Present worldwide installed capacity of earth energy systems has reached 12,000 MW of thermal energy according to an international analysis, and the annual energy use is 72,000 TJ (20,000 GWh) from a total of 1.1 million installations, although the report notes that data are incomplete.
Five of the top countries in the world for earth energy installations provide 17,810 GWh a year of green heat, according to the analysis. The 942,400 installations in Canada, Switzerland, Germany, Sweden and the United States account for 10,200 MW of thermal equivalent, with two-thirds of the installations in the U.S. Sweden is in second place with 230,000 installations, 46,400 in Germany, 36,000 in Canada and 30,000 in Switzerland.
Earth energy systems, also called ground-source or geothermal heat pumps, use the relatively constant temperature of the earth to provide space heating and cooling, as well as water heating, for residential and commercial buildings. They are “one of the fastest-growing applications of renewable energy in the world, with annual increases of 10% in about 30 countries over the past ten years,” it explains.
“While installations of these systems have been quietly growing, there has been limited recognition that they make a contribution to the adoption of renewable energy,” the report notes. “This is partly because they are purely associated with the provision of heating and cooling and, therefore, do not figure in renewable electricity considerations.”
Other factors include uncertainty over the sustainability of energy from the ground, and a widespread notion (“based on air source heat pumps”) that there is no net gain in energy output and that earth energy systems are an energy efficiency technology. The paper argues that current efficiencies of ground-coupled systems exceed 140%, with 70% of the final energy coming from the ground.
Assuming annual energy use of 65,000 TJ (18,000 GWh) and using power generation with fuel oil at 30% efficiency, the annual savings are 35.8 million barrels of oil or 5.4 million TOE, it estimates, for a saving of 16 megatonne of CO2. The figures would double if the units are used for cooling, too.
An earth energy system can reduce overall CO2 emissions by 50% compared to conventional space heating technologies based on fossil fuels and, “with the use of renewable-derived electricity, there need be no CO2 emissions associated with the provision of heating (and cooling) of a building,” it notes. “There are suggestions that, in order to maximize the delivery of renewable energy, it makes economic sense to couple expensive renewable electricity to ground-coupled heat pumps as quickly as possible.”
The analysis was performed by the Oregon Institute of Technology in the US, the Institute of Applied Geosciences at Justus-Liebig University in Germany, the Institute of Geophysics in Switzerland, GeoScience in England and Lund University of Technology in Sweden.