PV excess without tank

[Stinsy]

Have you considered a heat battery? Something like the Sunamp device?

Hi. No i have not heard of these, will look into it, thanks

Pro's: smaller than a DHW tank storing the same amount of energy. Standing losses are tiny.

Con's: really heavy (all the time unlike a DHW tank which is light when you install it and only gets heavy when you fill it), much more expensive than a DHW tank for the same amount of energy stored.

[AE-NMidlands]

Have you considered a heat battery? Something like the Sunamp device?

Hi. No i have not heard of these, will look into it, thanks

Pro's: smaller than a DHW tank storing the same amount of energy. Standing losses are tiny.

Con's: really heavy (all the time unlike a DHW tank which is light when you install it and only gets heavy when you fill it), much more expensive than a DHW tank for the same amount of energy stored.

I thought they had a phase-change filling (sodium acetate solution?) which mopped up lots more energy...

[nowty]

Hi. No i have not heard of these, will look into it, thanks

Pro's: smaller than a DHW tank storing the same amount of energy. Standing losses are tiny.

Con's: really heavy (all the time unlike a DHW tank which is light when you install it and only gets heavy when you fill it), much more expensive than a DHW tank for the same amount of energy stored.

I thought they had a phase-change filling (sodium acetate solution?) which mopped up lots more energy...

Stinsy is correct, as they are about 3 times the price of the same equivalent amount of hot water size.

[ecogeorge]

[/quote]
I'm sure that the advice at "the other place" was that you can supply pre-heated water to (some?) combi-boilers and the gas doesn't fire up if it's not needed...
A
[/quote]

My thoughts are yes -the above is true but depends on make .........
Have you room for a unvented cylinder ?? I'm sure you could plumb on the outlet side of the combi with a zone valve and thermostat ??? use from cylinder when available ??
Or storage heaters ??
Swimming pool ?
George

[nowty]

I did the pre-heated water thing through a gas combi, worked with my Bosh Worcester one as long as the input water was no higher than about 45 degrees. Above that it still worked but ended up with long cycles of no heat so the temp fluctuated too much. I ended up using a blending valve so the temp was a max of 45 degrees even though the pre heat tank was at 60 degrees.

I now still have the pre-heat tank going through the combi but I have the combi switched off and no longer use the blending valve, so its 60 degrees straight through. The reason is if I have a leccy power cut I can still use the combi with cool water going through it in case of emergency. As I have a whole house leccy backup the electrics of the combi still work in a power cut.

I also have a heatpump in parallel with my combi boiler so I can heat the radiators with heatpump or gas combi controlled with zone valves controlled via WiFi sockets.

I'm paranoid to lose the gas combi but I have not used it since April 2021, one day I suspect I will pull the plug and re-do the plumbing without it.

[Stinsy]

I thought they had a phase-change filling (sodium acetate solution?) which mopped up lots more energy...

That isn’t how it works. There is no “extra energy” just storing the same amount of energy in a smaller amount of space.

[AE-NMidlands]

I thought they had a phase-change filling (sodium acetate solution?) which mopped up lots more energy...

That isn’t how it works. There is no “extra energy” just storing the same amount of energy in a smaller amount of space.

all right then, would you accept that "More energy per unit volume" is correct?
For a newbie I think I was right and Stinsy confirmed it " smaller than a DHW tank storing the same amount of energy."

[Moxi]

I know OGB was very pleased with his but when I delved into these units further there seemed to be a lot of internet "chatter" about their propensity to split and leak, presumably due to the phase change process causing pressure differentials.

I know from my hand warmers, which use the same phase change material, that the pouch swells as the material crystalises and gives off its heat.

That said I am sure the manufacturers have designed to limit this but I just couldn't convince myself that the "risk" was small enough to take the plunge myself.

Moxi

[Stinsy]

I thought they had a phase-change filling (sodium acetate solution?) which mopped up lots more energy...

That isn’t how it works. There is no “extra energy” just storing the same amount of energy in a smaller amount of space.

all right then, would you accept that "More energy per unit volume" is correct?
For a newbie I think I was right and Stinsy confirmed it " smaller than a DHW tank storing the same amount of energy."

Correct, you’re using the “phase change principle” whereby it takes a lot of energy to change a substance from solid to liquid. Eg it takes c. 1.2kWh to heat 100L water from 5℃ to 15℃. However heating 100L of ice from -5℃ to 5℃ takes c. 10.4kWh. So you get a bit less than 10x the energy storage for the same volume/mass of water.

While you can’t practically do this with water because the phase-change occurs at too low a temperature and the way ice crystals form creates pressure that can damage the enclosure, lots of substances do have a phase-change at usable temperatures. Eg wax.

The challenges with exotic phase change materials are that it is difficult to compete with the cost of media (water is essentially free), and with water you can ship the container to site and install it empty. So you have to REALLY REALLY need the space.

[Nobodyimportant]

Newbie to the forum here but I work in this stuff daily under an innovation research project.

I had this dilemma for my own home too, Combi, PV, no heat storage and a small battery.

Whilst looking for my own solution I found this valve - https://www.intatec.co.uk/product/intas ... ter-valve/

It seems to be intended for solar thermal systems originally, but would work just fine with a PV diverter fed tank too.
Seems to allow a blend of Combi hot water and/or Tank hot water depending on the temperature in the tank. This removes the issue I would have with water Inlet temps being too high for my boiler, and allows for 100% utilisation of just the tank if its charged, without needing to blend in summer for instance.

You could also night charge on a favourable smart tariff in winter.

This would work really well with a mixergy tank, which allows for stratification of heat, and the effective charging of an exact % of the tank to meet requirement.
They do a slimline tank that would go in the attic if needed as well. Something I will probably look at investing in this summer ready for winter 23/24.