By Jason Deign

Everyone is looking to cut the cost of energy storage. But when it comes to storing a lot of energy, say gigawatt-hours instead of megawatt hours, cutting the cost of battery manufacturing, for instance, probably won’t do the trick.



It’s at this scale that other technologies come into play. The most obvious one is pumped hydro, which still accounts for the lion’s share of all energy storage worldwide.

Pumped hydro has limitations too, though, such as where you put it and how you pay for it. That is why a host of energy storage firms are looking at alternative bulk energy storage concepts.

Some of these concepts, such as flow batteries or hydrogen storage, are already well enough established to count as mini-industries of their own. Each has its own ecosystem of businesses.

Beyond these mainstream energy storage technologies, though, are ideas that are still largely experimental, populated by an assortment of companies driven more by enthusiasm than market clout.

What follows is a selection of ones we’ve come across recently. By all means, marvel at their ingenuity, but don’t write them off just yet… who knows if some of the names on this list will be helping to power our grids tomorrow?

Cryoenergy: using air for thermal energy storage

Secretive Florida-based start-up Cryoenergy hopes to breathe new life into an existing concept, liquid air energy storage, by taking components perfected in the industrial gas sector, breaking them down and optimising them.

Cryoenergy’s aim wasn’t initially to produce an energy storage system. But when used to store energy you “get a much better efficiency overall,” claimed founder Mark Cann.

The company is due to release details of its technology in the coming weeks, but for now observers remain to be convinced.

“Liquid air storage has been around for a long time, so if it was economically viable I would imagine we would have seen it by now,” said Daniel Finn-Foley, an energy storage analyst with GTM Research.

Energy SRS: gravitational potential energy storage

Take a weight attached to a long cable wound around a drum. Suspend the weight over a deep borehole. Drop the weight down the borehole and use the motion of the drum to drive a turbine. Winch back up when energy is available.

That’s the simple concept espoused by Energy SRS of Swansea, UK. The company reckons its gravitational potential energy storage system would have a round-trip efficiency of up to 80% for a 3.4MW, 1.2MWh unit.

Exergyn: an engine that runs on hot water

Dublin, Ireland-based Exergyn claims the amount of energy lost globally each year as wasted hot water is equivalent to twice the oil and gas output of Saudi Arabia. And it wants to turn that wasted heat into electricity.

As described in Scientific American, Exergyn’s secret is a shape memory alloy called Nitinol, which contracts under hot water and can thus be used to drive a piston.

According to its website, Exergyn hopes to trial a 10kW ‘Exergyn Drive’ prototype this quarter. “The Exergyn Drive can also store energy and provide solutions for energy storage applications,” it says.

HeatVentors: improving efficiency of heat systems

The European Institute of Innovation and Technology says Europe wastes €20bn every year through poor thermal storage. Hungarian firm HeatVentors aims to stem that loss with phase-change materials.

In details posted on start-up website F6S, HeatVentors says its HeatTANK product could increase thermal storage system efficiency by up to around 15%, while decreasing the volume needed by almost 88%.

Highview Power Storage: liquid air energy storage

Like Cryoenergy, Highview Power Storage is focused on liquid air energy storage.

The difference is that Highview is already well on the way to commercialisation, with a 5MW, 15MWh demonstrator due to go live any moment now. If Highview can get it right, the company could be onto something.

“The closest analogue would be pumped hydro, but liquid air wouldn’t require a geological component such as an existing dammed reservoir,” said Finn-Foley of GTM Research.

Max Bögl Wind: turbine-powered wind batteries

Another way to get around the need for an upper reservoir for pumped hydro installations is to store water in wind turbine towers instead. That’s the view of Max Bögl Wind, based near Nuremburg in Germany.

Max Bögl is working on a pilot project that, when complete, is expected to have a total capacity of 16MW and 70MWh.

Pintail Power: two storage concepts for the price of one

Former concentrated solar power executive Dr Bill Conlon isn’t taking any chances when it comes to energy storage.

His company, Pintail Power, aims to “synergistically combine thermal and cryogenic energy storage,” according to his LinkedIn page.

The cryogenic component is our old friend liquid air, while for thermal storage Pintail appears to favour hot oil. Further details will presumably have to await a pilot, whenever that may be.

Catch up with the latest industry innovations at Energy Storage Europe in Düsseldorf, Germany, from March 13 to 15.