The Swedish city of Gothenburg doesn’t just have an electrical grid–it has one for heat, too. Deep below its streets, some 620 miles of pipes carry warm water from refineries and incinerators into apartment buildings across the city. The result is cheap, relatively green heating in a part of the world where winter temperatures can drop below freezing for several months of the year.
While popular in the Nordic countries, the concept is slowly spreading. Manhattan’s iconic steam system is a form of district heating, and Sheffield, Southampton and Nottingham in Britain all warm parts of their city centers with waste incinerators connected to hot water networks. But there’s still plenty of scope for the expansion of the industry–a 2013 study, for example, found that London wastes enough heat to supply 70 percent of its calefaction needs.
“It’s really about finding energy that’s been, or is about to be, wasted and then circulating it,” explained Jonas Cognell from GÃ¶teborg Energi, the municipally owned company that runs the network. Its pipes snake into the heart of Sweden’s second city from the major industrial areas on its outskirts, like the oil refinery at the port run by Finnish energy giant ST1 and the waste incinerator operated by local recycling company Renova. It even extracts heat from the city’s sewer system.
Renova’s plant incinerates household trash that can’t otherwise be recycled–burning 535,000 tonnes of it during 2014. The interior of the plant is a maze of piping, much of which is dedicated to carefully cleaning the waste before it’s burned. “We treat the waste, and the energy recovered is used as heating and electricity instead of fossil fuels,” said Christian LÃ¶whagen of Renova. “It’s positive for the environment if the alternative is [a] landfill.”
“The plant is so productive that Gothenburg doesn’t produce enough waste to feed it, so the company imports 100,000 tonnes of pre-sorted combustible waste from Britain annually. “We have extra capacity and it’s not good business to have the plant on half throttle, And it has a positive effect for the environment if the alternative is a British landfill.” said LÃ¶whagen. As a result, the company hit an all-time production high in 2014 of more than 1,778,000 megawatt-hours (MWh), of which almost 1,400,000 MWh went into Gothenburg’s district heating system. When waste-to-energy incineration is counted as recycling, Sweden now recycles 99 percent of its waste.
The network of pipes that crisscross Gothenburg today was first laid in the 1950s. Initially the network grew into scattered islands, but during the oil crises of the 1970s the city began to look at the concept more seriously. “After that, a lot of work went into getting the system interconnected,” said Cognell. Originally it had been oil-fueled, but that principle was swiftly abandoned in favor of harvesting heat from heavy industry.
Today, that waste heat represents almost half of the energy going into the district heating network, with the rest filled out by renewable biomass burning, a gas-fired cogeneration plant (which also produces power) and a small amount still from fossil fuels. Ninety-five percent of apartment buildings in the city are connected to the network, as well as 12,000 single-family houses, and the high proportion of industrial-waste heat allows for far lower prices than do similar networks. Cognell said, “You can roughly say that there are 250 distribution systems in Sweden and 240 of those systems are more expensive.”
“If you look at the European situation, they waste so much heat,” he added. “By using a district heating system, you can reuse the energy that would otherwise have been wasted.” Happily, LÃ¶whagen believes things are improving. “We have many study-visits at our plant and they come from all over the world,” he said. “So hopefully the technology is spreading.”
How We Get To Next was a magazine that explored the future of science, technology, and culture from 2014 to 2019. This article is part of our Power Up section, which looks at the future of electricity and energy. Click the logo to read more.