POWER FROM SPACE

In space, there’s neither atmosphere nor seasons nor weather conditions such as rain and clouds that could affect human exploitation of the sun’s rays. In other words, ideal conditions for producing solar energy to satisfy our hunger for energy here on Earth. As early as 2030, research and development may well be advanced enough to enable entire fleets of satellites to generate energy from space – around the clock and in a climate-friendly manner. [2] In spite of the fact that all studies and research projects to date have not produced the desired results, the vision of energy from space remains an attractive one for research teams worldwide.

HIGHLY EFFICIENT SOLAR MODULES FOR USE IN SPACE

The principles underlying the generation of solar energy via satellites are always similar: mirrors on the satellites concentrate the sunlight and direct it towards photovoltaic modules. These modules are so situated as to receive intense and direct solar radiation for generating as much electricity per surface area as possible. Ultra-light and highly efficient solar modules for use in space are currently being developed by the Space Solar Power Initiative (SSPI), among others. [3]

In 2012, worldwide interest greeted aerospace engineer John C. Mankins’ satellite design, which the US space agency NASA has been examining ever since: the SPS-ALPHA (Solar Power Satellite via Arbitrarily Large Phased Array) is equipped with hundreds of thin mirrors that form a funnel. The shape is designed to capture the sun’s rays, bundle them and direct them onto a photovoltaic cell. There, the radiation is converted before it is sent to Earth. This is what the satellite could look like:

But how exactly can the energy’s journey to Earth work in the future? And how can this happen in a way that produces maximum energy-efficiency and cost-effectiveness? Previous projects for space-based solar energy systems failed mainly because they failed to meet the latter criteria. According to the current state of research, two approaches are imaginable: the electricity generated in space could either be transmitted to Earth in the form of microwaves or “beamed” to Earth by laser beam.

According to CNBC, NASA is not at the moment pursuing any other research projects in this area.

POWER TRANSMISSION – METHOD 1: MICROWAVES TRAVELLING THROUGH SPACE

One possible concept for the future provides for huge microwave satellites collecting solar power at a distance of 36,000 kilometres from the Earth – in the geostationary orbit. The solar energy is first bundled in a photovoltaic and transmission unit and then converted into microwaves. The charge carriers – the electrons – are made to oscillate until electromagnetic waves – the microwaves – appear. The latter are to be bundled and then beamed wirelessly from the transmitter antenna in space to the receiver antenna on Earth. In the ground station, the microwaves would be reconverted into electrical energy and fed into the terrestrial energy network. [4]

What counts in favour of this method of transmission is that, because of the microwaves’ considerable range, the solar satellites could be stationed at an altitude that would be almost constantly bathed in sunlight – and this would enable satellites to generate solar energy continuously. Another advantage arising from the high altitude: satellites in geostationary orbit travel at the same speed at which the Earth rotates, that is their orbital velocity corresponds to the speed of the Earth’s rotation. In this way, the satellite would “hover” above a certain point on the Earth – ideally above the receiving station that is to pick up the microwaves.

So much for the theory. In practice, researchers across the globe are working intensely on finding solutions for the transmission of energy by microwaves – especially in Japan, where land for wind or solar parks is scarce. In 2015, the Japan Space Systems foundation succeeded for the first time in transmitting 1.8 kilowatts of electricity over a distance of 52 meters – using only microwaves. [6] And back in 2008, US-American scientists managed to transmit 20 watts of solar power via microwaves over a distance of 148 kilometres between the islands of Maui and Hawaii. The Japanese space agency JAXA, in cooperation with researchers from the universities of Tokyo and Kobe, plans within the next few years to send into orbit test satellites for solar energy generation in space. [7]

POWER TRANSMISSION – METHOD 2: LASER BEAMS POINTED AT THE EARTH

Laser technology offers a further possibility for the wireless transmission of energy to Earth. In the future, smaller satellites, orbiting at a distance of only 400 kilometres to take into account the shorter range of the laser beams, could beam solar energy to Earth. This is how it might work: the solar cells generate electrical energy that a laser converts into electromagnetic waves (that is, light). The laser beam is pointed at a photocell on Earth that receives the light waves and reconverts them into electrical power.

The advantage is that, in contrast to microwave satellites, laser beams are capable of transmitting the energy more precisely because of their smaller diameters. On Earth, only a small receiving station would then be needed to absorb the energy from space. The downside is that clouds or rain could impair such transmission by laser beam. [8]

Does this technology have a future? JAXA scientists, who have been researching the use of cosmic solar energy for a long time, are convinced it does. Making the beam orientation of high-power lasers in space more precise and improving the efficiency of electrical-current-to-laser conversion are among the challenges that they’re working on. [9]

From a technological standpoint, quite a lot is feasible already. This is demonstrated by the US American Power Transmitted Over Laser (PTROL) project: in October 2019, the scientists succeeded in transmitting 400 watts of power over 325 metres by laser. [10]

Here you can watch the test demonstration:

CHALLENGES: ACCURACY, TRANSPORT AND STATICS

Researchers and developers still have a long way to go before the first solar energy systems will be in operation in space. For example, they must ensure that the microwave beam hits the receiving antenna accurately. If the beam were to miss its target, the consequences could be devastating – with people, animals or vegetation going up in flames. The solar power system must also have such a high degree of mechanical stability that it will be able to float through space for years – preferably without maintenance. In addition, the individual modules must be both light enough and foldable enough for rockets to be able to transport them into space and for robots to be able to assemble them.

By the way: once wireless transmission of energy has been fully developed, it could also be used on Earth – in places where it’s difficult to lay cables, such as when connecting offshore wind turbines to the power grid. According to Japanese researchers, the wireless electrical refuelling of electric vehicles is another possible application. [11]

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[1] https://www.energy.gov/articles/space-based-solar-power
[2] https://blogs.helmholtz.de/augenspiegel/2015/08/klar-soweit-no-19
[3] https://www.caltech.edu/about/news/space-based-solar-power-project-funded-46644
[4] http://www.ak-energie.at/pdf/ET2016/ET2016-6_Andreas%20Berger_Drahtlose%20Energie%C3%BCbertragung.pdf
[5] http://www.kenkai.jaxa.jp/eng/research/ssps/ssps-mssps.html
[6] https://www.ingenieur.de/technik/fachbereiche/energie/kraftwerke-im-weltall-im-visier-strom-fliegt-luft/
[7] https://www.energy.gov/articles/space-based-solar-power
[8] http://www.kenkai.jaxa.jp/eng/research/ssps/ssps-lssps.html
[9] https://www.nrl.navy.mil/news/releases/researchers-transmit-energy-laser-power-beaming-demonstration
[10] https://www.mhi.com/news/story/1503121879.html