Photo: Pierre-Elouan Réthoré

Outdoor path lighting will benefit the climate

Electrotechnology Energy
Colourful lighting along the paths around the Svalin co-housing complex shows residents when the electricity in their sockets is climate-friendly to use.

The Svalin co-housing complex near Roskilde is serving as a living laboratory for the DTU-managed research project Energy Collective, which is studying the user’s role in relation to the purchase, sale, and consumption of electricity.

Svalin’s solar cells generate green electricity, which emits approximately 60 g of CO2 per kilowatt hour on a sunny day. Energy from fossil fuels such as coal on the other hand emits up to 500 g of CO2  per kilowatt hour.

During the day, when the sun is shining down on the 20 energy-friendly wooden houses and the solar cells on their roofs, most of the residents are at work. Carbon dioxide emissions from the complex are therefore low, and the 19 lights along the paths in front of the houses are green.

However, if the light turns red, it shows the residents that a lot of CO2  has been emitted to generate their electricity, explains Pierre Pinson, Professor at the Center for Electric Power and Energy, DTU Electrical Engineering and project manager for the Energy Collective.

Green behaviour through nudging
Pierre-Elouan Réthoré lives in Svalin. He is a senior researcher at DTU Wind Energy, a member of—a collective of citizen researchers working with emerging technologies for the benefit of society—and a partner in the EnergyColletive project. He has developed the algorithm that makes the path lighting change colour from green to yellow and then red depending on whether the electricity being used in the co-housing complex has cost a little or a lot on the climate account.

“I hope that visualizing whether the electricity comes from green energy or not can change our behaviour, because it speaks to our feelings. So the lighting project is not just for fun, as it also has a behaviour-altering effect which means that we take more responsibility for our own energy consumption,” says Réthoré.

The lighting along the paths shows carbon emissions in real time. So, by looking out of the kitchen window and seeing whether the lights are red, orange or green, residents can make an informed decision on whether to use their washing machine, recharge their electric car or wait depending on whether the lights are red or green. And according to him it works:

“On several occasions, I’ve decided not to recharge my electric car because the lights were red,” says Réthoré.

The process of visualizing and making us aware of our behaviour is one of the Energy Collective’s aims.

“The lighting project is a visual approach to achieving this objective, and which in the long term can be implemented in society at large. This might be in the form of an interface like an iPad or Toon, which can be hung in the kitchen and show the consumer when the electricity is green,” says Pierre Pinson.

Functions like traffic lights
Every three minutes, a small computer program downloads information on the average proportion of green energy in the Zealand power grid from At the same time, it registers how much energy Svalin’s solar cells are producing as well as how much electricity is being consumed in the houses.

“When it’s sunny, Svalin basically produces so much green energy that the co-housing complex can be self-sufficient, and the lights along the paths are therefore green,” says Réthoré.

If the lights change to orange, it means that the energy is coming from dirty and green energy sources in the electricity supply. This happens if Svalin’s power consumption exceeds the energy produced by the houses, and it is necessary to make up for the deficiency by using electricity from the power grid which does not contain 100 per cent green power, he says.

In the peak period between 17:00 and 20:00 on weekdays, when people have come home from work and switched on their ovens, the energy will often have to come from the grid. And if the share of green energy in the power grid is low, the lights will therefore be bright red.