Like all other semiconductor devices, solar cells are sensitive to temperature. Increases in temperature reduce the band gap of a semiconductor, thereby effecting most of the semiconductor material parameters. The decrease in the band gap of a semiconductor with increasing temperature can be viewed as increasing the energy of the electrons in the material. Lower energy is therefore needed to break the bond. In the bond model of a semiconductor band gap, reduction in the bond energy also reduces the band gap. Therefore increasing the temperature reduces the band gap.
In a solar cell, the parameter most affected by an increase in temperature is the open-circuit voltage.
Maximising the amount of electricity you produce (i.e. number of kWhs) is key to ensuring healthy returns on investment and shortening the payback periods. So you can start not only making money by producing electricity via the subsidies available, but also use the electricity you produce to lower you bills.
One of the key factors impacting the amount of electricity your solar panels produce is the temperature at which they operate. It is easy to presume that more sun and therefore more heat result in more electricity but this is wrong.
Different solar panels react differently to the operating ambient temperature, but in all cases the efficiency of a solar panel decreases as it increases in temperature.
The impact of temperature on solar panel efficiency is known as the temperature coefficient.
If you look at the data sheet provided by your solar panel manufacturer they will refer to a term normally described as the temperature coefficient pMax. This value, which is normally given in the form of negative percentage, reveals the impact of temperature on the panel.
Solar panels are power tested at 250C, so the temperature coefficient percentage illustrates the change in efficiency as it goes up or down by a degree. For example if the temperature coefficient of a particular type of panel is -0.5%, then for every 10C rise, the panels maximum power will reduce by 0.5%.
So on a hot day, when panel temperatures may reach 450C, a panel with a temperature coefficient of -0.5% would result in a maximum power output reduction of 10%. Conversely, if it was a sunny winter’s morning, the panels will actually be more efficient.
Each type of solar cell has a different temperature coefficient is detailed below:
o Both monocrystalline and polycrystalline cells have a temperature coefficient pMax of between -0.45% to -0.50%
o Amorphous based thin film panels have a rating of between -0.20% to -0.25%.
o The Hybrid solar cells currently on the market sit in the middle with a temperature coefficient pMax of between -0.32%
Firstly in the process of making the panels, companies use a thermally conductive substrate is help vent excess heat from the glass layer.
Your solar panel installer will also try to ensure there is a free flow of air above and below the solar panels when they are mounted, by elevating the panels a few inches off the roof. In addition it is possible to add ventilation systems or fans to your solar PV system to help assist the movement of air around the panels.
However, it is important to ensure you try to install your panels where there is decent natural ventilation, just another factor to consider when choosing the position for your solar PV installation.
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