Solar PV immersion heater switch??

Hightower · 28 March 2012, 20:42

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?

Pikey Dave · 30 March 2012, 19:06

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.

Hightower · 31 March 2012, 11:27

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.

Pikey Dave · 31 March 2012, 15:53

Quote:

Originally Posted by Hightower

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.

Hightower · 02 April 2012, 01:22

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

Mollers · 02 April 2012, 08:38

Quote:

Originally Posted by Hightower

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.

Pikey Dave · 02 April 2012, 10:01

Quote:

Originally Posted by Mollers

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

Mollers · 02 April 2012, 10:11

Quote:

Originally Posted by Pikey Dave

Aye that's the problem, too much talk & not enough action

Whoops!

As Elvis once said, " A little less conservation, a little more action".

Pikey Dave · 02 April 2012, 10:41

Quote:

Originally Posted by Hightower

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!

Hightower · 02 April 2012, 18:23

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

Pikey Dave · 02 April 2012, 20:32

the inverter should have a display that shows instantaneous power

Hightower · 02 April 2012, 21:19

It does, but as it's in the loft and not easily accessable it's next to useless. I'll have to monitor the wheel on the meter to see what my real time energy usage is.

NeilH · 02 April 2012, 21:22

We had them fitted a few weeks ago (the 'free' ones). The inverter does show the current amount being produced but ours is in the attic and after the first couple of days the enthusiasm to go and see what it is generating wanes! The meter in the garage shows we have so far generated 569Kwh but I've no idea how much of this we have used. I've bought an electric chain saw and will be using it when it is sunny!
Apart from sticking the washing machine on during the day I hadn't really thought of ways to maximise the free energy.
Cheers
Neil

Pikey Dave · 02 April 2012, 22:35

Quote:

Originally Posted by Hightower

It does, but as it's in the loft and not easily accessable it's next to useless. I'll have to monitor the wheel on the meter to see what my real time energy usage is.

What make is the inverter? if it's an SMA "sunny boy" you can get a bluetooth monitor which will work over about 50m & give you full readout of instant, accumulated power etc.
You can also download the free software from SMA's website & use a laptop with bluetooth to monitor the inverter.

Hightower · 03 April 2012, 02:13

It's made by Fronius, don't know the exact model number but there doesn't seem to be any Blue Tooth facility but you can hardwire a network and use USB datalogging. To be honest, if it means taking panels off etc I won't be touching it as the system isn't mine to play with. I'll have to find some other passive way to help me.

EnglishLes · 03 April 2012, 08:04

Quote:

Originally Posted by Hightower

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 have attached one of those 'this is how much electricity you are using' things to the PV output and this displays how much is being generated now on a radio linked display in the kitchen. I believe the power companies give them away if you ask for them.

Hightower · 03 April 2012, 17:24

Quote:

Originally Posted by EnglishLes

I have attached one of those 'this is how much electricity you are using' things to the PV output and this displays how much is being generated now on a radio linked display in the kitchen. I believe the power companies give them away if you ask for them.

I tried that on the wire from the inverter to the meter, but it didn't register anything. Possibly because the clamp went over the entire multi core cable instead of just the live one?

Pikey Dave · 03 April 2012, 19:22

Quote:

Originally Posted by Hightower

I tried that on the wire from the inverter to the meter, but it didn't register anything. Possibly because the clamp went over the entire multi core cable instead of just the live one?

You need to pick up just the 1 wire. If you pick up the L&N they cancel each other out. B&Q sell a decent one for about 30 quid

Hightower · 03 April 2012, 19:58

Quote:

Originally Posted by Pikey Dave

You need to pick up just the 1 wire. If you pick up the L&N they cancel each other out. B&Q sell a decent one for about 30 quid

I can't touch the wiring, it's not my equipement. So I'm kind of stuffed!

What I will do is to monitor the readings from the inverter during different weather and get a feel for what it's producing. The light meter switch seems like the best way to go for me, so will be looking at purchasing/building one of these.

Pikey Dave · 03 April 2012, 21:27

Quote:

Originally Posted by Hightower

I can't touch the wiring, it's not my equipement. So I'm kind of stuffed!

What I will do is to monitor the readings from the inverter during different weather and get a feel for what it's producing. The light meter switch seems like the best way to go for me, so will be looking at purchasing/building one of these.

You don't need to touch the wiring, the pickup (current transformer) just clips around the cable, completely non-invasive