Could urban heat islands produce geothermal power?
From Hot water to get cities out of energy trouble? by Liz Kalaugher
Cities are generally warmer than the rural land surrounding them, in a phenomenon known as the urban heat-island effect. It’s not just above-ground temperatures that rise – the soil beneath also experiences several degrees of warming. Now, researchers have found that the extra heat stored in groundwater beneath cities around the world could provide enough geothermal energy to heat urban homes.
“In most cities, with a variety of populations and climates, the large amount of geothermal energy stored in the urban local subsurface is capable of fulfilling the annual space-heating demand for years and potentially decades,” Ke Zhu of the University of Tübingen, Germany told environmentalresearchweb.
Together with colleagues from Karlsruhe Institute of Technology, Germany, St Francis Xavier University, Canada, and ETH Zürich, Switzerland, Zhu measured groundwater temperatures in Cologne, Germany, and Winnipeg, Canada. Both cities had extensive underground warming, with temperatures 3–5°C higher than surrounding rural areas. Similarly, the subsurface beneath urban green spaces was cooler than that below business districts.
The urban heat-island effect arises because of factors such as buildings preventing heat from leaving the ground at night, changes in the properties of the ground surface and the absence of plants that provide cooling by evapotranspiration.
“Urban aquifers with elevated temperature are attractive shallow geothermal-energy reservoirs, and meanwhile there is high energy demand just above,” said Zhu. “In our opinion, it is important to study the geothermal potential of urban heat islands before planning large geothermal projects.”