Efficient heating with environmental energy – the heat pump makes it possible

The heat pump is one of the newest renewable energies that can be used to heat buildings. In addition to solar energy and the environmentally friendly alternatives with biogas and bio fuel oil, the heat pump offers a CO2-neutral option for builders and property owners.

Functionality – how the heat pump works

The heat pump uses the thermal energies already stored in the environment to convert them into usable heat for heating. The special thing about this technology is that nothing is burned here, as with wood, gas or oil heating systems, but a technical process converts the thermal energies into heat. The principle is the same as in a refrigerator. Thermal energy with low temperatures are to be raised to a higher level. With the heat pump it works only the other way round. The environmental heat can therefore not only be used in the heating system, but also to provide hot water for the household.

The energy sources of the heat pump – air, earth & water

The heat pump uses different energy sources to generate heat. The brine-to-water heat pump uses the earth as an energy source, the water-to-water heat pump uses the water as an energy source and the air-to-water heat pump uses the air as an energy source. Which heat pump is best for your property depends on a variety of factors, but especially on the location of the property.

The air-to-water heat pump – thermal energy from the air

The energy source air is the easiest to use by the heat pump. The heat pump works with a simple system that sucks in and blows out the air. For this purpose, the heat pump uses the outside air, which is always available and is therefore one of the renewable energies. But even if the heat pump works with outside air, it can be placed inside the house. It then uses ducts to draw in air from outside. But it is also possible to place the system outside the property. There is no need for ducts as the system directly uses the air that is in the surrounding area. However, it is important with a heat pump that works with air that it is always kept free of frost in winter. Since the system has to work with air temperatures below zero, it becomes increasingly difficult to convert the cold air into usable heat. The colder the air, the more difficult the conversion. To keep the efficiency of the heat pump as high as possible, regularly clear it of frost and make sure it is properly maintained.

The brine-to-water heat pump – Earth as an energy source

Thermal energy is also stored in the ground, which the brine-to-water heat pump uses to generate heat for heating. For this purpose, pipes are installed in the ground in which a mixture of water and antifreeze circulates. The liquid, also called brine, extracts heat from the earth and transports it to the heat pump, which feeds it into the heating system. Each metre of ground provides thermal energy of approximately 50 watts that the brine fluid can extract from it. For a normal building, an average of around 150 metres of depth is required, which can, however, be divided into several boreholes. Depending on the individual circumstances of the property, deep boreholes or shallow collectors can be installed. The deep boreholes go up to 100 metres deep into the ground and therefore require special permits and are also not permitted in every area. With this method, plastic pipes (probes) are then installed in the ground.

If this variant is technically or legally not possible, the variant of flat plate collectors can be used. Here, similar to underfloor heating, pipes are laid at a depth of 1.50 m, which can extract 25 watts per square metre. A modern single-family house needs about 350 square meters of pipes to provide heating. The big advantage over the air-water heat pump is that the heat can be extracted all year round without any loss. This fact increases the efficiency of the heat pump and thus reduces the electricity costs incurred. See also: money guide.

The water-to-water heat pump – thermal energy in groundwater

Thermal energy can also be found in the groundwater, which can be used to generate heat. The water-to-water heat pump has a relatively simple mode of operation, as it has two wells that transport the groundwater to the water-to-water heat pump and back again. The wells must be installed in the direction of flow of the groundwater with a minimum distance to prevent the groundwater, which has already cooled down, from entering the heater again.

However, before installing a water-to-water heat pump, the groundwater must be tested. Good water quality is a prerequisite for installation, because chemical ingredients can put a great strain on the heat exchanger and thus limit efficiency enormously. In addition, the use of groundwater in a water-to-water heat pump is subject to approval and is not permitted everywhere. However, the thermal energy that can be used from groundwater is the most constant throughout the year, as the temperatures in the groundwater are not subject to large fluctuations. The water-to-water heat pump is one of the most effective variants of the heat pump.

The cost of a heat pump – installation, operation and energy source

The costs involved in installing a heat pump are generally divided into three areas. The cost of the energy source, i.e. the extraction of thermal energy from the air, earth or water, the cost of the system itself and the cost of operation and maintenance. Depending on which system is suitable for your property, the costs differ depending on the model and the system.

Costs for the extraction of environmental energy from air, earth or water

The choice of thermal energy from which the heat is to be extracted decisively determines the costs. An air-source heat pump, for example, requires hardly any additional technology, whereas with a brine heat pump, the drilling and additional materials must also be paid for. The cost of one metre of deep drilling is around 60 to 80 euros, while one square metre of surface collector costs 10 to 20 euros. The water heat pump also requires costs for the drilling, because the two wells must be laid to the groundwater and back. The costs here amount to about 5000-6000 euros for both wells. Depending upon condition of the environment and situation of the real estate the prices can deviate however also. An exact offer can only be made by a specialist.

Costs for the heat pump itself

The heat pump itself consists of the same components, regardless of the energy source itself, and can be combined with all three options. Depending on the size, installation costs range from 8000 to 12000 euros. However, the installation of a heat pump can be subsidised by various grants. Again, depending on the size required and individual circumstances of the location, prices may vary. For precise prices, request a quote from a specialist company.

Costs for the operation of the heat pump

All heat pumps operate electrically and require electricity to convert the thermal energy into heat. However, the level of these operating costs is highly variable. They depend on the selected energy source, the energy status of the property and the type of heat transfer to the various rooms. It is therefore not possible to give an exact price here and it must be calculated individually for each property.

Solar collectors – the heart of the solar system

Without the collector, a solar system could not convert the solar energy into usable heat. The collector is therefore the heart of the solar system, which makes it possible to use the renewable energy in the home. Want to learn more about solar systems and the cost? Calculate the cost of your individual solar system with our solar system calculator! But which different models are there among the collectors and which one is the right one for my solar system?

Flat plate collector – the proven model

Flat-plate collectors were the first collectors to be used to harness solar energy. They are therefore still the most widespread model today and form a market share of a proud 70%. Their reputation is probably not entirely unconnected to this, as flat-plate collectors are considered to be very inexpensive, reliable and, above all, they offer a technology that has certainly proven itself over the years.

Structure of a flat plate collector – absorber, housing and the heat transfer fluid

A flat plate collector has two simple components. A housing and a blackened metal sheet that is located inside the housing. This metal sheet is also called an absorber, because the dark coating ensures good absorption of the incident solar radiation. The absorber also efficiently converts the incident solar energy into heat. In order for the heat to be transported, pipes run along the back of the absorber in which heat transfer fluid flows. This flows cold into the collector and leaves it hot. To protect the collector from external conditions, such as the weather, it is covered by a safety glass. This glass is very stable and at the same time highly transparent, so that as little radiation as possible bounces off it. This ensures that as much solar energy as possible reaches the absorber to be converted into heat. To ensure that the housing also contributes effectively to heat generation, it is particularly well insulated and therefore hardly loses any heat energy. The efficiency of the solar system is thus increased.

Differences in flat plate collectors – structure, shape & piping

Even if the flat plate collectors are combined into one model, there are still differences. Different flat plate collectors differ in the housing material, the different connection of the tubes and other features. Depending on the application, the different designs have their advantages and disadvantages.

• Shape of the absorber – The absorber can be made of different materials. There are absorbers made of steel, stainless steel or aluminium sheets. These can be connected in different ways, for example by spot welding or roll bonding. There are also differences in the copper pipes in which the liquid is conducted. They can be pressed in but also soldered.
• Coating of the absorber – The absorber layer has developed further and further in recent years. After all, the layer should be able to absorb as much of the solar energy as possible. Today’s technology provides for highly selective layers that have a particularly high degree of absorption. It also has a low emissivity of the long-wave thermal radiation.
• Laying the heat transfer tubes – The tubes can either be laid in a tube register, where they are parallel side by side and connected at the top and bottom, or they can be laid in a meandering pattern, which means snake-like in one piece.
• Housing material – The material of the housing can also vary depending on the model. The most common are aluminum, stainless steel but also plastic. Even wood would be an option as a housing for a solar collector.

Tube collector – the better thermal insulation ensures higher efficiency

The tube collector came after the flat plate collector and is an alternative to it. Despite different technology and less market share, this model also has its advantages.

Structure of a tube collector – vacuum, heat pipe and the glass tubes

The tube collector model differs from the flat plate collector in one particular point, namely in the insulation. While with the flat plate collector only the housing is insulated, with the tube collector every single absorber is insulated and this in a special way. Here, the absorber is encased in an evacuated glass tube, as vacuum has particularly good thermal insulation properties and allows neither losses through convection nor through heat conduction. Several of the tubes together are connected to a collector and then form a tube collector. Since this way of insulating is much more effective than that of a flat plate collector, the efficiency is much higher here, since less energy is lost. Due to the technology, this model is also called a vacuum tube collector.

Different design of tube collectors – heat pipe, CPC & direct flow

The tube collector models are additionally differentiated into different designs. On the one hand, the direct and the non-direct flow tube collectors – they are also called heat pipes. Another form are the CPC – vacuum tube collectors.

• Direct flow tube collectors – In this design, the heat transfer fluid flows directly through copper tubes into the glass tubes. Here it is heated and when it exits it is combined with the other tubes in the collector. It is then transported to the heat exchanger via the solar circuit. In the event of a defective vacuum, it is not difficult to replace one of the tubes independently of the others.
• Heat-Pipe (non-direct flow) – The heat-pipe uses a thermodynamic process for heat transfer in which a heat pipe ( head-pipe ) passes through the glass tube containing a readily vaporizing liquid, such as water or alcohol. When heated, this liquid evaporates and rises to the head of the glass tube where heat is transferred by condensation of the vapor to the heat transfer fluid passing outside the head. The rest of the liquid flows back to the bottom of the tubes and repeats the process once room temperature is reached. This is sufficient to cause the liquid to condense, as there is a negative pressure in the tubes – the vacuum.
• CPC vacuum tube collector – This design is a variation of the direct flow tube collectors. Here too, the copper tubes run through the glass tubes, but the special feature is that two glass tubes are arranged concentrically and lie in front of a parabolic mirror. The absorbent coating is applied to the inside of the glass tubes. The parabolic mirror helps to make the collector even more efficient, especially at low irradiation. The yields are therefore comparatively higher and the collector works more effectively.

The heat transfer fluid – what needs to be considered

The heat transfer fluid stores the heat and transports it through the solar circuit to the solar storage tank. The heat is then released from the fluid and used to heat tap or heating water. The cooled fluid then flows back and starts its journey all over again. The question that arises, however, is what is suitable as a heat transfer fluid. Here the answer is relatively simple, because normal water is already perfectly suitable for this task. However, as there is a risk of frost, especially in cold months, which could cause irreparable damage to the collector or absorber pipe, the water must be mixed with an antifreeze. But the heat transfer fluid must also be able to withstand high temperatures. Especially in CPC vacuum tube collectors, temperatures of up to 350 °C can occur. To ensure that the viscosity does not suffer due to the antifreeze and such high temperatures, thus reducing the heat capacity, a mixing ratio of 40% propylene glycol and 60% water is usually aimed for. This mixture not only withstands cold temperatures as low as -25°C, but is also suitable for high temperatures. When purchasing the heat transfer fluid, pay particular attention to high temperature stability, good corrosion protection, the lowest possible viscosity, high environmental compatibility and a high heat capacity.

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 successfuly 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.

Photovoltaic system – the different variants of renewable energy generation

The system that is chosen by most is the so-called photovoltaic system that generates electricity with the help of solar energy. With such a system, the owners are independent of public grid providers and do not have to pay more for their own electricity. But also with the photovoltaic systems there are different variants, each of which has its advantages and disadvantages.

Feed-in system – earning money with your own electricity

The most commonly used variant of the photovoltaic system is the feed-in system. This produces electricity for the household and feeds the electricity that is not consumed into the public grid. As required by law, the house is connected to the public grid and feeds surplus electricity into it. For this, the Renewable Energy Sources Act (EEG) stipulates that the producer must be remunerated. The so-called feed-in tariff varies between 10 and 13 cents per kilowatt hour (kWh) depending on the nominal output of the system and is fixed for the next 20 years. To illustrate this: An average family consumes only about 30 % of the electricity generated. 70 % is fed into the public grid and remunerated. However, there is a trap here that private individuals often fall into, because selling electricity is a trade and as soon as a private individual does this, he becomes a freelancer and is self-employed. Taxes and lots of paperwork are just waiting for you. To avoid this, check out our guide on all things solar without the tax office! Through an electricity storage, the self-consumption can be increased up to 75% and the owner benefits twice from the electricity.

Advantages

• Reimbursement of sales tax on the purchase price of the plant
• Good price-performance ratio
• Feed-in tariff according to EEG as additional income

Disadvantages

• Registration of the plant as a trade
• Subject to the obligations of the EEG
• Increased bureaucracy

Such feed-in systems are particularly suitable for property owners who have a constant average electricity consumption and want to drastically reduce electricity costs. On the contrary, such a plant can not only reduce annual electricity costs, but also be used as a source of income.

Zero feed system – all the electricity for your own home

The second variant of the photovoltaic system is the so-called zero feed system. As the name suggests, no surplus electricity is fed into the public grid. In the best case, 100% of the electricity produced is consumed in one’s own household, so that nothing is fed into the public grid. In order to ensure this, the system must be precisely adapted to the individual needs of the owner and also have a suitable electricity storage system. The electricity production is additionally controlled by an inverter, so that the output of the system exactly matches the electricity consumed and no electricity is fed into the public grid. The owners of such a system thus forego the feed-in tariff under the Renewable Energy Sources Act (EEG), but at the same time they avoid all the obligations that the feed-in tariff entails. You do not have to register a business and you do not have to pay taxes for the electricity fed into the grid. Although the photovoltaic system is intended to generate 100% of the electricity required, the property is still connected to the public grid so that it can continue to draw normal electricity if the solar power is not enough.

Advantages

• No increased bureaucratic effort, such as business registration, etc.
• Greater independence
• No obligations under the EEG

Disadvantages

• No feed-in tariff
• No refund of sales tax

The zero-emission system is therefore particularly suitable for private individuals who have a high energy consumption. The installation of a suitable electricity storage unit is mandatory for such a system, so that the self-produced electricity can be used most effectively.

Photovoltaic island system – independent of the public power grid

The photovoltaic stand-alone system variant does without the connection to the public grid and assumes that the solar system can always supply the electricity storage system with energy. The household is therefore supplied with electricity solely from the solar modules and does not rely on electricity from the public grid in an emergency. The owner is therefore not dependent on electricity from the public grid at any time. Here we will first distinguish between two types.

Stand-alone system without mains connection

As the name suggests, this model is a system that is not connected to the public grid in any way. The house relies exclusively on energy from the photovoltaic system. The system was designed for such a case so that both solar modules and energy storage are so large that they can independently supply the entire house with electricity without resorting to another power source. The electricity in such a house is therefore produced and stored 100% by the photovoltaic system. However, this system is usually only installed when a connection to the public power grid would be too costly. This is particularly the case for remote houses, mountain huts or individual infrastructures.

Island system for backup power

Independence from public electricity can also be made possible for German homeowners. The installation of an island system for emergency power is the solution here. In the event of a failure of the power grid, the stand-alone system for emergency power can then intervene. It makes it possible for both feed-in and zero feed-in systems to become an island system in an emergency. In the event of a power failure of the public grid, this system switches to backup power within a few seconds and the house remains normally supplied with electricity. So, the household is not dependent on the public grid and does not have to worry about a power outage. Here it is ensured that there is always enough power available. During installation, the entire house is disconnected from the public grid and a backup power system is set up that can communicate with the storage system.

Advantages

• Function as a backup power system
• Maximum independence from the public power grid
• Protection against power failures

Disadvantages

• Significant additional costs
• Is rarely used
• There is hardly any economic benefit for the owners

Such an investment does not always make economic sense for the homeowner. So before you decide on this option, first check your average daily consumption, the appropriate size of the system and the design of the solar storage tank. With this, you can calculate whether an investment would be profitable for you or not. The independence that owners have with such technology from the public grid is undisputed and will change and influence the energy policy of Germany in the coming years.