Solar Panel Guide Discussion

ronlizpatsimon

Hello Cardew,
As you may know; I,m one of those who use the surplus PV generation to heat my hot water tank. Allowing for the different prices of Gas and Electricity; I calculated that if you have at least 2.5kw of spare generation; it pays to turn the hot water tank's thermostat up to maximum until the top temperature is reached. To get the most benefit you need to turn that thermostat fully down first thing in the morning - otherwise the normal gas fired boiler will fire up and heat the tank before the sun is strong enough to take over the job.

Cardew

ronlizpatsimon wrote: »

Hello Cardew,
As you may know; I,m one of those who use the surplus PV generation to heat my hot water tank. Allowing for the different prices of Gas and Electricity; I calculated that if you have at least 2.5kw of spare generation; it pays to turn the hot water tank's thermostat up to maximum until the top temperature is reached. To get the most benefit you need to turn that thermostat fully down first thing in the morning - otherwise the normal gas fired boiler will fire up and heat the tank before the sun is strong enough to take over the job.

Hi,

Are they not two different thermostats?

i.e. you turn up the the immersion thermostat situated under the cover at the top of the immersion heater. This has no effect on the water temperature from the gas CH boiler.

The 'tank thermostat' determines how hot the water will be heated by the CH boiler and will have no effect on the immersion heater.

Agreed with 2.5kW spare PV capacity you will save money; but having to play with the thermostats, watch your output constantly for clouds, and/or ensure a kettle or appliance is not switched on, requires dedication!

John_Pierpoint

It is even more fun deciding at 06:30 hours if it is time to turn on the immersion heater using Economy 7 or leave it until noon and possibly heat the tank for nothing.

I know I could go and check all the conversion factors on the interweb but does anyone have the figures for the kWh required to raise the temperature of 140 litres of water from 15 to 75 degrees?

ronlizpatsimon

Thanks for that Cardew.
I had missed out the operation of turning off the boiler function (using the programmable timer override).
Perhaps I did not fully understand your explanation but I get the impression that you think that there is no thermostat which controls the immersion heater? i,e, if its switched on, it keeps constantly heating - unless it has an inbuilt thermostat?
Yes, my method do require dedication - but then I,m obsessed with making savings - at least in this first year of operation.

ronlizpatsimon

Hello John.
You must have the shower running a long time to reduce your storage tank to 15 degrees!

grahamc2003

John_Pierpoint wrote: »

It is even more fun deciding at 06:30 hours if it is time to turn on the immersion heater using Economy 7 or leave it until noon and possibly heat the tank for nothing.

I know I could go and check all the conversion factors on the interweb but does anyone have the figures for the kWh required to raise the temperature of 140 litres of water from 15 to 75 degrees?

9.8

and my message is too short to post so everyone has to waste a bit of time reading this too.

zeupater

John_Pierpoint wrote: »

It is even more fun deciding at 06:30 hours if it is time to turn on the immersion heater using Economy 7 or leave it until noon and possibly heat the tank for nothing.

I know I could go and check all the conversion factors on the interweb but does anyone have the figures for the kWh required to raise the temperature of 140 litres of water from 15 to 75 degrees?

Hi

Rule of thumb, but accurate enough for most ....
1kW for 1hour raises 1tonne by 1degreeC ....

So 140 litres raised by 60C = 0.14tonnes*60kWh=8.4kWh .... so a 3kW immersion for 2.8hours (8.4/3), or a 1kW heater for 8.4hours ....

HTH
Z

Cardew

ronlizpatsimon wrote: »

Perhaps I did not fully understand your explanation but I get the impression that you think that there is no thermostat which controls the immersion heater? i,e, if its switched on, it keeps constantly heating - unless it has an inbuilt thermostat?
Yes, my method do require dedication - but then I,m obsessed with making savings - at least in this first year of operation.

I stated:

i.e. you turn up the the immersion thermostat situated under the cover at the top of the immersion heater. This has no effect on the water temperature from the gas CH boiler.

i.e The immersion heater has an adjustable thermostat see:

http://www.diydata.com/problem/immersion/immersion_adjustment.php

ronlizpatsimon

Thanks Cardew. Very useful information

Martyn1981

orrery wrote: »

It does, but we really do need to focus on real measures to deal with the problems we face. We need signalling over the mains to indicate energy availability, we need intelligent appliances that take power when it is available and don't when it isn't.

Repeat after me "If we all concentrate on the small things, we'll only ever make small savings."

Hi. I think I heard recently of fridges and freezers that 'over' cool (how technical am I!) during set times, presumably to match cheap electricity and avoid peak demand. Is that the sort of thing you are referring too. New to me, very cool!

I agree with the sentiment of the quote, but I still disagree with the separation. I personally think, "If we all concentrate on the big and small things, we'll achieve bigger savings."

But as an optimist, I'm hoping the small comes with or after the big. Though that may well leave me disappointed when as you and Zeup say, people only think small.

Mart.