Solar Diverter: How It Works, Installation Costs and Whether It Is Worth It

At midday, a UK home’s solar panels may be generating far more electricity than the fridge, router and other background appliances require. Without another use for it, the excess flows into the grid. Yet the same household may later use gas or imported electricity to heat the water stored in its cylinder. A solar diverter offers another route for that midday surplus.

Also called a solar power diverter, the device monitors electricity flowing towards the grid and redirects the available excess to the cylinder’s immersion heater. The energy is then stored as hot water for washing, bathing or showering later in the day.

However, diverted electricity is not necessarily free. If the household receives a Smart Export Guarantee payment, every diverted kilowatt-hour may replace income that could have been earned through export. Whether diversion is worthwhile therefore depends on the cylinder and immersion heater, daily hot-water demand, existing heating fuel, export tariff and the amount of genuine surplus available after household consumption.

What Is a Solar Diverter and Is It the Same As an Inverter?

A solar diverter, also known as a PV diverter or immersion diverter, is a control device that redirects surplus solar electricity to a resistive electrical load. In most UK homes, that load is an immersion heater fitted inside a hot-water cylinder. The diverter monitors whether electricity is about to leave the property and adjusts the immersion heater’s power consumption to match the available surplus.

Although these components may operate within the same household energy system, each performs a different job:

A PV diverter is therefore not the same as an inverter. The inverter performs electrical conversion, whereas the diverter decides how an available AC surplus should be used. A typical diverter operates on the AC side after the inverter has converted the panels’ DC output.

The diverter does not generate extra electricity, increase the panels’ output or store electricity itself. It simply controls an existing load so that more surplus generation can be retained within the home as hot water rather than exported immediately.

How Does a Solar Power Diverter Work?

A solar power diverter continuously balances solar generation against electricity being used within the home. The process works as follows:

• Solar panels generate direct-current (DC) electricity.
• The solar inverter converts this output into alternating-current (AC) electricity.
• Appliances operating at that moment consume the available solar electricity first.
• A current transformer, usually called a CT clamp, measures the direction and amount of power flowing at the grid connection.
• When the CT clamp detects export, the diverter sends a matching amount of power to the immersion heater.
• The device continually raises or lowers the immersion load as solar production and household consumption change.
• Diversion stops when the cylinder thermostat reaches its set temperature or when there is no longer a surplus.
• Depending on the system’s priority settings, remaining electricity may charge a battery, supply another controllable load or enter the grid.

Variable control is essential. An ordinary immersion heater may be rated at 3 kW. If it were switched fully on while the panels had only 800 W spare, the home could import the remaining 2.2 kW from the grid. A proper diverter modulates the heater’s input so that it follows the measured surplus instead of simply switching the entire load on or off.

Control arrangements vary between products:

The cylinder thermostat remains responsible for stopping the immersion heater once the target water temperature is reached.

Is Your Home Suitable for a Solar Diverter?

A solar power diverter needs both an electrical surplus and somewhere useful to store the resulting heat. Having solar panels alone is therefore not enough. Before requesting a quotation, check the property’s generation profile, hot-water system and export arrangement.

Usually Suitable When:

A home is more likely to benefit when:

• It already has solar PV and regularly exports electricity.
• The property has a hot-water cylinder with a working electric immersion heater.
• The household uses enough stored hot water to absorb the diverted energy.
• The cylinder is well insulated and retains heat until it is needed.
• The consumer unit, electricity meter and immersion circuit are accessible for assessment and installation.
• The avoided cost of heating water is greater than the value of the export payment surrendered.

Often Unsuitable or Less Useful When:

An immersion diverter may offer limited value when:

• The property has a combi boiler and no hot-water cylinder.
• Appliances already consume most solar generation during daylight hours.
• A battery absorbs nearly all available surplus.
• Most hot water comes from electric showers, which heat mains water directly rather than drawing from the cylinder.
• The household receives a valuable export rate.
• Summer hot-water demand is low, leaving little capacity for diverted energy.
• The cylinder, immersion element or circuit requires costly replacement or alteration.

The installer should also check the cylinder’s capacity, insulation condition and immersion-element rating. A cylinder may contain one element or two, and the diverter must be configured for the intended load and priority. The immersion thermostat and its independent thermal safety cut-out remain essential: the diverter controls available power, but these controls prevent the water or element from overheating.

• No cylinder? A standard immersion diverter is generally unsuitable.
• Cylinder but no immersion heater? Obtain a quote for cylinder and electrical work first.
• Cylinder and immersion but little export? Review smart-meter or inverter data before buying.
• Regular surplus and meaningful stored hot-water demand? A diverter may be a good candidate, subject to installation cost and lost export income.

Solar Diverter Installation: Equipment, Process and Electrical Requirements

A solar diverter installation is usually a retrofit to the property’s existing AC electrical and hot-water systems. It does not normally require new solar panels or replacement of the existing solar inverter. However, the installation must be designed around the meter position, consumer unit, immersion circuit and cylinder controls.

A typical installer will:

• Survey the solar PV system, electricity meter and hot-water arrangement.
• Confirm that the immersion element, thermostat, cable and protective device are suitable.
• Position the CT clamp at the correct grid connection point and verify its direction.
• Install the diverter near the hot-water cylinder or immersion supply.
• Connect the required wired CT cable or wireless transmitter.
• Configure the import/export direction, export threshold and load priorities.
• Test the response while solar generation and household electricity demand change.
• Confirm that the cylinder thermostat and thermal cut-out stop heating correctly.
• Explain the display, monitoring, manual boost and timed-boost settings to the homeowner.

The distance and obstacles between the electricity meter and cylinder often determine the monitoring arrangement:

A competent electrician familiar with solar generation, immersion-heater circuits and current UK wiring requirements should complete the work. This allows the earthing, isolation, cable capacity, circuit protection and manufacturer’s installation conditions to be checked together.

The retrofit may become more involved if it requires a new dedicated circuit, long cable route, local isolator, wireless CT equipment or replacement immersion element. The electrician should also confirm whether the chosen model can control one load or two and how it will interact with any battery, EV charger or existing energy-management equipment.

How Much Does a Solar Diverter Cost in the UK?

The solar diverter cost depends on more than the price of the control unit. For a straightforward UK retrofit, a reasonable planning allowance is around £450–£900 fitted, although published estimates vary. Some lower figures assume a simple installation or a diverter purchased alongside a new solar PV system.

These figures are planning ranges rather than fixed national prices, and the optional items should not automatically be added together. Sunsave currently gives a broad estimate of £300–£500 including installation, while Better Home Energy lists approximately £300–£550 for the unit and £550–£900 fitted. The difference illustrates why homeowners should check what each published price includes.

The main variables are:

• Whether the diverter is fitted with a new PV system or retrofitted later
• The distance between the electricity meter and hot-water cylinder
• Wired CT cabling versus a wireless transmitter
• The condition of the immersion heater and its existing circuit
• Whether one cylinder or multiple heating loads will be controlled
• App monitoring, temperature sensing and smart-control functions
• Installer call-out charges, labour time and location

Request an itemised quotation showing the diverter model, labour, CT equipment, isolators, cable work, electrical alterations, cylinder work and applicable VAT. It should also identify any optional upgrade separately, making comparisons between quotations much clearer.

Are Solar Diverters Worth It? Calculate Savings Using Export Opportunity Cost

To decide are solar diverters worth it, do not value every diverted kilowatt-hour at the household electricity import rate. The diverter may replace gas, oil, LPG or direct electric heating, and the electricity could otherwise have earned an export payment. Both sides of the calculation matter.

Use:

Annual net benefit = (useful diverted heat × avoided water-heating cost) − lost export income

Then estimate:

Simple payback = fitted cost ÷ annual net benefit

The avoided water-heating cost should reflect the fuel and equipment that would otherwise produce the same useful heat. The lost export income is the electricity no longer sent to the grid multiplied by the applicable export rate.

Comparison: 1,000 kWh diverted per year

These figures exclude cylinder heat losses, maintenance and future tariff changes. At an illustrative fitted price of £600, the simple payback would be about 30 years in the gas case but three years in the direct-electric case. These are examples, not forecasts.

The difference is substantial because a diverter stores electricity as resistance heat. Replacing electricity bought at 25p/kWh while surrendering 5p/kWh of export leaves a 20p margin. Replacing useful heat worth only 7p/kWh leaves a 2p margin. A diverter may therefore be more financially attractive when it displaces direct electricity, oil or LPG than when it replaces efficient mains-gas heating. A high export tariff can reduce or even eliminate the benefit.

Use current tariff rates rather than the example figures. SEG suppliers set their own rates, contract periods and eligibility conditions, while payments are calculated from export-meter readings.

Legacy Feed-in Tariff customers require a separate check. Some installations of 30 kW or less receive deemed export payments based on a percentage of generation rather than measured export. For these households, diverting electricity may not reduce export income in the same way as metered SEG export.

Solar Diverter vs Solar Battery: Which Should Use the Surplus First?

The main difference in a solar diverter vs battery comparison is the form in which energy is retained. A diverter converts surplus electricity into stored heat, whereas a battery keeps it as electricity for later use. Neither should automatically receive priority in every home.

Three priority arrangements are possible:

• Home loads → battery → hot water → export: This preserves flexible electricity first. The diverter activates after the battery reaches its target state of charge or cannot accept more power.
• Home loads → hot water → battery → export: This may suit a household with immediate hot-water demand, a small battery or a high value placed on reducing conventional water heating.
• Time- or tariff-based dynamic control: Priority changes according to battery charge, cylinder temperature, anticipated evening demand and import or export prices. This requires compatible controls and careful configuration.

The best order depends on whether the stored energy will genuinely be used. Charging a battery that remains full has little value, but neither does heating a cylinder beyond the household’s needs. Cylinder losses, battery losses and sacrificed export income should all be included in the comparison.

The Jackery SolarVault 3 Pro Max is one home-battery option for households that want to retain surplus solar as flexible electricity rather than convert it immediately into heat. It combines battery storage with smart energy management, but adding a separate diverter requires system-level planning rather than treating each device independently.

If both devices monitor the same grid connection and react to an identical export threshold, they can compete for the surplus or repeatedly change state. The installer should therefore verify CT and smart-meter positions, inverter compatibility, export limits, control hierarchy and activation thresholds. A clear priority, such as charging the battery before heating water, helps prevent conflicting responses.

A battery and diverter are not automatic substitutes. A household with strong evening electricity demand and substantial hot-water use may benefit from both, provided recurring generation is sufficient and the controls allocate the surplus predictably.

Solar Diverter vs Solar Thermal: Which Is Better for a UK Home?

The fundamental difference is how each system captures and uses solar energy. Solar thermal collectors absorb heat at the roof and transfer it through a fluid circuit to a hot-water cylinder. Solar PV first generates electricity; a diverter then sends only the unused electrical output to an immersion heater.

Direct solar thermal collection can usually deliver more useful heat per square metre of collector area because it avoids converting sunlight into electricity and then electricity into heat. However, PV offers greater flexibility: the electricity can serve appliances, an EV, a battery or the grid whenever the cylinder cannot accept more energy.

Neither option should be presented as covering all annual hot-water demand in a UK home. Solar availability and water use vary by season, so a boiler, heat pump or immersion heater will normally provide backup. Energy Saving Trust explains that solar water heating generally works alongside a boiler or immersion heater and is unlikely to meet 100% of hot-water demand, particularly during winter.

The better choice therefore depends on the starting point:

• Existing PV and an immersion-equipped cylinder: investigate a diverter before adding a separate roof-based thermal system.
• Limited roof area reserved specifically for water heating: assess whether solar thermal’s higher heat yield per square metre justifies the additional pipework and maintenance.
• Electricity needed for appliances, EV charging or storage: PV provides more routes for using the collected energy.
• No hot-water cylinder: neither is a simple add-on; installing suitable thermal storage would form part of a wider heating-system change.

Choosing a Solar Diverter: Geatures and the Eddi Solar Diverter Example

Choose a diverter from the property’s electrical and hot-water requirements rather than from app features alone. Before ordering, check:

• Maximum supported load and minimum diversion level
• Control of one load or two prioritised loads
• Wired CT and wireless transmitter options
• Compatibility with the existing PV and inverter arrangement
• Battery-aware settings or adjustable export thresholds
• Manual, scheduled and tariff-based boost modes
• Temperature-sensor support
• Display, app and historical energy data
• Coordination with boilers, heat pumps or tariff schedules
• Warranty length and UK technical support
• Installer experience with the model
• Ability to define priorities between the cylinder, battery, EV charger and grid

Products can also be grouped by how closely they depend on other equipment:

The eddi solar diverter is a recognisable UK-market example, but it should not be treated as the default choice for every property. The current single-phase eddi supports a compatible resistive load up to 3.68 kW and offers app control. It is supplied with a CT clamp and a 5 m cable; where the meter or consumer unit is farther away, the CT cable may need extending or a compatible wireless harvi sensor may be required.

Specifications, accessories and installation conditions can change, so confirm them against the latest manufacturer documents and the proposed wiring arrangement. The best model is the one that measures grid flow reliably, works with the cylinder and immersion element, and follows the intended battery, hot-water and export priority without control conflicts.

Advantages, Limitations and Final Buying Checklist

A solar diverter is most useful when the home has recurring export, suitable hot-water storage and a heating cost worth displacing. Its lower purchase price can be attractive, but low cost alone does not guarantee a short payback. Assess what the device can usefully replace and what happens to the surplus after the cylinder is hot.

Main advantages

• Uses otherwise exported generation: More solar output is consumed within the property, although the lost export payment must still be considered.
• Reduces conventional water heating: Diverted energy can reduce the work done by an immersion heater, boiler or another source serving the cylinder.
• Lower upfront cost than a battery: A diverter normally requires much less investment than electrical battery storage.
• Automatic operation: Once correctly commissioned, it adjusts the immersion load as the available surplus changes.
• Retrofit potential: Many existing PV systems can accept a diverter without replacing the panels or solar inverter.
• Uses existing thermal storage: A suitable hot-water cylinder provides storage without installing an electrical battery.

Main Limitations

• A compatible cylinder, immersion element and electrical circuit are required.
• Stored heat can serve cylinder-fed hot-water demand but cannot later power appliances.
• Annual savings depend on solar surplus, season, heating fuel, water use and export value.
• Diverting metered exports can reduce Smart Export Guarantee revenue.
• Once the cylinder reaches its set temperature, further surplus needs another destination.
• Batteries, EV chargers and diverters can compete if thresholds and priorities are not coordinated.
• Cylinder standing losses reduce the heat available when the water is eventually used.
• The diverter itself cannot supply household electricity during a power cut.

Pre-Purchase Checklist

• Download at least 12 months of solar generation, grid import and export data.
• Record the cylinder capacity, insulation condition, immersion rating and number of elements.
• Estimate annual useful surplus, excluding electricity already consumed by household loads.
• Identify the current water-heating fuel and calculate the avoided cost per useful kWh.
• Confirm whether export payments are metered SEG, deemed FIT or another arrangement.
• Decide whether retaining surplus as electricity or hot water better matches later demand.
• Obtain an itemised fitted quotation and calculate net annual benefit and simple payback.
• Ask the installer to document CT locations, export thresholds and load priorities for the diverter, battery and EV charger.

FAQs

The following are the frequently asked questions about the solar diverters:

What are the key differences between a solar diverter and a solar battery?

A diverter converts surplus electricity into heat and stores it in a hot-water cylinder. A battery stores electricity that can later supply a wider range of household loads. Diverters usually cost less, but batteries are more flexible. Neither provides backup electricity unless the battery system has a dedicated and correctly installed backup function.

Can I use a solar diverter with a battery?

Yes, provided the controls are compatible and the priorities are configured correctly. A common arrangement charges the battery first and diverts power after it reaches a target state of charge. The installer should coordinate CT locations, activation thresholds and export settings so the battery and diverter do not compete for the same surplus.

Does a solar diverter work with a combi boiler?

Not usually if the property has only a combi boiler and no hot-water cylinder. A standard immersion diverter needs a cylinder containing a compatible electric immersion heater. A combi boiler produces hot water on demand, leaving no stored body of water for the diverted energy. Homes with a separate cylinder require an individual assessment.

Will a solar diverter work in winter?

Yes, but only when the solar system generates more electricity than the home is using. Shorter days, lower solar output and higher household demand normally leave less surplus during winter. The diverter may operate for shorter periods or remain inactive on some days, so the normal water-heating source is still required.

How long does a solar diverter last?

There is no guaranteed lifespan covering every model and installation. Industry estimates commonly suggest around 10–12 years, but actual life depends on product quality, temperature, usage and electrical conditions. Compare the manufacturer’s warranty with the expected financial payback and ask whether replacement parts and UK technical support are available.

Can a solar diverter power radiators or underfloor heating?

Some models can control compatible resistive electric loads, such as storage heaters or electric underfloor heating. They do not directly heat ordinary water-filled radiators unless the wider system includes a suitable electrical heating element and controls. Check the permitted load type, maximum rating, thermostat requirements and manufacturer’s wiring conditions before specifying space heating.

Does using a diverter reduce SEG payments?

Usually, yes. A diverter reduces the electricity physically exported, and Smart Export Guarantee payments are calculated from export-meter readings. The financial loss equals the diverted export multiplied by the applicable SEG rate. Legacy Feed-in Tariff customers receiving deemed export payments may be affected differently and should check their specific arrangement.

Can an eddi solar diverter be added to existing solar panels?

Yes, an eddi solar diverter can generally be retrofitted because it monitors AC power flow rather than requiring a particular solar-panel brand. Suitability still depends on the meter position, CT connection, immersion circuit, load rating and other energy devices. Longer distances may require an extended CT cable or a compatible wireless sensor.

Final Thoughts

Before buying a solar diverter, confirm that the property has a suitable hot-water cylinder, immersion element and electrical circuit. Then use at least 12 months of data to measure genuine export after household consumption.

Calculate the cost of producing the same useful hot water with the existing fuel, then subtract the SEG income that diversion would remove. Compare the resulting annual benefit with a solar battery, timed immersion control and solar thermal system. If a battery or EV charger is already installed, agree the surplus priority and control thresholds with the installer. Finally, obtain an itemised installation quotation before calculating payback.

A diverter can be a relatively simple way to increase solar self-consumption, particularly when surplus electricity replaces costly water heating. It is not automatically worthwhile where efficient gas heating, limited export, no suitable cylinder or a valuable export tariff leaves little net benefit.