The use of photovoltaic systems in German single-family homes is constantly increasing. How much photovoltaics you need depends on several factors. In this article, you will learn how to determine the optimal size of a PV system.

First things first

• For every 1,000 kWh of electricity consumption per year, you need about 1 kWp of PV power.
• For a house with a heat pump, a PV system with about 8 to 9 kWp is recommended.
• An electric car increases the demand for PV power by 2 to 5 kWp, depending on the annual mileage.
• The space requirement is 2 to 3 solar modules per kWp PV output.
• For a PV storage system you need between 0.8 and 1.5 kWh of storage capacity per kWp of PV power.

How much photovoltaics do I need for a single-family home in Germany? 

For a single-family home with an electricity consumption of 3,000 kWh per year, you need about 4 to 5 kWp of photovoltaics. For a consumption of 5,000 kWh, you need around 7 to 8 kWp and for 10,000 kWh, around 12 to 14 kWp.

How much photovoltaics do I need for a single-family home with a heat pump? 

For a single-family home with a heat pump, you need a photovoltaic system with a nominal output of around 8 to 12 kWp. A heat pump consumes around 2,000 to 3,500 kWh of electricity per year. Together with the average electricity consumption of a single-family home of around 4,500 kWh, this results in a total consumption of around 7,500 kWh.

How much photovoltaics do I need for a single-family home with an electric car?

For an electric car, you need an additional 2.5 to 5 kWp of photovoltaics on average. This depends primarily on the number of kilometers you drive per year. If you drive 10,000 km per year, you should plan on 2 kWp of photovoltaics. If you drive 20,000 km, you should plan on 5 kWp.

How many solar panels do I need? 

For one kWp of PV power, you need about three to four solar modules, depending on the nominal power. For example, you only need 14 solar modules with 400 W. For 300 watt modules, the number increases to 17.

The following table gives a overview about the required number of solar modules for system outputs between 3 and 15 kWp.

How much storage capacity do I need?

The recommended storage capacity for a PV system in a single-family home is approximately 0.8 to 1.5 kWh per kWp PV output. 

Avoid this Under- or over-dimensioning of the PV storageA storage unit that is too large causes unnecessary costs and extends the payback period. A storage unit that is too small cannot fully absorb the solar power generated, resulting in less self-consumption and lower cost savings.

How do I determine the optimal size of a PV system?

The size of a photovoltaic system depends on various factors. This is how you determine the optimal PV output:

• Current power consumption: The most important factor when dimensioning a PV system is the current power consumption. You can determine this by checking your last annual bills.
• Available roof area: A larger PV system requires more space. On average, you need about six to eight square meters of roof area per kWp. A 10 kWp system therefore requires around 60 to 80 square meters of roof area. Also take into account possible shading from trees or other buildings, which reduce the efficiency of the PV system.
• slope and orientation of the roof surface: The inclination and orientation of the PV system have a major influence on the yield of the PV system. A south-facing orientation with a roof pitch of 30 to 40 degrees is ideal. Deviations from this can reduce the yield.
• location of the PV system: The photovoltaic location influences the radiation intensity and thus the yield produced. In Germany, an optimally aligned PV system delivers between 900 and 1,200 kWh per kWp per year. Regions with more sunshine, such as the south of Germany, achieve higher yields than regions in northern Germany.
• Future developments in the household: Plan for additional future consumers such as electric cars or heat pumps. These increase the electricity demand and therefore the required size of the PV system.