steadily been raising funds, with Primus Power’s $32 million round as one of 2017’s highlights. Bill Gates, Jack Ma, Richard Branson and many other tech billionaires are also investing in flow battery technology and energy researchers at IDTechEx project that the market for flow batteries will reach $4.5 billion by 2028.


Supercapacitors are energy storage’s speedsters. They can be charged in one to ten seconds and deliver energy almost instantaneously. They also have a long cycle lifetime and can be recharged thousands of times with very little change in their performance. The upsides are, to some degree, offset by their low energy density, meaning they are not optimal for storing a lot of energy or being used as a continuous power source.

However, they have many uses in relation to energy storage and renewables, including in microgrids and smart meters. Lux Research says that supercapacitors are going through something of a breakout 2018, with the market growing 128% to $836 million.

Compressed Air Energy Storage (CAES)

CAES involves taking excess energy and using it to compress air and pump it into a large holding space, for example an underground cave. When the stored energy is needed, the air is released and used to drive a turbine to make electricity. It is a cheap, relatively simple technology that can store energy for a long time; an especially useful quality in relation to renewables, which often see large seasonal fluctuations in energy production levels. Drawbacks include the need for large storage spaces – usually an underground cave – which are in limited supply or expensive to construct.

The technology has had its starts and splutters but is expected to grow at an annual CAGR of 27% until 2024. By then, the CAES market is expected to be worth more than $5 Billion. A big reason for that is likely startups like Hydrostor, Lightsail Energy, SustainX, Apex-CAES and Gaelectric who are all working on solutions that cut costs and use new forms of storage spaces for the compressed air.

Hydrogen Storage (Fuel Cells)

Hydrogen storage uses electricity, for example, excess production from solar panels and wind turbine generators, to extract hydrogen from water through electrolysis. Hydrogen is stored and can be re-electrified in fuel cells. While the efficiency of the process is relatively low (today around 30% to 40%), it is seeing a lot of interest, in part thanks to its high storage capacity.

Japan is perhaps the biggest advocate for hydrogen storage. The country’s goal is that one in ten households should have fuel cell technology installed by 2030. Japanese carmakers are also investing heavily in hydrogen storage, with Toyota recently making around 5700 of its fuel cell patents available on a royalty-free basis. While not the powerhouse it used to be, Japan is still one of the world’s largest economies, and its interest in hydrogen storage is one of the main reasons why the market is expected to reach $6.47 billion by 2025.

Methane Storage

Power to methane combines hydrogen from an electrolyser with carbon dioxide. The combination of the two is methane - natural gas. The gas can then either be stored or fed into the natural gas grid. It allows for storage of large amounts of energy, and the process of using CO2 means that the gas is almost emissions-free.

While still a relatively untested technology, researchers from the Karlsruhe Institute of Technology (KIT) in  Germany have trialled a methanation plant, capable of fitting in a standard shipping container.

Rail Energy Storage

When looking to store energy, you would likely not think of electric trains and big concrete blocks. However, that is the core of Advanced Rail Energy Storage’s solution. It uses electricity to drive small, electric trains, loaded with concrete blocks, to the top of a hill. When electricity is needed, the train slides back down the hill, and a regenerative braking system produces electricity as it goes. The longer the slope, the better.

While it may sound a bit bonkers, these systems are being tested in the US and calculations show that a large system could store thousands of megawatt-hours (MWh) of potential energy – enough to power a medium-sized city for several hours.

Electric cars

I believe that electric vehicles will play an important role in the energy storage grid of the future. Most cars stand still for more than 20 hours a day. During that time, an electric vehicle can double as a battery, saving up power during times when electricity demand is low and releasing it back into the grid during peak times.

Several companies are already trialling the technology. The potential is underlined by Technavio’s research report into the global vehicle to grid market, which is expected to grow at a CAGR of more than 18% until 2021.