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Old 28 March 2012, 15:42   #1
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Solar PV immersion heater switch??

I'm getting a Solar PV system fitted to the house under the "rent a roof" scheme this week and want to make the most of the free energy it produces during the day.

I'm wanting to fit an immersion heater in to the hot water tank so that any surplus energy can heat the water and hopefully save on gas.

You can buy immersion heater switches online but they're costing something like 170 which isn't cheap enough in my eyes.

Can anyone help me design/source one that would be more cost effective than the market available ones?
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Old 30 March 2012, 14:06   #2
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I have a similar system. I had a 1kw immersion heater made by these (ordinary immersion heaters are 3kw) it cost 80. I had a boss fitted to the bottom of the hot water cylinder to fit the 1kw heater. I fitted a 10 immersion heater timer from B&Q, this is set 9-5. In summer the PV system consistently produces +1.5kw during the day, this runs the heater & the background load of the house. It's not a perfect system but it worked well last year. We halved our leccy bill & our oil bill compared to the previous year. We buy our leccy from British Gas (as you do) they have just fitted us a smart meter which shows how much we are importing from the grid, we also have a "Sunny Beam" monitor which shows how much the PV system is producing. We have been contacted by these who are trialing systems to link the Smart meter, PV monitor & immersion heater control all together to control the heaters to automatically divert all the surplus PV power into the hot water. We've signed up for the trial, so watch this space.
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Old 31 March 2012, 06:27   #3
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Unlike you, I can't make any money from importing the electric back to the grid as the "Tenants" get the feed in tarriff. I do however get all the free electricity that the panels produce. The Idea is to harness all of the surplus energy the system produces and channel it in to the water tank heating.

I could do it your way, but it doesn't take in to account other electrical devices drawing power so might start drawing power from the grid.

There are switch boxes available that do switch the immersion heating on and off but these are pretty expensive.

I'd like to find a way of doing this without the large outlay.
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Old 31 March 2012, 10:53   #4
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There are switch boxes available that do switch the immersion heating on and off but these are pretty expensive.
I've not seen these, can you point me to them. The method I described doesn't take the export tariff or FIT into account. It's just a way of using the PV as efficiently as I can without getting into any sophisticated control system. As long as the PV is producing 1.5kw I'm winning. The immersion heater takes a kw & the background load of the house is around 500w. What the CLNR is proposing, is to tie the immersion heater to some kind of smart controller that will automatically switch the immersion heater as the output from the pv rises & falls as the sun comes out. That way you won't actually export any power to the grid, it will all be absorbed into the hot water. The problem with the system I've got is it's "dumb" the immersion heater is on, & if the sun goes in, the heater will draw power from the grid, which then costs. I've been looking for some kind of switch that "knows" if the sun is out & switches on the heater accordingly.
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Old 01 April 2012, 20:22   #5
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Found a couple of controllers, the first is a voltage/load sensitive one and the second cheaper one controlled by light levels. Let me know what you think?

There are some reasonable costing 1/1.5 KW immersion elements for sale on there too.

Solar Panel Immersion Heater Switch - Use Surplus Power To Heat Water | eBay

IMMERSION WATER HEATER CONTROLLER TO USE SURPLUS SOLAR PV POWER | eBay
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Old 02 April 2012, 03:38   #6
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I'm getting a Solar PV system fitted to the house under the "rent a roof" scheme this week and want to make the most of the free energy it produces during the day.
How does that work?? I thought it was all 'fed in'.

There have been plenty of attractive houses and cottages around here that have been ruined by splattering PV panels all over the roofs.
Planning will wake up soon, this is a conversation area.

I've hidden solar (water) on the rear of our's.
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Old 02 April 2012, 05:01   #7
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How does that work?? I thought it was all 'fed in'.

There have been plenty of attractive houses and cottages around here that have been ruined by splattering PV panels all over the roofs.
Planning will wake up soon, this is a conversation area.

I've hidden solar (water) on the rear of our's.
Aye that's the problem, too much talk & not enough action
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Old 02 April 2012, 05:11   #8
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Aye that's the problem, too much talk & not enough action
Whoops!

As Elvis once said, " A little less conservation, a little more action".
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Old 02 April 2012, 05:41   #9
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Found a couple of controllers, the first is a voltage/load sensitive one and the second cheaper one controlled by light levels. Let me know what you think?

There are some reasonable costing 1/1.5 KW immersion elements for sale on there too.

Solar Panel Immersion Heater Switch - Use Surplus Power To Heat Water | eBay

IMMERSION WATER HEATER CONTROLLER TO USE SURPLUS SOLAR PV POWER | eBay
After thinking about it & doing a bit of digging, I've realised it's dead easy to do & that I've been using the bits required at work for years. I might even have the bits kicking about in the shed to do it. Doh!! However I'm going to see what the CLNR come up with, as they are offering to do it for free. The problem with the current models similar to the ebay one is that they aren't "smart" i.e. they will switch on the heater when the output of the pv rises to around 1.5kw. Unfortunately this doesn't take into consideration other loads that may be on at the time e.g. washing machine, dishwasher etc. So what would happen is that the switch would see the panels generating 1.5kw & switch on the heater, but you might already have 2-3kw of load on the system with washing machine etc, resulting in you now demanding 3-4kw which you would have to take from the grid & pay for. What the CLNR is proposing to do, is monitor the output from the PV AND the input from the grid & divert the difference to the immersion heater, so if the internal demand rises above the output of the PV, the heater would be switched off until the dishwasher etc, finishes. Phew!
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Old 02 April 2012, 13:23   #10
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The good news is that the electrician came today to wire everything up and it all seems to work OK, generating 12KW of electrical power. The bad news is that there is a display on the meter, but only displays the total energy produced and not what it's producing at any given time I'm sure there is a way of changing the display but I can't find any manuals on-line for it and would prefer not to push the button randomly
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