**3.1. Using local renewable energy resources**

**3. Favourable energy sources and plants**

combined heat and power plants.

6 Sustainable Energy - Recent Studies

such as fossil fuels.

District heating can use heat resources that are more or less impossible to supply to and con‐ vert to heat in single houses. Such energy sources include surplus heat from industries, heat produced through combustion of waste and unrefined biomass, as well as heat from larger

**Figure 3.** Common plant types and energy flows for district-heating supply at a local Swedish energy company

Figure 3 shows the district heating system in the second largest Swedish city Göteborg (Gothenburg). There is a large city-wide district-heating network with a large heat demand, which means that the system can host many different forms of heat supply. There are two combined heat and power plants, which produce electricity and heat; a natural-gas-fired combined-cycle unit and a waste-fired steam-cycle plant. Industrial surplus heat is bought from two oil refineries. Wood and oil-fired boilers, as well as electric heat pumps produce heat only. The heat is distributed through the district-heating network to the consumers to the right in Fig. 3. This is one example of how district heating enables efficient energy uti‐ lisation, but the system also includes components that may be considered less sustainable,

CHP plants offer better fuel use. In condensing power plants, most of the fuel energy is nor‐ mally wasted. Electricity produced in CHP plants, which produce district heating, can dis‐ place electricity from condensing power plants. Due to higher efficiency, less fuel is needed for the electricity generation in CHP plants than condensing power plants because the major frac‐ tion of the fuel yields district heating. Therefore, the carbon-dioxide emissions caused by the power production are lower for a CHP plant even if it is fed with fossil fuel. But the environ‐ mental benefit is of course even larger if renewable fuels are used for the CHP production.

Available local renewable energy supplies influence the suitability of various solutions at a location. In some places, solar energy may contribute to district-heating supply. But most useful for district heating are biomass fuels and combustible waste.

Biomass fuels can be derived from forestry and agriculture. Use of biomass fuels can initiate local biomass industry and promote local business and development. The demand for bio‐ mass fuel from a district-heating plant can make entrepreneurs develop supply systems for, for example, wood fuels, such as tree branches from forests.

Today, much waste is landfilled. Using the waste as fuel or for energy extraction in other ways reduces the landfilling. Waste is a resource and various waste fractions should be sep‐ arate to make it possible to use them in the most suitable way. The separation can take place at the source, that is, in households and firms, etc. For example, biodegradable waste can yield biogas, which can be used as automotive fuel, whereas other combustible waste (e.g. from households or building demolition) can be used as fuel for electricity and district-heat‐ ing production.

Utilisation of local renewable energy resources means higher security of energy supply and lower dependency on fuels from other regions and countries. Use of local fuels and genera‐ tion of electricity reduce the energy bought from other places and increases the money that can create wealth locally. Switching from fossil to renewable fuels also reduces emissions of fossil carbon dioxide and decreases the local contribution to global warming.

However, biomass may be a too valuable resource for producing only heat, which is an en‐ ergy form of lower value than electricity and automotive fuel. Biomass could rather produce combinations of different energy carriers, such as heat, steam, electricity, automotive fuel and cooling (Sect. 6). Biomass certainly is a renewable energy source but its extraction must anyhow be carried out in a sustainable way. Land also produces food and raw material and a dilemma is that the wealthy can pay more for fuel than the poor can pay for food.

Waste is of renewable, as well as fossil origin. Waste volumes are normally increasing with economic growth but less waste than now should be generated in a sustainable society. Waste incineration may therefore partly be seen as a transition technology rather than being a basis to the present extent in a long-term system.
