A sunny morning can generate far more electricity than a household is using at that moment, while the hot-water cylinder is quietly reheating later using grid energy or gas. That leads many homeowners to ask: can solar panels heat water? Yes, but the answer depends on whether you mean Solar PV panels that make electricity, or solar thermal collectors designed specifically to warm water.
Both can reduce the energy needed for hot water, but they work differently and suit different homes. The right choice comes down to your existing heating system, roof space, hot-water use and plans for the property over the coming years.
Can solar panels heat water directly?
Standard Solar PV panels do not heat water directly. They convert daylight into electricity, which can power appliances around the home. To use that electricity for hot water, a system normally needs an immersion heater in the hot-water cylinder and a solar power diverter.
The diverter monitors the electricity being generated and the electricity being used in the home. When there is spare Solar PV generation, it sends that surplus to the immersion heater instead of exporting it to the grid. The immersion then heats the water stored in the cylinder.
This is often a practical addition for homes with an existing cylinder and Solar PV installation. Rather than allowing all unused daytime generation to leave the property, some of it can be stored as useful heat for washing up, baths and showers.
Solar thermal is different. Its roof-mounted collectors absorb heat from daylight and transfer it, via a special fluid, to a coil inside a hot-water cylinder. This is a dedicated hot-water system, rather than an electricity-generation system.
Solar PV with an immersion diverter
A Solar PV and diverter arrangement is generally most effective from spring through to early autumn, when longer days can create regular surplus electricity. It can provide a meaningful contribution to domestic hot water, particularly for households that use hot water in the evening after solar generation has peaked.
The water cylinder acts as a thermal store. Unlike a battery, it does not retain electricity, but it can retain the benefit of electricity generated earlier in the day in the form of hot water.
There are limits. An immersion heater typically uses a significant amount of power, so it should only receive genuine surplus generation. If the system simply switches the immersion on regardless of available solar power, it may draw electricity from the grid and reduce the expected saving. A correctly selected and configured diverter is therefore essential.
Solar thermal collectors
Solar thermal collectors are built for one task: producing hot water. They can be very efficient at it, especially during brighter months, and can make a substantial contribution to a household's annual hot-water demand.
However, solar thermal needs dedicated equipment, including pipework, controls, a pump station and a compatible cylinder with a solar coil. It also needs careful design to manage periods of very strong sunshine, when the cylinder is already hot and there is nowhere for additional heat to go.
For a home starting from scratch, Solar PV is often considered first because the electricity can be used across the household as well as for hot water. That flexibility can be valuable if your routines, appliances or heating arrangements change. Solar thermal can still be an excellent choice where hot-water demand is high and roof space is available, but it is a more specialised system.
Which system is right for your home?
There is no one-size-fits-all answer. A family using several showers, baths and regular laundry cycles may have a very different hot-water profile from a couple who are out during the day. Your current system matters just as much.
If you have a conventional or system boiler with a hot-water cylinder, adding a Solar PV diverter may be relatively straightforward. The cylinder must have a suitable immersion heater and enough stored-water capacity to make the most of the available solar generation. A small cylinder may reach temperature quickly, leaving further surplus electricity unused.
Homes with a combi boiler have a different starting point. A combi heats water on demand and does not normally use a hot-water cylinder. Solar-generated electricity cannot be stored as hot water without introducing a cylinder and changing parts of the system. That can still be worthwhile as part of a wider heating upgrade, but it requires proper planning rather than a simple add-on.
Solar thermal also requires a cylinder, usually one designed with the appropriate internal coil. Replacing a cylinder only to accommodate solar thermal may be sensible if the existing unit is ageing or the household is already planning improvements. It is less attractive where a recently installed combi boiler meets the household's needs well.
How much hot water can solar provide?
Solar energy can reduce the amount of conventional energy used to heat water, but it should not be treated as the only heat source in a British home. Winter daylight is shorter, the sun is lower and household hot-water use often rises. Your boiler, immersion heater or heat pump still needs to provide reliable back-up.
During summer, Solar PV with a diverter may heat much or all of the day's required water on favourable days. Solar thermal can also perform strongly at this time of year. In autumn and winter, both systems contribute less, although they may still provide some useful pre-heating.
Several factors affect the result:
- Roof orientation, angle and shading affect how much energy reaches the panels or collectors.
- A larger household can use more solar-heated water, but it also needs enough cylinder capacity and back-up heat.
- Daytime electricity use matters for Solar PV. Appliances running while the sun is out use generation that would otherwise be available for the immersion.
- The condition and controls of the existing heating system influence efficiency and comfort.
A site survey should look beyond the roof. It should consider the cylinder, boiler or heat pump, electrical consumer unit, available pipe routes and the way the household uses energy. This is where tailored design makes a real difference to the outcome.
Solar PV, solar thermal and heat pumps
For homeowners considering a lower-carbon heating upgrade, Solar PV can work particularly well alongside an air source heat pump. The panels can help supply electricity for the heat pump during daylight hours, while the heat pump heats the cylinder efficiently at a controlled temperature.
In many cases, it is better to let a heat pump heat the cylinder than rely solely on an immersion heater. An immersion converts one unit of electricity into roughly one unit of heat. A well-designed heat pump can often deliver several units of heat for each unit of electricity used, depending on operating conditions.
That does not mean an immersion diverter has no place. It can provide a useful top-up, use occasional surplus generation and offer back-up. The controls must be designed so that the different heat sources work together rather than compete. For example, heating the whole cylinder with an immersion shortly before a heat pump's scheduled hot-water cycle may not be the most efficient approach.
A property moving away from an older boiler can benefit from considering Solar PV, cylinder size, insulation, radiator upgrades and heat-pump design as one project. For homes retaining a gas boiler for now, a diverter can be a sensible stepping stone that makes better use of solar electricity without compromising dependable hot water.
Practical points before installation
Before deciding on either approach, check the condition of your cylinder and its controls. A poorly insulated cylinder loses heat quickly, reducing the value of any solar energy stored within it. Modern insulation, correctly set thermostats and well-planned heating schedules are modest details that can protect savings.
Roof suitability is equally important. Shading from trees, chimneys or neighbouring buildings can have a marked effect, particularly on Solar PV strings. A professional assessment can identify whether panel layout, optimisers or a different technology would be appropriate.
It is also worth being realistic about maintenance. Solar PV has few moving parts, although electrical checks and occasional visual inspections remain sensible. Solar thermal systems have more components, including fluid, pumps and pressure controls, so they need periodic servicing to keep them operating safely and efficiently.
For homeowners in Burgess Hill and the surrounding Sussex area, combining solar work with an upgrade to the hot-water system can avoid duplicated disruption later. Turner Plumbing & Heating can assess the plumbing, heating and renewable-energy elements together, helping ensure that the finished system supports both everyday comfort and long-term efficiency.
The best solar hot-water solution is not necessarily the one with the most equipment on the roof. It is the one that fits your household's routines, stores energy sensibly and still gives you reliable hot water when the weather has other ideas.