Hi,
Objectively I am in favor of thermal storage with water!
Water-based thermal storage can be more efficient and more cost-effective than electric batteries for space heating applications in places where heat demand is high (Anchorage, Newyork city) and predictable (Schools, offices, shopping malls, multi-family buildings). I let those who can, to verify the claim by comparing the overall system efficiency and cost performance of 4 cases for heating a large hospital in Newyork for example!
Case 1- Sun --->solar thermal collector--->water thermos --->space to heat
Case 2- Sun --->Solar PV system --->heat pump--->water thermos --->space to heat
Case 3- Sun --->solar PV system ---->lithium battery --->heat pump--->space to heat
Case 4- Natural gas --->boiler--->space to heat
Water-based heat storage certainly has a low energy density compared to phase change material (PCM), however, this fact is often "exaggerated" as there is plenty of space around buildings to install water thermos. Parking lots, basements, garages, gardens, septic tank places, …. In many cases, it is feasible to install a 20m3 water tank (eg: 3-meter side cube or 20ft container) underground or above ground for a centralized thermal storage unit. When costs, environmental concerns, and scalability are taken into account, PCMs often don't stand a chance over water. In fact for cooling, there are companies using ice as a natural clean PCM.
I also think that distributed water thermos in tens to hundreds of cubic meters can be a good solution to limit peak power, solar/wind curtailment, pressure on batteries materials mining, and so on. As the saying "don't put all eggs in one basket" diversifying energy systems components can improve the security of energy services. Even if solar thermal turns out to be slightly more expensive than solar PV+heat pump, it can be good to keep solar thermal in the energy mix. Everything electric sounds nice, but it can be scary if you think of what if the electric system goes wrong.
out of topic: I went to a restaurant few days ago, and the waiter said I can see the menu only by scanning the QR code on the table. No paper menu anymore. I said so if I don't have a smartphone I can't eat, no battery I can't eat, if no internet I can't eat, if your website got hacked ...... he said yes no food, it is a tech world!
Before closing, I would share these 2 articles about water-based thermal storage projects one up to 5m3 and the other 50.000m3.
February 15, 2023 "PILOT PROJECT IN SEATTLE SHOWS CENTRAL HEAT PUMP WATER HEATERS CAN ACT AS MASSIVE HOT WATER BATTERIES THAT HELP REDUCE CARBON EMISSIONS"
June 30, 2022 " A steel 'thermos tower' in Berlin will be the largest heat storage facility in Europe"

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Elias OUEDRAOGO
Business Developer
Future Energy Company
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