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Basics
Frequently Asked Questions
PV Solar Electricity is a technology of the future and is getting more and more attractive as an alternative for conventional electricity production. Find out the answers on frequently asked questions.


How does the conversion of light into electrical power work?
Conversion of light into electrical power
 		  

The solar cells convert the sunlight into electrical power.

The solar cells consist of ultra-pure silicon which via selective doping receives the characteristics of a semiconductor. When sunlight shines on the surface of the solar cell a potential difference develops between the upper and lower sides of the cell. If one now connects the two sides of the solar cell with each other, electricity flows and the cell produces power. To generate the desired voltage several cells are connected in series; the desired current is achieved by connecting the cells in parallel.


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What does a solar cell consist of?
More than 90% of all currently used solar cells consists of a silicon wafer which is doped as a semiconductor.
To manufacture the wafer a block of the purest silicon is normally sawn into thin slices. During this process roughly the half of this block ends up as shavings which can no longer be used for solar cells since they are too contaminated.
To avoid these sawing losses the so-called EFG process (EFG: Edge-Defined Film-Fed Growth) was developed for which SCHOTT Solar owns the patents.

To manufacture EFG wafers the silicon is drawn out of the melt on an octagonal extraction frame, already with the desired thickness. With this process a silicon block is no longer created, instead a hollow octagonal tube with a very thin wall. The wafers are cut out of this frame using a laser with next to no loss of material.

The EFG process allows the manufacture of solar cells with significantly less energy. An important advance for the environment.

The diagram further down shows the individual steps of the EFG process: The octagonal tube from which the silicon wafers are cut, the wafers and the complete solar cell which is then installed in a solar module.

Solar cell
 		  
 


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How do the solar modules collect as much energy as possible?
Solar modules generate DC current as soon as the sun shines on them. This has to be converted into AC current if the solar system is to feed into the house mains. The inverter is the component which converts the DC current into AC current. The inverter also performs other tasks.
There is an operating point at which the solar modules supply the most energy. This Maximum Power Point (MPP) depends on the light intensity and the temperature of the solar module.

During operation of the solar system the inverter continuously searches for the MPP and adapts the current and the voltage of the solar modules such that maximum power is always fed into the mains. The inverter also monitors the mains connection and thus also ensures fault-free parallel operation with the public electricity network.

For the winning of energy from sunlight the angle of the solar module to the sun and how the sun shines on it play an important role.
If the sun is hidden behind clouds or if part of the solar module is in the shade or is dirty then the energy yield is low. For this reason it is important to ensure correct alignment of the module and to make sure that no shade falls on it. It is also important to ensure that the mounting angle of the module is sufficiently large to allow adequate self-cleaning via rain running off it.

The solar modules are installed on the roof in such a way that as much energy as possible can be generated. Most slanted roofs which point south are suitable for the installation of solar systems. A roof inclination of between 15 and 50?is optimal, taking into consideration the points referred to above.
Structures on the roof such as chimneys and skylights must in all cases be considered by the specialist during the planning of the system.

A typical solar power system requires approx. 10 to 30 m?of the roof area. If the solar power system is aligned southwards and installed by specialists an annual yield of 850 kWh per installed 1 kWp can typically be achieved in Germany.
The solar energy used is in proportion to the nominal yield which can be generated and is therefore suitable for comparing different systems.

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What about dirt on the modules?
Since the angle of inclination of solar power installations is more than 20?to the horizontal, the modules are automatically cleaned by the rain. In other words, the modules are self-cleaning. However, if there are a lot of trees nearby and leaves accumulate on the modules, these need to be removed as quickly as possible. Leaves shading individual cells can considerably reduce the yield of the whole installation.
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What does a solar module consist of?
The solar cells are extremely thin (normally about 0.3 mm) and are thus highly sensitive and must be protected against external influences. For this reason the cells are installed in a solar module. The solar module consists of a hardened sheet of glass behind which the cells are lined up. At the rear the cells are protected by a layer of plastic. The electrical connections of the cells are fed out of the module to a junction box.

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Does the installation need to be serviced?
In general, PV solar power installations need no - or very little - servicing since they contain no rotating parts, bearings or other high-maintenance components. However, customers are recommended to check the electricity meter regularly or to balance the computer and data logging systems to ensure that the yield figures are plausible and so detect any equipment failures as rapidly as possible.

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Is it worth having modules that track the sun?
In general, a typical roof installation is not suitable as a tracking system. The roof cannot be rotated and the modules are usually mounted as a fixed installation. Where there is freedom of mobility however this option should be considered. On the one hand, tracking can increase the energy yield by up to 15% whereas on the other this does entail extra costs. Moving parts are subject to wear and can fail. Without tracking, a PV solar energy installation needs almost no servicing.

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Can hailstones destroy the modules?
PV solar power modules are usually very well protected against hailstones. The module is tested in simulated weather conditions (test in conformity with the IEC standard), which includes being pelted with ice pellets. The likelihood of modules being destroyed by hailstones is relatively low.

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How much can the sun contribute to the energy supplies of the future?
The sun is an inexhaustible source of energy and will in future play an ever-growing role in meeting the energy requirements of the world. From a technical aspect, nothing has more potential than solar energy. It is environmentally friendly, applicable everywhere and forward-looking. Solar power installations give 2 billion people with no access to a conventional power supply their first opportunity of meeting the basic needs of a modern civilisation, such as light, communications, education and health services, and of being part of technological progress. This is because energy is at the heart of all development. And the sun is available on everybody’s doorstep for free.

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What are the essential components of a PV solar power installation?
Solar power installations consist of the following components:
  • solar modules for converting light into electrical power;
  • inverter for converting solar power into a form compatible with the grid;
  • electrical safety components;
  • AC meter to record the yield.

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    Are there other ways of using solar energy?
    Besides the generation of solar power (photovoltaics), solar energy can also be used for thermal applications. Thanks to solar collectors installed on the roof and connected to the domestic water system, solar energy can be used directly to heat domestic water and heating systems. Naturally, you can use both technologies on your roof at the same time.
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    Since when has solar energy been used?

    First used in space
    In 1839, the physicist Edmund Becquerel discovered the photovoltaic effect: the direct conversion of light into electricity. But the real breakthrough in solar research did not come until the 1960s with the development of space travel. The spacecraft required an ultrareliable, autonomous, lightweight supply of energy. Solar power was the ideal solution. This led to the typical solar sails which are still very much state of the art today. The development of these highly efficient cells was entrusted to a handful of companies including AEG-Telefunken, which was subsequently absorbed by Deutsche Aerospace (DASA). The precious know-how accumulated by both these companies has now transferred to SCHOTT Solar, providing a solid base from which to search for solutions with a bright future.

    Proven practical benefits on a global scale

    Following on from the enduring success of long-term solar technology in space, the challenge was to find a way of exploiting this technology on earth, too. This began with small applications such as solar-powered pocket calculators which no longer needed a battery. In the 1980s solar power plants first came into use ?primarily in the USA ?as an autonomous source of energy for remote houses whose habitants were keen on finding an environmentally-friendly alternative or addition to their diesel generators. In the 1990s, government sponsorship programmes provided a further boost for demand in a few key countries.
    The simultaneous advent of industrial series production facilities also triggered a substantial reduction in manufacturing costs, leading to further market expansion. Combining both economic and ecological benefits to optimum effect, photovoltaics is widely regarded as a technology with a highly promising future. Depending on the installation site, the energy payback period of solar power modules is between 3 and 7 years, i.e. much less than the 30-year service life our modules should provde. We at SCHOTT Solar continue to focus on optimising these advantages.

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