Solar energy is energy from the sun radiation which can be used chemically and/or in the form of warmth and electricity. Physically, it is electromagnetic radiation from the sun-surface. Compared to energy sources from fossils e.g. oil, gas, coal and especially uranium, solar energy is nearly endless as the sun will continue to exist for the next billion years.

Theoretically, photovoltaic systems could satisfy power demands of Germany and even the whole world. Due to the fact that the sun doesn’t shine every day and at night, one would require storage systems. No serious company can however claim that photovoltaic is the only solution to energy problems worldwide. Instead, it’s true that solar energy in form of photovoltaic and solar thermal power used in combination with other renewable energy sources (wind, geothermal, hydropower, biogas etc.) would lead to electrical power supply methods that are not only sustainable but also which go easy on resources.

There are three main types of solar energy systems: solar thermal, photovoltaic and solar thermal power plants. Solar thermal energy means using the warmth of solar radiation, which is becoming more and more important, for water heating. Photovoltaic derives direct power from the sun which can be used immediately. With solar thermal plants, one has to first heat a liquid with concentrated solar radiation. The heated liquid then propels a turbine which sets a generator in motion. The electricity required is then produced by the generator.

How is energy from the sun converted to electricity using photovoltaic? Photovoltaics use photoelectric effect to convert energy from the sun into electricity. Two semiconductor materials with different charge carriers are inserted in the photovoltaic cells and separated by a membrane. The electrons are separated from the semiconductors with the help of photons in the sun radiation. The electrons then flow through the membrane to the other semiconductor –flow of electric current!

What’s a grid-connected PV system (On-grid)? A grid-connected PV system works in a way that the electricity produced is fed into the public power grid. For this purpose, the direct current (DC) of the solar modules is converted into power that can be fed into the grid then fed into the public grid. In Germany, this is the most commonly used form of photovoltaic system. This power is legally secured and remunerated with fixed tariffs for a period of 20 years.

Unlike the on-grid PV system, electricity form an off-grid system is directly utilizes or temporarily stored in batteries for use when there is no sun radiation. In our latitude off-grid systems are commonly used as small sized plants for garden plots, weekend houses or mountain huts. In areas with a lot of sunshine and the less electrified regions of the world (Africa, Asia, South America), this system of photovoltaics is always the only possible solution. It’s a realistic and more and more applied electricity source thanks to the currently low costs.


This is a form of electricity that can be fed into a grid. See alternating current.

Refers to the counter that measures the amount of electricity obtained from the grid.


This is a form of electricity directly produced by modules. See direct current.

This refers to private usage of electricity that one produces with his/her own photovoltaic power plant.

A PV plant owner gets a payment at a level fixed by statute for feeding his/her power into the public power grid.

This component records the solar power fed into the public power grid. The feed-in meter reading is the reference for remuneration.


The priority purchase, transmission and payment of power from renewable energy sources is regulated under the Renewable Energy Act which came into force in 2000. After this law was adopted in a transformed form by 50 other countries, photovoltaics seized being a niche product and became a mass product making it competitive with the market prices of conventional energy sources.

See substructure.

With DC electricity there is only one direction flow of electrons. A DC system is only made up of a positive and negative lead.

This is the total sun radiation falling onto a horizontal surface on the ground. This is normally divided into diffuse radiation and direct solar radiation.

This is the unit of the peak capacity of a PV generator under standard test conditions (STC)

This is a physical unit for energy indicating energy and corresponding with the performance of one kilowatt during a period of one hour.

Energy utilized per unit of time.

This term refers to the point at which performance is at its highest.

For optimum yield of module performance, the power inverter or solar charge controller must continuously adjust the voltage (V) so that the modules attain their MPP.

This is crucial for determining performance of PV power systems. The ratios of the maximum possible output and the achieved output are determined and compared.

The term used to refer to the direct conversion of light into electric energy.

This is the sum of all modules of a PV plant.

This is a single module of a solar generator which produces direct current (dc) with the help of photovoltaic effects.

In order to store excess power from own solar plant, solar cylinders can be built. At the moment, solar cylinder possibilities are lead and lithium batteries. By using a solar cylinder, the autonomy of a household can be maximized to 100% depending on size.

These are the smallest energy producing components of a PV system. They are mostly identified by their rectangular shape and shimmering black or blue color.

Standard Test Conditions create uniform test conditions which make it possible to carry out uniform comparisons of photovoltaic modules under laboratory conditions. These conditions are: irradiation: 1000W/m2, cell temperature: 25°C, AM (air mass): 1.5 (Europe).

The term used for a series connection of single modules under each other.

This happens when the shadow of a nearby object is cast onto a part of a solar generator. This often leads to a reduction in performance of the PV plant.

These are devices that conduct alternating current electricity into direct current electricity.

This is electric current in which the direction of flow is reversed at frequent intervals .It is usually at 230V from household sockets.

There is no 100 percent level of efficiency in technology as there is always continuous loss (friction, warmth … etc.) during conversion of energy. PV efficiency is the ratio of the power of the sunlight incident on the device to the electric power produced by a cell.