Hot news flash out of Sweden. Wapnö castle, which maintains a dairy herd of 1,000 cows, has found a new use for their milk. Or at least for the energy that is released when the milk is cooled.
Milk leaves a cow's udder at a temperature of 37ºC, and must be cooled quickly to 3ºC in order to prevent it from spoiling. The Swedes are using the warm milk to heat water for the castle (presumably using a heat-exchanger) and plan to replace the castle's entire boiler-based heating system with heat obtained from the milk.
Now that's energy efficiency!