Is that this one https://spaceenergyinitiative.org.uk/space-based-solar-power/ ?

I haven't managed to get the geometry of what they propose into my head yet - it feels to me that as we're not at either of the poles, wherever you put the satellites there will be part of the planet in the way at some point of the 24-hours day - or are they thinking of a planet-wide constellation only some of which will be contributing at any point in time. In the latter case, I might suspect conflict with other countries planning similar systems (or maybe co-operation to feed into their system instead?).

They seem to be suggesting 2GW - which is hardly unlimited - UK demand is usually in the mid 30GW range (and we can already generate about 15GW from wind alone - although with more intermittency), but maybe it could be scaled up.

The microwave downlink sounds interesting - 2.9GW at 240W/m² seems to suggest a receiving aerial nearly 2.5 miles in diameter (if my maths is right)  - I'm not sure what's involved with such as device?

I wonder too about the installation, and given the seemingly short lifetime of things in orbit, the eventual de-commissioning and re-cycling of the materials involved.

There also quote 85% efficiency at the satellite end - I wonder what happens to all the waste (heat?) in the vacuum of space? If it's got to radiate out it's probably going to have to be reasonably hot - which maybe isn't good for PV panels or electronics.

Certainly and interesting idea - but probably need the reporters to come up with some more technical details to make a proper judgement though..

   - Andy.

I must say I see at as being harder than the website suggests.

Rectennas (an antenna with a rectification of the RF to DC ) have been demonstrated at moderate efficiencies but only at very power compared to what is proposed here there needs to be enough voltage to forward bias the diodes, but the diodes to rectify AC in GHz frequency range need to be small, low capacitance devices and because of this they are vulnerable to reverse voltage - those RF diodes typically used as mixers in satellite receivers (admittedly nearer 10GHz) have a capacitance of a few hundred fF (femto Farads =1E-15F) and reverse breakdowns of about 6V and forwards voltage drop of 0.4V, Typical max current per junction is a few tens of mA.

You need an awful lot of small diodes like that to make a gigawatt. (This design is typical, where a joint project with Glasgow and Southampton universities after much optimization  generates a few volts of DC into a 20k ohm load from RF at about 1GHz )

Beam tracking

From the satellite side to produce a spot on the earth a few miles across is going some in terms of narrow beam width- most satellite systems illuminate a good chunk of a continent at a time more or less ;-) RF is not opticss ,and I do not know what height the satellites are proposed, but the lowest orbit sensible would be many hundreds of miles, but those would whizz across the sky and need complex tracking to maintain a spot on target. Geostationary orbits are easier as the RF beam angles are fixed, , but at a height of 20 odd thousand miles the antenna array to make a beam that narrow is formidable. And that orbital track is high value and quite full already.

Then there is the generation of that much RF, this is the sort of power needed at CERN at peak pulse. There are RF sources on earth capable of (maybe tens) Megawatt levels not just pulsed, but they are rare and scary beasties, To add even one order of magnitude in power is brave, and to put kit into space where there is no cooling water and so on, would be a tremendous challenge.

And that is before we start to worry about the EMC implications of a gigawatt transmitter at some thousands of mile range - for not all the power will be generated on the right frequency (out of band sprogs, harmonics due to waveform quality, all the usual), and not all the energy at the intended frequency will be landing on the target either.

I Imagine that a much smaller, lower power system will  be demonstrated first, and it may be some decades  or even never that the system as described is actually operational.

Worth looking at certainly but a very hard spec to meet.

Mike.

I think that there was a similar system discussed on here a few years ago. One of the key points then was keeping the beam precisely aimed and what happened if it lost control. I am not sure how hazardous that level of microwave energy is, but i imagaine that the power density will be higher in the centre of the beam than around the edges.

I think that there was a similar system discussed on here a few years ago. One of the key points then was keeping the beam precisely aimed and what happened if it lost control. I am not sure how hazardous that level of microwave energy is, but i imagaine that the power density will be higher in the centre of the beam than around the edges.