Ecovat has designed a system where a supersized tank can store hot water underground. “In conjunction with sustainable systems for generating energy such as solar thermal panels and a heat pump powered by wind energy, the Ecovat system is able to heat thousands of homes without any CO2 emissions in winter. And can cool these down in summer too,” says founder Aris de Groot.

What motivated you to set up Ecovat and what problem did this resolve?

“In 2011 I looked into how you could make buildings more energy efficient on behalf of a client. It turned out that 80% of the average energy bill is spent on heat, most of which you use in winter. Whereas it’s mainly in summer when you can generate plenty of sustainable energy, as is the case with thermal panels. Even though you don’t actually need that heat right then. That’s when I started thinking about a way to store the heat that you generate in the summer so that you can use it in the winter.

“So I came up with the idea of making a huge underground tank which you can fill up with water up to 95 °C. In order to store that heat, the tank is insulated with foam glass, a thick layer of glass with a structure that looks like the inside of a Bros chocolate bar. As the underground tank is so large – it’s 30 meters in diameter and 30 meters deep and holds 20,000 cubic meters of water – it retains the heat better than if it were in a smaller tank. The larger the tank, the slower the rate that the water cools down. And the cheaper the heat becomes. The water can be extracted at several levels from the tank. The warmest water is at the top of the tank. The coolest water is at the bottom. That can be used in summer for cooling homes.”

Team members at Ecovat       Image: Ecovat

What was the main obstacle that you had to overcome?

“I had to find funding in order to flesh out my plan. And I had to figure out how to realize the Ecovat system technically. As far as the latter was concerned, it was a matter of trial and error. The insulation material was developed in collaboration with the TU/e in Eindhoven. That is 100 % sustainable and capable of withstanding pressures of up to 6 bar. It’s built to last at least 50 years. We also had to develop software which could regulate the energy flows in the Ecovat system, e.g., for when a lot of sustainable energy is generated.

Sometimes it’s the heat pump which is also part of the system that was problematic. Other times it was the thermal panels or the warm water coming from the Ecovat. The tricky thing is to make sure that the system is cost-effective and that all its functions are aligned properly with each other. After a pilot with a 2000 cubic metre tank in Uden between 2014 and 2017, it turned out that the Ecovat system really did work and that it is scalable. That means that if you connect a lot of houses to the Ecovat sytem, it will be commercially viable.”

What has been the biggest breakthrough so far?

“That we also sorted out any issues that were there before the Ecovat system was up and running.”

What can we expect from Ecovat in the coming year?

“That’s when construction will start on our first commercial Ecovat system for Mijnwater, an energy supplier in Heerlen. This will hold 20,000 cubic metres of heated water. It will be connected to the existing heat network and will heat 2000 extra homes belonging to three housing corporations.”

Where do you want to be in 5 years time with Ecovat?

“Then we’ll be building four Ecovat systems each year, with a turnover of about €60 million.”