District Energy - 2008 4th Quarter

Feature
Story
Harnessing Solar
District Energy:
Europe leading the way
for
Jan-Olof Dalenbäck, Professor, Building Services Engineering, Department of Energy and Environment,
Chalmers University of Technology, Gothenburg, Sweden

Countries around the world are increasingly recognizing the sun’s tremendous potential as a renewable energy source. According to the U.S. Department of Energy, every hour, more energy from sunlight strikes the Earth than is consumed on the planet in a year. In Europe, many large-scale centralized solar heating systems have been taking advantage of this abundant, environmentally friendly energy source for the past 30 years.

In Europe today, there are about 20 million sq m (215 million sq ft) of glazed solar collectors used in a variety of applications, corresponding to about 14 gigawatts of thermal power (GWth). Most of those collectors provide heat for or serve small thermosiphon domestic hot water systems with just 2-3 sq m ( 21. 5-32. 3 sq ft) of collectors. Perhaps 10 percent of the total number of systems are hot water plus heating, while very few are used for heating only. About 1 percent of the European collector market comprises large-scale centralized heating applications, with heat loads up to several GWth. About 9 percent of the heating loads in Europe is served by large-scale centralized heating systems (i.e., district heating and ‘block heating’ systems). There is thus a need and opportunity to connect solar heating applications to

large-scale centralized heating systems. According to the European Solar Thermal Technology Platform (ESTTP), that is indeed feasible if Europe adopts a more progressive solar district heating policy.

The Market

In Europe at present, there are about 120 documented centralized heating plants, each with more than 500 sq m ( 5,382 sq ft) of solar collectors. Of these 120 plants, 30 have a ‘nominal power’ (or capacity) of 1 MWth or more. [The solar industry defines the nominal power of 1 sq m ( 10. 7 sq ft) of solar collector as 0.7 k Wth to facilitate a comparison with the nominal wind power, photovoltaic power, etc.] The total col-

lector area of the 120 plants – about 200,000 sq m ( 2. 15 million sq ft) and approximately 140 MWth.

Large-scale centralized solar heating systems were introduced in Europe the late 1970s, in response to an interest in developing solar heating systems with seasonal storage to cover a larger part of the heating loads in the northern latitudes. Sweden played a leading role in these early projects together with the Netherlands and Denmark. In the ’90s, the interest in large-scale centralized solar heating increased in Germany and Austria, and about 100 new plants with more than 500 sq m ( 5,382 sq ft) of solar collectors have been put into operation across Europe since the mid-’90s. The

Figure 1. Number of European Centralized Solar Heating and Cooling Plants With More Than 500 sq m ( 5,382 sq ft) of Solar Collectors (year commissioned).