storing heat underground

Some innovative green buildings use piles of rocks in the basement to store heat or coolness, to even out the night and day temperature fluctuations in buildings without air conditioning or fossil-fueled heating.

Now, tests have shown that it is feasible to store heat underground to do the same thing over several months instead of just days, using what amounts to sub-surface radiators. Paving on roads and parking lots do a wonderful job of storing the sun's heat. In summer, this unfortunately contributes to the urban heat island effect, but where pavement is necessary, the heat could be harvested in summer to keep ice off roads in winter, or to heat buildings.

In the UK, scientists found in a trial on a section of road that enough heat was captured in the summer of 2006 to keep the road above freezing for almost all of the following winter. On average, the heated surface was 3C warmer than the surrounding ground. And a trial at an Edinburgh supermarket car park suggested that the system could cut the store's carbon footprint by 70% and slash annual fuel bills by £26,000 for an initial investment of about £180,000.