Solar immersion controller review

A solar immersion controller is a way of storing solar electricity in your hot water cylinder

Immersion controller	Daily boost	Warranty (years)	Wireless	Loads	Batteries	Price	Comments
diverTech	Basic settings	3	Y	2	Y	£354	Wireless CT clamp included in the package, but it is battery operated.
Eddi	Y	3	Optional extra	2	N	£439	One of the best controllers on the market at the moment, especially if you have an all electric hot water system. The most easy to use interface and really good App.
iBoost	Week/Weekend	2	Y	2	Yes, but optional mains adapter	£307	Most popular controller in the UK. The optional extra iBoost buddy allows data to be viewed on a desktop display. No App.
Power Diverter	Y	5	N	1	Y	£349	An expensive basic controller with no app or wireless. Being an Australian brand, it is difficult to buy in the UK.
Immersun	Y	3	Optional extra	2	N	£499	Great for multiple loads and very user-friendly interface. App available.
SOLiC200	N	10	N	1	N	£199	Excellent price and warranty but basic functionality.
SolarCache	No longer trading
Intelligent Solar Mark III	No longer trading
Optimmersion	No longer trading
Apollo Gem	No longer trading

Table updated 24 December 2024

Alternative solutions

Some battery manufacturers also offer car chargers which interface with the battery and solar system. This can have massive benefits.

It means there is only one app to control everything.
Artificial intelligence can automatically manage all devices to maximise savings.

Examples of integrated solutions include SolarEdge Home Hot Water Controller and myenergi eddi. The SolarEdge system even allows the immersion controller, battery and electric car charger to be used as an integrated system to control import and export (which can be incredibly useful since can avoid the cost of upgrading to three-phase).

myenergi eddi Solar Power Diverter

SolarEdge Hot Water Controller

Daily Boost

Having a solar immersion controller which can “daily boost” i.e boost on an individual day or over a weekend is very important if your hot water system is electric only (you do not have a gas or oil boiler).

This is because the hot water cylinder needs to be heated to 60 degrees once a week to kill potentially dangerous bacteria in the hot water cylinder (legionella). Having a programmer that comes on every day will reduce the benefit of solar, since the cylinder will already be hot and not give the solar a chance to heat it.

Wireless

A typical system comprises of two components. The immersion controller and and sensor clamp. The sensor clamp is placed around the incoming electrical supply to check to see how much energy is leaving the property from the solar system. This can be wired to the immersion controller or communicate using wireless.

A wireless sensor clamp makes installation much easier and less disruptive to the home owner.

Warranty

This is less important since history has shown many companies go out of business in the warranty period. Quality and reliability of the solar immersion controller is far more important.

Loads

Some solar immersion controllers can control multiple loads. This is very useful for hot water cylinders with a upper and lower immersion element. The controller can heat the top of the cylinder first, and once hot, switch to the bottom immersion. Water is drawn from the top of the cylinder, so heating the top first allows hot water to be drawn off. Once the top of the cylinder is hot, the whole tank can be heated if there is enough sun.

Many controllers can also control alternative loads such as underfloor heating, electric towel radiators and electric panel heaters.

Batteries

Having a battery operated wireless sensor means the batteries need replacing and you may not notice immediately that the system is not working.

The Eddi is unique since it does not require batteries or a socket – it harvests its energy from the wire it is clamped around.