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Readers tips of the month disagree about solar switching devices

Posted by NicoleYouGen on 28 February 2013 at 9:02 am

This month, our readers have given some conflicting tips about solar heater switching devices. Ted from Cornwall installed an Immersun system to route surplus power from the solar panels into the immersion on the cylinder. He is happy and says ‘even in February the panels are heating all the hot water.’ 

Nigel Surrey, who used his skills from working with financial management systems to design and build a PV Solar Panel Monitoring System, did not feel so warm about Immersun. He says: ‘Beware of solar companies pushing the sale of expensive solar panel immersion heater switching devices such as Immersun. The maximum savings can only be the amount users would spend on hot water heating bills and that is if one heated water from 100% generated power. This would never happen all year round. I rescued my father from falling prey to such tactics would would have taken him 15 years to recoup cost of ¬£1,250 at 100% of heating cost. Quick estimate based on his 1.7kW PV system it would have taken 100 years to cover his normal £12 per month water heating costs.’ 

This month our readers do seem to agree on two points: check out your installers and insulate. 

Solar PV has been positive for Pat Wells, a Norfolk business owner who works from home. The installation has saved his household £165 on electricity bills, on top of FIT payments. His advice for someone considering PV: ‘Asking to see previous installations is a must, and ask to speak to previous customers. Emails, and websites can be faceless, where as a telephone call or visit really helps. You also see what you are buying in action, and see the true results.’

He adds that he is now looking at energy reducing appliances. He says ‘It’s amazing how little time capital expense is recovered by the savings on electricity’.  

Keith Searle recently became SuperHome number 150. You might be interested in reading his story of becomming a SuperHome owner. His top tip: Before worrying about the energy source insulate to the highest standards you can manage.

A.WISE from Torfaen installed solar electricity panels using a company recommended by a friend. She says: ‘Always go for a firm that has been recommended, friends are usually a better guide than advertisements or selling agents. Don't be afraid to ask about the things you don't understand, these are the experts and they should be able to answer all your queries.’

Ted has installed solar PV and a heat pump. Last month, he swapped his LPG boiler for an 8.5 kW Ecodan with a cylinder for DHW. Ted says: ‘Take care with your choice of installer and do your research thoroughly’. He adds: ‘Monitor your installations to make sure they're performing as you expect’. And like Keith, he stressed the importance of insulation. 

One of the main points this month: research your installers. You can begin by checking out what previous customers say on YouGen). 

Click the link to find out more about the benefits of using solar PV to power your immersion, and be sure to scroll down to the lively discussion below the blog.

Read a review of the immerSUN device.

More information about Energy Storage on YouGen.

Find an installer


If you have a question about anything in the above blog, please ask it in the comments section below.

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20 comments - read them below or add one

Gilly Jones

Gilly JonesComment left on: 2 June 2014 at 2:56 pm

@dee1kanbi You might find this blog review on the Immersun useful by one of our energy experts.

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dee1kanbiComment left on: 31 May 2014 at 3:15 pm

Hi i have Question to ask anyone who knows more about Solar Iboost or Immersun devices for heating water for your homes.

How good is Solar iboost ? How much power do you need to be producing in order for the Solar iboost to start your immersion heater is your cylinder ??

What is best and efficient Solar iboost or Immersun???? 

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arwooldridgeComment left on: 20 June 2013 at 11:59 pm

@Beachlife, To feed an oil filled radiator in addition to an immersion heater is quite simple using the Sola Controla proportional heating controller.

The Sola Controla uniquely is rated a full 4kwatts and can therefore be overloaded unlike its 3kwatt competitors.  Indeed if you have 4kwatt peak PV power you can load the Sola Controla with two 3kwatt heating devices (pure resistive) , as no more power will flow than the peak PV power available. 

The proportional control circuit ensures the load power matches the available export power exactly (typically within 40 watts).

I  use 15 amp round pin sockets for dedicated heaters fed from a proportional supply. This prevents the wife or cleaner plugging in a hoover (they don't run very well on proportional power!) 

An even better load is to feed a storage heater, these work extremely well with excess PV power as the heat is stored during the day and released just when its needed in the evening/night.

One disadvantage of such overloading or parralleling is the power is shared equaly by both loads. The Sola Controla has another mode where by adding a cheap slave control modules you can control both loads and give priority to the DHW. This is therefore the preferred solution.


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Charlotte Heath

Charlotte HeathComment left on: 18 April 2013 at 10:30 am

Based on the nature of this discussion, I thought you might be interested to see the SOLiC 200 at work.


Of course it only makes sense to install one of these devices if the free hot water produced is going to be used

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RSE Electrical Services Ltd

RSE Electrical Services LtdComment left on: 7 April 2013 at 1:55 pm

We recently installed an immersun for a customer who uses oil for heating hot water and heating he is very happy as although the immersun unit may not heat the whole cylinder at the very least it is reducing the amount of oil that Hewas using to heat the hot water which is feeding  two mixer showers a bath and obviously sinks.....  His PV is a SolarWorld 2.5kW system

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glbellComment left on: 1 April 2013 at 2:18 pm

Does anyone have any feedback on the SOLIC 200 (especially if anyine has installed it)

I would also like to know if a oil radiator could be linked into the HW circuit so that I can either switch between HW or heating and once the HW is at temperature then it would divert to heating. Any thoughts?

thanks Graeme.

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GeronimoComment left on: 29 March 2013 at 10:24 am

As a pensioner my prime aim is to keep my bills as low as possible also bearing in mind I don,t have that many years to recover the costs of some of the system control units now available.Is,t a bit like spending a fortune on a car that will run on an oily rag ,if you don,t use it then you can,t save it.So my first priority after maximum insulation is run the home at the lowest sensible temperature.I have some two years ago installed 3.4kw pv system which is proving to be good value,i receive fit payments based on a 50% feed in of amount generated.What I have also done and it is only practical if you spend a considerable time at home is install a 1kw immersion in my cylinder and a remote switch.Monitoring my consumption meter ( free from n power) and my sunny boy remote generation meter I use most of my spare generated energy to heat my hot water or run an electric fire if on a good day the water has been satisfied. 

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PeterG229Comment left on: 26 March 2013 at 6:32 pm

Hi, I hope you received your solarimmersion switch 111. Mine (#368) arrived around 2 weeks ago, and is now fully fitted. I run it alongside my Wattson Plus meter, and have been producing some interesting graphs of how much, and when, it is diverting. After emailing the Company for advice and not receiving a reply after a week, I managed to speak to a Director for the technical support I requested. My advice so far? It does most of what it should do, but there are system faults which can't be worked round at the moment. I have decided to keep mine, rather than returning it. If you can wait awhile, there should be a system update later this year (though at a higher price?) My system info - East/West roofs total 3.2KW arrays, 2KW immersion heater, switch 5m from consumer unit linked by screened data cable (Unable to locate twisted pair as telephone extension cables (B and Q recommended) weren't twisted.

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beachlifeComment left on: 25 March 2013 at 7:35 pm

I understand that the immersun can heat the water using an immersion as a dump for excess generated electricity.

Is it possible to also use the immerson to power an oil filled radiator? If so how is this done? Do you need to have an extra socket installed dedicated for the radiator?

As I spend the winter months away from the UK thought this would be a good method of keeping the background heat of the house high enough to keep pipes warm enough to prevent freezing.

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PeterG229Comment left on: 24 March 2013 at 9:33 pm

A Solar Immersion switch - mark 111 has just been installed along side my Wattson Plus. There are some minor teething problems, but on the whole I am pleased that much of my excess solar power is being diverted to my hot water tank - I have reduced the temperature in my oil fired boiler, and set the immersion heater temperature up to 65 deg C. Can't wait till the sun returns, when I expect to turn off the boiler completely. An email for information about the dip switches remains unanswered.

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Fred1Comment left on: 4 March 2013 at 6:37 pm


Try one of the energy comparison websites if you are paying 5p for gas, my last bill showed 2.822p/kw for some  and 3.612p/kw for the rest, an average of 3.2p/kw.

I guess 1.6p for all you generate is not bad you probably use at least half of what you generate and perhaps two thirds, so you are getting  3.2p to 4.8p on what you actually put into the grid now....Be interesting to see once they install your export meter.

Good luck with the energy comparison websites, looks like you will save a lot if you move supplier


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DavePComment left on: 4 March 2013 at 5:53 pm

I guess if  FRED1 is getting 4p per Kw he must have an export meter as I only get 3.2p per Kw for 50% of what I generate (=1.6p) regardless of how much I manage to use. So it may be worth it for me provided they don't suddenly turn up with a smart meter in the next five years.

 I would agree that they don't save any Co2 though. 

I'd also be interested to know where he gets gas at 3p per Kw, mine's near to 5.

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Fred1Comment left on: 4 March 2013 at 3:19 pm

These black boxes of any type do not save co2, they distribute already generated solar electricity either to the house or to the grid. I, like many, are connected to the gas supply and normally heat water by gas. I guess if I paid say £450 plus £100 installation I could get a top of the range black box. This would then divert electricity from the grid , reducing my electricity export at about 4p/kw a loss to me. I would save the gas previously used for heating water at about 3p/kw. So I would lose money.

For those not on gas grid the savings would be real but small say  about £60/year taking say 9 years to pay back.....

I guess we will still have advertising saying install one of these and have enegy for free....



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DavePComment left on: 3 March 2013 at 8:32 pm

I currently manage my load switching manually as being retired means I spend quite a lot of time at home. I have 2 energy monitors one looks at the output and the other how much is being used, The immersion is currently on a timer and comes on for a couple of hours during the early hours on night tarriff and during the day I decide whether to run the washing machine, immersion or other devices dependant on how much solar is being generated. 

Although this has saved over a third of my normal grid consumption in the last year it is a bit of a chore and obviously not practical for many people.

I'm reluctant to spend £400 + on an Immersun or similar, but has anyone used the relay built in to the Solar Inverter. I have an SB 4000TL-20

I thought that a cheap way would be to fit additional 1Kw immersion (or replace the existing 3Kw unit) and set the inverter to drive a power relay, so switching on the immersion when the solar is providing about 1.5Kw as my base load (fridges etc) is about 500W . On days when the Solar did not produce enough then a boost could be given on the night tarriff.

Whilst this is not a complete solution it go some way toward automating the system.


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Solar Wind

Solar WindComment left on: 1 March 2013 at 6:14 pm

I built my own solar diverter last year based on a circuit I found on the OpenEnergyMonitor web site for less than £100, but the savings are small.

I managed to divert just over 1MWh of surplus solar PV during 2012 but at 6p per kWh for off peak energy which I normally use for heating water I only saved £60.00.  Pay back time though is less than two years.

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Cathy Debenham

Cathy DebenhamComment left on: 1 March 2013 at 10:43 am

And here are some more comments along the same lines from Twitter:

@YouGenUK - interesting read but most installers are charging around £500 for Immersun so the comparison is a little misleading :) says @SRELTD

@YouGenUK Mr Surrey seems to be a little misguided on his figures - I suspect that he prob offers an inferior competive product #maybe? says ‏@MetgenUK

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MMS Building Services Ltd

MMS Building Services LtdComment left on: 28 February 2013 at 9:37 pm

We are a small family firm installing three pv systems a week.  We only charge an extra £400 to supply and install an Immersun Unit.  And we get great feedback from our customers.

For an extra £400 they can get free hot water for four to five months a year....Why would you not.

And as for companies charging £1500 for Immersun...they are just crooks and conmen....

Name and shame.....


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Rudge Energy

Rudge EnergyComment left on: 28 February 2013 at 12:09 pm

Indeed, if you are a low hot water user, then such devices such as the ImmerSun may not be for you.. Many people have an electric shower and the main use of hot water is for hand washing only. The ImmerSun is not for them!

Other homes will use a number of baths or showers a day if the house is multi occupancy and using stored hot water. This kind of installation will benefit the most from an ImmerSun or similar device.

We have customers who have not used their gas boiler at all last spring, summer and autumn after having an immersion switch fitted.

With power prices due to start ramping up again soon, any technology that can save you power (including lots of insulation!) must be looked at for use in a power saving scheme.



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NicoleYouGenComment left on: 28 February 2013 at 10:36 am

Thank you for making that point, Nick. 

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Nick Hanna

Nick HannaComment left on: 28 February 2013 at 10:28 am

One point overlooked by the negative commenters on solar switching devices is that if you have a thermal store rather than just a hot water cyclinder then potentially you are saving much more than simply the cost of heating water.


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