Photovoltaics

The first step is to take a close look at the structure and load-bearing capacity of the roof. Not every roof is equally suitable for supporting the photovoltaic modules and at the same time ensuring sufficient solar radiation for a sensible system size. The load-bearing capacity is determined by a structural engineer or a specialized roofer/solar installer. The general solar irradiation can be calculated using free tools such as PVGIS and the possible yields for a specific roof orientation can be calculated using many different online tools. If there are sources of shade, such as roof structures (chimneys, bay windows, dormers, etc.) or trees and houses in the neighborhood, then you are well advised to hire a specialist to calculate the appropriate size and placement of the system.

The second step is to select the right mounting systems. A distinction is made here between roof shapes.

In contrast to tiled roofs, it is not possible to maintain the upper roof layer without drilling holes in sheet metal and bitumen roofs. For this reason, subsequent sealing is used, for example with self-sealing screws, patches/tapes, liquid bitumen or liquid plastic. Hanger bolts are often used here to ensure under-ventilation, onto which aluminum profiles are then mounted. In the case of folded and some trapezoidal sheets, installation can also be carried out on the vertical parts. Leading suppliers of assembly systems have already developed solutions here. Appropriate systems are also available for barrel roofs.

In most cases of roof installation, a roof penetration is necessary in the end, because the cables for the connection to the house electrics usually have to be routed through the roof. These penetrations must also be professionally sealed to prevent leaks and water damage. Special lead-through elements, which differ depending on the type of roof, ensure a watertight connection.

The balcony or façade is usually the most obvious place to install solar modules to generate your own energy. Due to the mostly vertical installation, slightly less yield can be expected overall than on the roof, but even such systems can pay for themselves financially after a few years. This is also due to the fact that in winter they deliver slightly higher yields than roof systems, as the sun is lower and therefore has a better angle of incidence on vertical modules. Sometimes systems with an elevation angle are also available, but due to the possible stronger wind load, you should pay close attention to the information on the wind zone, mounting height and terrain category or ask for it.

For façade mounting, systems with aluminum rails are usually used, which are screwed to the façade and on which the modules are then fixed with module clamps or linear systems. If a building is already planned with solar elements during construction, this is referred to as “BIPV” (Building integrated PV). In this case, special building law requirements for the solar modules must be observed.

There are a number of different systems that can be used for mounting on balconies, from brackets that enclose the handrail to mounting rails that can be clamped or screwed. If balconies need to be newly built or renovated, parapet elements with integrated solar modules can also be used. These are usually designed in a semi-transparent, frameless glass-glass version and are particularly aesthetically pleasing.

Note for tenants/property owners:
Attachment to a balcony or façade impairs the appearance of the façade. In addition, the installation of solar modules often requires structural changes such as drilling holes in the parapet/building envelope or similar. In this case, according to the current legal situation, the consent of the landlord or the community of owners must be obtained in advance. However, this does not apply, for example, to a solar module located on balcony areas or roof terraces that cannot be seen.
In addition, the legal situation is currently changing. A “privileging” of certain forms of photovoltaics in tenancy and residential property law is to be expected in the near future, which will include a fundamental approval of such projects. Nevertheless, landlords or owners’ associations can still specify how the project is to be implemented. It is still unclear how far these requirements can go.

A more recent development is solar fencing, which is available either as a complete system or as a retrofit kit for existing fences. The use of bifacial modules can be worthwhile here, especially for a fence that runs from north(west/east)den to south(west/east)en. These also generate energy on the back, which can be used for the morning/evening hours.

If you buy a PV system yourself, it is currently available for well under € 1,000.00 per kWp. Prices for storage systems are falling continuously and are often already well below € 1,000.00 per kWh. Therefore, it is primarily the costs for labor and equipment such as lifting platforms that drive up the overall price. It is therefore worth doing it yourself and obtaining comparative offers.

Modern LiFePo4 batteries have a service life of around 15-20 years. If these have to be replaced, this may reduce the return considerably. However, it is still unclear how storage costs will change over the coming decades. A further drastic reduction is very likely but of course never certain.

A purely south-facing orientation produces a higher yield, but an east-west orientation can increase the proportion of self-consumption, as there is no midday peak and generation is distributed more evenly throughout the day.

The optimum elevation for a south-facing orientation is between 20° and 40°, depending on the latitude (steeper in the north, flatter in the south). Elevation systems often tend to be at 20°, as this also keeps the area exposed to the wind small and thus the necessary ballasting lower.

Self-consumption of solar power increases the return on investment, as one kilowatt hour of solar power can be generated for just over 10 cents, whereas electricity from the supplier costs an average of around 32 cents per kilowatt hour. It is therefore worthwhile to monitor your own consumption and generation.
An electricity storage system can drastically increase the self-consumption rate by utilizing daily surpluses after sunset. However, it should match your own consumption behavior and the size of your system. The rule of thumb is: 1 kWh capacity per kWp module output of the system. Precise calculations are possible with several free online tools. We recommend the HTW Berlin independence calculator.

Battery storage systems are charged and discharged with direct current. In order to make their energy usable in the household, which is operated with alternating current, they require an inverter, just like the PV system itself. There are storage systems that are charged directly from the PV system with direct current (DC coupling) and those that are connected to the domestic grid independently of the PV system (AC coupling). With the latter, the mains current has to be converted back into direct current to charge the battery, which means additional losses. On the other hand, an AC-coupled storage system can also be charged with grid power when the sun is not shining. This can be an advantage if you use flexible electricity tariffs, for example. Cheap electricity can then be stored for times of high electricity prices. An AC-coupled storage system can also be useful with regard to future economic models such as flexibility trading or P2P trading. DC-coupled systems, on the other hand, also work when there is no mains supply, i.e. in the event of a power failure. They can then be used via an off-grid or hybrid inverter for a self-sufficient power supply. However, this then runs via a separate connection and not via the usual household electricity.
If you want to make the entire household capable of providing emergency power, you need larger storage units and a professionally installed electrical system with additional technology. A completely self-sufficient power supply requires a large amount of PV area, which cannot be realized on conventional properties. This has to do with the greatly reduced solar output in winter, which can only be compensated for with a large number of solar modules. In addition, a storage system with high output power and large capacity is required for peak loads.

If an energy management system is also used, this can be increased even further. The system uses control algorithms to ensure that the PV system, consumer and storage system are optimally coordinated so that even the last kilowatt hour of solar power can be used as efficiently as possible. There are already systems that incorporate the battery charge level, predicted consumption and even weather forecasts into the charging and discharging processes.

The simultaneous use of an electric car and a PV system with storage can exploit further synergies.

Many factors play a role in the calculation of profitability. The size ratio between the PV system and the storage system and their relationship to your own consumption behavior are particularly relevant. The higher the electricity consumption during the day and the smaller the PV system, the more of the PV electricity can be consumed directly, for example, which is detrimental to the profitability of a storage system. For larger PV systems or consumption that mainly takes place in the evening, however, a storage system is almost a must. Particularly in the long term, a PV storage system for PV systems from a size of 5 kWp almost always pays for itself within its lifetime. However, it should not be too large or too small, but should always be in proportion to the actual size of the system.