Using a photovoltaic system, sunlight can be converted into electrical energy. This is based on the “photoelectric effect,” which was discovered in the 19th century but was only physically explained and applied in the 20th century. Its first application was space travel. Today, this technology can be found on many rooftops, providing residents with electricity from free solar energy. Photovoltaics are also suitable for reducing electricity costs for businesses and local governments, while simultaneously contributing to climate protection.
Photovoltaics are based on solar panels. These cells convert radiant energy into electrical energy. These cells can be connected together to form modules, which are then installed on roofs, facades, and open spaces. Electricity production can be broadly divided into two stages:
The efficiency of photovoltaics depends on the solar cell manufacturing technology. In the Vitovolt 300 from Viessmann, we distinguish between monocrystalline and polycrystalline cells. The following table shows the differences between these two types.
| Solar cell type | Description | Efficiency |
|---|---|---|
| Monocrystalline elements | Powerful elements made of pure single crystals | From 14 to more than 19 percent |
| Polycrystalline cells | Made from cast silicon blocks with crystals of varying orientations | from 12 to more than 17 percent |
Vitovolt 300 monocrystalline photovoltaic modules feature ultra-dark monocrystalline solar cells housed under a special low-iron, highly transparent glass backing. Combined with a black anodized frame and a black Tedlar film under the cells, this creates modules that offer the highest performance, maximum stability, and a modern design. These modules come with an extended 10-year product warranty and a performance guarantee of up to 25 years, guaranteeing at least 80 percent of the rated power. Both monocrystalline and polycrystalline Viessmann solar panels are suitable for use in residential, commercial, and institutional buildings.
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Request a consultation now →With energy costs constantly rising, photovoltaic systems help users save money and reduce their dependence on utility companies. The energy generated can be used for on-site use or exported to the public grid. Thanks to the statutory remuneration and the savings resulting from self-consumption, the investment pays for itself in just a few years. A photovoltaic system also increases property value.
By installing photovoltaic modules, users demonstrate their responsible attitude towards the environment and actively contribute to climate protection by reducing CO₂ emissions. 8.5 m2 of photovoltaic surface area is sufficient to meet the electricity needs of the average person.
Our high-quality photovoltaic modules ensure cost-effectiveness and a long service life. Comprehensive services—from design and sizing to delivery and maintenance—complete the photovoltaic module portfolio offered by Viessmann’s professional partners.
Viessmann photovoltaic technology offers you perfectly coordinated components consisting of photovoltaic modules, inverters and installation systems, as well as energy storage systems and heat pumps for increased self-consumption.
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Currently, there are two ways to use solar energy generated by a rooftop photovoltaic system: it can be either fully exported to the grid or partially or fully used on-site. In the past, exporting all solar energy to the grid was more financially attractive [in Germany]. However, the combination of declining feed-in tariffs and rising energy costs means that self-consumption is becoming increasingly attractive. The cost of electricity per kilowatt-hour is typically much higher than the feed-in tariff for the same kilowatt-hour of solar energy exported to the grid. Therefore, generated photovoltaic energy is increasingly used on-site or temporarily stored in batteries, and only surplus electricity is exported to the grid. The latter is regulated by the Renewable Energy Act (EEG) [in Germany]. According to this law, energy suppliers are required to purchase any electricity that is not self-consumed and integrate it into their grid.
Self-consumption offers financial advantages, as solar energy generated by photovoltaic systems is cheaper than grid-connected power. An optimized system design with perfectly matched components ensures high levels of self-consumption.
[1] Photovoltaic system [2] Photovoltaic inverter [3] Photovoltaic meter [4] Consumer [5] Heat pump meter [6] Heat pump [7] Consumption and export/generation meter [8] Public grid
The most efficient way to generate heat from electricity is to use a heat pump. With a heat pump, one kilowatt-hour of electricity can generate up to four kilowatt-hours of heat by harnessing free energy from the environment. If a heat pump is used to cover space heating and hot water supply, then inexpensive solar energy provides an affordable heating solution. Those planning to combine a photovoltaic system with a heat pump should choose eco-heating, which specifically optimizes self-consumption and can be adapted to the photovoltaic system’s generation scheme. For this purpose, Viessmann has developed a carefully coordinated system consisting of a photovoltaic system and a heat pump.
Provided a photovoltaic system is installed over a large enough area, it generates enough energy during the day to cover the needs of a single home. However, this unstable power supply is subject to various peaks in demand—for example, when a dishwasher, washing machine, or dryer is running. And, of course, the heat pump requires more energy for the circulation pump during the heating season.
The energy storage system balances these peaks, providing additional power from its batteries exactly when needed. Vitocharge VX3 is a next-generation energy storage system from Viessmann that increases the self-consumption and efficiency of the entire system. The system charges the energy storage system when your home doesn’t require electricity. This electricity is then used as needed. If the energy storage system is fully charged and no consumers are connected, the excess energy is exported to the grid and billed accordingly.
Next-generation PV energy storage:
High efficiency
Optimizes energy consumption
Outstanding, compact design
Reduces energy costs
Using this system, annual results demonstrate a high level of self-sufficiency for the KfW Efficiency House 40. In the example described, energy costs would be only €86 for heat and electricity—for the entire year!
[1] Photovoltaic modules
[2] Solar collectors
[3] Split air source heat pump
[4] Heat pump outdoor unit
[5] Mechanical ventilation unit
[6] Energy storage
To ensure the technology operates economically and reliably, several factors must be considered. In addition to high-quality products and execution, proper planning is also crucial. Anyone considering purchasing a photovoltaic system should first check with one of our partners to ensure all necessary requirements are met.
The matrix shows an illustration of a suitable package for the existing roof area. The intersection of the roof height (Dachhöhe) and the roof width (Dachbreite) yields the corresponding package (shown in the figure).
South-facing, shade-free roofs are ideal for photovoltaics. At a slope of 30 to 40 degrees, the sun’s rays strike the Vitovolt 300 solar modules at the right angle, allowing them to generate a significant amount of electricity. If the slope is favorable but the orientation is shifted to the east or west, output will be on average 20 percent lower. To compensate for these losses, a more powerful photovoltaic system must be purchased. The Viessmann surface matrix shows the power output possible on your roof. Interested parties can enter the width and height of the roof surface to quickly see how many modules can be installed.
Solar modules add weight to the roof. A structural engineer will quickly determine whether the roof can support the equipment. If repairs to the roof structure are necessary, homeowners can apply for financing through a loan from the Kreditanstalt für Wiederaufbau (KfW) [or the local equivalent].
Viessmann’s Vitovolt 300 packages make choosing the right photovoltaic system particularly simple, based on just a few questions. The system a homeowner needs depends on the number of people living in the home and the intended use of the technology. For example, more solar modules will be needed if the photovoltaic system will supply electricity to a heat pump. In contrast, fewer modules are needed when combined with a fuel cell. This is because, in addition to heat, the fuel cell also produces electricity for its own consumption. The following table provides approximate standard values.
| People in the household | Average annual electricity consumption | Photovoltaics only | Photovoltaics and heat pump | Photovoltaics and fuel cells |
|---|---|---|---|---|
| 2 | up to approximately 3000 kW/h | XS | S | XS |
| 3 | up to approximately 3500 kWh | S | M | XS |
| 4 | up to approximately 4500 kWh | M | L | XS |
| 5 | up to 6000 kWh | L | XL | S |
| from 5 | up to 6500 kWh | XL | XXL | S |
| from 5 | from 6500 kWh | XXL | XXL | S |
What roof shape is suitable for a photovoltaic system, and is regular cleaning necessary? We answer these and other questions below.
Viessmann photovoltaic modules can be quickly and safely installed on both pitched roofs (with slopes from 10 to 60 degrees) and flat roofs. The only important factor is that the roof can reliably support the weight of the modules, even in adverse conditions.
In practice, about 30 percent of a home’s total energy needs can be met with photovoltaics. A higher level of self-consumption can be achieved with energy storage devices such as Vitocharge. A share of 70-80 percent is quite realistic. Using an electric car or e-bike also makes sense.
If you want to commission a photovoltaic system and receive a preferential tariff, there are several things you need to consider.
1. You must submit a grid connection application (a grid connection request) to your local energy supplier. You can find out who your local electricity supplier is by looking at your most recent electricity bill. If there’s no name there, only a 13-digit code, enter it on this website .
2. A grid compatibility check is performed by the utility company. As part of this check, the utility company verifies whether the local power grid is rated for the planned PV system. Typically, the first two steps can be completed with the help of your solar engineer.
3. Two weeks before commissioning, you must register your PV system with the German Federal Grid Agency (BNA). Specifically, the system must be registered in the German Federal Grid Agency’s Basic Market Data Register. Registration is crucial and forms the basis for calculating the electricity tariff. In other words: no registration = no reward!
4. After commissioning, you will receive a “system passport.” This includes all technical data for the system, all installation documents, and the commissioning certificate. The system passport is comparable to a car’s logbook and is necessary, among other things, for legal protection.
If you’ve commissioned a photovoltaic system and export some of the electricity it produces to the local grid, you’ll be required to pay taxes. The taxes you’ll pay depend, in part, on the size of your system. In general, a photovoltaic system may be subject to the following taxes:
Most mid-sized systems achieve such low productivity that their operators do not need to pay sales tax. However, VAT is only payable if more than half of the electricity generated is fed into the grid. System operators are only required to pay land transfer tax in the following cases:
In the income tax return, you only need to report profit (the preferential rate minus current expenses, including maintenance and repair costs, insurance, etc.). To clarify exactly what needs to be included in the return, it’s best to consult a tax advisor.
Modern solar modules are virtually self-cleaning due to their tilt and extremely smooth surface. Wind and rain also remove most dust. Cleaning is still recommended in the case of snow or coarser dirt, such as fallen branches. It’s best to hire a specialized company for this job, as working at height poses a certain risk. Furthermore, improper cleaning can void the warranty.
If you feed electricity into the public grid, you’ll receive payment from the utility for 20 years. After this period, the preferential tariff expires. However, you can still “offer” your self-generated electricity on the market. However, depending on the quantity, this may be difficult to find. Alternatively, you can use all the electricity on-site. Another option is to upgrade the system. You replace the old modules with new, more powerful ones. The existing mounting frame can usually be used.
Viessmann customers, suppliers, and guests now have the opportunity to charge their electric vehicles, ready for their next journey. Six charging stations have been installed in front of the information center at the Allendorf plant. 100 percent of the electricity is generated by Viessmann photovoltaic modules mounted on the roof of the charging station.
A BMW i3, painted a vibrant Vitaro orange, is also charging here. It complements Allendorf’s fleet and is used for travel around the property.
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