All about Solar Immersion Diverters

Pros and Cons of immersion diverters

Before smart meters, you gave excess electricity away to the grid for free, so an immersion diverter was a savvy investment back then. Instead of giving electricity away for free you could turn into hot water.

These days, you get paid for any excess electricity you give back to the grid. It is now much more financially beneficial (and better for the planet) to sell electricity to the grid, then buy back overnight to make hot water. (Overnight, electricity consumption is low enough that almost all of it is generated using renewables.)

Making a profit via selling and buying back

With the correct smart meter tariff and timings, you can make a profit here, too.

There are many smart meter plans that allow you to buy back electricity at a much lower rate in the middle of the night. For example currently (Jan 2023) with Energia you can sell any spare electricity to the grid in the day for 24 cents / unit, then buy it back in the middle of the night for 8 cents / unit. For every one unit you give them, they'll give you three back in the middle of the night.

If your primary aim with solar is to make hot water, you are still much better to sell the electricity to the grid, then buy back in the middle of the night to heat your hot water, as you'll end up with three times the amount of hot water.

Heat pumps are better than hot water diverters

The proliferation of heat pumps is also making hot water diverters much less attractive. If you have a heat pump, it is much better for both your pocket and environment to put the electricity into that produce your hot water. One unit of electricity in a heat pump will give three to four times the amount of hot water compared to putting that one unit into an immersion element.

How does a solar immersion diverter work?

• 1. The solar immersion diverter works by constantly monitoring the electricity usage in your home. This is monitored by the CT sensor clamp.

• 2. When your home is exporting electricity, the CT clamp tells the immersion diverter to send the surplus power to the immersion tank.

• 3. The immersion diverter device effectively heats your hot water cylinder for free, off the energy from the sun, reducing your reliance on electricity gas and oil.

• 4. When the demand in your house increases or the solar generation decreases, the immersion diverter will recognise this and reduce the amount of electricity that it is sending to the immersion.

How much energy can my hot water cylinder store?

Think of your hot water cylinder as a thermal battery. A well-insulated standard 120 litre cylinder can store between 8kWh to 10kWh of energy.

Can a solar immersion diverter work with batteries?

They both work in the same theoretical sense, by diverting the surplus energy for use at a later time. This can lead to both technologies "fighting" each other. The MyEnergi Eddi immersion diverter has a setting to incorporate battery storage on the site and will work well in conjunction with the battery.

Can I still use my immersion as normal for hot water?

Yes, indeed. All good immersion diverters have a boost functionality and timers to turn on the immersion if the water is not hot enough. For example, for showers in the morning, you can schedule the immersion diverter to come on to ensure you have enough hot water for the morning and hopefully, the solar panels have preheated the tank from the day before.

What if my tank does not have an immersion element?

You can add a device called a Willis heater. This is attached to the pipework outside your tank and effectively does the same job as an immersion heater.

This can also be worth considering where your immersion element heats only the top section of your hot water tank, which limits the amount of hot water that can be created by your solar panels.

Legionella - always boost your hot water once a week

Boosting your hot water to 65 °C is very important to remove the risk of legionella build-up in the hot water tank. Legionella is a type of bacteria that can cause Legionnaires' disease, a severe form of pneumonia. A good immersion diverter will have this functionality built-in, but it is no harm to manually boost to make sure.