FAQ

Frequently Asked Questions

1. What is the difference between a solar module and a solar collector?

In a solar collector, water is heated by sunlight which can then be used for daily hot water and heating requirements. In a solar module (also referred to as PV module or solar generator), light is directly converted into electricity.

2. What does PV mean?

PV is the international abbreviation for photovoltaic conversion and refers to the physical process by which sunlight is converted into electricity by means of a solar cell.

3. What are photovoltaics?

Photovoltaics denotes the direct production of electricity from sunlight (also referred to as photovoltaic effect). In 1839 the French physicist Alexandre-Edmond Becquerel discovered the phenomenon on which solar cell technology is based, the so-called photoelectric effect. However, the first photovoltaic cell was not developed until the 1950s.

Since then solar cells have been used in aerospace, pocket calculators, watches and emergency telephones. But the main application today is the supply of power to buildings and to the national grid.

4. What does kWp stand for?

Kilowatt peak (kWp) specifies the power of a PV or solar module under certain conditions, i.e. standard test conditions: STC (1.000 W/qm insolation, 25 °C module temperature, AM 1.5 spectrum).

5. What does Wp stand for?

The abbreviation W p stands for watt peak power [W p (1.000 W p = 1 kW p)]. This is the rated power -i.e. the power generated under certain test conditions (see kW p). The Wp rating does not therefore indicate the actual power supply but rather the maximum supply of a module under optimum conditions.

6. What does kWh stand for?

kWh is the abbreviation for kilowatt hour - the unit with which the energy produced is measured. 1 kWh corresponds to the continuous generation of 1000 watts over a period of one hour. It is also the unit used by your utility to charge you for the electricity you have consumed and to pay you for electricity delivered to the grid.

7. What is solar energy?

Solar energy is the energy which is produced from insolation (the amount of sunlight available to the module). The sun is the largest and richest energy source available to mankind. Despite the distance at which the earth orbits the sun (150 million kilometres), it supplies without fail radiant energy in the order of 15,000 times the primary energy requirements of the entire population of the earth. This means that solar power stations covering an area of only 3% of the Sahara desert could supply the entire energy requirements of Europe and Africa.

Solar energy is a renewable resource, classified as a directly usable form of energy. Wind is an indirect form of energy and biomass (wood, grasses and biogas) are stored solar energy. All of these energy forms together form the basis for a sustainable energy supply.

8. How does a PV installation work?

Individual solar cells are interconnected to so-called solar modules (also referred to as PV modules or solar generators) which convert sunlight into electrical power. When light falls on a PV module, the radiation energy is converted into direct current (DC). The direct current is then converted into mains-compatible alternating current (AC) by means of an inverter. The inverter is installed in a suitable location between the solar modules and the meter box.

A PV module is therefore capable of using sunlight and turning it into electricity. It can do this even when there is some cloud cover in the sky or when it is completely clouded over. Even artificial light can be used in this way. But, of course, the yield depends on the quantity of light.

9. What are monocrystalline, polycrystalline and thin-film solar arrays?

There are three types of cells: monocrystalline, polycrystalline and amorphous cells.

For the manufacture of monocrystalline silicon cells ultra-pure semiconductor material is used. Out of a silicon melt, monocrystalline rods are drawn and subsequently sawn into thin slices. This process ensures relatively high cell efficiency but does not tell you much about the resulting efficiency of a module. Originally all monocrystalline material came from chip production.

More cost-effective is the use of polycrystalline cells. This process involves casting liquid silicon into blocks which are subsequently sawn into slices. During solidification of the material different sizes of crystalline structures are formed at the edges at which defects occur. Such defects lower the efficiency of the solar cell. However, this degradation can often be compensated in the module since - unlike the monocrystalline material - rectangular cells are produced resulting in better utilization of the area available for modules.

If a photovoltaically active layer is deposited on glass - or another substrate - it is called a thin-film solar cell. The thickness of the film is less than 1 µm (the thickness of a human hair by comparison is 50-100 µm). Due to the low material costs, production costs are lower. The efficiency of thin-film cells is, however, considerably lower than that of crystalline type cells.

There are many types of thin-film technologies available with different characteristics. Their importance will increase in future. To date they have been mainly used for low power applications such as watches and pocket calculators or as facade panels.

10. What does solar cell efficiency or power mean?

The power (the product of current and voltage) of a solar cell is temperature-dependent. Higher cell temperatures result in lower power output and thus in lower efficiency. The efficiency figure (or cell efficiency) states how much of the insolation is converted into available electrical power. The higher the efficiency of a cell, the better its capability to convert radiant light into electric power.

The higher the efficiency, the more power is generated by a given area of solar panels. Thus a solar module with an efficiency of 12.5% generates 125 watts of peak power per square metre. If the efficiency is 10%, 100 watts of peak power is generated (under standard test conditions with 1000 watt insolation per square metre). In other words, the first module produces 25% more solar power per annum with the same size of installation.

11. What is a grid-connected PV installation?

A grid-connected PV installation is an installation tied to the national grid. The grid works like a large ‘lake' which is fed from a variety of sources and which has many outlets such as domestic consumers, businesses and industry. The more solar power is fed in, the cleaner the grid becomes.

12. What is a stand-alone or off-grid PV system?

Stand-alone systems are found where there is no connection to the grid. This occurs, for instance, where a connection to the grid would be too expensive. Examples are light buoys in the sea, street lamps in remote areas, the illumination of motorway signs and the like. Although such niche applications in Central Europe are only used where the connection to the grid would be uneconomical, in many parts of the world they are the only way to supply electricity that makes ecologic and economic sense. Thus billions of people are given the opportunity to carry on working after sunset without depending on expensive fuel or without being poisoned with the waste gases from cheap fuel. Such systems usually work with direct current and battery backup.

13. Can I touch a solar module without getting an electric shock?

Naturally the solar module as such is not live. Nevertheless, due to the way the modules are connected in series within the system, dangerous voltages are present. Thanks to high protection standards, they are just as safe as other domestic appliances.

14. What is the life expectancy of a solar installation?

A PV module has an average life expectancy of over 30 years. The design life of the inverter is usually over 20 years, but this is not always achieved. In the event of such a breakdown, replacement at a reasonable cost is not a problem. For the system as a whole it is possible to identify possible losses of efficiency - at least on an annual basis - using publicly available insolation data. Our experts can analyse the cause quickly and rectify the problem, if so desired.

15. Do I need to clean the installation every week?

PV installations do not require a lot of care. Rain ensures that they remain clean if the angle of inclination is at least 10 to 15 degrees. If necessary, the modules can be cleaned with a cloth. This can be done, for example, when gutters are cleared.

16. Do I need to protect the installation from snow?

Each Ecostream installation is installed in such a way that it can withstand most weather conditions. Moreover, they contain toughened safety glass. Gales, snow and harsh frost are therefore no problem. The modules even withstand hail under normal conditions. For installations in areas with extreme weather conditions, insurance cover is an option. However, according to the data from the insurance industry, claims are very rare.

17. Is there a greater danger of a lightning strike with a PV installation on the roof?

Studies have shown that the danger of lightning strike does not increase with the installation of a PV system on the roof. However, the electronics and in particular the inverter of the system are very sensitive. This means that with lightning strikes in the vicinity there is a risk of damage. Such incidents are referred to as indirect lightning strikes.

The risk of damage due to induced transients from load switching is low, but when it happens, the damage is considerable. A short circuit as a result of a lightning strike can destroy a lot of equipment. However, often damage due to induced transients is included in home insurance - in which case your solar generator would be covered. Please check with your insurer.

18. Does my installation generate electricity when the sun is not shining?

It can happen that on a slightly overcast day in May a higher yield is measured than on a warm and sunny day in August. One of the reasons for this is that the efficiency of the solar module with which sunlight is converted into electricity decreases as the module warms up.

19. What about subsidies?

Subsidies vary in each country.

20. What rate will I be paid for the electricity I "export" to the national grid?

Rates are not the same in every European country.

21. What contribution do I make to the environment?

If you invest in a solar installation, you also invest in the environment. Thus a PV installation with an area of 8.5 square metres and a power output of 1 kWp, for instance, renders on average 850 kWh p.a. which corresponds to a reduction in CO₂ output to the atmosphere of approximately 70 kg p.a. which amounts to 14 tonnes in 20 years. With an installation of this size your own roof can contribute slightly more than one quarter of the power an average family of four consumes. Possibly more important is, perhaps, that with this decision you are simulating a market which will develop products at a lower cost and thus save far more CO₂ .

22. What does the term NEG (net energy gain), exactly mean?

By net energy gain (sometimes also referred to as energy amortization or energy payback) we mean the time it takes for a solar installation to generate the amount of energy it took to produce the installation. A PV installation on the basis of amorphous silicon has - according to a study by the Technical University of Berlin - a payback time of 17 to 41 months. Crystalline modules have a payback time of a similar magnitude, whereas monocrystalline modules perform slightly worse due to the more costly process. Power stations, however, which run on fossil fuels, can never compete.

Study: A solar module generates the amount of energy used for its manufacture within three years. One of the ways to compare different processes is to use, in addition to known criteria such as the cost and impact on the environment, the time it takes to reproduce the energy used to manufacture the installation itself. Example: Large power stations run on fuel, water power or nuclear energy and require considerable amounts of energy for their construction. A new study by "Energy and Environment Economics" reveals that now only one to three years are necessary until a solar generator has reproduced the energy used in its manufacture. The study examined the manufacture of two types of solar generators in a factory run by Siemens Solar Industrie. It is expected that the modules will produce between 9 and 17 times the energy as it took to manufacture them by the end of their life.

23. What ongoing maintenance costs are there?

After the initial costs for the purchase and installation of the solar system, there are no further costs for fuel. Only small amounts need to be budgeted for maintenance, repairs and insurance.

24. What is meant by roof pitch?

Although the question of the pitch of the roof is asked when planning a solar installation (for instance for an online-calculation), it is not the inclination of the roof that matters but the inclination or pitch of the solar module. By means of a support structure, solar modules can be brought into an appropriate position even if the pitch of the roof or the roof orientation is not favourable.

To make best use of the radiation from the sun the angle of incidence of the sun rays should be 90 degrees. The optimum angle of inclination and orientation must correspond to the latitude of the location (Freiburg in the Black Forest in Germany, for instance, is situated on the 48th degree of latitude and Lübeck on the Baltic Sea is at 54 degrees.

Since the sun is higher in the sky in the summer than in winter, it also depends on the season in which the solar installation is mainly used. During the long days of summer, for instance, photovoltaic installations generate the highest yield. As a rule of thumb, the latitude less 10° is used for the installation angle for use in the summer, and for main use in winter the latitude + 10°.

The angle of inclination should not be confused with the orientation to the South. In practical terms, small deviations from the optimum angle of inclination or orientation have only a slight effect on the yield. If shadows are cast onto the solar module, the effect on the yield is greater.

25. What is the optimum orientation of a solar installation?

A solar system should be oriented to the south, although the installation does not have to face due south. Even if solar modules are installed on a roof which deviates up to 40° from south, only small losses are incurred. In terms of inclination, the modules can be at an angle from 20° to 60° without much of an impact. Smaller angles of inclination increase the yield in summer whereas larger angles of inclination increase the yield in winter. Since annual yield is what counts in the case of grid-connected installations, our advisor will assist you with this calculation.

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