Review of the ImmerSun: Is Self Consumption the Future? 1

How the ImmerSun Works

When you have someImmerSUN sort of renewable energy like solar panels within your home or business, there will be times that you won’t use all of the electricity is produces.  The ImmerSun “diverts” this energy into useful appliances within your home, be it your immersion heater, wall heaters etc.  As these devices are being ran for free, then you should need less energy within your home, resulting in lower energy bills.

Any good solar champion will tell you that as a Solar Panel owner, you should turn on your washing machine, dishwasher and other items you normally use, ideally when its sunny, or at least day light.  This little box goes further and automates the “turning on” but in a much more cleverer way.


 Why Buy an ImmerSUN, What’s the Point?

As the renewable energy market moves more and more towards self consumption and self storage, these types of after-market devices are ideal for retrofitting into existing houses or businesses. The problem with renewable energy is there is plenty of it when you quite likely don’t need it.  If somehow you could turn on appliances to effectively “store” this free energy, then you are onto a winner, as your home would use less energy overall.

For many installations connected to the grid, the grid is effectively acting like a battery (as far as the billing/savings are concerned), any unused energy generated is sent back down the incoming cable and back into the grid for neighbouring properties to “absorb”. Most of the time, this is not measured, as PV owners who rely on the feed-in tariff get paid a rate for their generation and the export (the bit sent back out of the property), but as the export is “deemed” to be 50% of the generation regardless of how much of it got used in the property or not, so you might as well use it for something useful than to let it go out of the property to “someone else”. You can use your unused generation to :



  • “Dump” heat into your immersion heater – saving money
  • Turn on appliances, such as panel heaters, underfloor heating, pre-heating your building for free
  • Store energy that you will use later on
  • Grid Voltage Stabilisation (ensure you stay within UK G83 grid connection regulations)
  • Be Greener, more environmentally responsible, taking less from the grid and fossil fuels for your home


ImmerSUN Installation

Installation was a breeze really, but then again I suppose its based on where you locate the unit and what is around it.  If you mount the thing miles from the supply and load then expect quite a bit of hassle.  Below you can see it with the lid off.  I must admit wiring the heaters into the connections are quite a bit of a squeeze, and if you end up being too generous on the length of the cables (2.5mm), you won’t get the cover on!. You will also notice that if you install anything above or below the unit (like my last picture below) which is too close, you will have a hard time getting the cover off!..but they DO TELL YOU THAT, in the instructions 😉



How I connected the ImmerSUN up:

Terminal One to a 3 KW Immersion heater which is top mounted in the tank.

Terminal Two to 3x 900 watt Herschel Inspire Glass infra-red panel (Infra-red) wall heaters around the house, this is to pre-heat the house prior to the gas boiler coming on. I have installed a relay that once the internal house temperature is what I need, it turns off the Infra-red heaters and dumps output to 3x Warmup Underfloor heaters located in rooms (a 3.2m² which pulls around 389 watts, a 4.00m² heater pulling around 700 watts and just under 2m² pulling around 300w)

Terminal Three to a Victron MutltiPlus which is a battery charger and inverter, that stores energy during the day and lets the house use it of a night, I’ve used a number of old Fork Lift Truck traction batteries as the storage device and a Raspberry Pi to monitor the power flows out of the building.  When the house is importing it will start up the Multiplus inverter and push power into the distribution board till the battery’s are around 50% discharged then quit (to preserve the life of the batteries), when its exporting, the ImmerSUN dumps the excess back into the batteries.

As founder of Squeaky Energy, I was in a fortunate position to connect the Immersun to a large solar array to see what it could really do, not just in a domestic setting but see how it could work in a business or even a power plant with it’s own energy storage system.

ImmerSUN Features

  • Ability to set different types of heaters
  • Manually Boost Heaters using manual control or external relay
  • Link together up to 5 of these units (ideal for 3-phase)
  • 7-Day programmable Boost Timer
  • Destratification Option – Connect up a pump to circulate water in your water storage cylinder. Stratification is the layering that occurs naturally because of temperature. Use this to mix the water in the storage vessel so your thermostat on the Immersion heater does not go off too early, getting a nice full tank of hot water!
  • Shows the amount of electricity you are importing
  • Good range of reporting options to display savings etc
  • Nice soft-starting (using proportional control so to reduce power surges)


Here are some of the features from the menu:

ImmerSUN Reporting

You get a whole range of reporting metrics from the unit which is pretty cool. Simply set your “buy” price for your electricity on a per Kilowatt Hour Basis and let the ImmerSUN tell you how much it has saved you.  Of course, you can only save if you give it something to do. If you just connect it to a hot water cylinder and leave it at that and then never use the Water, the ImmerSUN cannot do any more, it will simply allow any excess power to export, effectively wasting it, which will reduce your return on investment and the amount of savings shown on the reports.

 Running the ImmerSUN

Starting up takes just a few seconds while it boots up then the little picture of the house is present and shows the status. I have noticed that when it going full pelt the fan on the right of the unit really winds up a bit and at its maximum, you can hear its on and doing things. Heat wise it does get quite warm, if you knew what it was doing (proportional AC Power Control). you would forgive it as its quite hard work keeping an eye on its load while monitoring the incoming/outgoing power flows.  I notice that its very quick to react to a change in power flows, so lets say you had some excess and it was “dumping” 3KW into a cylinder, let’s say you turn the kettle on, its pulls it back instantly!, which is quite impressive.


  • Utilises the free electricity you don’t use and send “next door”
  • You can link up to 5 of them together (different phases or circuits etc)
  • Automates turning on appliances when the power is there for them
  • Compatible with most hot water and electrical space heating systems
  • Great reporting, shows what you have saved in real-time
  • You can even hookup an ImmerSun to run your Aga Cooker!

Things to Consider:

  • There is no web front end or reporting package, so you have to read the display to find out how its doing, better still a mobile app, so I could see how it was performing any-time I like, I’m told its on the way to being developed, this will be an excellent addition and look forward to the software update.
  • If you have a three-phase supply(like I have), expect you have to buy three of these babies! if you have a three-phase inverter, otherwise you won’t be making the most of the power as energy generated will go back down the other two phases you are not using!. I’m using it with a Sunny Tripower 12000TL connected to a large PV array, as I only have one ImmerSUN I ended up wasting a lot of energy while at the same time causing an unbalance the phases (which could make the DNO cross!)
  • It’s not internet enabled, so you cannot control/monitor it remotely. In the new world of Internet Connected Devices, this unit is out in the cold and by itself, leaving you to squeeze into the immersion cupboard each time you want to control it.
  • It’s does not Integrate into Hive or Google Nest, ImmerSUN could use their API to make this slot in nicely with home automation as the ImmerSUN does not know what is going on around it, having no external sensors or input other than relying on the circuits connecting to it being open circuited to assume they are “hot”. It would be nice to integrate with external weather stations or meteorological forecasting systems so it can make smart choices about the priority order of your heaters around your lifestyle, local conditions etc.

With the ImmerSUN, you export less energy, because of course you are using it yourself.  This won’t be an issue for most people who are on a deemed tariff where the export is NOT being metered plus it promotes self consumption, but customers whose exports are measured will have to do some maths to see if its worth losing it, at the end of the day, if your import cost is higher then what your ImmerSUN is using it for minus what you would lose in export rates, then of course it makes sense.

Best Use of the ImmerSUN

  • Use it to pre-heat your water heater cylinder (if you have one) saving you money on your primary heating source (make sure you install a de-strat pump!)
  • Connect Infra-red heaters to it, pre-heating your home for free
  • Let it “dump” free heat into your underfloor heating or even cooling (air-con)
  • Use it to ensure you soak up every bit of energy your renewable plant generates, effectively lowering fuel bills

Savings made with the ImmerSUN

Savings made so far with the ImmerSUN

Savings made so far

According to the ImmerSun unit, since I installed the device in Oct 2014, I have saved £133. This is of course based on if I had turned on those appliances anyway, and some things like underfloor heating I can do without, so if I had paid the usual cost for the electricity to power these devices then the unit is correct and the savings are pretty good and the unit should pay for itself within 3.6 years max*.

As it comes with a 3 year warranty, even if it is blows on the 36 month, I should of had a good return, so any real gain will be made after the 3.6 years have passed assuming its still going strong. Another thing to remember is that the cost of electricity is likely to go up also which only speeds up the return on investment.

Cost of ImmerSun £318.00

Installation Cost : £166

Total Outlay £484.00

Savings Made so far £133.00 (1035 KWh)

Time Left till ROI: 2.63 years


Remember: Check that you have a big enough solar array in the first place, as if you are running a small array and already a large user of energy then you may have little excess power for ImmerSUN to “divert” so buying one will be a total waste of money!


Swimming Pool Dumping

ImmerSUN's Pool heating

Pool now Hot

One excellent mode is the ability to set the heater type to “Pool” and using the Electro Eco 8T83 Electric Swimming Pool heater, I set it to effectively “dump” excess energy from the Solar PV into a Swimming Pool, pre-heating the pool before to the natural gas boiler kicked in to bring the water to its usual temperature of 28C.

Obviously this has the effect of lowering energy bills as the gas boiler does not need to work as hard as before due to the pre-heating. One important point to consider when using the ImmerSUN this way is to connect up the stratifying pump output to the main pool circulation pump, either through a contactor or a relay or changeover control box.  This is because you will need the pools pump operating anyway, but want it to run on for a while after the thermostat has opened to cycle though the pool and ensure the heat is even throughout and ensure that you are pulling your chlorine through the skimmer for long enough for a full cycle.


Using ImmerSUN with Hydro

Using ImmerSUN with Hydro

There are many competitor systems on the market, I’ve tested quite a few, some produce “dirty” electricity that is not only dangerous and could interfere with the electricity network, but can also damage sensitive devices as these use the likes of Burst-Fire control and Phase-Angle for the AC Power control.

The ImmerSUN is properly certified and appears to be a popular device and fully complies with Directive 2004/108/EC-Electromagnetic Compatibility (limiting Harmonic Current Emissions from the device) and have developed their own power control system.

Don’t be fooled by the marketing (that I’ve seen around in some electrical wholesalers) that its only for use with solar panels as its not.  Solar is ideal, but if you have any type of energy generation system (I have used the ImmerSUNwith my Baxi Ecogen (domestic Micro-CHP bolier), you might have a wind turbine or even better a good friend of mine has a large estate and has a small river going through it, he’s got small scale hydro-power system that provides power to his house, when he is not there during the day, he could use the ImmerSUN to divert excess energy into his appliances instead of letting it go to waste, which is what it is doing now!

So far, ImmerSUN looks like a good investment, I like the unit and it does the job well, it has a lot of good features and is well built and reliable. It will be interesting to see how the ImmerSUN develops, what new features it has and how the company that makes them will look to integrate with other renewable energy devices while keeping up with consumers habits and expectations.



The Future

I’m replacing the relays (sat on the terminal two of ImmerSUN) with the Rapberry Pi and a bunch of wireless temperature sensors dotted around the house.  By connecting the Pi’s GPIO’s to a range of 20A contactors, I can create a script to control these as I see fit and organise the priority of the dumping priority based on personal preferences. By pulling in the MET office data (using the API), my program can predict the future weather conditions and decide the priority on the fly, between space heating via Infra red or underfloor heaters. Using Google now, my program will be able to tell when I’m likely be home, so I can wire this into the external boost function of the ImmerSUN to pre-heat or top-up a few degrees if required, without any input.

The ImmerSUN is developing all of the time, so I hope to update this page with future trials of add-ons and newer revisions of both the software and hardware of the ImmerSUN.

Thanks for reading.

*This assumes that electricity was the primary heating source in all these cases.  If I was using mains gas, then as gas is more efficient at heating water for example, then these savings would be reduced but at least the displaced Co2 would be a benefit. Units like the ImmerSUN will also help bring down the return on investment for your Renewable Energy installation cost as you take advantages of the free energy more.  ImmerSUM is model A1060-12 running software version 2.71.2/3 and reviewed between 10/10/14 and 10/10/15. Savings are based on import cost of £0.12p per Kwh. .  One downside of importing less energy (electricity) is that your relative cost could increase as many providers charge one rate for the first x units of the period then a discounted rate thereafter. If you are a low user you could get caught between this and pay more per unit but overall the bill could be lower.


  • Adam

    Great write up, thank you