A combined collector is a solar system, module, or component that generates useful heat energy in addition to electricity. Photovoltaic thermal collectors, also referred to as PV/T collectors, hybrid solar collectors, photovoltaic thermal solar collectors, or solar cogeneration systems, are power generation technologies that transform solar radiation into useful thermal and electrical energy.
They are frequently abbreviated as PVT collectors. PVT collectors combine photovoltaic solar cells, which convert sunlight into electricity and are frequently organized in solar panels, with a solar thermal collector, which transports the PV module’s otherwise wasted waste heat to a heat transfer fluid. These technologies can achieve better overall efficiency than solar photovoltaic (PV) or solar thermal (T) alone because they combine electricity and heat generation inside the same component.
Since the 1970s, extensive research has gone into developing a wide range of PVT technologies. The various PVT collector methods handle a variety of applications ranging from low temperature heat below ambient up to high temperature heat above 100 °C, and they differ significantly in their collector design and heat transfer fluid.
What is the solar spectrum and how is it used in PVT collectors?
PVT collectors, which integrate the production of solar heat and electricity into one unit, are more efficient overall and make better use of the solar spectrum than traditional PV modules. While the majority of the solar spectrum (65 to 70 percent) is converted into heat, raising the temperature of PV modules, photovoltaic cells normally achieve an electrical efficiency between 15 and 20 percent.
Contrarily, PVT collectors are designed to cool PV cells and increase their efficiency by transferring heat from the cells to a fluid. In this method, the extra heat is turned into something helpful, such as heating water or serving as a source of low temperature for heat pumps. PVT combined collector utilise the solar spectrum more effectively as a result.
The majority of solar cells (such as silicon-based ones) have an efficiency decline when cell temperatures rise. Efficiency decreases by 0.2 to 0.5 percentage points for every Kelvin that cell temperature rises. As a result, cooling the PV cells can reduce their temperature and boost their effectiveness. Another advantage of lower operation temperatures is longer PV cell lifetimes.
This is a good way to increase the overall system efficiency and dependability, but the thermal component performs worse than it could with a pure solar thermal collector.
In other words, the maximum operating temperatures for the majority of PVT systems are restricted to values that are lower than the maximum cell temperature (usually below 100 °C). Nevertheless, depending on cell efficiency and system design, two or more units of heat energy are still produced for every unit of electrical energy.