The study has been performed with the simulation software HOMER developed by the National Renewable Energy Laboratory (NREL). HOMER can be used for the sizing of hybrid systems based on the Net Present Costs (NPC). The modeled systems supply the household electricity for single family houses. The load profile for the electrical consumption has been derived from usage patterns and the average yearly electricity consumption for single family houses in Sweden (about 6000 kWh). Two additional load profiles with 3300 kWh and 1800 kWh have been generated, assuming the application of power efficient appliances and other energy saving measures to reduce the annual electricity consumption. The system size has been limited to 6 kW PV power which corresponds approximately to the available area of the south roof of a single family house, 3.6 kW wind turbine power and a battery bank size of 120 kWh. For the simulation a Bergey XL.1 wind turbine with a hub height of 20 m was used (max. 3 turbines each 1.2 kW). Another variable has been the capacity shortage which defines the percentage of load that is accepted to be uncovered. The applied prices and other economic parameters have been identified for Swedish conditions

In total 11 locations have been studied from the very South to the very North of Sweden (Table 1) using the local annual solar and wind resources (Figure 2).

Kir Lul Ume Ost Bor Kar Arl Nor Got Vis Lun [4]

In Figure 4 the Net Present Costs are compared for capacity shortages of 0, 5 and 10 percent. It can be seen that the costs are highest for locations in the North of Sweden with low winter radiation and low wind speeds. For these locations also the difference between the no capacity shortage and 5% capacity shortage allowance are most significant. If no capacity shortage would be allowed the NPC would amount between $23,000 and $49,000. In this case, for the most locations, the use of a small diesel backup generator would probably be more cost effective to provide the uncovered load than an increased systems size.

Simulations with the 1800 kWh load profile have been done to compare PV-Wind Hybrid systems with PV-alone systems. The results in Figure 5 show the hybrid systems to be consistently less expensive than the PV-alone system. Logically at locations with higher wind speed such as Lund and Gothenburg the difference is greater than for locations with lower wind speed such as Borlange. Using a Hybrid system is reducing the NPC by 36% (for Borlange) and 64% (for Lund).

$70 000

$60 000

$50 000

Q $40 000 СЛ

3 $30 000 $20 000 $10 000 $0