To generate electricity using the sun's radiation, you need photovoltaic cells — usually referred to as PVs. The cells are set up in panels, and the more sunlight that hits them the more electricity is generated. To power something big, or multiple users, lots of panels are set up in arrays. So does Denmark have enough sunshine for solar power generation to be practical?

Solar City Copenhagen was set up in 2004 by Copenhagen Municipality, the Danish Energy Authority, Copenhagen Energy, Valby neighbourhood council and a group of private companies. Its aims are to "establish Copenhagen as a demonstration centre for solar energy systems and energy optimization" and to contribute to renewable energy supply and CO2 emission reduction through promotion of solar power generation. It has developed an action plan, runs workshops and conferences, and supports pilot projects.

There are a number of localised solar-related projects in Copenhagen, including (see right hand column) the Kollektivhuset building-integration scheme in Hans Knudsens Plads and the Carlsberg district scheme. There are also small-scale systems that feed electricity back to the grid, such as the those at Copenhagen University College of Engineering, Tivoli amusement park and Heimdalsgade School. There is even a solar-powered ice cream vending cart!

An example of the solar city in action is the network of solar-powered pay-and-display parking ticket machines. There are 1,600 of these, each with a 15W solar panel charging a 75A battery, all connected to online monitoring.

Outside Copenhagen, Denmark has larger PV installations. For example, the Marstal district heating plant on the island of Aerø in the Baltic Sea is one of the world's largest solar heating projects. It has 18,365 sq m of solar panels and supplies one-third of the town's total power.

Solar cells are made using silicon, which is an abundant natural element. However, producing the very thin layers needed for PVs is expensive and efficiency in operation is typically only around 17%. The Danish National Laboratory for Sustainable Energy in Roskilde, just west of Copenhagen, has been developing polymer solar cells that can be printed onto plastic film. While they can be 10 times less efficient and have a shorter life than crystalline silicon cells, they are very much cheaper and faster to produce. Trials are ongoing.