Photovoltaics: the potential of floating solar systems

Ein Nachteil von Strom aus Sonnenenergie ist, dass die Solaranlagen Platz brauchen. Und der ist gerade in der Nähe von Ballungsgebieten – also dort, wo der Strom benötigt wird – knapp. Sollte die solare Stromproduktion bis zur Mitte des Jahrhunderts also tatsächlich, wie etwa vom norwegischen beratungsunternehmen DNV vorhergesagt, um das Dreizehnfache wachsen und Sonnenstrom zur dominierenden erneuerbaren Energiequelle werden, dann muss man Orte finden, an denen man die Anlagen bauen kann.

Eine Möglichkeit wären die die fünf Millionen Quadratkilometer an Seen, die es auf der Erde gibt. Dort lassen sich schwimmende Photovoltaikanlagen betreiben (im Fachjargon werden sie in Anlehnung an das englische Wort „float“ für Schwimmen scherzhaft „Floatovoltaics“ genannt). Sie haben eine Reihe von Vorteilen: Auf Wasserreservoirs und Stauseen hemmen sie die Verdunstung, was gerade in dürregeplagten Gegenden hilfreich ist. Zudem kühlt das Wasser die Solarmodule, wodurch sie effizienter arbeiten.

In China gibt es solche Installationen bereits in großem Stil. Die leistungsstärkste schwimmt auf einem gefluteten Kohlebergwerk im Osten des Landes und hat laut chinesischen Medien eine installierte Leistung von 650 Megawatt. Das entspricht der Leistung von etwa 45 der größten offshore Windturbinen.

Researchers led by Eastyn Woolway of Bangor University in Wales have calculated the global potential of solar energy on water. To keep the analysis realistic, they did not simply take the total area of ​​all natural and artificial lakes, but rather imposed some restrictions. A suitable body of water cannot be more than ten kilometers from the metropolitan area. Protected areas were excluded, as were lakes that dry up seasonally or freeze for more than six months. Finally, the systems analyzed must cover a maximum of ten percent of the water body and not exceed 30 square kilometers in area.

Depending on geographic latitude and height above sea level, electricity production fluctuates to varying degrees throughout the year. Overall, 1,302 terawatt-hours could be obtained annually, the researchers wrote in the journal Nature Water. For comparison: This country's electricity requirements were 467 terawatt hours last year. With these assumptions, solar systems on all suitable lakes in the world could theoretically cover nearly three times Germany's electricity needs.

Basically the potential will be greater. The researchers themselves write that the upper limit of ten percent of the area of ​​water bodies was chosen conservatively. In some cases, greater coverage may be warranted.

The study, broken down by country, concluded that they could cover an average of 16 percent of their electricity needs through floating solar systems on local lakes. However, values ​​vary greatly from country to country. Germany has only 0.05 percent, and Finland has 17 percent. Five countries, including Papua New Guinea, Rwanda and Ethiopia, can fully power themselves with solar energy systems on local waters.

However, the environmental consequences are unclear. Researchers confirm that in some lakes, solar power plants located on the water can directly improve the environmental situation. This is the case, for example, when its shade prevents excessive growth of algae. “But we still don't know exactly how floating panels might impact a natural lake ecosystem under different conditions and locations,” says study author Woolway. But the potential user is clear, he explains and demands: “So we have to advance the research so that this technology can be used safely.”