Immersion Heater - PV electricity

[suntrap]

Yes, I expect the £50 a year is out of date, but does £150 a year assume that you will never have to heat water with gas, i.e. that there will always be enough surplus from the panels?

The other reason for not doing this is that I reckon it's greener to export the energy where some of it will be used to offset electricity generated at low efficiency, rather than gas being burnt for heat at high efficiency. But you don't benefit financially.

 

[inie meanie]

I think I will fit a timer valve on the hot pipe and listen to the screams! he he.

 

[sharpener]

Download a better browser - there are far more important reasons for it than being able to read those forums.

Not my PC. I will try with Firefox tomorrow. But I am deeply mistrustful of web sites which cause unexplained crashes.

I was actually talking about the voltage transformer.

As I subsequently realised, hence my edited reply above about capacitative/resistive dividers, no phase shift with them (at least at 50Hz)!

But as the saving is so small (of the order of £50 a year if you're on mains gas?) I've shelved the project for the time being.

We are on oil so it has a much better payback, hence I am keen to make some progress before the longer, more productive days are here.

 

[echase]

But as the saving is so small (of the order of £50 a year if you're on mains gas?) I've shelved the project for the time being.

I don’t know what the saving is but bear in mind that using a gas boiler in the summer to heat water is not as efficient as you think due to all the heat losses in the boiler and pipework. In winter the lost heat may help to warm your house but in summer it is a total loss and a nuisance if your house is too hot already. I started designing my controller because my pipe runs are particularly long and I was wasting a lot of gas on water heating. Also the maintenance costs of a boiler are high, unlike an immersion. Units like mine give a calculated payback of about 3 years which is pretty good for an energy saving/controlling device. PV panels take >10 years. How long does double glazing take?

 

[inie meanie]

Yes, I expect the £50 a year is out of date, but does £150 a year assume that you will never have to heat water with gas, i.e. that there will always be enough surplus from the panels?

The other reason for not doing this is that I reckon it's greener to export the energy where some of it will be used to offset electricity generated at low efficiency, rather than gas being burnt for heat at high efficiency. But you don't benefit financially.

Ok this is the green response. The power station burns gas to convert to electric at very very best 59 % efficiency, then there are losses due to transmission. few % every time a transformer is used to step up and down, then the resistance losses over many miles. I think use it at home first before wasting it over large losses in the grid. Using it is green . Your boiler is emitting co2 etc every time it runs and it is not a perfect converter of heat.

 

[sharpener]

The other reason for not doing this is that I reckon it's greener to export the energy where some of it will be used to offset electricity generated at low efficiency. But you don't benefit financially.

Quite. It would be much better for the grid if I were to export all my production during daylight and continue to run the washing m/c and dishwasher in the small hours. But they have designed the financial (dis)incentives so that this doesn't make sense either.

 

[hobbsy]

Spent quite a long time reading all 36 pages of this with quite a lot of interest.

A few thoughts:

1) Once smart meters are installed (starting 2012) which measure export those who own their own panels will see little benefit in doing this. Currently 50% is assumed at 3.1p/kWh which is the same as gas however you're free to go "nuts" like the renta roof users and use as much of what you generate as you like. Once they measure everything that is exported there isn't really much benefit in heating water which you may not use at the same cost as gas (around the same 3p/kWh - differences in efficiency between gas boilers and immersion heaters aside)

2) Looking back on the bright side it may take until 2020 for smart meters to be rolled out everywhere. With that in mind (and changing the subject slightly) if you had a combi boiler but still wanted to take advantage of this usage of "wasted" power would it be worthwhile fitting a storage tank heated as described in the thread (in a smart manner!) and using the coil normally used by to heat the tank via a gas boiler to pre-heat the cold mains water feed to the combi? This way it would assist with both HW and CH albeit fairly minimally on cold overcast days. However any rise in input temp would reduce the gas needed. Is anyone doing this already?

 

[bradburts]

The other reason for not doing this is that I reckon it's greener to export the energy where some of it will be used to offset electricity generated at low efficiency, rather than gas being burnt for heat at high efficiency. But you don't benefit financially.

Agreed, we should have fitted solar thermal but we're too tight probably, that and the RHI has still not happened.
Its best for all that the electricity is exported. Turning sun to electric to hot water is just mad.
Plus you have to lay out a lot of cash or risk turning sun into electricity into airing cupboard fire before heating the fireman's hose...

 

[bradburts]

Spent quite a long time reading all 36 pages of this with quite a lot of interest.
if you had a combi boiler but still wanted to take advantage of this usage of "wasted" power would it be worthwhile fitting a storage tank heated as described in the thread (in a smart manner!) and using the coil normally used by to heat the tank via a gas boiler to pre-heat the cold mains water feed to the combi? This way it would assist with both HW and CH albeit fairly minimally on cold overcast days. However any rise in input temp would reduce the gas needed. Is anyone doing this already?

I know someone who uses old radiators to preheat water for a boiler and also provide a warm circuit for a heat pump.
Also its quite easy to put a black face on a south wall, batton and glass/perspect sheet and funnel that heat to, say, car heat exchangers.
Doesn't look too great but cheap and reliable. You could make it a feature somehow.
Costs you pennies and would allow you to export your hard earned solar electricity.

 

[echase]

Ok this is the green response. The power station burns gas to convert to electric at very very best 59 % efficiency, then there are losses due to transmission. few % every time a transformer is used to step up and down, then the resistance losses over many miles. I think use it at home first before wasting it over large losses in the grid. Using it is green . Your boiler is emitting co2 etc every time it runs and it is not a perfect converter of heat.

Transmitting gas also uses a lot of power to pump it. Hopefully not much is lost to leaks.

 

[inie meanie]

Agreed, we should have fitted solar thermal but we're too tight probably, that and the RHI has still not happened.
Its best for all that the electricity is exported. Turning sun to electric to hot water is just mad.
Plus you have to lay out a lot of cash or risk turning sun into electricity into airing cupboard fire before heating the fireman's hose...

I thought this forum was for the development of electronic systems to turn exported electricity into hot water and save our selves some money. If you dont want to contribute why are you wasting your CO2 immissions and time in clogging up this forum????? Blunt yes I know!

 

[pauldreed]

I thought this forum was for the development of electronic systems to turn exported electricity into hot water and save our selves some money. If you dont want to contribute why are you wasting your CO2 immissions and time in clogging up this forum????? Blunt yes I know!

Agree!

 

[suntrap]

Spent quite a long time reading all 36 pages of this with quite a lot of interest.

Well done!

would it be worthwhile fitting a storage tank heated as described in the thread (in a smart manner!) and using the coil normally used by to heat the tank via a gas boiler to pre-heat the cold mains water feed to the combi? This way it would assist with both HW and CH albeit fairly minimally on cold overcast days. However any rise in input temp would reduce the gas needed.

Not sure how it would help with heating as there would be no water flowing through the coil. I think the other problem would be that the coil is in the wrong place - it needs to be at the top of the tank to make best use of the heat in the stored water, which otherwise wouldn't convect.

 

[suntrap]

I thought this forum was for the development of electronic systems to turn exported electricity into hot water and save our selves some money. If you dont want to contribute why are you wasting your CO2 immissions and time in clogging up this forum????? Blunt yes I know!

But the ideas discussed on this thread can be used in a greener fashion by offsetting electricity rather than gas consumption, by, for instance, powering fridge-freezers.

 

[sharpener]

Turning sun to electric to hot water is just mad.
Plus you have to lay out a lot of cash...

Once the solar PV is installed it makes perfect economic sense to use it for water heating, since under the "deemed export" rule the marginal cost of own consumption is zero. Unless you go for the EMMA the extra capital expenditure for the controller is small and should have about the same payback (6 years).

Plus I do not fancy a load of extra plumbing and the need for frost protection etc. Besides which, on account of where my tank is situated, it would be a major job to change the immersion heater for a 1 kW one let alone change the tank for one with more elements or a second coil.

I didn't make the idiotic rules, I am just trying to optimise my usage given what they are.