The heat wave we have been experiencing in recent weeks has not only affected people’s lives. Solar panels are also suffering from the high temperatures, but how does this extreme heat affect the performance of photovoltaic production?
Although one might think that photovoltaic production is directly proportional to temperature (more heat = more solar radiation, right?), too high temperatures can negatively affect the photovoltaic cells, decreasing the performance of the panel.
Higher production in summer or winter?
A photovoltaic module is defined (among other parameters) by what is called the peak power. The power that the manufacturer tells us that the panel has is the power that occurs when the sun is producing an irradiation of 1000 W in 1 m2 at a temperature of 25ºC. It is under these conditions (known as standard measurement conditions, or STC) that the photovoltaic cells are operating at 100% efficiency. This performance is usually achieved on sunny winter days when temperatures are mild. As the temperature changes, silicon, the semiconductor material from which photovoltaic panels are normally made, changes its properties. Under conditions of high ambient temperature and intense solar radiation, the silicon heats up, causing a voltage drop in the PV cells and causing a decrease in the power output of the panel. This results in lower energy production.
Although we have said that the performance is better in cold seasons, we can also state that, under normal conditions, this negative effect of heat on the photovoltaic performance is compensated by the increase in solar hours that occurs in the summer season. Therefore, even if the module has a lower instantaneous efficiency, the output will be higher throughout the day than on winter days when there are fewer hours of sunshine.
What temperature factors affect performance?
Factors affecting the efficiency of the panel are:
ambient temperature, which is compensated by the number of hours of sunshine. In other words, in winter the cold temperatures favour the correct functioning of the panel components, but the photovoltaic production is lower than in summer due to the lower number of solar hours.
In addition, not only the ambient air temperature, but the heat build-up on the surfaces in contact with the panel also affects the panel. For example, a panel placed coplanar on a roof is likely to be warmer than one raised on a structure that allows air to pass through, or than a floating panel (more on this later in the article).
Temperature coefficient: PV panel manufacturers provide a temperature coefficient figure for their panels, which ranges from -0.2%/°C to -0.5%/°C. This is the percentage rate at which the efficiency of the panel decreases as the panel temperature rises above 25°C.
Finding the perfect weather conditions is very difficult, but in the case of photovoltaic installations, it is not necessary either, as solar panels have an operating temperature range that goes from -40ºC to 85ºC. As we will see, variations in efficiency caused by temperature can be compensated in various ways.
How to avoid temperature-related efficiency drops
One way to compensate for the decrease in production yield is to slightly oversize the PV field, in order to compensate for the extra energy production.
In addition, there are some cooling systems for panels, although they are not yet used systematically, such as distribution blades, a novel technique that helps to better distribute the radiation captured by the panels, while at the same time distributing the temperature to achieve greater efficiency; or the installation of panels with rainwater collection systems. This water is stored in the side frames of the panel and when temperatures rise, the system distributes the water and cools it.
In any case, in order to know the real operating conditions of the panel, it is necessary to consult the technical data sheet provided by the manufacturer. It goes without saying that in order to ensure correct operation during the lifetime of the panel’s guarantee, we must turn to authorised manufacturers with proven experience.
Floating photovoltaics for refrigerated panels
Floating PV systems are those in which the modules are supported on structures that float on the surface of a body of water, typically an irrigation pond, reservoir, lake or swamp.
These systems have a slightly higher efficiency (between 10-15%) compared to ground-based solar systems due to their cooling effect on the underside of the panel, as the water heats up less than the ground or building roofing materials.
It should be noted that in order to be able to use this type of system, it is necessary to have a body of water in which to install it.
You can read more about floating photovoltaics in the following article: “Floating photovoltaics: the alternative to using land and roofs for solar power generation“.