Everything You Need to Know About Photovoltaics

Learn what space travel has to do with PV systems, how they function and how you successfully plan your very own system. If you want to know something specific, e.g. about mounting systems, the navigation on the left will help you find it quickly.

What does a photovoltaic system do?

A PV system converts incident sunlight into electricity. Its main components are solar modules that are made from solar cells that are connected in series or parallel. These solar modules convert sunlight into usable energy. Besides photovoltaic systems, solar thermal systems also convert sunlight into a usable power source, which is heat instead of electricity. This can then be used for heating or hot water supply.

How does a solar cell work?

The central components of a photovoltaic system are solar panels and their solar cells. The cells consist of semiconductor material. When the tiny photon particles of sunlight hit the material, they trigger current flow. In this way, the energy of the sunlight is converted into electrical energy, or more precisely: into electricity, as you use it every day. This process is called the photoelectric process.

The output current is direct current (DC). It can either be consumed directly, stored in a battery or fed into the public power grid. However, because most electrical devices and the power grid operate on alternating current (AC), the DC must be converted into AC with so-called inverters. Since the sun is always shining – regardless of it being used as a power source or not – solar power counts towards renewable energies (also known as regenerative energies).

History: From outer space to the pocket calculator to your roof

Outer space is where the first solar cells were used. As early as the 1950s, they powered satellites. Those solar cells had an efficiency of 10% and were made out of silicon (silicium). On earth, they were first used in photometers, a built-in camera device. Until the 1970s, however, solar cells were mainly used in space technology.

Rethinking energy generation

Due to the severe oil crisis in 1973-74 and the tragic accidents with nuclear power reactors in Harrisburg and Chernobyl, people started to rethink how electricity was generated. For the first time, renewable energies were brought up and the use of solar cells on earth was suddenly up for discussion. This led to an increased investment in solar cell research and development around the world in the 1980s. Through these efforts, the efficiency of silicon solar cells has almost doubled today. While the first solar cells were still used for pocket calculators and other small devices

What you need: Components of the photovoltaic system

  • Mounting system
  • Solar Panels
  • Solar Inverters
  • Power Storage
  • Cables & Connectors

  • Bidirectional Meters

Photovoltaic systems and their use

A solar roof for more independence from the grid

A distinction is made between on-roof systems and in-roof systems. In on-roof systems, the solar modules are mounted on the roof of the house with the help of a mounting frame. The angle of inclination can also be easily optimized for pitched roofs. It is the simplest and most common way to install a PV system. Mounting frames are usually specifically designed for different roof types such as sheet metal roofs, tiled roofs, slate roofs and roofs made of corrugated sheet metal. An additional advantage is natural ventilation of modules through the gap between roof and panel. We advise you to choose a truly weather-proof mounting system to avoid unpleasant surprises.

Flat roofs usually have only a small inclination or none at all. Therefore, the solar modules should be angled at least 6° through the mounting system. A tilt of up to 13° is possible and recommended.

With an in-roof system, solar modules replace the standard roof tiles. This is more pleasing to the eye and weatherproofs the system at the same time. The downside is that installing them is more complex and therefore more expensive. The cooling of in-roof solar modules is also more complex than with an on-roof system and reduces the efficiency by about 0.5%. In-roof systems are only suitable for tiled roofs that are designed as pitched roofs with a relatively large inclination, as otherwise the efficiency is severely impaired. This solution is not possible for sheet metal or bitumen roofs.

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Mini systems for carport, garage, facade (and satellites)

A mini PV system requires only one to two square meters of space. This makes it ideal for carports, the facade or a summer house. You can produce up to 600 W of electrical power with them, depending on the solar modules used. The only technical requirement is that the respective roof or facade must be stable enough to support the weight of the solar modules plus mounting system.

You can use the electricity produced to charge your electric car, hybrid plug-in or similar. Of course, you can also use the electricity in your household and thus reduce your electricity bill. However, you usually cannot produce all the electricity required for a household with a mini PV system. Before planning your PV system, you should also find out if your local building authority imposes any restrictions.

Ground-mounted PV systems (solar parks)

For installing a PV system, you don’t need a roof or even a house. As a PV fan you surely know the impressive pictures of huge solar farms or “parks”. Here, too, mounting systems are in use to keep the modules in place. There are two fundamentally different mounting systems for solar farms: fixed mounting and tracking systems.

Free-land PV systems

For fixed mounting systems a steel or aluminum frame is screwed onto concrete blocks or anchored into the ground. The inclination and orientation of the modules cannot be changed after installation.

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The fixed ground-mounted system has several advantages compared to a roof-mounted system:

  • There is usually more space available.
  • The orientation can be chosen freely and is not determined by a roof.
  • This also means that the inclination can be adjusted almost at will.
  • More space also means more modules. Here it is also worthwhile using modules with lower efficiency, which are cheaper to buy.

Tracking system

With tracking systems, the modules track the orientation of the sun. Tracking systems are available with single-axis and two-axis tracking. With single-axis tracking, the orientation of the modules changes either horizontally or vertically depending on the position of the sun. Horizontal tracking follows the position of the sun from east to west. Vertical tracking aligns the modules to the south and rotates – depending on the height of the sun’s position – over the horizon. The two-axis tracking is a combination of horizontal and vertical tracking.

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Advantages of the tracking system:

  • The power yield of the PV system increases significantly compared to fixed mounting.
  • In Central Europe alone, the increase in power yield is 20% with single-axis tracking and 30% with two-axis tracking.

Disadvantages of the tracking system:

  • Higher investment costs.
  • The system requires more maintenance. This increases operating costs.
  • The tracking system requires electricity.

floating PV system

A special form of installation is the floating PV system, for which the solar modules are mounted on flotation devices usually made from plastic. The investment costs are 20% to 25% higher than those of a conventional installation on solid ground.

PV systems connected to the public grid

Grid-connected systems bear their name because they are connected to the public power grid. The majority of all installed PV systems are grid-connected systems.

Non-coupled off-grid systems

There are also PV systems that are not connected to the public grid. Since this also means that there is no possibility of feeding into the public grid, these systems are usually connected to a battery.

How you plan a photovoltaic system

Usage requirements for PV systems

Before you start planning a photovoltaic system, you should check the requirements:

  • Do you need a building permit for the plant? Find out by asking the local building authority.
  • Is the roof stable enough for a PV system?
  • Is the sunlight sufficient to operate the system efficiently?
  • What about funding? Are there subsidies you can take advantage of? You can find various possibilities via a search engine.

Which PV system is the right one?

First of all, you have to decide between a roof-mounted system or a ground-mounted system. With a roof-mounted system, the following questions arise:

  • In which cardinal direction is the roof aligned?
  • Is it a pitched or a flat roof?
  • Is the roof area shaded by trees or surrounding buildings?

A south-facing pitched roof with a pitch of approximately 30° would be ideal. But even if your roof has an inclination between 10°-60° and is oriented to the southeast or southwest, it is still very much suitable for a PV system. There is only a slightly lower yield. Care should be taken when felling large trees to prevent shading. Find out beforehand whether it is permitted and what compensation measures you may have to take.

Use a PV software for effective planning

With a PV planning software, photovoltaic systems can be custom tailored to every roof, modules, and inverters used, while at the same time selecting the best possible variant of PV mounting system. Ideally, the PV software offers you the following options: planning of the inverter design, yield calculation with optimized shading areas and string planning.

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How many square meters of PV system do you need?

Depending on whether you want to cover part or all of your own needs, the number of modules you use will vary. If you are now wondering how many modules need to be installed to cover your energy needs and whether an area of that size is available, the following information will help you:

  1. If available, take your electricity bills for the past five years. Add up the total consumption figures and divide the result by five. You have now calculated your average electricity consumption for the period. Let’s assume that this would be 6,000 kWh/a.
  2. To fully cover your consumption, the PV system should ideally produce 125% of your calculated average. In our example this would be 125% x 6,000 kWh/a = 7,500 kWh/a.
  3. Now read the regional energy yield from the map of your region.
  4. Probably your roof is not facing south at an angle of 30°. It is helpful if you now take a deviation amount from a corresponding table. Let’s assume that your roof would be oriented 40° to southwest with a 20° roof pitch. The table then shows a deviation value of 95%.
  5. Now we calculate the personal energy yield as: Regional energy yield x deviation value = 1,000 kWh/m² x 95% = 950 kWh/m².
  6. Next, we calculate the required size of the PV system: (7,50
  7. /(95
  8. = 7.9 Kwp.
  9. A typical solar module measures 1.67 m x 1.00 m and delivers 300 Wp = 0.3 kWp output. To achieve 7.9 kWp, 7.9 kWp / 0.3 kWp = 27 modules are required. These need an area of 27 X 1.67 m² = 45 m².

Leave mounting and installation to professionals

In any case, you should leave mounting and installation of your new PV system to a specialist company. In general, we advise against working as a layman, as working with electronics is dangerous and can endanger both you and others. In addition, if the installation is not carried out professionally, the warranty for the components of the PV system will usually void.

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How to operate a photovoltaic system

Ensure high yield by keeping modules clean

A PV system is exposed to all kinds of environmental influences 24/7. This means that they get grungy by dust, bird droppings, falling leaves, plant pollen, etc. Especially at the touch points between frame and glass dirt settles and is not easily removed even by rain and snow. Even moss or lichens can be found.

Meaning: The PV system must be cleaned on a regular basis. You should only do this yourself if all parts of the system can be reached by telescopic poles without climbing. Otherwise, you should leave this work to companies that specialize in cleaning PV systems. The costs for this vary from region to region.

For cleaning, we recommend lime-free water, a gentle cleaning agent and a cloth or sponge – without scratchy parts.

Ensure proper function through maintenance and repair

The best way to do this is to conclude a maintenance contract with the company that installed your system. They installed it; they know how to handle it. Maintenance includes visual inspection of the solar modules as well as checking electrical connections and inverters.

Be prepared for the next hailstorm with insurance

Since your PV system is constantly exposed to environmental influences, insurance is worth considering. Damage caused by hail, heavy rain or lightning can happen quickly. Therefore, an appropriate insurance for the PV system makes sense.

A good insurance should cover the following risks:

  • Fire
  • Storm
  • Hail
  • Snow pressure
  • Overvoltage
  • Animal bites
  • Theft
  • gross fault

Know whether tax payments are due

If you do not consume all the electricity produced by the PV system yourself, you become an entrepreneur for tax purposes in some countries. The feed-in tariff is the price per kWh that the energy company pays you for the electricity fed into the public grid.

If you do not do so, you must pay VAT on both the electricity fed into the grid and on the electricity, you consume yourself.

Feeding into the public grid

In order to feed your surplus electricity into the public grid, a contract with the public energy provider is necessary. These companies usually also rent you an export meter or a bidirectional electricity meter. The more electricity you consume yourself, the more interesting the PV system is from an economic point of view. The feed-in tariff is significantly lower than the price you have to pay for the electricity you use. Therefore, it is usually worthwhile to purchase an electricity storage unit to bridge periods with less solar radiation.

How long does it take for a PV system to pay for itself?

According to the Frauenhofer ISE, a PV system generates a return on equity of approximately 5%. But every system is different and it also depends on usage, region, etc. When using battery storage and an intelligent control system, most own consumption of electricity is usually achieved.

Factors that influence time to amortization:

  • Acquisition costs
  • expected power yield
  • Own consumption share
  • feed-in tariff
  • electricity price
  • financing
  • tax payable

A photovoltaic system usually pays for itself after 9 to 12 years. With a service life of at least 20 years, this leaves several profitable years.