The 80% figure is real but it is a peak combined number, not an annual one: roughly 15–22% electrical plus 55–60% thermal, measured at low fluid temperature and full sun. Annual combined utilisation of a domestic PVT array is closer to 45–60%. Referenced to solar radiation alone, an uncovered panel can even exceed 100%, because ambient heat is added.
Where does the 80% number come from?
It comes from adding two efficiencies that are measured differently. A PVT panel's electrical efficiency under standard test conditions is 15–22% for current crystalline modules. Its zero-loss thermal efficiency — the collector efficiency curve intercept measured under ISO 9806 with fluid at ambient temperature — is typically 0.55–0.60 for an uncovered panel. Add them and you land in the high seventies or low eighties.
The arithmetic is legitimate. The claim becomes misleading only when the conditions are dropped. That intercept applies at zero temperature difference between fluid and ambient, at full irradiance, with no wind penalty. Push the fluid 20 K above ambient and an uncovered panel with a heat loss coefficient near 12 W/m²K has already given most of that thermal efficiency back.
What efficiency does a PVT panel reach over a year?
| Metric | Typical value | Conditions |
|---|---|---|
| Peak electrical efficiency | 15 – 22% | STC, 25 °C cell temperature |
| Zero-loss thermal efficiency (uncovered) | 0.55 – 0.60 | Fluid at ambient, full sun |
| Peak combined efficiency | 70 – 82% | Both of the above, simultaneously |
| Annual combined utilisation | 45 – 60% | Real store temperatures and load profile |
| Thermal output vs solar input, source duty | Can exceed 100% | Ambient heat added to solar (IEA SHC Task 60) |
The last row is the one people find hardest to believe and it is the most defensible. When an uncovered panel runs as a heat pump source with the fluid below ambient, it collects air and condensation heat as well as sunlight. Referenced to the solar radiation striking the panel, thermal yield can exceed 100% — energy is not being created, it is being drawn from a second reservoir that the reference frame ignores.
Why can a hybrid panel beat separate PV and thermal on total yield?
Because the same square metre does two jobs and the two jobs help each other. Silicon loses 0.25–0.34% of rated power for every degree the cell sits above 25 °C — about −0.34%/K for mono PERC, −0.29%/K for TOPCon and −0.25%/K for HJT. A panel cooled to 30 °C instead of running at 60 °C therefore returns several per cent more electricity, which is the mechanism behind do solar panels work better when cooled?
The cost is temperature. Keeping cells cool means keeping the fluid cool, which caps the useful thermal grade. That trade-off is the entire design tension in PVT and it is why the honest comparison is total useful energy per square metre, not headline efficiency. Where roof area is the binding constraint, PVT usually wins; where it is not, PVT versus separate PV and solar thermal is a genuine competition.
How do I check an efficiency claim on a datasheet?
Ask for three numbers and ignore the headline:
- η0 (zero-loss efficiency) and whether it is quoted on gross or aperture area. Gross-area figures look worse and are the ones a Solar Keymark certificate reports, so quotes using different area bases are not comparable.
- a1 and a2, the heat loss coefficients, plus the wind coefficient for uncovered panels. A high a1 means the thermal efficiency evaporates as soon as the fluid warms.
- The temperature coefficient of power, in %/K, for the electrical side.
With those you can compute output at your actual working temperature instead of at the test point. A manufacturer that publishes full curves, stagnation temperatures and gross-area figures is telling you something a single percentage cannot. Solimpeks publishes Solar Keymark-tested data for its PV-T Hybrid Panels on that basis.
So is 80% a fair thing to say?
It is fair with the conditions attached and unfair without them. A precise version reads: an uncovered PVT panel converts up to about 80% of incident solar energy into useful electricity and low-grade heat at its test point, and 45–60% across a real year, while an equivalent PV module converts 15–22% and discards the rest as waste heat.
That second clause is the one that matters commercially. The comparison is not PVT against a theoretical ideal; it is PVT against a PV module that throws away roughly four fifths of the sunlight it absorbs. Judged that way, even a conservative annual figure of 50% combined utilisation is a large gain per square metre — provided there is a real, year-round load for the low-grade heat.
Frequently asked questions
Is a PVT panel more efficient than a PV panel?
In total energy per square metre, yes — typically three to five times more, because the thermal output dwarfs the electrical one. In electrical efficiency alone the two are close, with PVT slightly ahead in hot weather thanks to cell cooling.
How can thermal efficiency exceed 100%?
Only when efficiency is referenced to solar radiation alone. An uncovered panel running below ambient temperature also absorbs heat from the air, rain and surroundings, so the useful thermal output can exceed the sunlight striking the panel. No energy balance is violated.
Does a glazed PVT panel have higher efficiency?
It has higher thermal efficiency at raised temperatures and reaches 50–70 °C outlet, but it runs the cells hotter and typically gives up 5–8% of annual electrical yield. Choose by the temperature the load needs, not by the efficiency headline.
Which efficiency figure should I use for a payback calculation?
Neither peak figure. Use annual yield in kWh per m² of electricity and kWh per m² of heat at your real store temperature, taken from the certified performance curve. Peak efficiencies overstate a domestic system's output by a wide margin.