Energy | 12. January 2010 | posted by Jan Oliver Löfken

Question of the week: How much energy does the Sun send us every day?

Our Sun is a gigantic fusion reactor with an expected lifetime of about ten billion years. Although this period of time is unimaginably long from a human perspective, half of it has already elapsed. That means that our star, a very ordinary one in astronomical terms, will still be radiating the same amount of energy as it now does long after our resources of uranium, coal, gas or crude oil have been used up. How much energy from the Sun reaches us here on Earth?



Only a tiny fraction of the Sun’s heat, which reaches temperatures of 15 billion degrees, reaches the Earth in the form of radiated energy. However, compared to the world’s energy requirements, even this ‘tiny fraction’ of what is known as global radiation still constitutes a gigantic amount of energy. In the course of a calendar year, the intense rays of the Sun deliver an average of 1340 watts of energy to every single square metre of the Earth’s surface. That is enough power to operate a hair drier continuously. When this intensity is diminished by the atmosphere and by cloud cover, delivering only diffuse light, this figure can drop during daylight hours to as little as 50 watts. Nevertheless, even in Germany, the overall quantity of energy per square metre during a calendar year still represents 900 to 1200 kilowatt-hours – compared to between 2200 and 2800 in the mostly cloudless Sahara, where there is uninterrupted exposure to direct sunlight. Depending on the type of technology employed, five to ten percent of this energy can be converted into usable electrical current. That means that about 20–40 square metres of desert could meet the total annual energy needs of a typical household.


DESERTEC: Fläche in der Sahara für die Energieversorgung der Welt, der EU und Deutschland. Bild: DLR."The largest, most compact and most reliable source of energy"

What could be more self-evident from a human point of view than to tap into this virtually infinite energy source? However, in the past, energy researchers have always focused their attention in the first instance on fossil fuels, or on other renewable forms of energy. “As a student back in the eighties, I learned that the Sun is the least concentrated form of energy,” recalls Franz Trieb, an energy researcher at DLR. “Now, we know different: solar power is the largest, most compact and most reliable energy source on this planet, and this resource can now be utilised in an increasingly cost-effective manner.” For example, solar cells are able to convert sunlight directly into electrical power, or mirrors can concentrate the rays of the Sun in solar-thermal power stations to generate steam at high temperatures. By passing this through a steam turbine and generator system, electricity can be generated. Thanks to thermal energy storage units, this electricity can now actually be delivered at the precise time it is required. This second process alone is now running so efficiently that solar-thermal power stations on a desert surface area measuring 300 by 300 kilometres would theoretically be able to meet the complete electricity needs of the whole of humankind.  In practical terms, radiation from the Sun should certainly be capable of meeting regional energy needs across large areas.

Parabolrinne auf der Plataforma de Almería (PSA) in Spanien

DLR researchers are working on a diverse range of applications and technologies associated with the conversion of the Sun’s radiation into usable energy. This range extends from solar-thermal power stations with parabolic mirrors or solar towers linked to compatible heat storage systems to solar-powered furnaces in which high temperatures can be achieved for chemical processes. Last but not least, the DLR ‘ideas factory’ is largely responsible for the concepts underpinning the ambitious desert electricity project DESERTEC, which aims, within the next few decades, to generate electricity from solar power for North Africa and Europe.

The DLR energy question of the week in the ‘Future of Energy’ Science Year

The German Federal Ministry of Education and Research (Bundesministerium für Bildung und Forschung; BMBF) has chosen 'The Future of Energy' as the theme for Science Year 2010. This has prompted science journalist Jan Oliver Löfken to answer a different energy-related question each week in this blog. Do you have any questions about the form energy provision might take in future? Or would you like to know, for example, how a tidal power station works, and how efficiently it can be used to generate electricity? If so, please send in your question by e-mail. Science journalist Jan Oliver Löfken will then research answers to your questions, and will publish them every week in this blog.


About the author

Energy journalist Jan Oliver Löfken writes among other things, for the Technologie Review, Wissenschaft aktuell, Tagesspiegel, Berliner Zeitung and P.M. Magazin on issues involving energy research and industry. For DLR, he answered the Energy question of the week during the Year of Energy 2010. to authorpage