On the other hand, if one would designate the waste incine rator as a base load, e.g., ensuring high utilization of the invest- ment, followed by an air source heat pump plant for mid load and at last, apply natural gas boilers for peak load, a better re- sult can be achieved. In this case, the optimal solution would be as shown in Table 2 and visualized in Figure 4.
Table 2. Optimum technology mix for a multi-source operation.
Capacity [MW]
Share of annual demand
Plant utili - zation
Heat cost [EUR/MWh]
Plant
WtE boiler Air source heat pump Natural gas boiler
42
79.4%
71.7% 16.9
12
11.8%
37.4% 36.1
An alternative mix could be at point B, where the mix is a 38 MW WtE unit, a 25 MW heat pump unit, and a 37 MW natural gas boiler. The increase in the annual heat generation cost when moving from point A to B is only 2%. However, the flexi- bility impact of doubling the heat pump capacity from 12 MW to 25 MW could easily pay off, as the additional heat pump ca- pacity will offer significantly increased sector coupling oppor- tunities. For example, increased possibilities to take advantage of fluctuations in the power prices, provide balancing services to the power system and reduced reliance on natural gas, and consequently reduced dependency on imported fuels as well as reduced CO2 emissions. A larger heat pump plant could also take greater advantage of higher efficiencies achieved during daytime temperatures, compared to night temper- atures, and charge a thermal energy storage if available and limit, or avoid, operation at the coldest period of the night. Another opportunity could be to exploit synergies with other energy sectors, such as the cooling and industry sectors. Con- cerning the cooling sector, the heat pump could operate in synergy with district cooling systems or large building com plexes, such as malls, hospitals, or other large complexes. In respect to the industry sector, the heat pumps could utilize waste heat from various industry processes and, by that, achieve high heat pump efficiencies for the district heating utility and either save the industry the cost of cooling off their waste heat or, in some cases provide a revenue stream to the industry. For additional information on the potential of excess heat, see [2] . Figure 6. Sensitivity of the heat cost on the heat generation technologies capacities.
46
8.8%
7.2% 48.7
Total:
100
100%
-
22.0
Figure 4. Heat costs from the optimum mix of heat generation technologies, and their respective utilization.
Figure 5 visualizes the duration curve given the cost optimum heat generation mix.
Figure 5. The optimal heat supply mix given the defined CAPEX and OPEX for each heat generation technology.
By analyzing the sensitivity of the heat cost to the capacity distribution between the heat generation technologies, see Figure 6, interesting opportunities can be identified.
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