Photovoltaics – Turning the Sun’s Rays into Electricity

In just one hour, the sun bathes the earth with enough energy to satisfy our energy needs for a year. In times of scarce and expensive raw materials and fossil fuels, it’s becoming increasingly important to utilize this renewable energy source to its fullest extent, and this is where photovoltaics, among other technologies, comes in.

Photovoltaics, a sub-segment of solar technology, is concerned with directly transforming sunlight into electrical current by means of solar cells. This has a lot of advantages. Generating electricity in this way, as a rule, doesn’t produce harmful waste products such as carbon dioxide, nor does it make any noise. In around three years, a solar system generates enough electricity to cover the cost of its manufacture (with an average for Germany of some 950 kWh per kilowatt installed capacity per year – more quickly in the south due to the greater amount of solar irradiation¹⁾.) A photovoltaic system doesn’t require a specially designed structure either – innovative technology allows it to be easily installed on existing buildings, for example on the roof. So anyone deciding in favor of this nearly inexhaustible and clean energy from the sun is also making a lasting contribution to protection of the environment and our climate.

Simple operation

A typical photovoltaic system consists of any desired number of interconnected solar modules. The solar cells embedded in these modules, which consist of crystalline silicon, or are based on thin film technologies, use the so-called photovoltaic effect to turn the sunlight falling on them into a direct current.
A frame keeps the module stable, while the solar cells inside are safely protected from weather conditions and mechanical disturbances.

A metal conductor carries the current to an inverter, which turns the direct current into alternating current. A counter records this, and usually the current is then fed into the public electricity network. The operator of the system receives a predetermined payment from the local energy provider, this being legislatively defined in the ‘Renewable Energy Act’.

High-power technology

Depending on its size (1 to 2.5 square meters), a solar module generates 100 to 300 watts of electrical power. To illustrate what this means: The operator needs about ten square meters of interconnected modules to generate a kilowatt of power. Under optimum conditions, a sun-facing roof on a private house can provide about 30 to 50 square meters of usable installation space, thus providing three to five kilowatts of power. The amount of electrical power generated in the course of a year by such a system (around 2,500 to 5,000 kWh) corresponds to the typical annual power usage of a family of three to four persons.

The right direction

Solar modules are well suited to facades, but the most common form of private installation is on a roof oriented, in the northern hemisphere, as far as possible towards the sun in a southerly (southwest – southeast) direction. The surface area of the roof also plays an important role – at least ten square meters should be planned for. The optimum inclination of the roof is between 20 and 45 degrees. The roof area reserved for the solar system should be free of shadow throughout the year. If no suitable surfaces are available on the roof, or if a roof system is being extended, it is possible, for example, to mount the modules vertically on the outside wall of a building.

Source: 1) E.A. Alsema, Copernicus Institut Utrecht, 09/2007