Solar PV Power Immersion Heater - Have I Lost The Plot?
Discussion
caziques said:
I'm not up to speed on these feed in tariffs, but it would seem a bit stupid to use electricity which you get paid some stupid amount for - to replace gas which is vastly cheaper.
Try to keep up chap!!!!!I'm using the rent a roof scheme, so i so I get first refusal on any power generated, the "overspill" goes to the grid & British Gas get the FIT. Hence why it makes sense to use as much of the power generated as possible.
The EMMA device is lots of dosh which will take a long time to recover.
As I see it during the week the house will usually be only using 'background' devices. Therefore, if you can control it so that it only switches on when the roof is supplying enough power, switching on an immersion heater will use power that would be otherwise be sold back to the grid, but that you won't get paid for.
The voltage output from a solar cell rises with the amount of light it receives. If you take a separate small PV panel, and place it so that it receives the same amount of sun as the roof, then the output from this cell will be proportional to the output from the roof.
If you connect the output from this separate 'sensor' panel to a voltage controlled switching circuit, you can use that to control the immersion heater. As the light increases, it will get to the point where the sensor decides to switch the immersion on, which will then use the surplus power being produced by the roof panels.
You would need to experiment to establish the correct switching point, and make sure you don't use it when you're home and using the dishwasher/tumble dryer etc.
As I see it during the week the house will usually be only using 'background' devices. Therefore, if you can control it so that it only switches on when the roof is supplying enough power, switching on an immersion heater will use power that would be otherwise be sold back to the grid, but that you won't get paid for.
The voltage output from a solar cell rises with the amount of light it receives. If you take a separate small PV panel, and place it so that it receives the same amount of sun as the roof, then the output from this cell will be proportional to the output from the roof.
If you connect the output from this separate 'sensor' panel to a voltage controlled switching circuit, you can use that to control the immersion heater. As the light increases, it will get to the point where the sensor decides to switch the immersion on, which will then use the surplus power being produced by the roof panels.
You would need to experiment to establish the correct switching point, and make sure you don't use it when you're home and using the dishwasher/tumble dryer etc.
Isn't there a version of these that stores the leccy for when you get home??
My roof area has increased a fair bit following an extension and I'd love to be able to power my kitchen (all electric) assentially for free. Combi boiler for heating so no benefit there.
It's completely useless if you have to use the power on an instantaneous basis - unless you're on the dole/retired of course.
My roof area has increased a fair bit following an extension and I'd love to be able to power my kitchen (all electric) assentially for free. Combi boiler for heating so no benefit there.
It's completely useless if you have to use the power on an instantaneous basis - unless you're on the dole/retired of course.
I am in the same position I am installing a 3.75 kw PV system and want to use surplus electricity to pre heat the hot water in my cylinder. I have managed to get a quote (email 06/05/11-pc) for a 1kw, 25 inch long, 2.5 inch Bsp screw fitting, inc thermostst. immersion heater from peter crisp At Elmatic,petercrisp@elmatic.co.uk unfortunatley his best price is £171 less 10% plus VAT and carriage.I suggest all you out there who are interested bombard him with requests so that he can get the price down. £40 would seem reasonable.
Lets hope for a result
Lets hope for a result
1kw immersion heaters used to be available from any plumbers merchants or electrical wholesalers. A bit of 'googling' should get some hits too.
Solar panels are only about 15% efficient, solar thermal panels (that just heat hot water) are about 90% efficient. But if you have surplus electrical power then use it for this by all means, just don't install PV solar panels specifically for heating.
Solar panels are only about 15% efficient, solar thermal panels (that just heat hot water) are about 90% efficient. But if you have surplus electrical power then use it for this by all means, just don't install PV solar panels specifically for heating.
Interesting topic this, just been looking at the BG website and it think we might fall down on the size of our roof. It's a town house so therefore very narrow.
Still will be worth giving them a call in the morning to get them round to have a look
How did you find the install process OP? painless?
Still will be worth giving them a call in the morning to get them round to have a look
How did you find the install process OP? painless?
Hi I agree the idea is a good one. Have you thought about using the DC direct from the PV and use a low volatge DC immersion?
That way 100% of the power goes to the immersion. Or switch the AC from Inverter output directly to the immersion in the winter and work together with the Solar HW input. In the Summer the Solar HW would drive the tank and the PV output feeds the distribution panle as per normal.
Any ideas?
That way 100% of the power goes to the immersion. Or switch the AC from Inverter output directly to the immersion in the winter and work together with the Solar HW input. In the Summer the Solar HW would drive the tank and the PV output feeds the distribution panle as per normal.
Any ideas?
johnuready said:
Hi I agree the idea is a good one. Have you thought about using the DC direct from the PV and use a low volatge DC immersion?
That way 100% of the power goes to the immersion. Or switch the AC from Inverter output directly to the immersion in the winter and work together with the Solar HW input. In the Summer the Solar HW would drive the tank and the PV output feeds the distribution panle as per normal.
Any ideas?
Interesting thread resurrection That way 100% of the power goes to the immersion. Or switch the AC from Inverter output directly to the immersion in the winter and work together with the Solar HW input. In the Summer the Solar HW would drive the tank and the PV output feeds the distribution panle as per normal.
Any ideas?
1. How low voltage would the DC be then? (it depends)
2. It's rent a roof. Do you think the owner of the system would let him tap off the DC?
3. Where did the OP's Solar HW come from?
Just thought the DC idea is out, the generation meter is after the Inverter and taking the DC would decrease the income.
That leaves:
Switching the AC from the distribution board in the winter to the immersion running 100% on PV output and combine the solar hot water to supply the house requirements.
Run the Solar Hot water panles in the summer and switch the PV AC output back to the grid.
Spend £1,500 EMMA box from Cool Power and using that to switch all free electricity all the year to an immersion and forget about the solar hot water panels
Any ideas?
Any body have actual data to show how much power is lost to the grid broken done by months/weeks or days? Any size PV system will do as I can pro rata.
That leaves:
Switching the AC from the distribution board in the winter to the immersion running 100% on PV output and combine the solar hot water to supply the house requirements.
Run the Solar Hot water panles in the summer and switch the PV AC output back to the grid.
Spend £1,500 EMMA box from Cool Power and using that to switch all free electricity all the year to an immersion and forget about the solar hot water panels
Any ideas?
Any body have actual data to show how much power is lost to the grid broken done by months/weeks or days? Any size PV system will do as I can pro rata.
There are some similarities with perpetual motion being put forward on this thread.
PV is an expensive way of producing power, I suspect the price in NZ will be similar to the UK.
ie 7,000 pounds for a system that produces 4000 kW hrs a year (probably less in the UK due to lack of sun). This is not enough for a cylinder full of water every day.
A solar hot water system should be far less than this, and store the energy as hot water.
The factors to take into account is the overall cost to produce 1kW of energy. PV is useless for water heating.
If you don't have gas in the UK, and have a hot water cylinder - then the most cost effective way of saving money is either solar or a hot water heat pump.
It's not about perpetual motion but trying to claw back the electricity we get paid for and give away to the grid. If we can harness that power, however little for the cheapest up front cost you can win.
Anybody have good data on an average day in Jan or Feb output from a PV system, by the day would be great and I'll do the maths.
Anybody have good data on an average day in Jan or Feb output from a PV system, by the day would be great and I'll do the maths.
johnuready said:
It's not about perpetual motion but trying to claw back the electricity we get paid for and give away to the grid. If we can harness that power, however little for the cheapest up front cost you can win.
Anybody have good data on an average day in Jan or Feb output from a PV system, by the day would be great and I'll do the maths.
A 1kw system south facing produces typically 1. kw a day in January. 1.75 a day in February.Anybody have good data on an average day in Jan or Feb output from a PV system, by the day would be great and I'll do the maths.
The best output is July at 3.8 kw a day per 1 kw of roof panels.
Edited by Kevp on Friday 18th November 20:16
I still think you're barking up the wrong tree. I posted a simple way of harvesting surplus for a water heater using a sensor panel earlier.
However, if you really want to do the maths, here's my output for last December, January and February from a 3.88kWp system facing 175 degrees at about 51lat and with 30 deg pitch. (in kWh)
December 97, January 110, February 127
Whole year figures here:
Figures courtesy of www.bdpv/fr my info on there as pauld.
However, if you really want to do the maths, here's my output for last December, January and February from a 3.88kWp system facing 175 degrees at about 51lat and with 30 deg pitch. (in kWh)
December 97, January 110, February 127
Whole year figures here:
Figures courtesy of www.bdpv/fr my info on there as pauld.
Thanks
Just to start my maths off a 4Kw could produce 4Kw on a Jan day and could produce 7Kw on a Feb day. Just took 1Kw system and * 4
Does that sound right?
Anybody else have any data?
If that's correct am I right in saying that on that Jan day a 3Kw immersion would have been powered the equivalent of 4/3 = 1.33 hours if all power was available continues ?
Just to start my maths off a 4Kw could produce 4Kw on a Jan day and could produce 7Kw on a Feb day. Just took 1Kw system and * 4
Does that sound right?
Anybody else have any data?
If that's correct am I right in saying that on that Jan day a 3Kw immersion would have been powered the equivalent of 4/3 = 1.33 hours if all power was available continues ?
OK, Rule number one:
DON'T MIX UP KW AND KWH
The first is a rate (like miles an hour) and the second is an amount (like miles). A panel can generate 3kW in full sun, but if it only gets full sun for 20minutes, you'll only get 1KWh.
1kWh will raise 200 litres by about 4 degrees, or a bath of water about 10 degrees. So you need 2-3kWh to get a decent bath full of hot water. At this time of year, you're unlikely to get a bath of tepid water after a full day.
Rule number two:
Electricty is (a) expensive and (b) inefficient.
A solar thermal panel is about 85% efficient, a PV panel is about 25% efficient. So, you're wasting a vast amount of energy using PV to heat your water. In winter, when you're a net importer (if your water is heated by electricity) you'll pay roughly three times the price than you would by gas - just when you're using the most hot water.
Rule number three:
You need the most power when there's the least sun.
Most panels produce close enough to nothing in the core winter months - just when you need it. Sure, the average annual sounds great, but most of that is between May and August. As you get paid irrespective of whether you use the electricity, it makes the most sense to export it all, and reduce your consumption bill as much as possible by using as little electricity as possible. Heat with mains gas, logs or even oil and you'll be saving money overall.
Rule number four:
Low voltage and low wattage elements heat less (or more slowly).
All electric heaters are 100% efficient, so a lower 'power' heater just takes longer to do the job. It doesn't save you a single kWh, or a single penny. But you will be waiting a lot longer for hot water.
DON'T MIX UP KW AND KWH
The first is a rate (like miles an hour) and the second is an amount (like miles). A panel can generate 3kW in full sun, but if it only gets full sun for 20minutes, you'll only get 1KWh.
1kWh will raise 200 litres by about 4 degrees, or a bath of water about 10 degrees. So you need 2-3kWh to get a decent bath full of hot water. At this time of year, you're unlikely to get a bath of tepid water after a full day.
Rule number two:
Electricty is (a) expensive and (b) inefficient.
A solar thermal panel is about 85% efficient, a PV panel is about 25% efficient. So, you're wasting a vast amount of energy using PV to heat your water. In winter, when you're a net importer (if your water is heated by electricity) you'll pay roughly three times the price than you would by gas - just when you're using the most hot water.
Rule number three:
You need the most power when there's the least sun.
Most panels produce close enough to nothing in the core winter months - just when you need it. Sure, the average annual sounds great, but most of that is between May and August. As you get paid irrespective of whether you use the electricity, it makes the most sense to export it all, and reduce your consumption bill as much as possible by using as little electricity as possible. Heat with mains gas, logs or even oil and you'll be saving money overall.
Rule number four:
Low voltage and low wattage elements heat less (or more slowly).
All electric heaters are 100% efficient, so a lower 'power' heater just takes longer to do the job. It doesn't save you a single kWh, or a single penny. But you will be waiting a lot longer for hot water.
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