Introduction and Structure - Renewable Energy: Technology, Economics and Environment - page 12

The system boundary for the economic as well as environmental investigations
is defined by the respective feed-in points into the house distribution network for
domestic hot water (e.g. storage tank exit) or space heating (e.g. boiler exit).
However, heat distribution losses within the respective buildings as well as the
power consumption of the circulating pumps for the heating system and the do-
mestic hot water system have not been considered. These system elements have
been assumed to be the same for all observed technologies based on fossil and on
renewable energies. These conditions are defined to allow for a direct comparison
of the obtained results.
The investigated district heating networks are three systems that have been de-
signed to deliver heat for space heating of dwelling houses (i.e. buildings that are
characterised by consumer behaviour comparable to household customers). The
energetic key figures of the different district heating systems are illustrated in Ta-
ble 1.2. However, the district heating networks are characterised by transfer
losses. Due to these losses, as well as the losses at the building substation and at
the domestic heat water storage of the supplied buildings, the heat to be fed into
the district heating network by the heating station exceeds the overall head de-
mand of all connected consumers. With an average utilisation ratio of the district
heating network of 85 %, and an average utilisation ratio of 95 % for the building
substations i.e. domestic hot water provision, the heat to be fed into the heating
network by the heating station amounts to 9,900 (DH-I), 32,200 (DH-II) and
64,400 GJ/a (DH-III).

T able 1.2 Key figures of the investigated district heating networks
Demand case DH-I DH-II DH-III

Heat demand a

52,000
64,400
0.85
0.95
a all connected consumers; b including the losses of the heat distribution network and building
substations; c average value of the entire year; d average utilisation ratio of all connected consum-
ers (hot water 80 %, space heating 98 %).

in GJ/a 8,000

9,900
0.85
0.95

26,000
32,200
0.85
0.95

Heat at heating station b in GJ/a

Utilisation ratio of the network c

in %

Utilisation ratio of the substations d in %

Electricity provision. For power generation systems no supply tasks have been
defined. The system boundary is the feed-in point into the power grid. For this
reason, potential requirements for net reinforcements and modifications within the
conventional power plant park have not been considered. Capacity effects have
not been investigated either.

Economic analysis. Key figures of any energy generation opportunity are the
costs. They will thus be analysed in detail for every option discussed in depth. For
this purpose, first the investments for the most important system components of
the applied conversion technology as well as the overall investment volume will