On Tuesday, April 5, 2016 at 11:47:24 AM UTC+12, Rick Jones wrote:
Fred J. McCall wrote:
Rick Jones wrote:
Just a peanut-gallery guess, but a big, honking solar power
satellite is the first and only thing which comes to mind.

Even that's not worth it. It's still cheaper to build them down
here.

Thin film inflatable optics

A reflective sphere that's transparent on one hemisphere and reflective on another, when oriented toward the sun, focuses the sun in a confocal way. By molding small ridges into the reflective hemisphere, sunlight can be brought to a precise focus.

This provides the ability to concentrate sunlight to over 20,000x its ambient intensity at Earth. So, a 30.5 meter diameter concentrator can focus light on to a 216 mm diameter wafer that efficiently converts the beam to laser energy and transmits it using conjugate optical techniques to a receiver..

Operating at 500 nm wavelengths a 216 mm diameter objective can efficiently beam energy to another 216 mm diameter objective a distance of 69.53 km.

Concentrating 1600x ambient increases the mass of the thin disk laser and increases broadcast range. At 1600x intensity sunlight is focused to a spot 762.5 mm in diameter and beams to a similarly sized spot 865.34 km distant.

Systems 1,000 m in diameter have been contemplated that efficiently beam energy to Earth from GEO to receivers 762.5 mm in diameter.

A kg covers 16 sq meters in the best designs I've seen for space applications.

Echo satellite comprised of a 30.5-metre (100 ft) diameter balloon was made of 0.5-mil-thick (12.7 µm) metalized 0.2-micrometre-thick (0.00787-mil) biaxially oriented PET film ("Mylar") material, that was 99.8% reflective. The sphere itself was 94.26 kg total mass. The entire satellite, including inflation hardware, massed 180 kg. This is 16.2 m2 per kg of mass. 4.05 m2 per kg of projected area.

GBO film is made of layered birefringent PET film that efficiently reflects sunlight with 99.99% efficiency with 0.2 micrometer thick PET film. A 30..5 m diameter ball of this material is 0.9 kg! Now PET film that does not have birefringence reflectivity built into it, masses the same and is perfectly transparent. With MEMS based systems, ultra low pressure gas, and other details this provides over 64.8 m2 per kg of mass. This is 16.2 m2 per square meter of area normal to the sun using stable spherical configurations..

Similarly sized systems on Earth, must operate at 2 bar and be 150 microns thick. So, a 30.5 m diameter sphere is 625 kg of material. 36,248 kg of pressurised air. Another 625 kg of hardware to support it. 1250 kg at $1.50 per kg is $1875 air is nearly free just the cost of pressurisation. Electronics, tracking and other hardware add another $125 - for $2,000 per unit..

The system on orbit masses 46.5 kg overall and at $150 per kg (100x the cost of a terrestrial unit) it costs $697.50 to build. This cost compares favourably with other nanosatellites.

A Falcon Heavy costing $90 million and reusable say 100 times, cost $900,000 for the cost of the rocket and say another $1.1 million for the cost of the propellant and recovery operations. Say $2,000,000 - per launch. 53 metric tons divided by 46.5 kg for the satellite described above, means 1140 of these devices may be orbited at once. Dividing this figure into the $2,000,000 cost is $175.43 A total cost of $872.93 per satellite.

On orbit 999,460 Watts of sunlight are intercepted 24/7 and converted with near perfect efficiency. This nets 8.761 million kWh. $1.57 million per year when sold at $0.18 per kWh

On Earth 730,620 Watts of sunlight are intercepted at the surface for 4 hours out of every 24 hours. 121,770 Watts on average. $193,000 per year when sold at $0.18 per kWh.

Both are tremendously profitable - $1.57 million per year for $873 invested for the orbital system. $193,000 per year earned for each $2,000 invested in the terrestrial system. Now, if the systems turn out to be 70% efficient overall, we merely multiply the revenue figures by this factor. $1 million and $135,000 respectively. We have achieved 82% efficiency in the lab and can go higher. Others have reported similar figures.

Now when we look at taking power from sunny regions and transmitting them to cloudy regions via optical fiber, or open air transmission, we can match or do better than the cost of wired transmission from similar installations like hydroelectric dams. However, as in the case of the generator above, we do far far better beaming energy directly to where its needed from space..

The almost (shy 3 minutes?) 24 hour sunlight at GEO is a nice draw,
though I suppose that even with storage enough for 24 hour supply it
is still cheaper to do terrestrially.

No, if you have boosters that you can use 100x or more, and use best practices, you can make terrestrial solar very cheaply, and space solar astoundingly cheaply. There's no contest once launch costs are reduced by a factor of 50 or so.

Space based solar power
https://vimeo.com/37102557

Terrestrial solar power
https://vimeo.com/52213948


rick jones
--
I don't interest myself in "why." I think more often in terms of
"when," sometimes "where;" always "how much." - Joubert
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