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If your solar panels generate more electricity than your home is using, the surplus power can be exported to the grid, stored in a home battery, or redirected to another useful load. A solar diverter takes the third approach, typically sending surplus solar electricity to an immersion heater to heat water.
This can help you use more of the electricity generated by your solar panels at home rather than exporting it. However, a solar diverter and a home battery use surplus solar energy in different ways: a diverter converts it into heat, while a battery stores electricity for later use.
This guide explains what a solar diverter is, how it works, its advantages and limitations, typical UK costs, and how it compares with home battery storage.
What Is a Solar Diverter?
A solar diverter, also called a solar power diverter or solar immersion diverter, is a device that redirects surplus electricity from a solar PV system to a useful load, most commonly an electric immersion heater in a hot-water cylinder. When solar generation exceeds your home's electricity demand, the diverter can send some or all of that surplus power to the immersion heater instead of exporting it to the grid.
For example:
- Solar panels generate: 3 kW
- Home is using: 1 kW
- Surplus solar: 2 kW
- Diverter sends some or all of that surplus to the immersion heater
The immersion heater then uses the surplus solar electricity to heat water. In this way, the energy is effectively stored as heat in the hot-water cylinder rather than stored as electricity. A solar diverter is therefore primarily a solar self-consumption device, not an electricity-storage system like a home battery.
How Does a Solar Immersion Diverter Work?
A typical solar immersion diverter consists of a control unit, an electricity-monitoring sensor and a connection to an immersion heater. Solar panels generate electricity according to available sunlight, and your home uses this electricity to power appliances and other electrical loads. When generation exceeds household demand, the remaining electricity becomes surplus. The diverter then works as follows:
- The diverter monitors electricity flow. A current sensor, often a CT clamp installed around the home's incoming supply cable, measures whether electricity is being imported from or exported to the grid.
- Surplus electricity is detected. When solar generation exceeds household demand, the diverter detects the surplus that would otherwise be exported.
- Surplus power is sent to the immersion heater. Instead of allowing the electricity to flow to the grid, the diverter gradually adjusts the power supplied to the immersion heater. Many modern diverters can modulate their output rather than simply switching the heater fully on or off. This allows them to make use of smaller amounts of surplus generation. If household demand increases or solar generation falls, the diverter can reduce or stop the power sent to the immersion heater.
-
The immersion heater converts electricity into heat. The immersion heater heats the water in the hot-water cylinder, effectively turning surplus solar electricity into stored thermal energy. The important distinction is that the hot water becomes the energy store. The diverter itself does not store electricity.
What Are the Benefits and Drawbacks of Solar Power Diverter?
Benefits of a Solar Power Diverter
- Higher solar self-consumption. A diverter can increase the proportion of your solar generation that you use at home instead of exporting it to the grid.
- Productive use of surplus solar electricity. Hot water is a predictable household demand, particularly in homes with conventional hot-water cylinders. A diverter allows surplus solar electricity to contribute to that demand.
- Lower grid electricity use for water heating. If you would otherwise heat your hot water using electricity from the grid, solar-generated electricity can provide part of that energy and reduce grid consumption.
- Lower upfront cost than battery storage. A solar diverter and immersion-heater system can have a considerably lower upfront cost than installing a home battery, although the two technologies provide different functions.
Drawbacks of a Solar Power Diverter
- No electrical backup. A diverter cannot keep your lights, refrigerator or other appliances running during a power cut because it does not store electricity for later use.
- Hot-water system requirements. Homes without a compatible hot-water cylinder and immersion heater may need additional equipment before a diverter can be installed.
- Limited hot-water storage capacity. Once the cylinder reaches its target temperature, it cannot continue absorbing surplus solar energy. Additional surplus electricity will need to be exported or used elsewhere.
- Less flexible energy storage. Stored hot water cannot power your appliances later. A battery stores electricity that can be used across a wider range of household loads.
- Potential loss of export revenue. Diverting surplus solar electricity means less electricity is available to export to the grid. Under the UK's Smart Export Guarantee (SEG), eligible households can receive payments for electricity exported to the grid, so the value of using surplus electricity for hot water should also be considered against the export payment you could otherwise receive.
- Dependence on solar generation. Cloud cover, winter conditions and shading can reduce the amount of surplus electricity available for diversion, so the benefit can vary throughout the year.
How Much Does a Solar Power Diverter Cost in the UK?
A solar power diverter typically costs around £300 to £500 in the UK, including the diverter unit and standard installation. Actual costs can vary depending on the model, installation requirements, and whether additional electrical or hot-water system work is needed.
The total price may include:
- Solar diverter unit
- Electricity-monitoring sensor
- Installation labour
- Electrical protection and wiring
- Immersion-heater connection
- Additional plumbing or cylinder work, if required
Installation costs can increase if additional wiring, electrical protection, immersion-heater modifications, or work on the hot-water cylinder is required. When comparing quotes, check what installation and electrical work is included in the price. Cost alone does not determine whether a solar diverter is worthwhile. Its value also depends on your surplus solar generation, hot-water demand, existing water-heating costs, and potential export payments.
How to Choose a Solar Diverter
When choosing a solar diverter, consider whether your home is suitable, how much surplus solar electricity you have available, and which features you actually need.
Is Your Home Suitable for a Solar Power Diverter?
A solar diverter is generally most relevant if you have:
- Solar PV panels
- A grid-connected electricity supply
- A compatible hot-water cylinder
- An immersion heater
- Regular hot-water demand
- Periods when solar generation exceeds household electricity consumption
A home with solar panels but no immersion heater or suitable hot-water cylinder may not be a straightforward candidate. Homes that rely solely on a combi boiler without a hot-water cylinder, for example, do not have the usual hot-water storage setup used by an immersion diverter.
Your hot-water demand also matters. If your existing heating system already produces hot water efficiently or your household uses relatively little hot water, the potential benefit of diverting surplus solar electricity may be smaller.
How Much Surplus Solar Electricity Do You Have?
A diverter only has electricity to redirect when your solar panels are generating more power than your home is using. Check your inverter or energy-monitoring data to see how often and how much electricity you export to the grid.
Homes that regularly export surplus solar electricity have more opportunity to use a diverter. If your household already consumes most of its solar generation during the day, there may be relatively little electricity available for water heating.
Your export tariff should also be considered. Under the Smart Export Guarantee (SEG), eligible solar PV owners can receive payments for electricity exported to the grid. Diverting electricity to hot water means giving up the export payment on that electricity, so compare the value of the avoided water-heating cost with what you could otherwise receive for exporting it.
What Features Should You Look for in a Solar Diverter?
Once you know a diverter suits your home, compare models based on compatibility and the level of monitoring and control they provide.
Key features to consider include:
- Immersion-heater compatibility: Check that the diverter supports your existing immersion heater and its electrical load.
- Power modulation: Look for a system that can adjust the power sent to the immersion heater as surplus solar generation changes.
- Energy monitoring: Some systems show household consumption, diverted energy, and grid import or export.
- Wired or wireless monitoring: Different systems use wired or wireless connections between monitoring components, which can affect installation.
- Maximum load: Check the maximum heater load supported by the diverter.
- Smart controls: Depending on the model, features may include apps, boost timers, temperature monitoring, or control of additional heating loads.
- Warranty and installer support: Check the warranty and availability of technical or installer support.
A qualified installer should confirm compatibility with your solar PV, electrical, and hot-water systems before installation.
Solar Power Diverter vs Solar Battery: What's the Difference?
A solar diverter and solar battery can both help you make greater use of surplus solar electricity, but they handle that energy differently. A diverter uses surplus electricity to heat water, while a solar battery stores electricity for later use.
|
Feature |
Solar Diverter |
Solar Battery |
|
Stores energy as |
Thermal energy (hot water) |
Electrical energy |
|
Main use |
Water heating |
Household electricity |
|
Can power appliances later? |
No |
Yes |
|
Can provide backup power? |
No |
Some systems can |
|
Limited by hot-water capacity? |
Yes |
No |
|
Typical upfront cost |
Generally lower |
Generally higher |
|
Energy flexibility |
Lower |
Higher |
In practice, this means the same surplus solar electricity can serve different purposes. For example, surplus generation at midday could be used by a diverter to heat your hot-water cylinder or stored in a solar battery for use when solar output falls in the evening.
The main difference is how flexible that stored energy is. A diverter is primarily useful for households with regular hot-water demand and a compatible cylinder. Once the water reaches its target temperature, however, its ability to absorb additional surplus energy is limited. A battery can store electricity for a wider range of household loads, and some systems can also provide backup power during a power cut.
The choice therefore depends on how you want to use your surplus solar energy. For households that want to use stored electricity across multiple loads or add backup capability, an expandable battery system provides a different set of functions from a solar diverter. For example, the BLUETTI Apex 300 home battery backup starts with 2,764.8Wh of capacity and 3,840W of output, with expandable capacity for higher energy needs.
Can You Use a Solar Diverter With Battery Storage?
Yes, in many systems a solar diverter and battery storage can be used together. However, they need to be configured so that both systems respond appropriately to the available surplus solar electricity.
A typical setup may use solar electricity for household loads first, then charge the battery, with additional surplus directed to the immersion heater. However, this is not a universal priority order. How surplus electricity is shared between the battery, diverter and grid depends on the equipment, monitoring setup and system configuration.
Using both technologies allows surplus solar energy to be stored in two different forms:
- Battery: stores electricity for later household use.
- Hot-water cylinder: stores energy as heat for later hot-water use.
How useful the combination is also depends on how much surplus electricity remains after battery charging. A larger battery may absorb much of the available surplus on some days, leaving less energy for water heating. At other times, such as periods of strong solar generation when the battery has limited capacity available, a diverter can make use of additional surplus that might otherwise be exported.
Whether using both makes financial sense depends on battery capacity, surplus solar generation, hot-water demand, electricity prices, export tariffs and installation costs.
Are Solar Diverters Worth It?
Whether a solar diverter is worth it depends on how much surplus solar electricity you have, how you currently heat your water, and what you could earn by exporting that electricity.
A solar diverter may be worth considering if you:
- Regularly export surplus solar electricity
- Have a compatible hot-water cylinder and immersion heater
- Have regular hot-water demand
- Would otherwise use grid electricity or another paid energy source to heat water
- Receive relatively little value from exporting surplus electricity
- Want to increase solar self-consumption without necessarily needing electrical backup
The key financial comparison is between the value of using surplus solar electricity for water heating and the value of exporting the same electricity to the grid. If using 1 kWh of surplus solar avoids more in water-heating costs than you would receive for exporting that 1 kWh, diverting it may provide greater financial value.
However, the benefit may be smaller if you have little surplus solar generation, low hot-water demand, or an attractive export tariff. A battery can also change the calculation if it already absorbs much of your available surplus electricity.
For this reason, a solar diverter is not automatically worthwhile for every solar household. Its value depends on your surplus generation, hot-water demand, existing heating costs, export tariff, and installation cost.
Conclusion
A solar diverter provides a straightforward way to increase solar self-consumption by using surplus PV electricity to heat water. It can be particularly useful for UK homes with a compatible hot-water cylinder, an immersion heater, regular hot-water demand, and surplus solar generation.
Unlike a solar battery, a diverter stores surplus energy as heat rather than electricity, making it a more specialised solution for water heating. Whether it is worthwhile depends on how much surplus solar electricity you have and whether using that electricity for hot water provides more value than exporting it. Before investing, consider your installation cost, hot-water demand, existing heating costs, and export tariff.
For many households, the key question is therefore not simply “Can I use a solar diverter?” but “How much surplus solar electricity do I have, and what is that electricity worth to me?”
FAQs About Solar Diverters
Can a Solar Diverter Work Off-Grid?
A solar diverter can potentially be incorporated into an off-grid solar solution system, but its operation depends on the specific system architecture and equipment.
In an off-grid system, there is no grid electricity to export, so the diverter's traditional role—redirecting electricity that would otherwise be exported—is different.
An off-grid system normally needs appropriate battery storage, inverter capacity and energy-management controls. The diverter should therefore be selected as part of the overall off-grid system rather than treated as a standalone solution.
Is It Better to Divert Excess Solar Power or Export It to the Grid?
There is no universal answer.
The relevant comparison is between the value of exported electricity and the value of using that electricity to heat water.
For example, diverting surplus electricity may be attractive when:
- You have significant hot-water demand.
- You would otherwise heat the water using grid electricity.
- Your export payment is relatively low.
Exporting may be more attractive when:
- Your export tariff provides a high payment.
- Your hot-water demand is already satisfied.
Your electricity import rate, export rate, hot-water requirements and system efficiency should therefore all be considered.
How Can I Divert Excess Solar Power to Heat Hot Water?
The most common approach is to install a solar immersion diverter connected to a compatible immersion heater. A simplified system looks like this: Solar panels generate electricity to power household loads, while any surplus solar energy is sent to a diverter, which directs the excess electricity to an immersion heater that heats water in the hot-water cylinder. A qualified electrician should assess the existing solar PV, electrical supply and hot-water system before installation.
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