Utilisation of Geothermal Energy - Renewable Energy: Technology, Economics and Environment - page 456

In general, heat production costs decrease with increasing plant size. Due to the
relatively high investment costs of tapping geothermal heat resources heating
plants with relatively small thermal capacities are characterised by relatively high
investment costs. Also, the heat production costs of small heating stations
equipped with deep wells and direct heat transfer are higher compared to geo-
thermal heating systems characterised by relatively shallow wells supplemented
with heat pumps. The use of heat pumps is thus more cost-effective than deeper
wells according to the assumptions made here. This might change with strongly
increasing costs for the electricity to be purchased from the grid and/or with in-
creasing costs for fossil fuel energy.
Heat production costs are influenced by many factors which, depending on the
site-specific conditions, have to be optimised with regard to minimising the over-
all system costs. Heat costs can be further reduced by decreased costs for drilling
a well, optimised district heating networks as well as by an optimised heating
plant configuration.
To better estimate and evaluate the impact of the various factors influencing the
described heat production costs, Fig. 10.9 illustrates a variation of the predomi-
nant sensitive parameters of geothermal heat supply systems with peak load cov-
erage (DH-II) for a house connection with a heat demand of 8 kW (SFH-II). For
the house substation constant costs are assumed. Also, the geothermal efficiency
of 85 % remains unchanged.

56

Overall investment
9.73 Mio . € = 100 %

52

Depreciation period
22 a = 10 0 %

48

Interest rate
4.5 % = 10 0 %

Fuel costs
63 k€ = 10 0 %

44

Operating costs
130 k€/a = 100 %

40

36

32

70 80 90 100 110 120 130

Parameter variation in %

Fig. 10.9 Variations of the main parameters having an impact on the heat production costs
of geothermal/fossil-fuel fired heat supply systems (DH-II) according to the supply case
SFH-II with a capacity of 8 kW (the depreciation period of 22 years corresponds to the
average depreciation period of all plant components, house substations not varied; see
Table 10.2)

Hence, investment costs and full load hours are the factors mostly influencing
the heat provision costs. The full load hours - and thus the useable heat - might