Solar Panels > Solar Panels eBook > Chapter 4: Photovoltaic (PV) versus Thermal Solar Panels

Chapter 4: Photovoltaic (PV) versus Thermal Solar Panels

Photovoltaic versus thermal solar panels are not to be confused. When envisioning solar power, we generally think of photovoltaic cells. These cells capture solar energy and convert it directly into electricity, which can be used immediately or stored by directing it into a battery. The energy produced by photovoltaic cells converts light photons into mobile electrons, which carry electrical current, but a significant amount of heat should not be produced directly. PV energy conversion systems capture energy during daylight hours only. If it is directed to a battery, this electricity can be drawn upon at night, but the process is somewhat less efficient than that of thermal systems.

In contrast to PV systems, solar thermal systems convert the energy captured as light directly into heat. A main difference between these systems and PV systems is that thermal systems divert captured energy into a fluid reservoir, thus heating the fluid. Different working fluids include water, oil, nitrogen, helium, and salt solutions. Even air can be used as a fluid medium for thermal energy storage and use. The generated heat can be used to power a heat engine, which then can be used to power an electrical generator. Different engine types can include gas turbines, steam engines, or Stirling engines. Despite the fact that thermal systems are a more indirect method for generating electricity, they can be quite efficient, with efficiencies between 30 and 40 percent and frequently generating 10s to 100s of megawatts of power.

In addition to its use in generating electricity, heat harnessed by thermal solar panels can be utilized directly as such. One of the most common applications of this in the home is solar water heating systems. Like PV solar panels, solar water heaters use solar panels to capture light from the sun. However, in contrast to their PV counterparts, thermal solar panels direct the light into a liquid antifreeze solution flowing through collectors into a heat exchanger. The heat generated by the system is then transferred directly into the hot water supply of the home, which is kept in an insulated tank and ready for use.

Thermal solar panels can also be used to generate space heat for the home. Because it can power an electrical generator, thermal power can also operate portable devices and moving vehicles.

In upgrading the home with the use of solar energy, many people choose to first install a thermal water heating system. Relative to photovoltaic powering of the home’s electrical system, thermal water heaters are more energy efficient and are frequently more cost effective, especially in homes where an average to above average quantity of hot water is consumed. In general, thermal panels are larger and more energy efficient than PV solar panels. While PV panels average 15 square feet and operate with approximately 15% energy efficiency, thermal panels are approximately 40 square feet and can be as much as 50% efficient.

In addition, the installation of thermal water heating systems is a way to decrease the electrical power burden required for a home. Because much of a home’s power goes to heating hot water, a home that already contains a thermal solar water heater will have lower electricity requirements if the homeowner subsequently chooses to install PV panels as well.