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Lots of space, no neighbors, favorable weather - the sea offers the best conditions for generating green electricity.
There are already 1,500 offshore wind turbines installed off the German coast.
Now the solar industry is also moving to the water: in the next few years, several floating, firmly anchored photovoltaic systems are to be installed in the North Sea.
For example, RWE and the Dutch company Solarduck have announced that they will take part in a renewable energy tender with a combined wind-solar park off the Dutch coast.
The start-up Oceans of Energy, also from the Netherlands, is planning a similar project off Belgium.
By the end of the decade, there could even be floating photovoltaic systems in the North Sea that will produce more power than the currently largest German solar parks.
More space for photovoltaics
The installation in the sea is a smart move because it allows much more space to be used for photovoltaics.
On land, the construction of new solar parks is repeatedly slowed down by civil protests - although the systems are often an advantage for nature conservation, since flora and fauna remain largely undisturbed here.
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Some small offshore pilot plants have already gone into operation: In 2019, Oceans of Energy installed a first solar island around 15 kilometers off the Dutch coast.
The system is currently being expanded to an output of one megawatt - which corresponds to around 150 typical single-family house systems.
The German company Sinn Power has launched a small solar system off Crete.
And Norway's Ocean Sun operates several facilities in the country's fjords.
Rough conditions at sea
All these installations primarily serve to test constructions and components.
"The conditions at sea are rough," says Konstantin Ilgen from the Fraunhofer Institute for Solar Energy Systems ISE.
“The systems have to withstand waves ten meters high and more.
They are exposed to water, salty air and strong UV rays.
All of this takes a lot out of her.«
A number of floating solar systems have been installed on inland lakes in recent years.
However, Ilgen believes that the knowledge gained there can only be transferred to the high seas to a very limited extent, since the respective conditions differed greatly.
"There is still a lot of experience to be gained in offshore photovoltaics," says the Fraunhofer researcher.
However, he is convinced: »The industry will get the challenges under control.«
Gigawatt systems from 2027
Benjamin Lehner from the Dutch Marine Energy Center in the Netherlands agrees.
"The industry is very good at building plants that float in the sea - gas and oil platforms, for example, or recently floating wind turbines," explains Lehner, who heads an EU research project on floating solar energy.
»We benefit from this in offshore photovoltaics.«
The solar island from Oceans of Energy has already passed an initial endurance test: several winter storms with wind speeds of over 100 kilometers per hour and waves up to ten meters high - including storm "Zeynep", which caused severe damage in the Netherlands and other countries bordering the North Sea caused.
The modules are installed on floats so that they can follow the ups and downs of the water masses like an air mattress.
The industry is currently making the leap from kilowatt to megawatt systems, explains Lehner.
"In terms of area, the former are on the order of a living room, the latter several soccer fields," explains the expert.
If there are no major setbacks and sufficient political support, he expects the construction of the first gigawatt-class plants, i.e. the output of large coal-fired power plants, to start between 2027 and 2030.
Use the infrastructure of offshore wind farms
The combination of offshore photovoltaic and wind energy is attractive for several reasons.
In this way, the solar islands can use the electrical infrastructure of the wind farms, especially the grid connection.
In addition, the generation profiles of wind turbines and photovoltaic systems complement each other well: when the weather is calm, the sun often shines, when the weather is bad, the wind usually roars.
Last but not least, the combination of the two technologies ensures that the sea areas are better utilized.
In the longer term, it would even be possible to use electricity to produce hydrogen by electrolysis at sea.
An industrial consortium is currently preparing the construction of the first combined wind energy and hydrogen park in the German Bight.
Supplemented by offshore photovoltaics, the interaction of wind and solar could ensure higher utilization of the electrolysers.
Floating solar parks can also be used to supply remote islands, seawater desalination plants or oil and gas platforms with electricity.
»Use all potential for climate protection and energy transition«
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The question remains: Do we really need photovoltaics at sea for the energy transition - or does it not make more sense to first exploit the great unused opportunities on land?
»It will certainly be some time before offshore photovoltaics can supply any electricity worth mentioning.
In addition, the quantities will initially be small compared to photovoltaics on land,” says Fraunhofer researcher Ilgen.
»But what speaks against going this route as well?
We should use all potential for climate protection and energy transition!«