At present, about 8,000 roofs in Berlin carry photovoltaic or solar thermal systems. If all suitable roof space of the German capital were consistently fitted with solar arrays, they could provide approximately 3.2 million megawatt-hours of electricity a year. In other words: 500,000 roofs could theoretically generate enough electricity to meet about 77 percent of the private power consumption in Berlin.

This data has been provided by the Berlin Solar Atlas, a project of Berlin Partner GmbH, the German capital's business promotion agency, in association with the Berlin Senate. The Atlas is available online for anyone to consult. The online three-dimensional model of the city shows whether a particular roof is suitable for installing solar panels and how much solar energy it is capable of capturing. Further information also describes the opportunities for avoiding CO2 emissions and the expected costs.

"The integration of such an analysis of a city's solar power potential into a virtual three-dimensional city model is unique worldwide", says Berlin Partner Managing Director René Gurka. "The Solar Atlas points out the huge potential for renewable energies that even tightly-packed cities have, and can help people take advantage of such opportunities."

The Solar Atlas uses the existing 3-D city model of Berlin, which is based on the official geodata of surveying authorities. In addition, all of Berlin's rooftops have been measured by laser and photographed from the air. This – together with additional information including the slope of the roofs, the direction they face in, and the amount of shadow that falls on them as well as further data such as average annual solar exposure and the prices of solar cells – is then used to calculate the solar potential of each individual roof.

To experience the Solar Atlas for yourself on Google Earth, you can download the relevant file from the following address: http://www.businesslocationcenter.de/dispatcher_solar3d/getserver.jsp. The Solar Atlas can also be consulted directly as a 2D image on the site of the Business Location Center Berlin: http://www.businesslocationcenter.de/solar2D

This analysis does not take account of factors like the structure and condition of roofs. However, it does include possible restrictions for listed buildings. "For this reason, the Solar Atlas can't replace individual consultancy and analysis by specialists", says René Gurka.

But the Atlas can supplement the already existing Solar Roof Exchange of Berlin. At the moment, this service made available by the Senate Department for Health, Consumer Affairs and Environmental Protection gives companies that operate solar arrays access to publicly-owned roofs. From 2011 onward, the new Berlin Solar Exchange shall promote the marketing of all suitable roofs – even those in private hands. Gurka: "Together with the Solar Atlas, private and public property-owners on the one hand and providers of solar technology on the other will have at their disposal an internet-based platform that brings together supply and demand."

Through generous Government aid, Germany has experienced a massive expansion of renewable energies in recent years. This has a whole series of different economic effects. For example:

• The green electricity levy, which has to be paid by all electricity consumers, will rise by almost 71 percent next year to a record high of 3.5 eurocents per kilowatt hour. In a three-person household, this may account for up to ten euros to the monthly electricity bill, depending on consumption.
• The development of renewable energy provides increasing employment, incomes and tax revenues for municipal coffers. The German Institute for Ecological Economy Research (http://www.ioew.de/en) estimated this value-added effects to 8.9 billion euro for the coming year. Last year about 340,000 people in Germany owed their jobs to the production of electricity, heat or fuels from renewable sources. This is more than double compared to 2004.
• Photovoltaic systems are becoming cheaper. The German Federal Solar Industry Association (http://en.solarwirtschaft.de) calculated that within the last twelve months, prices for turnkey solar power systems decreased by an average of 13 percent. If the development of prices for solar power plants continues like that, producing your own solar electricity can compete with normal household electricity prices soon. The Association expects that already in 2012 power from your own roof will be at the level of consumer prices, which the energy supply companies ask from their customers. This will be an important milestone on the road to competitiveness.