We admit to be fascinated by the potential of Ecovat, essentially a swimming pool of ca. 30 m deep and 70 m diameter, with a roof on it and concrete housing, well-hidden below the ground. These wind turbines, solar panels and solar collectors have meanwhile considerably matured, can compete with fossil fuel, so that aspect of the energy transition is in place. The remaining missing link is storage. Not storage in the hours range, like batteries or pumped hydro-storage, those are also maturing, but seasonal storage. Two approaches of seasonal storage exist: chemical and thermal. Ecovat covers the second option.
Remember that in Europe about 50% of the primary energy is used for heating purposes. That sector can be decarbonized with large bodies of warm water, water that can be brought up to temperature (90 C) with solar collectors and heat pumps. These heat pumps can be powered by intermittent renewable electricity. The beauty is that it doesn’t matter when that renewable electricity is available, like for instance at night, with everybody “on one ear”, since an Ecovat can keep its water warm for 6 months and only lose 5-10% of the heat. The larger the Ecovat, the lesser the losses. Ecovat is a perfect buffer that gladly can take in every available chaotic kWh it can lay its hands on and convert it into useful thermal heat and next wait patiently for somebody to pick-up that kWh, even months later. Ecovat would solve, not all, but a large part of the energy storage problem.
A few simple calculations. Heat capacity water = 1,163 kWh/m3/K. Heat storage capacity of 1 m3 water between 20-90C = 70 x 1.163 = 81.4 kWh. An average Dutch household uses per year on heating 15,000 kWh, almost all from burning natural gas. This corresponds to an Ecovat storage volume of 185 m3 (volume 6 x 6 x 5 m). For 1000 households, connected to a single large Ecovat, the volume would be 185,000 m3. That’s a sphere with a radius of 35 m or more realistic a cylinder with a dept of 30 m and a surface area of 6167 m2 or 78 x 78 m.
That seems large, however, these figures apply to existing homes that on average are 38 years old, that is were built at a time when concepts like “energy transition” were not yet en vogue. But this is 2019. Dutch law requires that new houses need to be designed with energy conservation in mind and preferably need to be energy neutral. And building technology has meanwhile advanced to the tune that new homes are indeed far more energy efficient.
[wur.nl] – Ecovat helpt seizoensvariaties in energievraag op te vangen
Ecovat frontman Aris de Groot estimates that the cost per newly built home for participating in an Ecovat storage scheme will amount to ca. 8000 euro and that 40-60 m3 (not the 185 m3 calculated above) of near boiling temperature water are sufficient storage capacity for a heating season. The lifespan of an Ecovat is guaranteed to be at least 50 years (more likely 100 years). That is extremely bearable, not in the least since the Dutch government and banking world are planning “inter-generational loans”, as well as loans attached to a building, not an owner, in order to facilitate the energy transition.
[engerati.com] – Ecovat plans thermal storage facility for Mijnwater
[topsectorenergie.nl] – Eindrapport TKI Energo Project: “Ecovat Total Energy System”
[stedin.net] – Ecovat wint innovatieprijs voor duurzame energie
[installatie.nl] – Ecovat wint flexprijs
[kivi.nl] – Systeemconsequenties van Ecovat, Kwantificering van kosten voor netverzwaring en piekcentrales (2018)
Renowned Dutch consultancy bureau Berenschot has investigated what the consequences would be for an all-electric national heating system based on heat pumps, especially in the dreaded case of “dark doldrums”, when supply of renewable electricity will go into hibernate mode. According to Berenschot seasonal heat storage systems like Ecovats could provide a solution for grid (peak) overload. Seasonal storage of heat will reduce grid requirements as well back-up power stations.