How significant are solar systems in terms of interference frequencies?
Emmanuel de Raemy: Solar systems with power optimisers cause interference, which is usually reported to us by ham radio operators. When we test the system, however, it turns out that there is interference not only in the band of amateur radio but that almost the entire shortwave range is affected.
So it's not just a matter for radio amateurs?
It is to be assumed that many more services are disrupted, but that those affected do not recognise this as a disruption due to a lack of knowledge and therefore do not report it to us.
How many installations have been reported so far?
So far, nine photovoltaic systems with DC optimisers have been clearly identified as sources of interference. Twelve more are under investigation.
Is it only about the optimisers or are systems with conventional string connections also affected?
We have never had problems with standard photovoltaic systems using inverters and strings.
How do the interference frequencies come about?
The power optimisers work like pulsing power supplies. This is achieved by using power electronic components that cycle very quickly. This is one cause of interference. In order to work properly, optimisers also have to communicate. In some cases Power Line Communication (PLC) is used for this purpose. This means that a communication signal is superimposed on the DC power currents of the photovoltaic system. This must be sufficiently strong so that the interference caused by the optimisers does not affect communication. This is another source of interference.
How do optimisers behave without PLC?
We see fewer problems with systems that do not use PLC for the communication of the optimisers, but currently there are two cases.
What role does DC cabling play? Is it enough to use well shielded cables?
Shielded cables could help. But then the panel would probably also have to be shielded, which is not possible. Therefore the optimiser must be correctly filtered so that the system does not emit radiation. The routing of the cables can have a certain influence on the radiated emission. Installers should strictly follow the manufacturer's instructions and record them by taking photographs. The photos can be useful in cases of liability.
Does the problem also occur with micro inverters?
So far, we have not received any fault reports from photovoltaic systems with micro-inverters. The reason could be that no such systems have been built in Switzerland, or that the micro-inverters cause less interference. The second assumption is more likely. Since the micro-inverters are connected to the normal power grid (AC 230 Volt), they cannot benefit from loopholes in the standards that would allow them to implement fewer EMC measures.
Are there such gaps in the standardisation of DC optimisers?
Standardisation always lags behind rapid technical development. Power optimisers fall between the cracks, the test requirements do not reflect reality.
What does that mean exactly?
Manufacturers should be aware that compliance with harmonised standards can only provide a presumption of conformity. One hundred percent conformity could only be achieved if all devices had to comply with more stringent threshold values. This would entail additional costs and would therefore affect the marketability of the product. (mfo)
In Part 2, Emmanuel de Raemy will go more into the legal ramifications of what happens when DC optimizers cause interference.
Emmanuel de Raemy is an expert on electromagnetic compatibility (EMC) and non-ionising radiation (NIR) at the Swiss Federal Office of Communications (OFCOM) in Biel.
