The Sweden Files: day three
Home » Blog » Annabel McAleer » The Sweden Files: day threeHow one Swedish suburb is turning summer sun into winter heat.
Solar collectors soak up autumn sun in Anneberg, Danderyd
The problem with solar energy is that when the sun goes, so does your power. But it won’t always be that way.
The housing development of Anneberg in Danderyd, north of Stockholm, has been designed around long-term solar storage. The town sits at a chilly 59°N—the same latitude Eskimos occupy in northern Canada. Although summers are crisp and clear, perfect for solar power generation, winter temperatures drop as low as -30°C, with an average around 0°C. For those months, solar panels don’t do much at all.
But Anneberg (and its sister project at Drake Landing near Calgary, Canada) has found a way to make the summer sun last all year.
The 50 Anneberg homes all have steeply pitched roofs, covered in a total of 2,400m2 of solar collector panels. These rooftop panels heat water that continually flows around a closed circulation system. This hot water provides each home with warm water and underfloor heating, via heat exchangers, but the clever part is where it goes next.
The still-warm water travels along 26 kilometres of plastic tubing, winding through 100 holes bored 65 metres deep into granite rock beneath the housing development.
Over summer, 75°C water heats the granite up to around 42°C. In winter, instead of using heat from the sun, the system draws heat from the rock. The houses stay warm, and by time the granite finally cools to around 30°C, the summer sun is ready to reappear. (About half the heat dissipates into the surrounding ground; the neighbourhood’s fruit trees and deer enjoy the warmth as much as the human inhabitants.)
Anneberg is six years into its experiment, and aside from a disastrous leak in the granite in its first year, where the system had to be drained and patched, it’s considered a success. The price paid for the homes has almost doubled since the project began in 2002, and the system meets about 60% of each home’s electricity needs—not bad, given the price of electricity in Sweden doubled over the same period.
