Rise in energy prices

The simulations of the base case were calculated with a comparably small rise in energy prices of

1.3 Подпись: 0Подпись:Подпись:image254%/a for natural gas and 0.3 %/a over 20 years for electricity [6]. However the current development of prices in Germany amounts to 9.7 %/a (non inflation-adjusted) over the last seven years [7] which indicates a higher annual rate of growth.

Therefore the rise in energy prices has been varied between

1.3 Подпись: 12%/a and 7.5 %/a. Figure 3 (e) shows that as expected the lowest values of the objective function get smaller with a growing rise in energy prices which means that the heat generation costs per kWh become smaller. More surprisingly, the dimensions of each optimal system in terms of the underlying objective function and therefore also the primary energy savings stay constant, showing that the dimensioning does not depend on the rise in energy prices within the examined range. Figure 5 shows an extrapolation of the simulation results calculated with different rises in energy prices. The trend line derived from the calculated points indicates that the analysed solar heating system would be economically rewarding with a rise in energy prices of 9 %/a without any subsidies.

4.3 Subsumption of simulation results

Reducing the price of the solar collectors by 30 % improves the cost/benefit ratio by 21 %. The resulting optimal collector area increases by 3.5 m2, whereby the storage device capacity keeps unaltered. Using a high efficiency flat-plate collector instead of the initially defined model reduces the cost/benefit ratio by 8 %, whereas a low efficiency flat-plate collector increases the cost/benefit ratio by 13 % without having stronger impact on the dimensioning of the system. A 40 % reduction in the storage cost improves the cost/benefit ratio by 24 % again without changing the optimal dimensioning. The difference in the cost/benefit ratio between a system with 7.5 cm of storage insulation and a system with 17.5 cm of storage insulation amounts to 21 %, whereas the optimal system with the thickest isolation consists of a storage 120 litres larger than the thin isolated tank, connected to solar collectors that are 3.2 m2 smaller than the pendant with the thin isolated tank. Considering a rise in energy prices of 7.5 %/a instead of 1.3 %/a leads to a reduction of additional costs of 250 € /a with equal dimensioning parameters.

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