Did you know… up to 70% of the electricity produced by your PV system may exceed your immediate needs and so is exported to the grid with no benefit for you. The ImmerSUN unit changes that by monitoring your grid connection and diverting any export to your immersion heater effectively using your PV as a solar thermal system at a fraction of the installation cost.

How it works

The immerSUN monitors the power coming into your house and as soon as you start to export power to the grid from the PV system this will be redirected to your immersion heater.

If the load in the house changes, for instance you put the kettle on or the washing machine comes on then the immerSUN senses the change in demand and alters the amount of power sent to the immersion accordingly.

Also if the PV production drops due to clouds or shading the immerSUN will alter the immersion feed. The immerSUN is constantly maintaining a balance whereby only the power that would have been exported is used by the immersion.

This means on a nice sunny day you will have a tank full of free hot water before you export any power to the grid. You can use all your appliances in the house as normal and as soon as you have any ‘spare’ power it is diverted to the immersion.

You will reduce your heating bills and carbon foot print further still by using the PV system you already have more effectively and you will use less fossil fuel to heat your water.

Feed-in Tariff payments

This will not affect any payments you receive for the feed-in tariff because these are paid for total generation before the power is used and the export payment is estimated so that will not be affected either.

immerSUN is easy to install and suits all new and existing PV systems.

Case Study

A south westerly facing 4kWp PV system with slight shading during winter was installed at the end of November 2011 and produced 2018kWh up to the end of July 2012. During the installation an export meter was fitted just for information purposes and out of the total generation of 2018kWh, 1264kWh have been exported. That’s 63% of the total generation
exported to the grid.

An immerSUN unit was installed at the beginning of August, after 6 weeks the PV system generated 504kWh with an export of 134kWh so the export has been reduced to 26%. That’s 6 weeks worth of free hot water and no fossil fuel being used.


Being experienced plumbers we can replace it with the latest highly efficient Part L compliant cylinder, which in itself will save you money by not leaking heat 24 hours a day.

If your cylinder is modern and does not warrant replacing we can install a longer immersion heater to get more out of the immerSUN.

We can install a de-strat pump controlled by the immerSUN which will pump the hot water from the top of the cylinder into the bottom once the immersion switches off. This cools the immersion allowing it to switch back on and so reheating the top of the cylinder. This sequence in repeated until the whole cylinder is full of hot water.

If you have a combi boiler we would need to install a pre-heat unvented cylinder with immersion heater and mixing valves depending on the type of combi you have.




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