Photovoltaic systems

More and more people are purchasing photovoltaics for their property and hope to save money on electricity costs. But what is photovoltaics actually? How does a photovoltaic system work? What about the political support for photovoltaic systems and when does the purchase become worthwhile? The following article answers these and other important questions about photovoltaic systems and solar power.

Definition photovoltaic system

What is a photovoltaic system? The term photovoltaic is a combination of the Greek word "phos" or "photos" back, which means "light", and the unit of measurement for electrical voltage, "volt". The power that a photovoltaic system can generate is expressed in kilowatt peak (kWp).

The name of this type of power generation is therefore program – after all, a photovoltaic system generates electrical energy from light. The aids are the so-called solar cells, which are also used in the classic solar system.

In recent years, the use of photovoltaics has grown strongly in Germany. The technical process is used, for example, to generate electricity for private households (as photovoltaic systems on roof surfaces), on solar vehicles or in pocket calculators. 1

Photovoltaic system function

Every photovoltaic system has photovoltaic or solar modules that convert sunlight into electricity. The solar cells are made of silicon, a semiconductor material characterized by its high conductivity when energy is supplied. As soon as the sun’s electromagnetic rays (photons) hit the silicon atoms in the solar module, their energy is transferred to the loose electrons. As a result, these are repelled by the atoms. In this way, a current flow is created in the connected line, which then continues into the house.

During this process, an inverter in the photovoltaic system converts the direct current into alternating current suitable for the grid. To record the amount of electricity fed into the grid, most photovoltaic systems also have a feed-in meter. 1

Difference between photovoltaic and solar systems

There is often confusion between photovoltaic and solar systems, or photovoltaic systems are often referred to as solar systems. However, this is incorrect, because solar thermal systems and photovoltaic systems are both considered solar systems. Since both have the goal of converting sunlight into electricity, they are often interchanged. The difference is that photovoltaic systems translate light energy directly into electricity, and solar thermal systems translate light into heat (for heating and hot water). 1

What kind of photovoltaic systems are there?

Without photovoltaic or solar modules – the sunlight could not be converted directly into electricity. Before buying, you should learn about the different types of solar modules, because they differ not only in terms of material and manufacturing, but also in terms of technology and performance. There are also differences in price. 2

In addition to the differences in solar modules, there are also different types of photovoltaic systems. The most important distinguishing features are the location, the type of installation, the orientation of the system and the connection to the public grid.

For example, a distinction can be made between roof-mounted, facade-mounted and ground-mounted systems. Photovoltaic systems that are mounted on the roof or on the wall of a house are usually intended to supply a building with solar power. If the system is large enough, nearby households can be supplied as well. Special roof systems are, for example, photovoltaic systems that serve as terrace roofing or form the roof of a carport.

Ground-mounted systems are photovoltaic systems on the ground. These are set up on tripods, so a building as a support is unnecessary. Mostly, ground-mounted systems are used in so-called solar parks to generate and sell green electricity. In addition, there are agricultural PV plants and even floating plants.

In addition to stationary photovoltaic systems, there are also mobile photovoltaic systems that can be used, for example, on caravans or boats. This category can also include balcony photovoltaic systems, which have only one or two modules and are often not permanently installed. 3

Photovoltaic system costs

When considering whether or not a photovoltaic system for personal use is worthwhile, factors such as the photovoltaic system installation, the public subsidy for photovoltaic systems and the cost of any necessary storage for photovoltaic systems come into play. Naturally, however, the initial focus is on the purchase costs for the solar modules and the installation costs.

How much electricity a photovoltaic system supplies depends decisively on its size, whereby the maximum electricity production is measured in kilowatt peak. Of course, the price of the system also depends on this – i.e. on the number of solar modules.

A single-family home with a family of three to four consumes about 4,000 kilowatt hours of electricity annually. Per kilowatt peak, the PV system produces up to 950 kilowatt hours of electricity. It follows that five PV modules would have to be installed to meet the family’s electricity needs. A PV system for a single-family home costs between about 14,000 and 18,000 euros. The price varies depending on the type of system.

The calculation must take into account the feed-in tariff for the share of the electricity that is fed into the public grid. In addition, there may be a subsidy for the purchase of an electricity storage unit. In view of the electricity price increases that are likely to be forthcoming and a system life of about 25 years, the investment pays off. 4

By the way: A lithium battery as electricity storage for photovoltaic systems costs around 1,800 euros per kilowatt hour. Lithium batteries are definitely preferable to lead batteries. The reasons are their technical disadvantages, such as the short service life and depth of discharge of lead batteries. In addition, they are only slightly cheaper than the lithium batteries. 5

When is a photovoltaic system worthwhile?

Whether the purchase of a photovoltaic system is worthwhile also depends on their personal goals and attitudes. Those who want to do something good for the environment can definitely answer this question with yes. However, the purchase is usually worthwhile from a purely economic point of view.

The reason for this is that the acquisition costs of photovoltaic systems have fallen. Another reason is that a large part of the solar power from the roof is consumed in the respective household. The photovoltaic system becomes more worthwhile the more solar power one consumes oneself as a producer. This is because electricity from the roof is much cheaper for private households than conventionally generated electricity from the grid, which has risen sharply in recent years due to taxes and levies.

With a classic photovoltaic system, around 30 percent of electricity consumption can be consumed directly by the customer. If you also install a battery storage system, you can even achieve around 70 percent.

Another advantage: with the electricity from the roof of your house, you become less dependent on the various electricity providers. The electricity from the photovoltaic system that is not consumed in your own household is fed into the public power grid. In return, owners of photovoltaic systems receive a corresponding feed-in tariff, which additionally increases the profitability of the system.

The prerequisite for a well-running photovoltaic system is that the roof surface is sufficiently large, stable and free of shadows. Furthermore, an orientation to the south and a roof pitch of 30 degrees is optimal. Note: Both orientation and slope are crucial for solar irradiation and thus the amount of electricity generated. Slopes greater than 60 and less than 25 degrees can reduce the output of the photovoltaic system by up to ten percent. 6

A photovoltaic system supplies electricity for the own household for the first time immediately after its commissioning. The installation of a photovoltaic system is particularly worthwhile for households that have a high own demand. 7

Does a photovoltaic system supply electricity even when the sky is overcast?

Since solar thermal and photovoltaic systems do not require direct sunlight to generate solar power, they operate even when the sky is overcast. However, when the weather is bad, the efficiency of the solar modules may be reduced.

Advantages and future of photovoltaic systems

In the field of photovoltaic and solar thermal energy, Germany is considered a role model in Europe. The Renewable Energy Sources Act (EEG), which came into force in 2000, as well as the feed-in tariff, have strongly promoted the expansion of photovoltaics in Germany. Although the level of feed-in tariffs has been falling since 2010, the acquisition of a photovoltaic system is still lucrative for system operators.

The special features of photovoltaics can be seen in the ecological advantages of this technology for electricity generation. For example, no exhaust gases, no radioactive radiation and no noise are produced during the operation of the corresponding systems. Only the production, transport and installation of photovoltaic modules and their disposal cause various environmental impacts. Nowadays, however, many manufacturers are already using green electricity to make the production of photovoltaic systems more environmentally friendly.1

Combinations of fuel cell heating systems and photovoltaic systems, for example, offer an interesting possibility in the context of the energy transition. In fuel cell technology , hydrogen fuel cells and direct methanol fuel cells generate heat and electricity mainly from natural gas. However, it is also possible to produce hydrogen by other means, such as electrolysis. If the electricity for this process comes from a photovoltaic system, the fuel cell heating also runs on renewable energy. 8


The use of photovoltaic systems on one’s own roof is not only environmentally friendly, but also economically advantageous in view of increased electricity prices. Plant operators benefit from the statutory feed-in tariff and subsidies for the purchase of the photovoltaic plant and the electricity storage system. A photovoltaic system is particularly worthwhile for private households if the majority of the electricity produced is consumed by the household itself.