The big guide to photovoltaics – everything you need to know about renewable energy

The topic of photovoltaics and solar power is very important, especially in the area of the energy transition. The possibility for private individuals to generate electricity and heat through solar energy is a big step in the field of renewable energies. The technology continues to advance, which is why it is all the more important to know about the topic. Especially for builders or property owners, this is an exciting area. But what exactly is photovoltaics and what should you know about it?

Photovoltaics – the prerequisites for your property

When planning a photovoltaic system, the first step is to find a suitable area for the system. A wide variety of options can be considered here. The site conditions must also allow the plant to be operated economically. The legal situation should also not be forgotten, as there are also a number of things to consider here. Builders and property owners who are interested in switching to renewable energies should deal with the topic in detail.

Photovoltaics – the installation options for the modules

When planning a photovoltaic system, the first question is usually where the system should be placed. Roofs are the most suitable, because these areas are available anyway and are usually not used for other purposes. In addition, they face the sky and the shading is usually rather low due to the positive elevation. But there are also differences in the roofs. Which roof is most suitable for the connection of the photovoltaic system?

Installation options on a pitched roof

The widespread pitched roofs offer ideal conditions for the installation of a photovoltaic system. The modules can simply be mounted parallel to the roofing. The existing roof covering is completely retained and continues to take on the function of weather and heat protection. A large-scale installation of photovoltaic modules leads to a reduction in the thermal load on the attic. Alternatively, there is also an in-roof installation, in which the photovoltaic modules are flush with the roof covering and even partially replace it.

For all builders of new buildings there is the possibility to install photovoltaic modules as a substitute for an ordinary roof. In addition to the production of electricity, these take on the function of weather protection and thus replace the usual roof covering.

Installation options on a flat roof

An ordinary flat roof also offers an ideal installation option for photovoltaic systems. Unlike pitched roofs, the inclination can be freely determined and does not have to be oriented to the inclination of the roof. The optimal alignment is simple, allowing productivity and efficiency to reach their maximum. Here, too, the installation does not negatively affect the existing roof structure.

Installation options for building-integrated photovoltaic systems

However, photovoltaic systems do not necessarily have to be installed on the roof, because there are other alternatives to use the renewable energy. One of these alternatives is the integration of the modules into the facade. For this purpose, facade components can be used, but canopies or similar are also possible. This alternative is also called building integrated photovoltaics (BIPV).

Photovoltaics – the individual site conditions for your property

Once the area for the photovoltaic system has been found, the question now arises as to whether the site conditions allow the system to be operated economically. For this, many factors must be taken into account that influence the yield and thus the economic efficiency of the system. This makes it possible to check whether the investment in a photovoltaic system is really worthwhile.

The influence of global radiation

Global radiation is one of these factors, because it indicates how much radiation falls on one square meter of horizontal receiving surface within a period of time (usually one year). It is therefore not a constant, but depends on the time of day and year as well as the location and the weather. In general, global radiation is higher in southern latitudes than in northern latitudes and greater in summer than in winter. Clouds cause the global radiation to have only a fraction of the values as in clear skies. For the planning of photovoltaic systems, this means that the distribution of global radiation in Germany varies depending on the location. In northern Germany, the average global radiation is therefore around 900-1,000 kWh/m2year, while in southern Germany it is around 1,200 kWh/m2year. A difference of about 20 % only within Germany. When planning a photovoltaic system, the global radiation at the individual location must therefore be taken into account in order to be able to estimate the efficiency of the system.

The correct roof orientation and pitch

The roof pitch and roof orientation are important factors that influence the economic efficiency of a photovoltaic system. In a new building, the roof can be optimally aligned, but in existing properties, the existing conditions must be used. Here, both the compass direction and the angle of the roof are important in order to ensure the greatest possible energy generation. In the case of flat roofs, as already described above, the orientation and inclination can be completely self-determined and thus individually adapted to the correct values. Depending on the location, a different orientation is the best, as this depends individually on the area. In general, the orientation to the south is the most optimal in most cases. The angle of inclination of 30-35 degrees is usually the most effective in the German wide, but this must also be determined individually depending on the object.

Planning the individual shading

The last location factor that influences the economic efficiency of the photovoltaic system is shading. This factor is most often underestimated, because even a little shade can significantly affect the performance of the photovoltaic system. This includes especially shadows caused by trees or nearby houses, but also small shadows from chimneys or antennas can have a negative effect on the performance. In the case of larger shadows, the system must be planned precisely. For smaller permanent shadows, it makes sense to install the system in such a way that it is not installed in certain places on the roof. A small permanent shadow can reduce the performance of the entire string and thus have a major impact on the economic efficiency. When planning, you should therefore pay close attention to the individual shadows on your property and include them in the planning to avoid performance reductions.

Photovoltaics – the legal aspects

The installation of a photovoltaic system always brings with it legal aspects, because here too there are legal rules and regulations that both builders and property owners must follow. What does the law stipulate, what regulations are there and what must owners of a photovoltaic system observe?

Building permit

Photovoltaic systems must generally comply with building laws. However, these depend on the respective federal state, because building law is a matter for the federal states. Depending on the federal state, there are therefore slightly different regulations for the installation of the modules. However, most federal states do not require a building permit for photovoltaic systems that are installed on the roofs of buildings. In this case, the building owner is responsible for ensuring that the system complies with the building code. The installation is therefore not subject to any additional checks by the authorities. However, systems that are to be installed on open spaces require a building permit in most federal states. In this case, the system must not exceed a specified size, which is usually nine meters long and three meters high. Systems that are to be erected on listed buildings normally also require a building permit. Find out individually for your federal state which legal principles you are subject to when building a photovoltaic system.

Photovoltaics – the individual planning of your plant

The planning of a photovoltaic system requires many considerations. A good system depends on many factors and should be individually tailored to you. Important aspects, such as the energy requirement or the size of the system, should be discussed in advance and well thought through. Which other factors are important and what should you never forget when planning your system?

Estimate and calculate the correct energy demand and dimensioning

At the beginning of the planning there is always the question of how big the system has to be, because the financial conditions generally depend on this. First of all, you need to find out how high your average energy consumption is. The photovoltaic system is then adapted exactly to your individual energy consumption. This is quite easy to find out by looking at your last electricity bill. Based on this information, further parameters can be determined, which will later lead to the required size of the system. For the individual calculation of your electricity consumption and the resulting minimum size of the required system, use our solar panel calculator.

The registration of the photovoltaic system with the authorities

If a grid-connected photovoltaic system is installed, it must be registered with both the Federal Network Agency (BNetzA) and the relevant grid operator.

Registration with the Federal Network Agency

The Renewable Energies Act (EEG) stipulates that operators of a photovoltaic system must register it with the Federal Network Agency. This applies both to own use of the electricity produced and to the energy that is directly marketed. Extensions to existing photovoltaic systems must also be registered. The registration of new or extended plants is done via the portal of the Federal Network Agency on the Internet and since 2011 this is also the only way to register photovoltaic plants. To register the system with the Federal Network Agency, you need the following data:

  • Name and address of the operator of the photovoltaic system
  • Location of the plant
  • Nominal power of the plant in kWp
  • E-mail address
  • The day on which the plant is put into operation

Register the plant before commissioning or on the same day of commissioning at the latest. Two weeks’ lead time is quite sufficient to notify the authorities of the installation.

Tip: The registration of your photovoltaic system is urgently necessary. If a system is not registered in time, the owner has no claim to the feed-in tariff!

Registration with the network operator

Grid-connected systems feed surplus electricity produced into the public grid. The Renewable Energies Act (EEG) provides for a feed-in tariff of between 10 and 13 cents per kilowatt hour for this feed-in. Before commissioning the system, the operator must therefore notify the grid operator of the photovoltaic system and submit an application for grid connection. This is a legal obligation that the operator must observe. In the case of plants that are not connected to the grid, the grid operator does not have to be informed.

Find the right offer for you

Once the decision for a photovoltaic system has been made, you only have to find the right company to accompany you on the way of planning, delivery, mounting and commissioning. For this, sufficient research on the Internet, in newspapers or in the surrounding area is a good idea, but even if you find someone, you must first check the conditions and qualifications.

Recognizing the qualifications of a good solar installer

Most system owners don’t have the expertise needed to know whether or not a solar contractor is a professional in their field. Nevertheless, in order for you to know some facts that a company should offer you when installing your system, here is a list of what a professional solar contractor should adhere to.

  • The company responds flexibly to your wishes with regard to the modules and does not insist on a particular product.
  • The company will look at your roof and house in person before providing a quote
  • The company offers you only one offer, in which all individual positions are listed exactly and no questions remain open for you.
  • The company does not put you under time pressure and takes enough time to answer all your questions in detail.
  • The company shall disclose to you the wiring diagrams and provide detailed information on registration, commissioning and the deposit of permits
  • The company makes realistic yield forecasts for the plant, which roughly correspond to what you have calculated yourself in advance.

Photovoltaics – the economics of solar cells

Economic efficiency is generally determined by comparing revenues and savings. This is also the case with photovoltaic systems, where a distinction is made between acquisition and operating costs in order to determine economic viability. While prices for photovoltaic systems have dropped significantly in recent years, feed-in tariffs have also become considerably lower. But what costs do you expect to incur when purchasing a photovoltaic system and what costs will you face in the coming years?

The acquisition costs for a photovoltaic system

The acquisition costs generally consist of the costs required for the installation of the system. This includes the solar modules, the inverter, the wiring and the installation itself. For builders and property owners, this aspect is probably the most important, as the level of investment required will, in case of doubt, determine whether a system is installed or not.

Costs for the solar modules

Solar modules themselves have lost enormous costs in recent years. This is due on the one hand to strong competition from low-cost Chinese suppliers and on the other hand to positive economies of scale. In general, this means that solar modules become cheaper the more of them are produced. Costs are usually compared in euros per watt peak. At the beginning of 2018, the costs were 45 – 90 cents per watt peak, depending on which model and which supplier was chosen.

Costs for the inverter

The costs for the inverter should not be underestimated. They usually account for 15 % of the investment costs. Depending on the conditions of the system and the external influencing factors, more than one inverter may be required. The costs for the inverter vary depending on the power size. For a kW inverter you can calculate with about 200 € net. Smaller inverters usually cost more than large ones, as the manufacturing costs are higher. For a 5 kW inverter a price of about 1000 € can be calculated. If your system requires two inverters, the price will double.

Costs for the cabling

The cabling also makes up a large part of the investment. The higher the cross-section of solar cables, the higher the prices. However, a high cross-section is necessary to prevent losses. The price of solar cables ranges from 1 to 5 euros for the quantity purchased, the cross-section and the cable material, with the costs of the connection cables for the inverters and the charge controllers being added to this. This entails further costs of 20 to 50 euros, depending on the supplier and quality.

Installation costs

With the costs for the assembly not only the costs for the craftsmen come on you, but also the costs for the assembly system. These are quite different depending on which system you have chosen. The prices vary depending on the quality and features, such as the snow and wind load, but also on the model of the system. On average, you can expect costs for the mounting system between 100 and 150 euros per kWp and with installation costs for the substructure with another 100 euros per kWp. It is difficult to make a blanket statement about prices, as they can vary greatly and depend on many factors, such as the individual property, the conditions, the quality and the exact products.

The operating costs for a photovoltaic system

After the investment in a photovoltaic system, the owner will still incur further costs, for example to maintain the system. These costs must also be taken into account when analysing the profitability, as they can amount to around 1% of the purchase costs per year. But what costs do owners of a photovoltaic system really face and what should they expect?

Costs for the inverter

Even though the inverter is one of the initial costs, it is not as durable as the solar modules themselves. The inverter must therefore be changed and replaced from time to time. Since the inverter is not the cheapest investment, reserves should be formed for this case. Depending on which grid operator the photovoltaic system is registered with, minimum fees of up to 10 euros per month are charged. The inverter requires electricity from the public grid for control, data logger, analogue monitoring and the like.

Maintenance costs

Of course, the system must be maintained to avoid failures and errors. Some companies offer maintenance contracts, where a contribution of about 150 euros per year is incurred and the maintenance is taken over. Such an investment is well worth it, since in the event of a failure, electricity can neither be generated nor fed into the grid. Depending on the plant, such a contract can be cheaper than charging for each maintenance job individually. In particular, such contracts are worthwhile for large plants that require more frequent maintenance.

Cleaning costs

The costs for cleaning are in comparison significantly lower than the maintenance of the system. Soiling caused by leaves, pollen, dust or the like is usually cleaned again with a rain shower. However, permanent soiling can lead to a loss of yield. Professional cleaning of the modules is normally only necessary every few years. In areas with high pollution, for example due to heavy traffic, the system should be cleaned more frequently. The average cost of professional cleaning is around 2.50 euros per square metre.

Insurance costs

Insuring the photovoltaic system can make sense for many owners. Depending on the size of the system, liability insurance and all-risk insurance can protect against failures in the feed-in tariff as well as against high repair costs and liability cases. The cost of insurance can be added annually to the operating costs, but is relatively moderate in comparison. Prices of around 50 euros per year can be incurred by owners. Depending on the circumstances and the external environment, insurance, cleaning and maintenance make more or less sense, this depends individually on your property.

Photovoltaics – the promotion & financing for builders and property owners

A photovoltaic system is a large investment that requires good financing. Although interested parties are lured with the feed-in tariff, these have become less and less in recent years. To successfully finance the photovoltaic system, however, some options are still open.

The feed-in tariff for photovoltaic owners

The feed-in tariff is set out in the Renewable Energies Act. The feed-in tariff is paid to those who feed surplus energy produced by the photovoltaic system into the public grid. The amount of this remuneration depends on the location factors and is determined by the legislator.

The Renewable Energies Act (EEG)

The Renewable Energies Act (EEG) came into force on 01 April 2000. It regulates the tariffs for electricity from various sources of renewable energy. The aim of the law is to promote renewable energies, such as water and wind power, but also solar energy, biomass and landfill, sewage and mine gas. The use of environmentally harmful energy sources is to be avoided and technology in the field of regenerative energies is to be promoted. In the course of the EEG, regulations on the feed-in tariff were also made in order to make the option of having one’s own solar system on the roof more attractive for builders and property owners.

Self-consumption remuneration

It was not until 2009 that the self-consumption tariff was introduced. Since then, the entire electricity produced no longer has to be fed into the public grid and compensation is paid for the consumption of solar electricity. However, this remuneration is much lower than the feed-in tariff.

The aim of the remuneration for self-consumption

The aim of the self-consumption remuneration was, in the first sense, to save costs for grid expansion and to save costs for the remuneration of solar electricity. However, owners of photovoltaic systems also derive an advantage here. They can use the self-produced solar electricity directly without having to feed it into the public grid beforehand. The owners therefore save money, as they are no longer dependent on the public grid and get the self-consumption remuneration on top, so to speak.

Photovoltaics – solar modules and how they work

The most important component of a photovoltaic system are the solar modules. Depending on the size of the modules, solar cells are connected together here. A photovoltaic system combines several solar modules and connects them to so-called strings. The entire unit of the strings then results in the solar generator. But how exactly does a solar cell work and how is solar energy converted into electricity?

The different types of solar cells

Solar cells convert radiation energy into direct current. The phenomenon that takes place in solar cells can be explained by the physical photoelectric effect. Solar cells consist of a negative electrode, an n- and a p-doped silicon, a boundary layer and a positive electrode. The electric field created between the n- and p-layer ensures the flow of current in a closed circuit.

Polycrystalline solar cells

In polycrystalline solar cells, the semiconductor material is silicon. This is melted and doped and cast into blocks using various casting processes. The silicon becomes solid and is called ingots when solidified. After the ingot is cut into slices, the original silicon is called wafers, which are coated with an anti-reflective layer. These polycrystalline solar cells have a lower efficiency than monocrystalline solar cells, but they are cheaper to produce.

Monocrystalline solar cells

Monocrystalline solar cells also use silicon as a semiconductor material, but the manufacturing process is different from that of polycrystalline solar cells. Due to the different manufacturing process, the production is more expensive, but the energy consumption and the efficiency is very high. During production, other crystals are formed here, which creates the difference between the two solar cells.

Thin-film cells

Thin-film cells have a completely different adjustment method than mono- or polycrystalline solar cells. The semiconductor is coated with a carrier material in these solar cells, which means that this method uses very little raw material and is very easy to manufacture. Which semi-material is used, is here in a large framework. In addition to silicon, gallium arsenide, copper indium selenide, cadmium telluride or dyes can also be used as coatings. However, the efficiency of these solar cells is lower than that of crystalline cells, but they are cheap and easy to produce.