Summers around the world are getting hotter. Since heat waves are becoming more frequent, the question arises as to whether photovoltaic systems can cope with these temperatures.
High temperatures affect different components of the photovoltaic system: inverters can fail, the efficiency of the photovoltaic modules decreases, existing cell damage increases, and the need for cleaning increases.
In this article, you can find out how investors, planners, and operators can prepare for periods of heat. You will also receive information that you can use to sort out the relevance of heat damage with regard to the operation of photovoltaic systems.
In this article, you will find empirical values from a technical consultant from SolarShopUs.com, as well as an evaluation of the data pool of the Meteocontrol monitoring system, to which more than 55,000 photovoltaic systems are connected worldwide.
How often do inverters fail due to heat?
If an inverter gets too hot, it usually switches itself off or reduces its output to such an extent that the increased ambient temperature does not damage it, which is referred to as temperature derating.
The example from the data pool begins one step earlier. It considers a specific warning message of certain string inverters. These report the overheating of an inverter even before a power reduction. 23,000 inverters in the United States that can transmit this error and that are installed in around 1,300 photovoltaic systems were evaluated.
Apparently, as the average temperature rises, the overheating warnings increase. It has not been tested whether there is a statistically significant connection. In June 2022, the daily number of overheating warnings was 0.038 percent of the connected inverters. The proportion of actual failures is smaller. Reasons for overheating can
- a defect in the ventilation
- a poorly ventilated site
- and a high ambient temperature.
The number of possible causes further reduces the weather-related proportion.
The evaluation of the data pool confirms the empirical value that inverters can usually withstand heat waves – provided the installation site is suitable. Another proof of the heat resistance of inverters is that photovoltaic systems are operated successfully in southern countries and even in desert regions. Nevertheless, overheating reports should be taken seriously so that no yields are lost and the lifespan of the devices is not shortened.
Does the module efficiency drop significantly in the heat?
A temperature increase of 37.4°F (three degrees Celsius) reduces the efficiency of solar modules by an average of one percent. As a result, the efficiency of the modules is several percent lower in summer than in winter, but the solar radiation in summer is many times higher. Accordingly, the losses from lower efficiencies are more than offset by the additional yields. On the yield side, sunny periods of heat are positive.
What can be done in the planning?
When planning photovoltaic projects, a suitable installation site for the inverter must be found. With smaller photovoltaic systems in the private sector, careless installation locations are more common, for example, an unshaded installation on a south wall or on a battery storage unit inevitably leads to overheating. However, planning errors also occur in the area of commercial photovoltaic systems if inverters are installed on roof surfaces without shade or at the edge of a row of modules, and are therefore at least temporarily exposed to direct sunlight.
For a cool installation of the inverter, shading must be ensured and the manufacturer’s requirements and the corresponding standards must be implemented. This also includes distances from walls and between several devices. In the case of a photovoltaic investment, it should be checked whether the inverters have been installed in accordance with good professional practice when the planning documents are viewed and at the latest during the acceptance process by a photovoltaic expert.
Sufficient rear ventilation of the solar modules can and must also be ensured in the planning. The rear ventilation of the modules is very good in open spaces and with elevated roof systems. In the case of roof areas, on the other hand, rear ventilation is usually more difficult.
Dust-repellent coatings can be taken into account when selecting the modules, provided that the corresponding modules are available. Theoretically, it would also be possible to consider the temperature coefficient when selecting the module. This is specified in the respective module data sheets. In practice, the deviations in the temperature coefficients are small, since almost exclusively crystalline photovoltaic modules are installed. In the past, when the proliferation of other cell types such as cadmium telluride was significant, there was greater design freedom in the choice of modules. With the current material supply bottlenecks, a fine adjustment of module parameters is hardly feasible anyway, since what is available has to be taken practically.
What can be done during operation?
If an inverter fails due to heat, the ventilation on site must first be checked. If, for example, an inspection reveals that an inverter is unshaded, shading must be applied afterward.
Performance losses due to temperature derating are more difficult to detect when the inverter reduces its performance due to heat. Reduced performance in monitoring can become unspecifically noticeable if the target yield is not reached. Temperature derating can be clearly diagnosed by analyzing performance characteristics.
Existing cell damage in solar modules worsens faster at high temperatures. Accordingly, the relevance of preventive measures increases with the temperatures, which can, for example, prevent shading from surface vegetation or module contamination at an early stage. Spot shadowing or hotspots or microcracks can be determined by thermographic images.
Heat periods are accompanied by drought. This creates more dust at some locations, which can settle on the modules. In addition, when there is no rain, the self-cleaning of the modules decreases. The need for cleaning could develop as it is today in very dry regions or deserts. Around two to three percent of the energy is lost there due to dirt, which is why the modules are cleaned once or twice a year. In many countries, natural rain is still sufficient in most cases for module cleaning, since only about one percent of the energy is lost.
However, if you always want to operate your solar system at its optimum, you should wash the solar panels at least once a month. This is best done with clear water and a little soapy water.
With careful system planning, proper installation, and professional maintenance, reliable operation of photovoltaic systems is possible even during increasing heat waves. The inspection should include heat-related error sources in its monitoring. If heat-related failures nevertheless occur, the cause must be determined and remedied quickly in order to prevent reduced yields and technical damage.