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Doesn't this suffer the problem that you're then putting heat into the device, which is in your house, during the warm season when you want your house to stay cool?
It's a large enough volume of water, that adding insulation is feasible.
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> I get that sand is inexpensive It depends where you are. Sand thieves are a thing in many places around the world. Here's a story from 2015 about how residents in one area have lost 25 hectares of land to sand thieves. https://tuoitrenews.vn/news/features/20150524/residents-losi... Or a police captain whose legs were severed while trying to apprehend sand thieves. https://www.vietnam.vn/en/dien-bien-moi-vu-dai-uy-c…
The article points out that it doesn't actually use what people usually think of as sand: "The sand itself will also be sustainably sourced – it’ll consist of crushed soapstone, which is a manufacturing byproduct of another local industry."
Waste material costs over €100/ton to dispose of across most of the EU. So therefore this material costs less than nothing!
That's why the project doesn't use water (which has a 4x higher heat capacity and can be pumped allowing the heat exchangers to be far smaller and eliminating the 'temperature decreases as it discharges' problem).
The fact I find most fascinating is that they have a local district heating system reusing heat produced from local industry. That’s efficiency on another level.
I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…
There's a pretty cool coffee mug based off the idea too https://joeveo.com/pages/the-temperfect-mug
By adjusting the amount of water in the mixture, you can fine-tune the phase change temperature to whatever the customers like for their coffee.
It also boils above 100C so when the customer puts it in the microwave it won't burst unless they boil the cup dry.
And when the customer does break it, it's non toxic and food safe.
I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…
I get that sand is inexpensive and simple and I like the idea - especially since it scales to an entire town (!) But I can't help but think of one "technology" that could make a scheme like this MUCH more effective. a phase change. for example, it takes 1 calorie for water to go from 30 to 31 degrees F, but but it take 80 calories to go from solid at 32 to liquid at 32 F. A project I remember reading about that was r…
> One new idea, for additional thermal protection, was the addition of phase-change material. Lithium nitrate trihydrate melts at 30° C, absorbing a large amount of heat, due to its high latent heat of fusion.
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It's more effective volume wise. I did the math, some time ago here are the rough numbers. Sand has way less heat capacity then water per kg (about half). Water can be heated to 95C with standard unpressurized vessel. Sand in this application is heated to 600C. Sand is denser then water (kg/m3). For the same heat energy stored this comes out to about 2.5x more volume of water(95C) compared to sand(600C). Water and Sa…
The temperature also matters. If you need at least 50 C water to run district heating, about half of the energy stored in near boiling water cannot be utilized. This is much less with 600 C sand.
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Any system that involves an electrical solar panel connected to a low-temperature electrical heater is likely to be better served with a solar hot water panel, by about a 10:1 ratio.
But this would stop you getting the sand hotter than 100c - which is one of the main advantages of using sand over water for heat storage.
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Are you including the maintenance costs of the water panel in your estimate? I used to buy this argument, but then: A) PV panels got ridiculously cheap B) everyone I know with solar hot water has emptied their systems because the maintenance hassles were not worth dealing with Using high grade intermittent current to produce resistive heat isn’t high on my list of efficient things to do, but unfortunately neither is…
Might be a location thing; there are vast numbers of solar hot water systems here in W.Australia and typical maintainence is maybe just replace the tank outright and flush the lines every 20 years or so. How 'clean' of salts, etc. is the water being put through your panels? Hard water clogs up faster.
That said, a heat pump running at 4:1 COP coupled to 20% efficient solar panels gets you right back to the same efficiency as solar thermal, with a lot more flexibility.
The fact I find most fascinating is that they have a local district heating system reusing heat produced from local industry. That’s efficiency on another level.
I think that's pretty common, no? Here in NL our district heat comes from a chemical refinery a few clicks away. For them the heat is an annoying waste product.
There are also a few cities that get heat into their networks from nuclear power plants and something similar is planned in the future for Brno as well.