The energy sponge - Isentropic

The increased use of renewable technologies means that energy availability will fluctuate more. To counter this, a number of so called "energy sponge technologies" are being developed which can soak up excess any energy from the the grid, and then "wring" it back out when less is available.

James Mcnaughten is the CEO of Isentropic, a company looking to store surplus electricity as a temperature difference.

Kat - So, can you start by explaining to me basically, how does your technique work? 

James - The technology works by what we call a thermomechanical process where we take electricity and we use it to drive a machine - a heat engine - which creates a supply of hot and cold. We store the hot and the cold and then when you want your electricity back, you take your hot and cold, and you run it back through the heat engine, and this generates electricity which you feed back into the grid.

Kat -  What can you store this heat in? I mean, in a jar? Where do you store it?

James - So, we've spent several years developing what we call thermal stores. They're very large devices and they're really quite sophisticated. But the critical point is that we use a very simple natural material which is crushed rock as the actual media within these thermal stores to store the heat and to store the cold.

Kat - So basically, you've got hot gravel and you got cold gravel.

James - That's exactly right.

Kat - It sounds so simple. So, when you're taking the temperature difference between your hot gravel and your cold gravel and turning it back into energy, is this actually an efficient process because I know with things like the hydroelectric storage where they let water run down and then pump it back up so you can let it run down and generate energy when you need it, they're not terribly efficient?

James - I think in terms of efficiencies, it's often sort slightly misunderstood.  With pumped hydro, they have roughly 75% rounds trip efficiency. So, for every 4 units of energy you put into them, you get about 3 out. And that's an inevitability when you have real physical processes going on and we're no different. But the critical point about energy storage is that, it allows you to move electricity from a time of day when you don't need it, to a time of day when you need it. Effectually, it reduces the waste on the system.

Kat - I think because that's obviously the problem as we've discussed. You can't just suddenly turn everything on, turn it off. But how quickly can you flip this process around from storing electricity to releasing it back out when everyone needs to put the kettle on during Corrie?

James - Well, our system is very fst. We can go from full charging to full discharging in less than a second.  We spent a lot of time making sure that it would be able respond on a very quick basis because that's really what we see the market needing. If you have cloud cover going over and you imagine a big solar farm, you suddenly see a very rapid drop in power generation. Likewise, with gusty conditions around wind farms, you can see very rapid changes in power output over short periods of time.

Kat - So, this sounds like a great idea - you've got a technology that works, it's quite efficient, it's really fast. The big question is, how close is it? How close are you to making this reality that could be plugged into our greed?

James - So at the moment, we're building our first commercial scale system in our factory where we based in Fareham in Hampshire. We also have a contract to build a larger system to go on to a UK substation that should be operating in 2017. In terms of the time to roll out, it'll several years beyond that before you're able sell at large scale. So really, from where we are now to being in a sort of the ability to just apply commercially, you're talking about 5 or 6 years.

Kat - What sort of thing are we talking about in terms of size? I mean, I'm imagining - Chris has said to me a gravel of pit! What kind of size would these units be sitting next to a substation?

James - If you took a 20 by 40-meter industrial building, that would supply - basically be able to store enough electricity to supply a small town. So, 2000 homes to give you a sort of feel for the scale of it. We can obviously make them smaller, but that is the sort of - I think the maximum size would expect them to be built in any one installation.

Kat -  And just very briefly, I mean, this is obviously a very exciting technology.  Are you hopeful now that people are really starting to change the way we think about storing energy? Are you positive that this could be the way to do it in the future?

James - We see massive changes in the market even in the last year and it's been driven so that this is a sort of global change in interest. People have seen how far the price of solar panels have fallen over the last 4 years and you now have the situation where in large parts of the world, people can install solar PV without any subsidy at all. And actually, save themselves money. We see this phenomenon going. To manage this large amount of solar and in countries that are less sunny but windy wind, what you're seeing is people looking for solutions like energy storage because if you don't have energy storage, you end needing to have far greater number of power stations just sitting idle waiting for when the wind drops or the sun goes in. Energy storage effectively allows you to reduce that number of power stations and to waste less electricity.