Thomas Sandberg and Knut Bernotat

8.1. AIMING AT SUSTAINABLE ENERGY SYSTEMS

The share of renewable energy is high in the Swedish energy system. In 2001, 177 TWh or 44 per cent of the total energy consumption in the country came from renewable sources. In the residential, service and industrial sectors, this share was as high as 58 per cent. Since 1991, bioenergy is the largest renewable source in Sweden and, in 2001, 98 TWh were generated from this source. This compares with 79 TWh from hydro and 0.5 TWh from wind (Swedish Energy Agency, 2002a; see also Ling, Chapter 3).

Even if these are impressive figures, some 122 TWh remain to be converted to renewable sources, not to mention the other 92 TWh in the transport sector. Scenarios developed for the year 2050 indicate that this is a manageable task for Sweden (Elforsk, 1996; SAME, 1999). The crucial point is to speed up the process and to make it cost efficient. Although the resources and technologies are there, administrative, economic and political structures delay the shift towards a sustainable energy system.

District heating supplies 46 TWh of the 93 TWh heat consumption in Sweden today. Nearly all this energy emanates from large-scale units connected to large-scale district-heating systems. Some 32 TWh are generated from biomass. Due to the large availability of electricity from hydro and nuclear sources, only 5 TWh of electricity is being produced in combination with heat. We argue that district heating, supplied by combined heat and power (CHP) production based on bioenergy, holds an important key to the shift towards larger use of renewables in Sweden in the next two decades. Most probably, this is also true for many other countries with moderate climate, where there will always be a large need for heating.

There are many ways to enhance the utilization of bioenergy in Sweden. In general, this includes:

• Continuing the conversion from fossil fuels to biofuels;

• Increasing the power production in sites where CHPs are installed and fueled by biomass;

113 Bioenergy — Realizing the Potential

© 2005 Dr Semida Silveira Published by Elsevier Ltd. All rights reserved.

• Introducing power production in sites where only heat is produced from biomass;

• Enlarging existing district-heating grids; and

• Building new district-heating grids and CHP units fueled by biomass.

Since large cities and many towns in Sweden already have a district-heating system, the remaining potential is in smaller places with a few thousand down to even less than one thousand inhabitants. Therefore, in this chapter, we focus on small-scale district heating grids supplied by small-scale CHP fueled by biomass. Our task is to calculate the potential for such systems in Sweden.

We first present a method to estimate the potential for small-scale district heating. The essence of the method is to identify clusters of buildings where the heat demand is large enough to justify small grids. We use this method to evaluate the potential of a small region in southeast Sweden, and of three counties in different parts of the country. Finally, we extrapolate the results to make a rough estimation of the potential for new district heating systems in the country as a whole, and to evaluate the potential generation of electricity from the CHP units.