Solar energy – good reasons to choose a photovoltaic system from Viessmann

A module surface area of 450 x 450 km would be sufficient to cover the power demand of the entire world. Our sun not only provides energy in abundance – it is also an environmentally responsible source of energy. Better still – the energy it delivers is free.

Although both the Vitovolt (photovoltaic) and the Vitosol (solar thermal) systems use insolation to yield energy, they differ in engineering and operation. Electrical power is generated directly in the photovoltaic module. However, in solar thermal systems, the heat yielded by the collectors is transferred hydraulically via a heat transfer medium, so it can be used for DHW or central heating.

Power from the sun

When it comes to conventional power stations, only one third of the primary energy expended 'translates' into usable power. Around two thirds of the primary energy is lost in power generation and distribution through the national grid. The provision of electrical power has a considerable impact on the environment. It is therefore particularly worthwhile to generate electricity using renewables such as the sun, wind, hydroelectric power and biomass, by means of a decentralised source close to the point of consumption.

Generating electrical power directly from solar energy, known as photovoltaics, is an elegant and reliable option. Generating roughly the amount of power an average person consumes in a year requires a photovoltaic surface area of approx. 8.5 m².


Operating principle

Basically, a mains-connected solar power system operates in three stages:

1. Harvesting energy

When light falls on the photovoltaic modules, electrons are released inside the solar cells. Positive and negative charge carriers collect at the respective electrical contacts, resulting in a DC current flow between the front and back of the cell. This photoelectric effect is created without mechanical or chemical reactions, and so is maintenance free and not subject to wear.

2. Power conversion

DC power generated by the solar generator is then converted by the inverter (commonly also known as a mains feed-in device) into AC power suitable for the grid (230 or 400 volt AC current at 50 Hz). Proven safety standards and fully developed processors, as well as cutting edge power electronics, ensure effective conversion of the solar power.

3. On-site consumption

The falling remuneration rates for privately generated solar power and the rising cost of electricity are motivation enough for developing an optimised energy concept for detached and two-family houses. In the meantime, using solar power in your own home – the more the better – has become much more attractive financially. Using a power storage unit for solar power generated at home increases the rate of power consumption on site and reduces the amount of power drawn from the grid still further.


Silicon solar cell

Photovoltaics | Silicon solar cell

General solar data

Annually, the amount of energy that reaches the surface area of the United Kingdom is equivalent to approx. 80 times the country's total energy consumption. Around half of this reaches the Earth's surface as direct insolation, the other half as diffused light.

Consequently, a total of around 950 to 1200 kWh/m² reach a horizontal surface every year. Solar cells convert more than 15 percent of this into electrical power, with around two thirds of the energy being yielded in summer and one third in winter.

Solar power has a safe future

Installing a photovoltaic system on the roof turns every homeowner into a power generator. In fact, it's really quite simple, just assemble the modules, plug in the connecting cables, connect the inverter, and you're done. You can add a power storage system as well, if required. The number of house builders interested in this form of power generation continues to rise.


Feed-in remuneration and utilisation of power generated on site

If you generate your own power, you can receive a guaranteed remuneration from your power supply utility for up to 20 years. In the United Kingdom, this is governed by the Feed-in Tariff scheme.

There are currently two ways in which the solar power generated by a rooftop photovoltaic system can be used: It can either be exported to the grid in its entirety, or it can be partially or completely consumed on site.

Photovoltaic system concept

Efficient on-site consumption of solar power

Since generating solar power on-site is cheaper than drawing power from the grid, on-site consumption offers financial advantages. An optimised system concept with perfectly matched components ensures this high level of on-site consumption.

[1] Photovoltaic system
[2] Photovoltaic inverter
[3] Photovoltaic generation meter
[4] Consumers
[5] Heat pump meter
[6] Heat pump with Vitotronic 200 (type WO1C)
[7] Consumption and export/generation meter
[8] Public grid