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Independence Calculator

Before installing a photovoltaic system, there are often several open questions that need to be answered:

  • Which size of energy storage system is the right one for me?
  • What is the optimum size of a PV system?
  • Which degree of self-sufficiency is possible?

All these questions can now be answered with just 3 clicks. The following independence calculator from htw-Berlin estimates the possible degree of self-sufficiency and the self-consumption rate for a typical photovoltaic system with battery storage based on the annual consumption.

Annual energy consumption

The annual energy consumption reflects the average energy demand recorded at a specific PV project installation site. As a PV system will last for at least 20 years, it is important to consider certain factors such as the possible increase in energy consumption due to the purchase of a new electric car, the installation of an air conditioning system or of other electrical appliances.

Photovoltaic power

The photovoltaic power indicates how much solar power can be generated by the photovoltaic modules installed on the roof. It is important to note that the maximum possible system output is limited to the existing roof area. For each kWp (kilowatt peak), a surface area of approx. 6.5 square meters is required. The standard dimensions for a solar module are currently around 170 x 100 cm. Thanks to the most up-to-date technology such as the Solaredge optimizer, roof surfaces can now be used to their full potential regardless of the orientation, inclination or presence of shadows.

Usable battery capacity

The usable battery capacity is the amount of energy that can actually be withdrawn from the battery. The battery storage capacity is often also defined as gross capacity, but you need to be careful here! As a general rule, energy storage systems can never be completely discharged. Furthermore, it is important to note that the battery loses capacity over its entire life cycle. That's why it is recommended to oversize the battery by up to 20%.

Self-consumption rate

The self-consumption rate indicates how much of the self-generated solar power has been consumed by the household. This rate also includes the solar power that has been temporarily stored in the energy storage system.

Degree of self-sufficiency

The degree of self-sufficiency, also known as independence, describes the degree of grid-independence. It indicates the percentage of energy consumption that can be covered by renewable, self-produced solar power per year. In Germany, a degree of self-sufficiency of up to 80% can currently only be achieved by installing a photovoltaic system and an energy storage system.

Direct consumption

Direct consumption is the term used to indicate immediately consumed self-generated solar power, which has therefore not been stored in an energy storage system. Direct consumption is the simplest and fastest form of solar power consumption. However, as many appliances are switched off precisely when the sun is shining, direct consumption is not always possible. A direct consumption rate of 30% is considered very good. This rate can be increased by installing smart appliances and by using smart home components.

Grid feed-in

Solar energy can be fed into the public grid if it is not used immediately (direct consumption) or saved for later use (self-consumption) in an energy storage device. In this case, the German Renewable Energy Sources Act (EEG) regulates the feed-in tariff that the PV system owner gets for a period of 20 years.

Grid withdrawal

Each PV system owner is, of course, always 100% protected. Should the PV system not produce enough power, or should the energy storage system be empty, the PV system owner automatically receives energy from the public grid. This process is called grid withdrawal.

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