In the whole of Sweden, district heating supplies 46 TWh, or 49 per cent of the total heat consumption in the country. Though this is a very significant accomplishment, there is still a large untapped potential for small-scale district heating in the country as a whole. Our analysis of three counties illustrates that assertion. Considering clusters of 500 x 500 m2 and a minimum heat demand of 0.5 GWh, the potential is as high as 28 per cent in Orebro, 42 per cent in Kalmar and 47 per cent in Vasternorrland compared with the total heat demand in these counties. Moving the limit to 1.0 GWh gives a potential 31, 22 and 39 per cent in the three counties respectively.

The numbers obtained are very impressive. For the purpose of illustration, if we use the percentage found in Orebro (28%) to estimate the total potential for

additional small-scale biofueled district heating in Sweden, we arrive at additional 26 TWh for the country as a whole. Although the method applied here to verify the existing potential for new district-heating systems is basically fuel neutral, our starting point is that the heat should be supplied from small-scale CHP units fueled with biomass and connected to the existing electricity grid.

In areas without district heating or electric heating, the heat supply is decen­tralized today with a furnace in nearly each building. Once these individual systems are centralized into small-scale clusters, it is possible to cogenerate heat and power. In comparison with the dominating power supply today, the new contribution from each cluster and small CHP will be small, but a program to tap this potential can result in significant additions of heat and power to the system as a whole. The national power system will benefit from the new heat and power supply in two ways: through a decrease in the consumption of electricity for heating purposes, and an increase in the capacity for electricity generation from the new small-scale CHP units.

To calculate the consequences for the power system, one must contrast the added heat and power from biomass-fueled CHPs with the energy carriers that are being used today. We have two rough estimates, one for our small region in Kalmar and one for the whole of Sweden. In both cases we use 500 x 500 m2 clusters with at least 0.5 GWh heat demand.

In our small region, small-scale district heating and CHPs can substitute 64 GWh of today’s heat consumption of 102 GWh. In one of the places in the region, heat is supplied by 60 per cent oil, 25 per cent electricity and 15 per cent firewood (Sandberg, 2001a, b). Applying those figures on the 64 GWh in the 53 clusters identified in the small region gives a substitution effect of 38 GWh from oil, 16 GWh from electricity and 10 GWh from firewood. The 16 GWh electricity are equivalent to a production capacity of 3 MW.

With an average heat demand of 1.2 GWh in each cluster and 3000 h operation time per year, we need a furnace with 400 kW heat capacity (Fredriksen and Werner, 1993). The power capacity can be assumed to be 100 кW or 5 MW for all clusters. With an operation time of 4000 h a year, the power production will be 20 GWh per year. Thus in our small region only, small-scale district heating fueled

by biomass-based CHP can add 8 MW of power capacity, or 36GWh of electricity to the grid. .

For the whole of Sweden we have estimated the potential for small-scale district heating and CHP at 26TWh. In 2000, the heat consumption outside district heating systems was 22 TWh or 42 per cent from electricity, 20 TWh or 39 per cent from oil and lOTWh or 19 per cent from biomass, mostly firewood (SCB, 2001). Thus the consumption of electricity for heating can be reduced by 11 TWh (42 per cent of 26 TWh), which is equivalent to 2.2 GW of generation capacity.

At the same time that electricity demand for heating is reduced, the installed capacity and generation of electricity can increase. To substitute 26 TWh with heat from a small-scale CHP, an installed heat capacity of 8.50 GW is necessary. The power capacity can be assumed to be 2.15 GW which, with an operation time of 4000 h a year, gives 8.5 TWh (Fredriksen and Werner, 1993). Thus a broad program to install small-scale district heating based on bio-fueled district heating and CHPs could result in 19.5 TWh of added electricity out of an increased capacity of 4.35 GW. In addition, we should not forget the reduced distribution losses: for 19.5 TWh, losses are estimated at 1.5 TWh.