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Creates safer solar power in our homes

Published: 23 September 2020

The Swedish Energy Agency and Energiforsk have commissioned researchers at Luleå University of Technology to investigate the problem that residual current devices, which are intended to prevent serious accidents, do not always seem to work at photovoltaic systems in domestic and industrial installations.

– If the residual current device does not work properly in industrial and residential installations with solar power, it can cause personal injuries and fires and the National Electrical Safety Board wants to prevent this. It must be safe to use solarcells, Math Bollen, says, professor of Electric Power Engineering at Luleå University of Technology.

Residual current devices save lives and prevent fire

The residual current device ensures that the electricity supply in the home, workshop and office is electrically safe, by quickly disconnecting the power if an earth fault occurs in an electrical system or in connected products, such as household appliances, computers and workshop machines. The outer casing then does not reach voltage levels that are dangerous even if the casing becomes live.

Disturbances affect the residual current device

It is now feared that there is a type of disturbance in the electricity grid at photovoltaic systems which could make that the residual current device does not always work in a building that has installed solar cells - and possibly also in adjacent buildings. At the same time, the number of photovoltaic systems is increasing rapidly, which means that it is important that regulations and recommendations can be adapted.

– The Electric Power Engineering group at Luleå University of Technology has for many years worked to map and understand disturbances in the electricity grid and we are one of the few groups in the world that have the right skills to be able to study failures with residual current devices at photovoltaic systems, Math Bollen, says.

Risks that residual current devices do not work

The university's research team in Electric Power Engineering will now study in detail what disturbances can occur at or near photovoltaic systems. The project will map the risks and quantify how DC components (including frequencies well below 50 Hz, quasi-DC components) can lead to a residual current device not tripping when it should. The research team will perform a quantitative assessment of the risks at photovoltaic systems and assess whether DC components can lead to the residual current devices being deactivated in nearby buildings as well. The project will map the risks through simulations, measurements and laboratory experiments.

– DC components that can occur in a photovoltaic system can cause some residual current devices not to trip, which can cause accidents and fires, Math Bollen, says.

He states that there is a great lack of knowledge in the field, including the origin and spread of DC components and supraharmonics (frequency components between 2 kHz and 150 kHz) in the vicinity of photovoltaic systems.

– The state of knowledge right now is that no one knows how serious the problem really is, Math Bollen, says.

The project is funded by the Swedish Energy Agency and Energiforsk.

Sarah Rönnberg, Associate Professor in Electric Power Engineering, is one of the project leader for the reserachproject.