RMS messing about with a sand battery

[Stan]

Well we’ve seen Nowty boiling water with PV directly connected to a kettle. I wonder if we could directly connect PV to a sand battery in a way that was inherently safe because sand can cope with very high temperature.

[Swwils]

For DIY isn't a water thermal store abit more accessible?

[Oldgreybeard]

For DIY isn't a water thermal store abit more accessible?

And massively better in terms of heat capacity. The heat capacity of sand is only about 830J/g.K, the heat capacity of water is about 4,200J/g.K. You can go even better by using a phase change material, like paraffin wax or sodium acetate. Our thermal store uses sodium acetate and stores about 3.24MJ in about 1/4 of the volume of a water thermal store of the same heat capacity. It's effective heat capacity, including the mass of the casing etc, works out at to be about double that of a water based thermal store of the same mass, or about ten times better than a sand based thermal store.

Personally I've no time for the man in that video. He will promote anything that gets him YouTube views.

[Stan]

RMS answered both of those points in that water is limited to below boiling point and better-performing materials are a lot dearer than sand. It was interesting to compare the thermal capacity of sand v. water. So if one were to heat sand to around 500C then it could hold as much heat as the same volume of water, roughly speaking. My thoughts revolve around something that I could make and with quite a large volume.
Just thinking.
I still like the idea of direct connection of PV to the heater load by DC because of simplicity.

[Joeboy]

I can't go the guy, his style is like nails on a chalkboard for me. A shame as I've never got beyond a couple of minutes in any of his videos. I'm sure there's good info in there? Much prefer Kryten!

I'd love to build a small sand and parrafinwax unit with as Stan says a direct DC electric coil.

[nowty]

Well we’ve seen Nowty boiling water with PV directly connected to a kettle. I wonder if we could directly connect PV to a sand battery in a way that was inherently safe because sand can cope with very high temperature.

That thread was shredded at one of the old places, I might have a go at re-writing it up.

[Swwils]

I would think you could get a large block of concrete to 700C or so without much fuss. You'd then just need better insulation to avoid loss, probably some vacuum element.

[Swwils]

I would think you could get a large block of concrete to 700C or so without much fuss. You'd then just need better insulation to avoid loss, probably some vacuum element.

Middle ground would be concrete at 500C or so with regular insulation.

Of the top of my head a 1500L tub with 500C concrete would be about 100 kWh. The blend valve wouldn't be cheap.

The biggest problem is loss, after a day or so it's just losing alot of the benefit.

[AE-NMidlands]

I would think you could get a large block of concrete to 700C or so without much fuss. You'd then just need better insulation to avoid loss, probably some vacuum element.

Aerogel? or is it too expensive to be worth considering?
And woud you need intermediate transfer circuits (and another heat exchanger) to get the heat back out? Obviously you can't just run water through
copper pipe embedded in it...
A

[Oldgreybeard]

The most practical answer is still the 40+ year old GEC Nightstor (https://www.ewjenkinsandson.co.uk/about ... or-boilers and http://hes.co.uk/nightstor-c-250.html)

Incredibly reliable, very efficient, and easy to maintain. The feolite blocks have both a high heat capacity and a high thermal conductivity, so can be heated to around 1,000 deg C fairly quickly and can store a pretty large amount of heat.