The simplest space-based power is, of course, PV. I recently discussed with the facilities manager of a major UK industrial player the (it seemed) no-brainer approach of putting PV onto the roof areas of their production buildings, only to discover that they were *very* wary of the prospect of high power DC gubbins in their roofspace. No worries about PV as a source, big worries about anything which wasn't a commodity and which could set fire to their roof/kill staff.Microwave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!
Quote from: Robotbeat on 05/12/2016 03:45 pm5) operate in an atmospheric windowI'll only refer to microwave transmission through the 1-10GHz atmospheric window.
5) operate in an atmospheric window
Yeah, klystron looks nice, but it's not high enough frequency.
And for the transmitter, we ideally want even higher efficiency (95%? 98%? Higher?) mainly to avoid needing huge radiators.
2.45GHz is not what I meant for high frequency. That's 12cm wavelength. We really want more like cm wavelength, so 30GHz. Otherwise the antennae are just way too big.
Quote from: Bob Shaw on 05/14/2016 12:48 amMicrowave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!Any major reason why PV on their roof would be different from PV on house roofs?
Microwave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!
Quote from: A_M_Swallow on 05/14/2016 01:04 amQuote from: Bob Shaw on 05/14/2016 12:48 amMicrowave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!Any major reason why PV on their roof would be different from PV on house roofs?They are incredibly risk averse - as simple as that. Homeowners are blessed with breezy ignorance, and their insurance providers are blessed with a deep knowledge of statistics. People in big businesses will stick with the status quo as long as possible.
On the other hand, the co-operative managed to put ahalf a megawatt of PV on the CIS Tower
...Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period)....
Quote from: SICA Design on 06/08/2016 04:14 pm...Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period).......except you MIGHT get about 25-50% of that power all the way to the ground and on the grid. And the cost of the solar arrays will be a small fraction of the total cost.
Quote from: Robotbeat on 06/08/2016 04:57 pmQuote from: SICA Design on 06/08/2016 04:14 pm...Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period).......except you MIGHT get about 25-50% of that power all the way to the ground and on the grid. And the cost of the solar arrays will be a small fraction of the total cost.Yes, 50% efficiency DC (space) to DC (grid) is the widely accepted figure.My viewpoint is based on what technologies can feasibly replace fossil fuels for a sustainable future. Given that land area is a limited resource required (amongst other necessities) for food production...
...Terrestrial solar farm - 10W/m^2 - 30 million hectares required, plus grid-scale storage...
Quote from: SICA Design on 06/08/2016 09:03 pm...Terrestrial solar farm - 10W/m^2 - 30 million hectares required, plus grid-scale storage... 10W/m^2 is not at all the best that you can do. Maybe relevant for old cells and poor fill factor in northern Europe, but not relevant to most of the world's population.30% efficiency, 90% fill factor, you can do over five times that in the desert, which is the best place to put solar farms and which doesn't compete with just about anything for land use. Even so, that'd require about 0.1% of the Earth's surface.
Additionally, that power figure is too high as it assumes heating value of fossil fuels, which is a bad assumption for heating and for vehicles because heat pumps and electrical devices are better by about a factor of 3-5.
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.
If you are comparing current technology, let's get some real numbers. What's the best microwave rectenna transmission efficiency at megawatt or greater power levels right now? What distance is involved? How does its efficiency actually scale with distance (ie, including side lobes or other non-idealities)? (At a megawatt, you would need 30 million of them to compare to your other energy alternatives that you were listing. That's not an inconsequential footprint.)What's the best power transmission efficiency from orbit to earth, ever, and at what power?Every decades-away, back-of-the-envelope, idealized future technology looks fantastically good when compared to current technology actually built, in full non-idealized reality.
50% Efficiency from in-space electrical power to terrestrial grid power is an accepted value (with established precedents) for those working in the field. It is easy to find examples which would not meet this, and no-one is claiming that Space-Based Solar for Earth will be easy.
Quote from: fatjohn1408 on 06/09/2016 08:44 amI worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.Polar Sun synchronous LEO?
Quote from: Alf Fass on 06/09/2016 08:52 amQuote from: fatjohn1408 on 06/09/2016 08:44 amI worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.Polar Sun synchronous LEO?I think that was our proposal if I recall, but I don't know if we made a trade off between the performance capacity of launchers between SSO and LEO. I think our launch costs (assuming the Ariane V at the time) were about 40% of total cost. So if this was launch cost to SSO that means switching to LEO could perhaps maximally save you 20% on costs (assuming SSO capacity is at least half of LEO equatorial capacity) and would probably increase the power output with way more than 20% (no eclipse)So yes SSO makes the most sense.What killed the project from being viable in our point of view was the cost of the launchers and the cost of the lasers. But even using the numbers for Ariane VI instead of Ariane V would already make the launch cost drop significantly and that's not even discussing SpaceX, Skylon, Blue Origin etc. Point is launch costs should have been a bit lower than we assumed back then.The cost of lasers might still be a bottle neck though.Other problems were clouds, so we thought the ground stations should be near Phoenix on the one hand (for US) and in in the northern Sahara on the other hand (for Europe/North Africa)