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Siemens Gamesa claims 70 patents to make “hot rocks” a game changer

We told you something last week about Siemens Gamesa and its attempt to break into the Electrothermal Energy Storage or ETES market, and talked this week to Hasan Özdem, Head of Technology Management and Projects at Siemens Gamesa, to dig a little deeper.

Our big concern in our coverage last week was that the two conversion rates – one where the system retains most of the heat (98%) from heating industrial stones, and the other which is that once converted back into electricity it only outputs 45% of the original source energy. The electricity creates hot air, blown over stones to heat them to 800 degrees and uses a stream turbine to turn the heat back into electricity.

Özdem attacked this problem straightaway. “We need terawatt class energy stores, and while conventional batteries claim to retain 95% to 97% of their electrical energy, the truth is usually closer to 80%. But we envisage multiple revenue streams, including keeping the energy as heat and using it for district heating systems and for other industrial uses, and converting back to electricity for some of it. We really compete with longer term storage like molten salt, which many concentrated solar developers use to store their energy. We hear they are moving away from it because it is more expensive, and it requires constant energy to keep the salt heated.”

Özdem is referring to the idea that molten salt has to be kept in liquid form or it just freezes and needs an awful lot of energy to make it molten again. “You have to divert some of your energy to molten salt, even if you would prefer to use or sell all of your energy. With our product you can let all the stones go cold, and then switch it on, like a peaker plant, whenever you need it. I could have it switched off for two years, and then just switch it on, no problem.”

“We have been benchmarked against molten salt at two potential customer sites and so far we have won hands down,” said Özdem. We had previously been told that molten salt could support electricity to heat and back to electricity at about 70% efficiency, by Özdem insists this is not the case, and especially not when you factor in the idea that it needs a constant energy supply to keep it molten.

The stones in question are volcanic rock, about half the size of a fist, and the trial discussed last week has sourced them from a quarry in Norway, and Özdem says there is another plentiful supply in southern Germany. “The cost of transporting the rocks was more than the cost of the rocks,” he said.

So surely then this is a weak business if it needs cheap components and no intellectual property is involved? “We have been working on this for 9 years, and during the course of our work we have filed 70 patents. What if you want to heat up just 30% of the rocks to 800 degrees? If you pass hot air over all of them it will dissipate and they will reach around 300 degrees and you will have no heat. We have solved those types of problems and patented the results and we can deliver it 24/7 for 30 years.”

Özdem talks about the pilot in Hamburg-Altenwerder which he says can store 130 MWh of energy for up to one week, and says this will gradually increase to more than 1 GWh and the heat retention is close to 98%.

He makes two arguments – that there are heat requirements that he can partner over, and that even if you get 45% of the original electricity back from say a wind farm, it is better than that farm being curtailed. He has one potential partner where 70% of its energy is being curtailed. It still collects subsidies, but that will not last forever. Instead that curtailed energy is converted into heat, and it is used by a couple of factories, one which makes concrete and it can now look for others, such as steel plants, and the textile industry – which use ready supplies of heat and this would cut down their electricity bills.

One use it is seen for is to provide jobs and a function for existing coal plants throughout Germany. It could use the existing stream turbine as the electrical output.

In March we came across a similar plan from the German Aerospace Center who built a pilot putting a molten salt thermal storage tanks, again using excess renewable energy. Both of these projects use the coal plant’s existing steam turbine to create electricity.

“Germany has decided to shut down all of its coal plants by 2038, and of course we are all trying to come up with ideas that can retain some of the investment. But this is not just about Germany, we have been approached by South African interests. Currently they have frequent power outages which are so bad they are affecting the country’s GDP. They want an energy store which can act as a battery during those blackouts.”

The fact this ETES system retains 98% of its heat leads Siemens Gamesa to come up with methods of using this to recycle heat. “This is not like making wind turbines (its main business) because every time we talk to someone about building one of these stores, it can be applied in very different ways and we have to customize the design.”

One suggestion it is pondering is whether or not it will have a function in the future energy economy if green hydrogen is adopted widely. “I am skeptical about the hydrogen market, but the heat store is a great way of raising the temperature of water so that catalytic electrolysis works even better, to create green hydrogen, and we could build a hydrogen plant on the side. In Scandinavia there will soon be a law stopping any ship which burns carbon from entering a port, and so perhaps hydrogen will take off?”

We point out to Özdem that the latest ideas are to use ammonia instead of bunker fuel, and he adds, “Well you need hydrogen to make ammonia, so this can still help.”

“In the end we seen many forms of storage being used in the coming carbon free energy economy, ETES, pumped storage, hydrogen, Lithium Ion, Vanadium Flow, but each will have a slightly different job and be at a different location in the grid.” Why not do all of them as a single energy storage specialist?

“Well we are doing that, but you have to begin with something which is a market leader and the rest of those batteries, which mostly can be bought off the shelf, can be used to surround them. We have to prove this works first, and get it widely adopted.”

In March we also talked about a UK firm Highview Power which partnered Spanish TSK engineering group to co-develop gigawatt scale, long duration, energy stores using Highview’s proprietary cryogenic energy store technology. That deal too talked about needs identified in Spain, the middle East and South Africa. So we figure these to technologies may be head to head as Highview claimed cryogenic or Liquid Air Energy Storage (LAES) was chasing €1 billion in 1 GWh chunks by 2021, claiming many of the same benefits – being scalable, clean, with a long lifespan and deployable today and TSK said it had already completed 10 separate energy storage projects.

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