Passive cooling relies on natural convection and only internal fans, if any, are used. Large heat sinks also makes the device heavy, which means handling and transport are more difficult.
In comparison, active cooling technology relies on one or more fans, which not only avoid hot spots, but also regulate the air circulation inside the inverter. This keeps the temperature of the power electronics low.
Due to the often limited amperage of MPP trackers for passively cooled devices, only one module string can usually be connected per tracker. This is because higher amperages also cause higher component temperatures.
Actively cooled devices, on the other hand, can dissipate more heat, which in turn allows higher amperages. This means greater flexibility in system design, as more parallel strings can be connected.
Inverters with active cooling also offer maximum flexibility during installation. In contrast to passive cooling, devices with an active cooling system can be mounted on a roof in a vertical, horizontal, and even flat position. This is because the cool air is drawn in from the side and the heated air is dissipated upwards. With heat dissipation up to five times higher than the passive version, actively cooled inverters can even be installed in locations with higher levels of solar radiation.
For the warranty to be maintained, all manufacturers of passive cooling systems stipulate that the equipment must be serviced at regular intervals. A variety of inverter factors, such as the cleanliness of the heat sinks, the operating status of the system, cable connections and the grounding terminal must be checked up to twice a year by an appropriate specialist.
Inverters with an active cooling system are usually maintenance-free, so ongoing costs are considerably reduced. However, regular checks should not be completely omitted, especially if the inverter is in an area exposed to high levels of dust or dirt.
Since the service life of electronic components is highly temperature-dependent, the hotter these components become, the higher the probability of failure.
For this reason, electronic components are cooled in a targeted manner by internal fans with an active cooling system, thus ensuring a longer service life of the power electronics. This also means considerable cost savings, as the load on the individual components is significant reduced and repairs are needed less frequently.
On the other hand, restricted heat dissipation in inverters with passive cooling can lead to local hot spots, which significantly reduces the service life.
A frequently quoted rule of thumb is as follows:
In order to avoid overheating of the electronic components, there is a so-called “derating” function – a controlled power reduction. With actively cooled inverters, the cooling effect caused by the fans is much stronger than with a passive cooling system, where greater yield losses are unavoidable.
As can be seen in the diagram, the passively cooled inverter switches to power derating at ambient temperatures of 30 °C, while the actively cooled Fronius inverter only starts this process from 40 °C.