Solar cells convert solar energy into electricity
A solar cell, also called a photovoltaic (PV) cell, converts solar energy into electricity through the photovoltaic effect. When the solar cell's surface is illuminated, an electrical voltage arises between the front and back of the cell. Each individual cell provides a low voltage of around 0.5 V. Solar cells are therefore usually connected in series, in what are called solar panels or modules. This increases the voltage to a level suitable for power generation. Solar cells are used for small scale energy systems such as individual households, but also for large-scale installations. An example of this is the large PV-farm Parc Cynog that Vattenfall built and operates in the UK.
Solar energy at Vattenfall
Solar thermal energy uses heat to produce electricity
With solar thermal energy, heat is used to produce electricity. This technology can use a greater proportion of the energy in sunlight than a solar cell. The process concentrates the sunlight on a specific point in order to achieve maximum heat. Water is vaporized or oil is heated up by the radiation and drives a thermal cycle with a turbine that generates electricity. Parabolic reflectors are currently the most common solution and have been used commercially since the late 1980s. This technology only works in places where it is really hot and sunny, like deserts or the south of Spain.
Solar thermal collectors convert solar energy into heat
Solar cells are sometimes confused with solar thermal collectors. Unlike solar cells, a solar thermal collector receives sunlight and converts the energy into heat. This heat is then transported by means of a liquid or gas and is transferred into a tank filled with water. The heated water in the tank then passes into the building's heating system either directly or via a heat exchanger. Solar thermal collectors can also be used for heat-operated cooling.
In the Netherlands, Vattenfall operates a large-scale thermal collector that supplies enough warm water for 1 million showers to 2,700 households.