The key to transferring all this heat to the living rooms and bedrooms of residents is hot water. This image shows the hot-water grid in 2005, when it was being installed. According to the University of Gottingen's Interdisciplinary Centre for Sustainable Development--the group that spearheaded the project--the households that participate now receive 100 percent of their heat from the hot water grid.

The town also uses 2 million kilowatt-hours of electricity every year, but itself produces around 4.5 million kilowatt-hours. All of the electricity produced feeds into the public network, and Juhnde profits from the surplus.