Environmental Engineering Reference
In-Depth Information
costs of 30 % and by the degree of efficiency of the district heating network on
the other hand. Thus, out of the examples analysed in this chapter the solar ther-
mal support of space heating and domestic hot water heating of multi-family
houses and solar-supported district heating with a short-term storage with com-
paratively low degrees of solar coverage (here 10.4 % and 6.2 %) are the most
favourable options in economic terms.
In addition to these solar heat generation costs, namely the costs resulting from
investments and operating costs of the solar system, the equivalent fuel costs are
also shown in Table 4.7. The costs of useful solar energy at the storage outlet are
assessed, considering the degree of utilisation of the conventional heating boiler
that supplies heat in combination with the solar installation. The equivalent fuel
costs have a major impact on the decision of a house owner whether a solar ther-
mal system will be installed or not, as they allow to immediately calculating the
direct annual cost saving for e.g. fossil energy carriers and the expected annual
amount of fuel saved. They enable the direct comparison between solar thermal
heat supply and the avoided fuel costs for fossil and sometimes also biogenous
energy carriers.
Such a comparison with the equivalent fuel costs shown in Table 4.7 reveals
that currently all analysed variations of solar thermal heat supply are generally
significantly more expensive than conventional space heating or domestic water
heating with oil or gas. When comparing domestic water heating with electricity
during the summer at an electricity price of approximately 70 €/GJ (household
tariff) with specific heat costs, all solar examples are more cost-effective.
However, these values should not be considered as generally valid mean or ref-
erence values. In special cases significant deviations can occur under the given
marginal and boundary conditions. The price for solar heat for open-air swimming
pools, for example, is between 7 and 14 €/GJ. Hence, in many cases solar open-air
swimming pool heating is currently already cheaper than conventional heating.
The reason is that times with a high level of radiation supply coincide with times
of a high demand for low-temperature heat - without a storage system, as the pool
water serves as a heat store. Furthermore, the uncovered absorbers used for open-
air swimming pools are cheaper than covered collectors.
In order to better assess and evaluate the influence of the different variables,
Fig. 4.17 shows a variation of the main sensitive parameters. A decentralised solar
thermal domestic water heating system (SFH-III) served as starting point. Accord-
ing to the example, a change in investment costs plus a variation of the interest
rate have the most significant impact on the heating costs for a given climate. In
the given example, an investment reduced by 30 % cuts the specific heat genera-
tion costs from almost 55 to around 41 €/GJ. This shows the importance of eco-
nomic incentives for the market implementation of solar thermal systems. Fur-
thermore, different climates have been analysed. Starting from Würz-
burg/Germany with a reference radiation of 100 %, different climates from Genoa
with 30 % or more, to Helsinki with 10 % less, irradiation are shown. Costs were
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