Photovoltaic cells are a non-mechanical device that uses the photovoltaic effect of semiconductor materials to directly convert sunlight into electricity. In people's view, photovoltaic cells should be not afraid of the sun "master", under the blazing sun, should be a time for photovoltaic cells to make a difference. Is this really the case?
Photovoltaic effect and photovoltaic effect
The use of solar energy has a long history of human beings. The conversion and utilization of solar energy can be divided into three main ways: photoelectric conversion, photothermal conversion, and photochemical conversion. Photovoltaic power generation is the use of solar photovoltaic conversion.
In 1839, French scientist Edmond Becquerel discovered that light can produce potential differences in different parts of semiconductor materials. This phenomenon came to be known as the photovoltaic effect, or PV effect for short. in 1905, Albert Einstein successfully explained the photoelectric effect using the quantum hypothesis of light, and thus won the Nobel Prize in Physics in 1921.
The photovoltaic effect is a phenomenon in which electrons are ejected from a conducting material when light is shone on it. Unlike the photoelectric effect, which occurs on a single conducting plate, the photovoltaic effect occurs on the boundary of two semiconductor plates and creates an electric field by accumulating along the boundary. When the two plates are connected with wires an electric current flows through them.
The original solar cell was designed and manufactured according to the photovoltaic effect, and when the surface of the cell is illuminated by light, an electric current will flow in the outer circuit.
Photovoltaic power generation, heat generation is inevitable
How do photovoltaic cells convert sunlight into electricity? Sunlight is a kind of electromagnetic radiation with a wide range of wavelengths. When shining on a PV cell, the radiation may be reflected, absorbed or directly traversed. Only the portion of the radiation that is absorbed is converted into electricity.
For a silicon semiconductor, it takes about 1.11 electron volts to "bump" an electron off its atoms at room temperature. This means that only absorbed photons with an energy higher than that can excite electrons and produce an electric current. If a photon has an energy of 1.7 eV and it takes 1.11 eV to "bump" an electron off a silicon atom, then the remaining energy (0.59 eV) is lost in the form of heat. Of course, there are other heat-producing factors that affect the efficiency of power generation. The result is that these factors act in concert to heat up the solar cell module, making it hotter than the ambient temperature.
The sun is hot, a "double-edged sword"
One would think that in the heat of summer, silicon-based photovoltaic cells would be unusually "excited" to produce more electricity, but who knows that silicon-based photovoltaic cells also like the cooler environment. Of course photons are still very much needed, after all, is the "raw material" for power generation!
So, how does the temperature of the solar panel affect the electrical output performance? In fact, the solar panel temperature is high, the same light conditions will produce less energy.
As the temperature rises, although the short-circuit current (PV cell positive and negative short-circuit current) basically unchanged or slightly increased, but the open-circuit voltage (PV cell positive and negative open-circuit voltage) will be reduced by a lot, almost linear relationship. The consequence of this is that the PV cell conversion efficiency is reduced and the output power is decreased.
The standard test temperature of PV cell is 25℃, if the temperature of solar panel reaches 60℃ or more, the reduction of output power cannot be ignored. Generally speaking, for every 1°C increase in silicon-based PV modules, the short-circuit current will increase by 0.04% and the open-circuit voltage will decrease by 0.4%.
However, even though the increase in temperature will reduce the conversion efficiency under the same light conditions, more power will be harvested in the hot summer months thanks to the abundant sunlight than in other seasons.
How to cool down the photovoltaic cells
Photovoltaic cells, like other electronic devices, work more efficiently at lower temperatures. Since photovoltaic power generation uses light rather than heat, photovoltaic cells are more suitable for a sunny and cool working environment.
How can we cool down the PV cells in the summer heat? How about adding a sunshade? No! The reason is simple, without the light, photovoltaic power generation will become empty. How about some "sunscreen"? Also not! The use of physical sun protection is tantamount to reducing the absorption of light; and the use of chemical sun protection will not help to reduce the temperature.
For rooftop solar panels, natural ventilation cooling is an economical and practical method. If installed with a gap between the roof surface and the panel, thus allowing airflow to cool the panel. However, it is important to avoid debris such as leaves from entering the gap to prevent excessive temperatures due to poor airflow.
The effect of different cooling methods on the efficiency of solar power generation has been studied. In addition to natural circulation cooling, forced circulation cooling and solar PV photothermal cooling have also been included in the experimental studies, which undoubtedly have important guiding significance for reducing the temperature of PV cells and improving the power generation efficiency.
Photovoltaic cells, as messengers of clean energy, have come into our lives and brought us a low-carbon breeze of environmental protection.
