Can PVT Generate Heat and Electricity at the Same Time?

Yes. A photovoltaic-thermal collector combines electricity generation with a thermal absorber that transfers heat to a fluid or air circuit. The two outputs need separate measurement and valuation.

A building might use the electricity directly or export it. The heat might preheat domestic water, support a pool, supply an appropriate heating load or serve as a heat pump source. These uses require different operating temperatures and different system configurations.

IEA SHC Task 60 provides a useful technical foundation, including work on PVT performance indicators and example systems. Its publications distinguish collector performance from the behavior of the complete system, an essential distinction when comparing commercial proposals.

Start With the Thermal Role

Ask the designer to state what the PVT thermal circuit is supposed to do before discussing combined efficiency.

PVT designs vary. An uncovered collector intended to support a heat pump cannot be assumed to perform like a glazed collector supplying warmer water directly. Compare the actual model at the relevant temperatures, wind and irradiance conditions.

The building's required delivery temperature also matters. A preheating contribution does not establish that the system can independently meet the final hot water requirement. Backup heating and the applicable hygiene strategy remain part of the complete design.

Count Heat Where It Becomes Useful

A proposal may report collector output, heat entering storage, heat leaving storage or heat supplied to a load. Each is a valid quantity, but they are not interchangeable.

For economic evaluation, count the heat that actually reduces the alternative system's purchased energy. Account for transfer losses, storage losses, periods without demand and heat that is rejected.

A simple annual multiplication of rated thermal power by sunshine hours is inadequate. Rated power describes a test condition; it does not describe changing fluid temperatures, controls, weather and building demand.

For example, the SOLETKS PVT-E product page lists 580 W electrical maximum power at STC and 1,180 W peak thermal power. These are power ratings, not annual kWh forecasts. The page does not establish that the two peaks occur simultaneously under the same operating condition. Ask for the thermal test conditions and model-specific performance data before estimating annual output.

For a direct-use system, a useful comparison schedule is:

Collector thermal output
- losses before the agreed delivery boundary
- heat unavailable to the load because of timing or temperature
- rejected or otherwise unused heat
= useful heat replacing the alternative heat supply

Avoid subtracting losses twice if the simulation already reports useful load-side heat. State the output boundary beside every reported energy figure.

Electricity and Heat Have Different Financial Values

Electricity used on site generally avoids the applicable import charge. Exported electricity earns the actual export payment. Neither should automatically be assigned the same value as thermal energy.

For a simple electricity calculation:

Electricity value = self-consumed kWh x avoided import price
                  + exported kWh x export price

Assume, purely for illustration, annual generation of 20,000 kWh, 70% self-consumption, an avoided import price of USD 0.20/kWh and an export payment of USD 0.05/kWh:

Self-consumed electricity = 14,000 kWh
Exported electricity = 6,000 kWh
Annual electricity value = 14,000 x 0.20 + 6,000 x 0.05
                         = USD 3,100

This calculation excludes demand charges, time-varying prices and other billing effects. A project model should use the actual tariff and generation-load overlap.

For direct-use heat replacing a boiler, estimate avoided fuel using the relevant efficiency and fuel price. For heat replacing heat-pump output, use the electricity that would have been required at that operating condition. One kWh of heat should not automatically receive the value of one kWh of electricity.

Compare the Additional Cost With the Additional Benefit

A PVT proposal may have a positive total energy value while still offering a weak return compared with conventional PV. An incremental comparison reveals the difference.

Assume two invented project budgets for the same site:

Equal electrical output is deliberately assumed to isolate the value of the thermal circuit. Actual roof layouts, module ratings and operating temperatures can produce different electrical yields; those differences must be included in a real comparison.

The PVT premium here is USD 20,000. Assume every useful thermal kWh displaces USD 0.08 of heating cost at the same delivery boundary. That is an assumed cost per kWh of useful heat, not a fuel input tariff.

The systems in these scenarios are not sized designs. The table shows what must be tested: whether the proposed collector field and building can actually achieve the useful heat assumed.

The 50-year result is not a service-life forecast. It indicates that this illustrative investment is unlikely to be justified by the stated annual savings over a practical study period. Simple payback also ignores financing, replacements, degradation and discounting; use a lifecycle comparison for the final decision.

Evaluate Heat Pump Integration at the System Boundary

When PVT supplies a heat pump's evaporator, source heat is an input to the heat pump. It must not be counted once as valuable delivered heat and again inside the heat pump's final output.

Compare the electricity needed to provide the same delivered heat in the reference and PVT-assisted systems, including the chosen auxiliary-energy boundary.

For an invented example, let annual delivered heat be 50,000 kWh. Assume a reference seasonal performance factor of 3.0 and a proposed factor of 4.0, both measured on the same boundary:

Reference electricity = 50,000 / 3.0 = 16,667 kWh/year
Proposed electricity = 50,000 / 4.0 = 12,500 kWh/year
Electricity reduction = approximately 4,167 kWh/year
Value at USD 0.20/kWh = approximately USD 833/year

The increase from 3.0 to 4.0 is an assumption, not a claimed PVT benefit. It must be supported by a suitable model or monitored evidence. Add any auxiliary consumption excluded from those factors and compare the additional installation and maintenance costs.

If PV electricity powers the heat pump, reconcile self-consumption and grid purchases in one energy balance. The same generated kWh cannot simultaneously be credited as an export and as avoided heat-pump electricity.

When Does PVT Deserve a Detailed Feasibility Study?

PVT deserves closer analysis when roof area is constrained, the site has a recurring thermal demand and the proposed collector can supply a useful temperature or heat-pump source condition. A building with both daytime electricity demand and a consistent hot water or pool load may offer a useful starting point.

Ask for a more cautious assessment when the thermal load is mostly seasonal, the plant room is distant, storage is difficult to accommodate or the reference heating system already supplies low-cost heat efficiently. These conditions do not automatically rule out PVT, but they can reduce the value of the added thermal circuit.

The decisive evidence is a comparison using the same weather, floor area or roof constraint, heat service and tariff assumptions. Include conventional PV plus a heat pump and separate PV plus solar thermal where those alternatives are feasible.

Include Service Requirements in the Comparison

PVT adds hydraulic components to the electrical equipment. Request a clear maintenance scope for fluid, pumps, sensors, joints, heat exchangers and controls, as applicable to the selected design. Check access to roof connections and whether servicing one part requires disturbing another.

Compare warranty coverage for the electrical and thermal portions separately. Ask which operating temperatures, fluids and maintenance records the warranties require. A long module warranty does not establish that every system component is covered for the same period.

For the thermal maintenance scope, use the SOLETKS solar thermal maintenance guide together with the exact equipment documentation.

What to Request Before Approving a PVT Proposal

Ask the supplier for a concise comparison package:

1. Exact module model, thermal role and proposed system schematic.

2. Electrical and thermal test data with operating conditions identified.

3. Annual electricity, useful heat and purchased-energy figures on explicit boundaries.

4. Monthly or hourly results showing demand matching and surplus heat treatment.

5. Installed scope, operating costs and replacement assumptions.

6. An alternative-system comparison with the same service requirements.

7. Metering positions and an agreed method for checking performance after commissioning.

Keep historical studies in context. The UK government's PVT evidence-gathering report was published in 2016; it is background research, not evidence of current product prices, current incentives or a specific SOLETKS model's performance.

Frequently Asked Questions