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Sigmetnow

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Solar Power from Space? It’s complicated.
« on: June 22, 2021, 09:04:42 PM »
Solar Power from Space? It’s complicated.

All that free power from the sun up in space, available all day, every day — as long as you are not in the earth’s shadow.  Why can’t we capture it and send it to earth?  Some day, it might be possible, but there are many obstacles….

<< Recap and continuation of a discussion which has been deleted from the Electrical Grid thread.  Feel free to add your two cents and correct anything I’ve said wrong! >>

The first thought that might come to mind is a using satellite with a huge array of solar panels, which orbits the earth and beams down power to a receiving station.  The first problem is:  due to the earth’s strong gravity, the super slow orbit that would take ~24 hours to complete (and thus keep a satellite constantly over the same spot on the earth), is only available at 35,000 km (22,000 miles) away from the earth.  This is why geostationary internet satellites have such terrible latency — because to stay in one spot as earth rotates, so that fixed rooftop dishes will always point to it — the signals must travel far out into space, then all the way back.
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Wikipedia:
A geostationary orbit can be achieved only at an altitude very close to 35,786 kilometres (22,236 miles) and directly above the equator. This equates to an orbital speed of 3.07 kilometres per second (1.91 miles per second) and an orbital period of 1,436 minutes, one sidereal day. This ensures that the satellite will match the Earth's rotational period and has a stationary footprint on the ground. All geostationary satellites have to be located on this ring.
https://en.wikipedia.org/wiki/Geostationary_orbit

Due to the earth’s gravity, satellites in orbit closer than this must move faster, to prevent them from falling back to earth. 

For example, the International Space Station in Low Earth Orbit circles the earth at a distance of about 250 miles [400 km].  It must maintain a speed of about 17,000 miles per hour [5 miles per second; 8 kps] to stay at that altitude.  And that speed results in an the station circling around the earth every 90 minutes.

If the ISS slowed, gravity would pull it down until it succumbed to reentry.  The station’s precise orbital speed at that altitude is what’s required to prevent the station from flying away from earth, or being pulled down to it.

Stable orbits require you going fast enough, in a direction pointed away from earth, so that you continually “fall toward earth but miss it.” ;)   

20 second video:
https://twitter.com/tyler0309/status/1397629811951128587

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Yeah, but it would be better if the satellite were closer
To orbit closer to the surface, at approximately the edge of space (100 km) and not be pulled down to earth would require a speed of 7.84km/sec.  This is much faster than the earth rotates — it theoretically would circle the earth every 87 minutes — but it would be stable only for a few minutes before collapsing.

https://en.wikipedia.org/wiki/Newton%27s_cannonball

https://www.freemars.org/jeff/speed/index.htm
 
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This is why we hear “Vehicle is pitching downrange” a few seconds after a rocket clears the launch tower.  Because orbits require “sideways” speed. A bullet fired straight up might reach orbital velocity… but then gravity would pull it right back down.

Orbital mechanics:  it’s the law! :)

If we launched a spacecraft straight up to the edge of space and wanted it to “hover” in place, it would require, essentially, a rocket engine firing forever, with just enough thrust at altitude to match the weight of the spacecraft, the rocket — and its crap-ton of forever fuel.  Consider what is required to keep an airplane or helicopter over one spot.  Much energy and fuel burned, and not able to be maintained for long.

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Near-earth power transfer from space might require a constellation of Low Earth Orbit satellites, each one beaming down power as it passed over an earth receiving station…. 

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There are proposals for “Geostationary Balloon/Airship Satellites”, floating in the mid-stratosphere (~70hPa).  But I see winds of up to 30 to 90kph at 70hPa altitude today, a relatively calm day, which would mean a lot of energy would be needed to remain in place, and quite a challenge to maintain a large array of solar panels, especially if an array is held up by multiple ships.  A solar array on the earth’s surface could be much larger, less vulnerable to the elements, and not require any energy to just remain in place.
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Geostationary balloon satellites (GBS) are proposed high-altitude balloons that would float in the mid-stratosphere (60,000 to 70,000 feet (18 to 21 km) above sea level) at a fixed point over the Earth's surface and thereby act as atmosphere analogues to satellites.
https://en.wikipedia.org/wiki/High-altitude_balloon

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What else? Some new kind of solar satellite? Laser links to send power to satellites on the dark side? Space batteries? How would power be transmitted from space down to earth?  What about clouds?  And how much Prohibited Airspace (it’s a thing) would be needed to keep airplanes away from where they might get burned up by it, let alone other satellites?
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NeilT

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Re: Solar Power from Space? It’s complicated.
« Reply #1 on: June 22, 2021, 09:24:35 PM »
Sig I did some reading about the thoughts on this.  35km to LEO is not a real problem because very short microwave can deliver a huge amount of power over long distances due to the lack of an atmosphere.

The LEO satellites can then beam it down to earth using lower frequencies and guidable transmitters.

There are benefits to space.  Much more of the solar power gets absorbed by the panels and is usable due to the lack of atmosphere.  Far enough out and the panels can get sun 24x7.  But bringing it down to earth loses up to 50% of the energy.

I was thinking that with low loss transmission, outside the atmosphere, with a sufficient number of downlink transmitters, power could be beamed wherever it is needed without needing the huge infrastructure of HVDC cables under the sea.

It is worth thinking about, at least.

There is quite a lot of research and information about top of atmosphere dynamics.  There is virtually zero wind or current or drag or anything like that.  The main problem with it is getting up there then staying up there.  Something the US military tried very hard to do and failed miserably.

Google wanted balloons for internet, due to the very low altitude it became prohibitive.

There is, possibly, a place for this tech, but it would require a level of space infrastructure which is, to our current technology, the equivalent of building the great pyramid with bare hands.

Loads of thoughts there though.  Like if you get 100% more energy for 100% more time and lose 50% of it on the downlink, you are still 100% up on the energy you were getting for the same panels.

Most analysis focuses on the loss.  Not on the opportunity.

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Re: Solar Power from Space? It’s complicated.
« Reply #2 on: June 22, 2021, 10:08:17 PM »
I read somewhere that geosynchronis orbits are essentially full over densely populated areas.

Sigmetnow

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Re: Solar Power from Space? It’s complicated.
« Reply #3 on: June 23, 2021, 12:48:41 AM »
I was thinking that with low loss transmission, outside the atmosphere, with a sufficient number of downlink transmitters, power could be beamed wherever it is needed without needing the huge infrastructure of HVDC cables under the sea.

Totally agree with this.  What with all the Bluetooth, and Qi charging, etc., cables seem so… last century.  We may not have the technology quite yet, but with access to space becoming more affordable, there will be more interest in figuring out how to transmit power and radio signals, next door and around the globe, without using cable or fiber.  Phased array antennas used to be very expensive gear, used mainly by the military, but now SpaceX Starlink is bringing them to the common consumer.

If we can transmit power at a distance in space, there will be no need to have large solar arrays in LEO — they can be some distance away in a sun-synchronous orbit that may not look like a traditional “orbit.”  Check out the planned path of the once and future James Webb telescope:

https://twitter.com/nasawebb/status/1405948904538001417
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Tor Bejnar

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Re: Solar Power from Space? It’s complicated.
« Reply #4 on: June 23, 2021, 01:11:15 AM »
Cross post below:
To minimize losses of transferring energy gathered in outer space to Earth's surface, would a dirigible parked at about 20 km up provide a platform to relay energy beamed from on high down to Earth?  From the Sceye website:
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We chose the form factor of an airship over balloons and fixed wing aircrafts as it allows for geostationary capability while lifting and powering far more payload than any other platform.

And good news:  Sceye has job openings!
Sceye, New Mexico consortium tests OpenRAN in the stratosphere for tribal broadband service
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A Swiss high-altitude platforms (HAPS) company Sceye recently conducted a test flight of its sleek, silvery stratospheric blimp with the aim of covering rural and tribal areas of New Mexico with 100 Mbps-level speeds.

Sceye’s HAPS achieved an elevation of 64,000 feet during a two-hour test flight last Wednesday, and the company also recently conducted tests to determine the range of its Open RAN-based LTE coverage. Sceye said that its tech allows OpenRAN-based LTE to reach a range of up to 140 kilometers — which it claims is “a long-range record in LTE OpenRAN architecture” — and 40 km beyond what standard LTE would be expected to achieve. It says that it will be able to cover “areas as wide as 27,000 square miles with high-speed broadband for all users of fixed and mobile, carving a path forward to providing true equitable access.”

“We view the successful flight and the record setting data connection as a significant milestone for our technology; one that could dissolve the rural broadband barrier,” said Sceye CEO Mikkel Vestergaard Frandsen. Frandsen founded Sceye in 2014 to focus on the possibilities of solar-powered HAPS for providing broadband service as well as improving environmental and disaster monitoring.
...

See more information on this European Space Agency site. "Sceye Services Enabled by HAPS Complemented by Satellite"
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NeilT

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Re: Solar Power from Space? It’s complicated.
« Reply #5 on: June 23, 2021, 03:35:27 PM »
In all of my reading, you need to get over 30km in order to get out of the issues with remaining stationary, i.e. you burn your budget of fuel trying to remain on station and force either refuel or to land and replace the lift vessel.

Although my thinking was that with a power conduit, burning hydrogen with oxygen, in a closed loop system, would give you endless propulsion fuel if you cracked the water back to hydrogen and oxygen using a small portion of the power going through the relay.  Food for thought.

But this kind of vessel has a huge problem which is the loss of lift gas.  Eventually it leaks and eventually it has to be refilled.

Most LTA vehicles are designed to lift, go somewhere and land.  This kind of infrastructure would need to be fixed, long term.

I managed to make a contact through work to talk about my idea on that.

My thoughts revolve around a vessel which can reach 70km or more, never have to come down and be able to keep itself in position as needed.  That kind of vessel could hold the required downlink transmitting circuitry on the bottom and the high frequency receiving circuitry on the top.

Enough of those and you have the requisite infrastructure for space based power to be viable.

Another consideration is that the higher losses of power down to earth come from using frequencies which are not harmful.  However there are places in the world where harmful frequencies are not an issue.  Allowing for less loss and greater power delivery.

It is an interesting field.
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Tor Bejnar

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Re: Solar Power from Space? It’s complicated.
« Reply #6 on: June 23, 2021, 09:54:38 PM »
Did you read
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Sceye is solar powered during the day and battery powered at night. We don’t rely on rocket fuel like satellites or single use plastics like balloons.
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We chose the form factor of an airship over balloons and fixed wing aircrafts as it allows for geostationary capability while lifting and powering far more payload than any other platform.
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Our hull fabric in comparison to the nearest alternative used by others in attempts to build the stratospheric platform
     5 times stronger relative to weight
     1500 times more gas tight
     UV and ozone resistant
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Our advanced lithium-sulphur battery
     Energy density more than 400 Wh/kg
     2 times greater energy density than best electric vehicles
     400 Wh/kg is the threshold at which airplanes go electric
That's their hype.  I don't know!  (I've just been a fan of dirigibles ever since I first read Nevil' Shute's Slide Rule: Autobiography of an Engineer in 1972.)

They don't appear to be 'just' some crazy Swiss hanging out in the New Mexico desert! (They're also crazy Swiss doing things with the European Space Agency.)

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NeilT

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Re: Solar Power from Space? It’s complicated.
« Reply #7 on: June 24, 2021, 03:27:04 PM »
Yes I know that they are putting a huge amount of effort into this.  But the point is that there is no such thing as a fully gas tight envelope for helium or hydrogen.  Also, at 20km, there is the statistical certainty that it will be overwhelmed by winds at that altitude.  From my reading you need to get over 38km before you can start to discount atmospheric drag from wind storms.

It is a fantastic advance on existing technology.  But it is limited by its very own design, which means it uses a lift gas which cannot be replaced whilst in flight without resupply.

Most of my reading says you need to be in the mesosphere to achieve truly viable operational capability as wind problems found in the stratosphere are rare.

The airship being worked on here falls into a category of long duration middle atmosphere flight.  To truly get to space based solar power we'd need permanent middle atmosphere platforms which are geostationary, locked to one place on the earth.

Having permanent platforms of this type would allow orbiting solar power farms to beam onto the required downlink platform for transmission of the power to earth.

Of course, even with this helium kind of ship, given the electric nature, it could borrow from the beamed power stream to hold itself in place and, thus, need minimal battery capacity.

However it still suffers from helium loss and helium is a finite gas.  For fixed operation hydrogen would be a far better choice.  Given that the platform would not be carrying passengers or low flying around populated areas.

Still not my idea but this is better than many others.
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Sigmetnow

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Re: Solar Power from Space? It’s complicated.
« Reply #8 on: June 24, 2021, 04:13:29 PM »
Just came across this graphic, which may help here until I find something better….
Click to embiggen.
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Sigmetnow

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Re: Solar Power from Space? It’s complicated.
« Reply #9 on: June 24, 2021, 04:48:39 PM »
How much lift does a hydrogen or helium balloon generate at stratospheric altitudes? 

Per wikipedia, high altitude balloons generally attain stratospheric altitudes “between 18 and 37 km (11 and 23 mi; 59,000 and 121,000 ft) above sea level. In 2002, a balloon named BU60-1 reached a record altitude of 53.0 km (32.9 mi; 173,900 ft).”
https://en.wikipedia.org/wiki/High-altitude_balloon

It’s one thing for a balloon to lift itself, and maybe a small package of instruments, to the stratosphere.  But attach high-power transmitters, receivers, antennas, batteries… and thrusters?, fuel, and fuel generators? … and the balloon has to lift much more than its own weight.  (Big satellites weigh several tons!)  I have a hard time seeing airship power maintaining anything similar at a high altitude, in place, using current technology. 

Change my mind. ;)
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NeilT

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Re: Solar Power from Space? It’s complicated.
« Reply #10 on: June 24, 2021, 05:23:19 PM »
How about this one?



It gives an idea of what can get to where with current technology.
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NeilT

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Re: Solar Power from Space? It’s complicated.
« Reply #11 on: June 24, 2021, 05:36:24 PM »
Change my mind. ;)



That is 2.7 tons.

https://www.nasa.gov/scientific-balloons/types-of-balloons

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Scientific balloons can lift up to 8000 lbs. (3600 kg), which is approximately the weight of three small cars!

I would expect commercial platforms to be a LOT bigger than a science balloon and stay up for a LOT longer.  It is, for instance, the difference between the Montgolfier brothers balloon and the Graf Hindenburg series.

I would also expect that the commercial application would be able to stay up for years.

So it is being done for tens of days to an altitude which is viable.  When pushing the envelope, it is worth aiming a lot higher.

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Tor Bejnar

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Re: Solar Power from Space? It’s complicated.
« Reply #12 on: June 24, 2021, 07:05:45 PM »
Thank you Neil for your several comments.
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Sigmetnow

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Re: Solar Power from Space? It’s complicated.
« Reply #13 on: June 24, 2021, 07:50:06 PM »
Good info, Neil. Thanks!
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That is 2.7 tons.

But only at altitude for a few days, or a couple months at most, right?  Even the longest duration in your table is 100 days.

Importantly:  those balloons are in simple free-flight, not stationary. 

“Thrusters at station-keeping, Captain.”

The Inmarsat I4 F3 communications satellite was a hefty 5960kg.
 Weather satellite (DMSP) weighs just over 4,500lbs total.

Just saying, powerful tech is much heavier than we’d like.  NASA rejected the Dynetics moon lander proposal because they determined it would require “negative mass”….
      
Quote
I would expect commercial platforms to be a LOT bigger than a science balloon and stay up for a LOT longer. …

I would also expect that the commercial application would be able to stay up for years.

So it is being done for tens of days to an altitude which is viable.  When pushing the envelope, it is worth aiming a lot higher.

It would have to be — much heavier than a science pack, and at altitude for much longer — but I still don’t see how it could be done.  Not saying it never will be done!  But I see no current technology that could lift a heavy power station to high altitude and keep it there, fixed over one spot.  In fact, have we seen any lighter than air craft that can station-keep in the stratosphere for months at a time?

Let’s keep looking.
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NeilT

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Re: Solar Power from Space? It’s complicated.
« Reply #14 on: June 24, 2021, 09:49:39 PM »
You're right, it has not been done.  Getting above the stratosphere solves the station keeping, there is virtually zero wind.  The reason it has not been done is because current tech is only aiming for the stratosphere because that is easier to get to.

Staying up?  Now that's a big one.  You need a lift envelope which can be maintained without resupply.  I have thoughts about that.  I'll find out, shortly, if others see it the same way.  Well hopefully.

But, no, nobody is doing that today. They're still trying to do what the incumbent automotive industry is doing.  Leveraging 100 year old technology with 21st century materials.  They need to take 21st century tech and create a new look at what they're doing.
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Sigmetnow

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Re: Solar Power from Space? It’s complicated.
« Reply #15 on: August 03, 2021, 10:20:54 PM »
—- Revealed:  Space-based Solar Power Project (SSPP)
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Eric Berger
Now that the cost of access to space is coming down it's important to actually have meaningful things to do with it. Space-based solar power certainly qualifies. Excited to see where this goes.
https://twitter.com/sciguyspace/status/1422638198618984453
 
Quote
Caltech
Today, we announce a $100M gift from Donald Bren, chairman of Irvine Company and a Caltech lifetime trustee, to form the Space-based Solar Power Project (SSPP).

The goal: Develop technology to capture solar power in space for use on Earth.
https://twitter.com/caltech/status/1422626285356912641
 
Caltech Announces Breakthrough $100 Million Gift to Fund Space-based Solar Power Project
Quote
Today, Caltech is announcing that Donald Bren, chairman of Irvine Company and a lifetime member of the Caltech Board of Trustees, donated over $100 million to form the Space-based Solar Power Project (SSPP), which is developing technology capable of generating solar power in space and beaming it back to Earth.

SSPP aims to ultimately produce a global supply of affordable, renewable, clean energy. A key benefit of harnessing solar power from space is that it provides access to the sun to create power all day, every day, free from weather constraints or darkness of night.

The project's first test, which will occur in early 2023, will launch technology prototypes for the solar power generators and RF wireless power transfer, and includes a deployable structure measuring roughly 6 feet by 6 feet. … 
https://www.caltech.edu/about/news/caltech-announces-breakthrough-100-million-gift-to-fund-space-based-solar-power-project

Space Solar Power Project
Quote
Collecting solar power in space and transmitting the energy wirelessly to Earth through microwaves enables terrestrial power availability unaffected by weather or time of day. Solar power could be continuously available anywhere on earth.
Our concept is based on the modular assembly of ultralight, foldable, 2D integrated elements. Integration of solar power and RF conversion in one element avoids a power distribution network throughout the structure, further reducing weight and complexity. This concept enables scalability and mitigates local element failure impact on other parts of the system.

Most recently we demonstrated the lightest (by an order of magnitude) integrated multifunctional prototype which collects sunlight, converts it to RF electrical power, then wirelessly transmit that power in a steerable beam.
 
RESEARCH
Our research solves the fundamental challenges associated with implementing space solar by integrating ultralight and shape accurate structures with high efficiency photovoltaics and large scale phased array power transmission into a two dimensional scalable, deployable spacecraft.
https://www.spacesolar.caltech.edu/
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Sigmetnow

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Re: Solar Power from Space? It’s complicated.
« Reply #16 on: August 03, 2021, 10:29:29 PM »
Space-based Solar Power | ACT of ESA
https://www.esa.int/gsp/ACT/projects/sps/

Solar Power Satellite concept
Space based solar power satellites (SPS) are large structures in space that convert solar energy, captured as solar irradiation, into a form of energy that is transmitted wirelessly (WPT) to any remote receiver station. This receiver could either be on Earth, or on a high altitude platform (aircraft), other spacecraft or even on the surface of the moon or other planets. The original idea took form in the 1970's by the Czech-US engineer Dr. Peter Glaser and ever since a variety of studies have been undertaken. These studies have led to a large diversity of concepts which use different forms of power generation, conversion and transmission principles.

How is the power transmitted to Earth?
Currently the so-called reference design transforms solar power into electricity via photovoltaic cells in geostationary orbit around Earth. The power is then transmitted via electromagnetic waves at 2.45 GHz to dedicated receiver stations on Earth, "rectennas", which convert the energy back into electricity used in the local grid.

How much power can solar power satellites deliver?
The power range of the concepts for SPS is from a few tens of MW to several hundred of GW. Just for comparison purposes, a modern standard nuclear power plant delivers about 1 GW and the energy need for Europe in 2020 is estimated to be about 500 GW. If we can come close to the theoretical transmission efficiencies via electromagnetic waves (50-60%) then we could produce around 400W electricity per square meter on Earth receivers, which is about two to three times the amount we could receive from the same area of terrestrial PV panel. Furthermore, this would be produced continuously, day and night.

The advantages and disadvantages of a space-based system
One of the main advantages of a solar power station is the continuous power generation. Unlike the day-night cycle of solar arrays on Earth, a SPS in geostationary orbit 35786 km above earth will continuously face the sun and provide a constant output over time. The solar irradiation (W/m2) outside of the Earth's atmosphere is also slightly higher. The continuous energy supply will also put much less stringent demands on the storage capabilities, which are in general large and expensive. A second advantage is obtained by the wireless power transfer to any location on the planet. This will remove the requirements of a large-scale electricity grid and allows for dynamically allocating power to the regions where it is required. A possible third advantage is the level geopolitical playing field in which the energy is equally collected and distributed by all participating countries.

Clearly, one of the main challenges for any space-based solar power satellite is the construction of large structures in orbit. Not only does it require significant amounts of material to be launched into space, these materials will need to be assembled, maintained and possibly replaced over time. In fact, due to the harsh space environment, the lifetime of current solar panels in space is significantly shorter compared to the Earth surface. A second complication is related to the wireless power transmission to the Earth surface, which requires transmission via electromagnetic waves at high transfer efficiencies. To stay below safety limits, this will require very large diameter receiver antenna's (or rectenna's), although in comparison to earth bases solar arrays the total area coverage will be smaller.
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