Abstract: . . .  13.15 21.39 n = 20 8.02 10.19 11.75 20.54 n = 25 7.10 9.37 11.02 20.21 Table 7-1: Annuity factor for typical values for fictitious interest i and planning horizon n -143- t i 0049- 561 804 6201 www.uni-kassel.de/re The net present value is calculated as the sum of all present values of the net cash flows as shown in the equation (7-2). In case that the annual cash flows remain equal, the annual net cash flow equals the annuity and can be directly used in the annuity calculation. For the example of photovoltaic power supply, there is often only one investment at the beginning of the planning horizon whereas all other cash flows consist of uniform payments such as annual fuel cost or maintenance cost. In this case, one adds the annuity of the investment, i.e. the investment transformed into average annual cost, directly to all other annual cost in order to obtain the overall annual cost of the project. The net present value of the beginning of the planning horizon (t = 0). the investment equals . . .
. . .  their specific lifetimes as well as a rate for planning and installation. -144- t i 0049- 561 804 6201 www.uni-kassel.de/re As an example, Figure 7-1 shows a configuration of a system, which is sized for 50-kWh/d energy demand with the mixed load profile presented in Figure 7-6. EIB – Bus EMS SMA – Bus DieselGenerator G Battery Storage Counter M Customer Consumer Counter … … … … PVGenerator AC – Bus Figure 7-1: Configuration of the system (Source: Kassel University) The system consists of 4 subsystems as follows: 1. 3 × PV generator (10 kWp) 2. 1 × Diesel generator (6.6 kW) 3. 2 × Battery Inverter (6.6 kW) 4. 1 × Battery Storage (100 kWh) Accordingly, investment costs of the system include: 1. PV generator 2. Diesel generator 3. Battery Inverter 4. Battery Storage 5. Additional components, i.e. Balance of System Components (BOS) 6. Planning and Installation Descriptions of the investment costs are presented in Figure 7-2 and Table 7-2. -145- t i 0049- 561 804 6201 www.uni-kassel.de/re . . .
. . .  lamp 1 Compact fluorescent lamp (CFL) 1 Fan, circulating 1 Fan, attic 1 Radio 1 Television, colour 19″ 1 Sewing machine 1 Drill, 318″ variable 1 Blender/Mixer 1 Refrigerator (12cu. ft./340 litre) 1 Vacuum cleaner 1 Iron 1 Clothes dryer, gas 1 Clothes washer 1 Toaster 1 Coffee maker 1 Hair dryer 1 Microwave oven 60 40 15 85 375 55 80 75 240 350 330 900 1000 500 1150 1200 1200 1500 2100 Table 6-1: Annual energy consumption of household appliances (Source: Center for Renewable Energy and Sustainable Technology) According to the knowledge of the solar potential and the energy demand it is now possible to size a suitable PV generator, which supplies the system with sufficient energy. The energy balance from the system could be generally determined as follows: Edemand ≤ Esupply Due to the uncertainty of demand prediction and the assumed radiation the energy supply should be basically higher than the energy demand. However, it could sometimes happen that the supply could not meet the demand and . . .
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