Can one solar collector make both electricity and high-temperature heat?

The short answer: yes, with a hybrid PV-thermal collector

A hybrid PV-thermal solar collector, usually shortened to PVT, makes electricity and heat from the same patch of sunlight. Ordinary solar panels turn only part of the light into electricity and waste most of the rest as heat. A PVT collector puts that waste heat to work, so it gets more total useful energy out of the same area than a panel or a solar water heater alone.

The catch is temperature. Solar cells lose output as they get hotter, while heat is most useful when it is hot. Getting both at once is the hard part, and a technique called spectral splitting is one of the most promising ways around it.

Why solar cells and hot water pull in opposite directions

A solar cell can only use photons with more energy than its semiconductor bandgap. Lower-energy light passes through unused, and the extra energy of high-energy photons is shed as heat inside the cell. That heat raises the cell temperature and cuts its efficiency further.

The penalty is well measured. Sandia National Laboratories gives crystalline silicon a power temperature coefficient of about -0.3 percent per degree C for newer technologies to -0.5 percent per degree C for older ones. The International Energy Agency's PVT research group puts it as a loss of 0.2 to 0.5 percent of efficiency for each kelvin of added cell temperature.

In a conventional PVT collector the heat absorber sits right behind the cells, so the fluid and the cells share one temperature. To protect electricity output, that absorber is typically kept below about 60 degrees C. The IEA group sorts PVT uses into low temperature up to 50 degrees C (heat pumps, pools), medium up to 80 degrees C, and high above 80 degrees C, and notes that domestic hot water needs 60 degrees C to control Legionella. Typical PVT systems deliver two or more units of heat for every unit of electricity.

How spectral splitting separates electricity from heat

Spectral splitting sends each part of the sunlight to the device that uses it best: the wavelengths a solar cell converts efficiently go to the cell, and the rest go to a thermal absorber that can run much hotter. Because the cell and the absorber no longer have to sit at the same temperature, the two outputs are decoupled.

This idea has been studied since the 1980s. A 2017 review in Applied Energy groups the splitting methods into interference filters, liquid absorptive filters, holographic, luminescent and diffractive optics, and designs where the solar cell itself acts as the filter, with proposed uses ranging from domestic hot water to hydrogen production and power generation.

A new design: a see-through perovskite cell above a Fresnel lens

A 2026 open-access study in Advanced Science uses a semi-transparent perovskite solar module as the filter. Its bandgap of about 1.6 eV means it absorbs light shorter than roughly 775 nm and lets much of the near-infrared through. The module sits above a Fresnel lens, so it is never under concentrated light. The lens, with a geometric concentration ratio of about 99, focuses the transmitted infrared 1.4 m below onto a coated aluminum absorber inside a vacuum chamber.

In the modeled system, which was checked against a solar-simulator test of the absorber, the heat output reached 88.0 to 154.9 degrees C while the perovskite module stayed at 38.5 degrees C and kept an electrical efficiency of 13.8 percent. Using the best semi-transparent perovskite cells reported in the literature, the authors project electrical efficiency rising to 21.3 percent, with thermal efficiency at 100 degrees C dropping only slightly, from 20.7 to 19.2 percent.

A side benefit: the cell sits on top, so it can still use diffuse skylight for electricity, which a concentrating design otherwise throws away.

What is still hard

Only direct sunlight can be concentrated, so a real collector needs a two-axis sun tracker, which the study did not build. The module tested reflected 18 percent of incoming light, mostly near-infrared lost at its transparent electrodes; the authors estimate that eliminating that reflection would raise the transmitted share from 28.6 percent toward about 40 percent. Perovskite cells also still need better long-term stability and large-scale manufacturing before designs like this leave the lab.