Why Optimise Hot Water With Solar PV?
Turn surplus solar into low‑cost hot water. A solar PV diverter sends excess generation to your cylinder’s immersion heater instead of exporting it, cutting imports and carbon while preparing your home for a future heat pump. It suits homes with PV and an immersion, households planning a heat pump, and families with higher hot water use.
In summer, diversion can cover most daily hot water; in winter it still makes a useful dent (results vary with array size, orientation, shading and habits). Safety and compliance come first: Clima Tech brings 20+ years’ experience with MCS, REFCOM, NICEIC and Gas Safe accreditation. New to PV? See why solar panels are a smart investment.
How PV Diverters Work: Simple, Safe, And Smart
A PV diverter monitors import/export at your consumer unit. When your panels generate more than your home is using, it diverts that surplus to the immersion heater. It does not interfere with the PV inverter.
Core elements include a CT clamp on the meter tails, a compact controller near the consumer unit, and a dedicated cable to the immersion. Each diverted kWh displaces bought energy (or gas for water heating), which is often worth more than a typical SEG export rate. Diverters can run alongside batteries; priorities are set in the controls to suit your goals. Installation must comply with BS 7671 and Part P. Book our NICEIC team via electrical installation services.
Smart Cylinder Control Strategies That Stretch Every kWh
Use the sun by day, cheap tariffs by night:
- Pre‑heat target: set a daytime PV target around 50–55°C so the diverter lifts the tank when the sun shines.
- Comfort setpoint: schedule a short off‑peak boost to reach your preferred setpoint (often 55–60°C) only if PV falls short.
- Hygiene: run a weekly 60°C+ pasteurisation at the cylinder; time it for sunny periods where possible.
- Automation: use forecasts to decide on pre‑heat and whether to skip the overnight boost. Simple dashboards show cylinder temperature and kWh diverted so you can fine‑tune.
Read our guide to PV, smart tariffs and year‑round control.
This image was generated with AI and may not always represent the product or service exactly.
Cylinder Coils And Tank Design: Getting The Hardware Right
An immersion is a direct electric element inside the cylinder; an indirect coil is a heat exchanger used by a boiler or heat pump. For today’s PV and tomorrow’s heat pump, a twin‑coil, heat‑pump‑ready cylinder (a large, low‑temperature coil plus an immersion) is ideal.
Size the cylinder to occupancy and draw‑off pattern (many homes use 150–250 litres) and choose high‑grade insulation to keep heat loss low (look for very low standing losses). Heat pumps need generous coil surface area for efficiency. Moving from a combi? A conversion with a new cylinder, pipework and safety controls is straightforward. See our guide to hot water cylinders for heat pumps.
Legionella Protection And Scald Safety: Non‑Negotiables
Stored hot water must not sit too cool for too long. Best practice is a periodic pasteurisation to 60°C or above at the cylinder (commonly weekly), achieved via PV on sunny days or a short, low‑rate electric boost.
Thermostatic mixing valves (TMVs) blend water to safe tap temperatures while the cylinder remains hot for hygiene. Clima Tech commissions and documents TMV settings, checks overheat cut‑outs and thermostats, and provides handover records for full peace of mind.
Pairing With Heat Pumps: Avoid Clashes, Boost Efficiency
Let the diverter handle daytime pre‑heat when the sun shines. The heat pump then targets efficient setpoints (often 48–52°C for daily use) and runs a scheduled anti‑legionella lift. Keep priorities and call times separate to prevent short cycling and to preserve COP.
Seasonal tweaks help: expect strong PV contribution in summer, with smart‑tariff top‑ups in winter. Funding is available via the Boiler Upgrade Scheme. Clima Tech manages the whole process, from heat loss survey to MCS commissioning.
What Can You Save? Real‑World Scenarios For UK Homes
A 3–4 bed home with 4–6 kWp PV typically uses 4–8 kWh/day for hot water. In summer, PV can often cover most of this; in winter, it may still deliver a useful share. Actual savings depend on array size, roof orientation, shading and cylinder insulation.
- Illustrative example: 1,200–1,800 kWh/year diverted.
- Value: if your import is ~28p/kWh and SEG is ~15p/kWh, each diverted kWh can be worth ~13p more than export.
- Maximise benefit with fast‑responding diverters, clear priorities with any battery, and a well‑insulated cylinder.
This image was generated with AI and may not always represent the product or service exactly.
Hardware, Wiring And Standards: What Good Looks Like
Expect a tidy, compliant install:
- CT clamp fitted at the correct point on meter tails and oriented properly.
- Compact controller mounted accessibly with labelled circuits and isolators.
- Neat, correctly sized cable run to a suitably rated immersion and thermostat/sensors positioned and set correctly.
- Verification of immersion rating, protective devices and cable sizing; functional and safety testing recorded.
All work is signed off by NICEIC electricians to BS 7671 and Part P, with MCS paperwork provided when part of a broader renewables project.
Local Case Study: Suffolk Family Maximises PV Hot Water
A Suffolk family with a 5 kWp array wanted lower bills and heat‑pump readiness. We installed a twin‑coil unvented cylinder with immersion, a PV diverter, TMVs at key outlets, and a weekly 60°C hygiene cycle.
Year‑one data showed around 1,200 kWh diverted, strong summer coverage, and verified pasteurisations in the app. Depending on tariffs, that’s a material saving versus export, plus lower imports and a smooth path to a future heat pump — all backed by Clima Tech’s accredited install and aftercare.
Our Process: Survey, Design, Install, Aftercare
We start with an in‑home survey to understand your hot water demand, roof and electrics, then size the cylinder and specify controls. You get a clear, itemised quote.
Installation is tidy and efficient, with full commissioning records and handover. We offer optional monitoring, annual checks and responsive support. With 20+ years in HVAC and renewables, Clima Tech delivers safe, dependable systems built to last.
FAQs: Diverters, Cylinders And Heat Pump Readiness
Diverters can work alongside batteries and EV chargers. We set priorities so self‑consumption is maximised without starving the battery or car. A twin‑coil, heat‑pump‑ready cylinder keeps options open.
We’ll help you schedule weekly 60°C pasteurisation and any off‑peak boosts. Typical installs take a day for a diverter and 1–2 days for a cylinder swap, with minimal disruption. Warranties and maintenance are covered in your handover pack.
Related Services And Next Steps
Ready to capture more of your solar? We upgrade cylinders, install PV, and design heat pump systems that work together. Our accredited team handles electrics, controls and commissioning in one joined‑up service.
Explore our solar panels service, then book your free survey via our contact page. Clima Tech is MCS, REFCOM, NICEIC and Gas Safe accredited, with a trusted local track record.
FAQs
Will A PV Diverter Work If I Already Have A Battery?
Yes. We set priorities so the battery charges before or after the cylinder, depending on your goals, tariffs and the season. Priorities can be changed at any time.
What Size Cylinder Do I Need?
Many homes need 150–250 litres, sized to occupancy and hot water patterns. As a rule of thumb, allow 35–50 litres per person/day. For future heat pumps, choose a twin‑coil model with a large, low‑temperature coil.
How Long Does Installation Take?
A diverter usually takes less than a day. A cylinder replacement typically takes 1–2 days, including commissioning, safety checks and handover.
Do I Still Need A Weekly 60°C Cycle?
Yes. A periodic pasteurisation to at least 60°C at the cylinder helps protect against bacteria. We automate this, using PV when possible or a short off‑peak boost.
Will A Diverter Affect My SEG Payments?
You’ll export less because you’re using more on site. SEG pays only on what you export, but the extra self‑consumption usually gives better value per kWh than exporting.