device to use unused soler pv export power to run heater or hot water

legoman62

solarpvman wrote: »

think carefully

even if you have a 4kw system your immersion heater is 3kw. You VERY rarely have surplus energy to use the immersion.

SO you have to buy a 1kw immersion element for the hot water tank (3 times as slow to heat up) and get that installed AS WELL as buying and installing all the electronic jiggery pokery this thread istalking about.

you have to buy the 1kw element so that you are in an energy surplus position to make it worth using.

How much will all that cost? and how much will you save?

also remember that to heat water buy electric costs 3x as much as per gas to do the same job. So you have to be VERY sure that your new electric based solution is only on at the right times AND you have to never really want to use the immersion as the main heat source as a 1kw element will be too slow.

i was going to do it all but decided against.

don't get carried away like i nearly did

Actually, using energysavingexp’s excellent switching idea costs nothing to run.
It only uses available excess output from Solar PV
Costing between £15.00 and £25.00 to buy means very little outlay
I’ve been using mine for over 6 months now with no problems.
Agreed, you may need to install a 1kw immersion (£35.00) for maximum benefit.
My existing 3kw immersion was nearly 30 yrs old, and probably not up today’s electrical standards so I decided to change it.
I did this myself (not too difficult for the average DIYer)
My main hot water source was my gas boiler and it has had a 6 month holiday (virtually no gas usage)
Just off for a free bath!

OK….. You can carry me away now.:D

John_Pierpoint

Massive thread here:

http://www.navitron.org.uk/forum/index.php/topic,18186.150.html

Natchuff

Hi,

This looks very interesting, can you provide me with details please?

e-mail - [EMAIL="Fish_house@hotmail.co.uk"]Fish_house@hotmail.co.uk[/EMAIL]

Thanks .

the.shepherds

can you send me datails as well please

the.shepherds

me too please, thank you

Energetic_2

The immersun is very effective. Worth paying the extra IMO...

Unless you can build your own ;-)

Dave_Fowler

Energetic wrote: »

The immersun is very effective. Worth paying the extra IMO...

Unless you can build your own ;-)

The one I built is working very well. Cost about £120 though, so not too cheap.

Exported about 4 kWh since 24th October - turned up thermostat on HW tank to allow more power to be used when I found I was exporting in late afternoons.

Dave F

grahamc2003

Dave_Fowler wrote: »

The one I built is working very well. Cost about £120 though, so not too cheap.

Exported about 4 kWh since 24th October - turned up thermostat on HW tank to allow more power to be used when I found I was exporting in late afternoons.

Dave F

I think you'll need to do some maths to see whether there's a net gain in doing that. The heat losses from the tank will increase of course when sitting at a higher temperature. While it's difficult to calculate the actual heat loss from the tank, it's easy to calculate the relative heat loss at different temperatures. For example, the heat loss when sitting at 65C will be about 8% greater than when sitting at 60C (the heat loss is proportional to absolute temp to the power of five).

So if your heat loss in a well lagged tank at 60C is say 2 kWh/day (= 83W), then at 65C it will be 2.15kWh/day (=90W), so in this example, you'd have to put in an extra 150Wh each day to cover the extra losses (note that's not 150Wh in total in the tank, but an extra 150Wh on top of what you would have put in if the temp were set to 60C (iyswim!).

There are lots of variables (an important one being exactly how many hours each day the tank is at its max temp, among many others). I expect most will have a very well insulated tank, but if not, it may be marginal whether or not there's a benefit by turning the thermostat up.

Dave_Fowler

grahamc2003 wrote: »

I think you'll need to do some maths to see whether there's a net gain in doing that. The heat losses from the tank will increase of course when sitting at a higher temperature. While it's difficult to calculate the actual heat loss from the tank, it's easy to calculate the relative heat loss at different temperatures. For example, the heat loss when sitting at 65C will be about 8% greater than when sitting at 60C (the heat loss is proportional to absolute temp to the power of five).

So if your heat loss in a well lagged tank at 60C is say 2 kWh/day (= 83W), then at 65C it will be 2.15kWh/day (=90W), so in this example, you'd have to put in an extra 150Wh each day to cover the extra losses (note that's not 150Wh in total in the tank, but an extra 150Wh on top of what you would have put in if the temp were set to 60C (iyswim!).

There are lots of variables (an important one being exactly how many hours each day the tank is at its max temp, among many others). I expect most will have a very well insulated tank, but if not, it may be marginal whether or not there's a benefit by turning the thermostat up.

I can't see how I can not gain from using the higher temperature. I am using electricity which would otherwise be exported. It costs me nothing to run the tank hotter - except perhaps a shorter life expectancy of the immersion heater.

One of the benefits of running the tank at a higher temperature is that with the indifferent weather, when there are rarely two days of reliable sunshine together, I can go two days without having to top up the HW tank using the gas heating.

Dave F

scotsblood

Another one who would like details please!:j