Hot water debate

Solarchaser

Martyn1981 said:

QrizB said:

If you were part of a group with 10,000 other owners and you all decided to change your habits, each drawing 3kW from the grid for a total of 30MW, that might be noticeable and could result in a CCGT burning slightly more gas than before. But on a windy night it could mean30MW less abatement (where wind turbines are switched off to prevent grid instability). And I guess this is the idea of Octopus Go; it provides a larger load at night when wind can make up a bigger proportion of demand and helps prevent abatement.

Hiya. That's a really good point, and reminded me that hot water (domestic or commercial) is a potential energy storage medium. Pretty much as you've described, smart devices could be used to mop up extra RE generation and store it as hot water, heat pumps adding more heat, even air cons (in hotter countries) doing some extra cooling. All taking advantage of low cost leccy during excess supply.

This is essentially my idea to use large water tanks to store excess solar in summer and to store octopus cheap rate in winter, and use that for hot water provision and central heating (though not doing cooling), and this offsetting normal usage from things like gas combi and electric showers when the grid is dirtier.

silverwhistle

Martyn1981 said:

That's a really good point, and reminded me that hot water (domestic or commercial) is a potential energy storage medium.

So is cold! So it's not a rigorous regime:-), but I try and remember to freeze a bit more ice when the immersion tank is HOT and I'm not charging the PV. Nothing better than a chilled ice bucket on the patio in this weather containing your cold drink of choice..

michaels

WE are going to do our morning hot water from 4.5p per hour overnight leccy rather than 14p per hour (October rate) gas.  What is the hottest we can safely set the immersion to max storage?  Unfortunately it is only a 180l tank so will only do the morning showers not the evening ones too. 

WE have a 24kwh leaf to also store cheap rate leccy but it may only store about 12-14kwh which may not be enough to provide water heating as well as all our other leccy needs during the expensive period.

70sbudgie

It is one of my bug bears that when people talk about domestic energy storage, they seem to forget that it was very common until combi boilers became a thing.

I know this is a new concept, but I'm very excited for the "sand battery" technology to advance enough to be domestic scale. Imagine storing ALL your summer excess generation to heat your hot water / radiators in the winter?

https://www.bbc.co.uk/news/science-environment-61996520

QrizB

michaels said:

WE are going to do our morning hot water from 4.5p per hour overnight leccy rather than 14p per hour (October rate) gas.  What is the hottest we can safely set the immersion to max storage?

Your immersion heater will have a thermostat. The max setting is likely to be 60-65C or so. Mine is set to the max and it's not causing any problems. (If you have very young, very old or other vulnerable people in the house, 65C might be too hot for safety and you might need a blend valve as mentioned previously.)

Unfortunately it is only a 180l tank so will only do the morning showers not the evening ones too. 

Depending on exactly where in the tank the immersion heater is fitted, you might have far less. My tank is around 150 litres but the immersion heater is mounted in the crown of the tank, not the side, and only heats about half of it.

WE have a 24kwh leaf to also store cheap rate leccy but it may only store about 12-14kwh which may not be enough to provide water heating as well as all our other leccy needs during the expensive period.

Per this calculator, to heat 180kg (litres) of water from 10C to 60C will take about 10.5kWh.

Reed_Richards

Water has about 5 times the specific heat capacity of sand.  So to store the same amount of energy in a 300 l tank of sand you would need to heat the sand to 220 C instead of water to 60 C (I'm assuming "background" temperature is 20 C.  So "domestic scale" sand batteries are never going to happen, if by "domestic scale" you mean one per house.  A sand battery might just work as an add-on to a district heating scheme (as per your link) but we're not big on district heating in the UK.    

Pile_o_stone

We have our PV attached to two immersion heaters on our tank. The iBoost diverts excess solar to the top immersion heater  first, where I  set the thermostat to 80C. Once the top of the tank reaches 80C, it  diverts to the immersion at the bottom of the tank. This immersion maxes out at 60C. On a good day we get a 350L tank full of water at 60C. We have a mixer valve that prevents scalding water getting to the taps.

Not only are we saving money because we are not using the gas boiler to supply hot water for showers, etc., we have had weeks where the boiler has not been used at all, which I  assume will prolong the life of our boiler.

Reed_Richards

Pile_o_stone said:
....we have had weeks where the boiler has not been used at all, which I  assume will prolong the life of our boiler.

Or shorten its life, it's hard to know.  Some things benefit from regular use.

BUFF

Reed_Richards said:

Pile_o_stone said:
....we have had weeks where the boiler has not been used at all, which I  assume will prolong the life of our boiler.

Or shorten its life, it's hard to know.  Some things benefit from regular use.

This is why most modern boilers will run the ch pump intermittently without the boiler firing if the ch is left "on" over the summer but with the set temp lower than the ambient .

Magnitio

Pile_o_stone said:

We have our PV attached to two immersion heaters on our tank. The iBoost diverts excess solar to the top immersion heater  first, where I  set the thermostat to 80C. Once the top of the tank reaches 80C, it  diverts to the immersion at the bottom of the tank. This immersion maxes out at 60C. On a good day we get a 350L tank full of water at 60C. We have a mixer valve that prevents scalding water getting to the taps.

Not only are we saving money because we are not using the gas boiler to supply hot water for showers, etc., we have had weeks where the boiler has not been used at all, which I  assume will prolong the life of our boiler.

What rate do you pay for your gas and what rate do you get paid for exporting electricity? The large difference between these (i.e. electricity export being greater than gas) and a comparison of environmental impact was the main reason for the debate.