Solar + Immersion Diverter: The Smart Way to Heat Water for Free

If you already have solar panels or you are planning a new installation, an immersion diverter is one of the smartest add-ons you can choose for an Irish home. Instead of exporting excess solar energy back to the grid, a diverter automatically sends that spare electricity to your hot water tank. The result is free or low-cost hot water for much of the year, reduced reliance on your boiler, and lower energy bills.

In this guide, we explain how immersion diverters work, why they pair so well with solar PV systems in Ireland, and when they make the most financial sense.

What Is an Immersion Diverter?

An immersion diverter is a small device that monitors your home’s electricity flow. When your solar panels produce more power than you are using, instead of exporting that energy to the grid, the diverter redirects it to your immersion heater.

This means your hot water tank becomes a thermal battery, storing energy as heat. You get more value from your own solar generation and reduce the need to heat water using gas, oil, or electricity from the grid.

To understand how solar generation varies through the day and across the year, see our guide How Weather Patterns Affect Solar Output Across Ireland.

Why Immersion Diverters Work So Well in Ireland

Irish households use hot water throughout the year, especially in the morning and evening. At the same time, solar systems often produce their highest surplus during the middle of the day. An immersion diverter bridges this gap by capturing daytime solar energy and storing it as hot water for later use.

Key benefits include:

• Lower water heating costs
• Less boiler runtime and fewer burner cycles
• Improved self consumption of solar energy
• Better overall system efficiency
• Reduced wear on heating systems

If you are already thinking about ways to maximise your solar investment, you may also find value in How to Monitor Your Solar Performance Like a Pro.

Solar vs Boiler Water Heating Costs

Water heating is one of the biggest sources of energy use in Irish homes. When you heat water using solar electricity diverted into your immersion, the marginal cost is effectively zero because you are using energy that would otherwise be exported.

Compared with:

• Gas or oil heating with rising fuel costs
• Standard immersion heating charged at your day rate
• Night-rate heating that still relies on grid supply

A diverter allows you to prioritise free renewable energy first.

If you are considering additional ways to reduce energy bills, you may also be interested in pairing solar with smart energy storage. See our article How to Integrate Your EV Charger with a Home Battery for more insights on energy optimisation at home.

How Much Can an Immersion Diverter Save?

Savings will vary depending on:

• Your household hot water usage
• Tank size and insulation quality
• Solar system size and output
• The amount of excess energy available
• Your heating fuel type and tariff

Many homeowners see meaningful reductions in annual heating costs, particularly during spring and summer when solar surplus is highest.

A well designed solar system with good orientation and minimal shading will generate more usable surplus energy. If you are planning a new installation, see our guide East vs West vs South: The Best Roof Orientation for Solar in Ireland for practical insights on system layout.

Do You Still Get Paid for Exported Solar?

Yes. An immersion diverter only uses energy that would otherwise be exported to the grid. You still receive payment for any remaining exported units through your microgeneration tariff.

The choice is not export or hot water. It is about prioritising value. In most households, replacing paid energy with free hot water delivers greater day-to-day savings.

When an Immersion Diverter Makes the Most Sense

A diverter is especially worthwhile if:

• You have a hot water cylinder with an immersion heater
• Your solar system regularly produces more than you consume
• You want to reduce gas or oil boiler usage
• You are not ready to invest in a battery, but want better self-consumption

Homes with electric showers, regular laundry, or daytime occupancy may export less energy, but most properties still benefit from some level of water heating using solar.

If you are planning to expand your system in future, you may also be considering capacity decisions. For a deeper look at system sizing strategy, read Should You Oversize Your Solar System? Pros and Cons.

Solar Diverter vs Battery Storage

Some homeowners choose between a diverter and a home battery. In reality, the two technologies work well together.

A diverter is typically:

• Lower cost to install
• Simpler to integrate
• Focused on hot water savings

A battery is designed for:

• Storing energy for evening use
• Tariff optimisation
• Backup capability in some setups

Many households benefit from both, with the diverter handling thermal storage while the battery manages electrical storage.

Practical Considerations Before Installing One

A professional installer will assess:

• Tank capacity and insulation
• Immersion power rating
• Electrical safety and wiring routes
• System monitoring and controls
• Expected solar surplus availability

They will also ensure your diverter works seamlessly alongside any future upgrades such as EV charging or battery storage.

If you are considering a wider smart home energy setup, explore How to Integrate Your EV Charger with a Home Battery to see how these technologies connect together.

Final Thoughts

A solar immersion diverter is one of the smartest and most cost-effective ways to increase the value of your solar system in Ireland. By turning unused electricity into hot water, you improve your self-consumption, reduce running costs, and make your home more energy efficient without changing your daily routine.

If you would like advice on whether an immersion diverter is right for your home, WattCharger can assess your system design, hot water demand, and potential savings.