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Various issues with this tech: 1. "A 2,000 MW SSP system would require a ground receiver covering about 30 square kilometers" 2. The satellite would be in geo

by xt00 5y ago

Various issues with this tech: 1. "A 2,000 MW SSP system would require a ground receiver covering about 30 square kilometers" 2. The satellite would be in geostationary orbit, or 22,000 miles up, so a directed microwave beam would need to be sent that distance in as tight a beam as possible, so likely the transmitter side on the satellite would be a large dish (to go along with the large surface area of the solar panels, so maybe if the solar panels are solved, then a large dish is ok) 3. Now, if you flew an airplane through that 30 sq km area what happens, or various wildlife like birds fly through that area? Slight cooking? 4. Likely that receiver can't be located near a city because people would be freaked out about being irradiated by a giant microwave beam, so you need transmission towers going across the land to the city you are hoping to power 5. If something goes wrong with your giant power plant in the sky you need to spend serious money to go up and try to fix it. Or, you can dispense with all of that say, ok lets put up a 30 sq km solar array and a battery bank with it and just live with the fact that you don't get sun all of the time. Far cheaper and easier to maintain and upgrade in the future. If this was a discussion about doing this from a space solar farm beaming energy down to mars, then that would be a different story since putting mass into orbit around a planet is cheaper than getting it onto the ground -- so it may actually make some reasonable sense for powering a mars base for some period of time rather than deploying tons of solar panels down on the surface of mars, then on the surface you come up with a low cost way to create some receiver that is low mass and ideally would be just a bunch of wire on a spool that somebody drives back and forth building up over a month or something.

evgen 5y ago
The receiving rectenna would be large, but from what I know it would basically consist of a spaced array of small vertical antennas. The sat does not need to be in geostationary orbit and in fact a better solution is to have a constellation at lower orbits. This also eliminates the last problem you posed because if something goes wrong with the sat you just de-orbit it before you had planned and write it off. If you fly through the beam or walk through it you would not know. Do you feel a slight warming when you put your hand on top of your wifi antenna? There are problems with space-based solar and beaming energy, but none of your objections make the list.
- xt00 5y ago
  The non-geostationary design in low-earth orbit is mentioned with not much detail in this article and would generate far less power for a particular receiving location since it only periodically receives power -- so there are various objections to that approach as well. In the case of the geostationary energy being sent through the atmosphere to the receiver -- they mentioned 2000MW of power being delivered -- assuming you use the area of a house (as viewed from top down) as an area to compare against, by some rough calculations roughly 10KW would be impinging upon a house surface that is roughly 1500sqmeters -- so 10KW of microwave energy directed into a house area -- that is non-trivial, so I assume your comparison between wifi antenna's was in reference to the low earth orbit solution -- the geo stationary solution referenced in the article is very powerful and would be in a totally different class from the approx sub 1W range coming from your wifi antennas. So I would be worried to walk through it.
- senectus1 5y ago
  >in fact a better solution is to have a constellation at lower orbits only that this turns the cost of something that is already very very expensive into something that is hideously ridiculously expensive.
  - evgen 5y ago
    No it doesn’t. The major cost is not the satellite structure, it is getting up there. Low orbit costs significantly less.
deleted 5y ago
[deleted]
jeffbee 5y ago
30 sq km isn't even a lot less than the land you'd need for a simple terrestrial PV station of the same capacity. NREL said in 2012 that the total space needed for PV is 8 acres per MW, so 2000 MW would occupy 65 sq km.
- T-A 5y ago
  Are you comparing peak power? Keep in mind that space-based solar can work around the clock, while ground-based hits peak power only around noon and does nothing at all at night, so it needs to (1) be complemented with something else for baseload and (2) be oversized by some multiple to deliver enough power through the day.
T-A 5y ago
> if you flew an airplane through that 30 sq km area what happens, or various wildlife like birds fly through that area? 30 square kilometers is 3e7 m^2. 2000 MW is 2e9 W. So you're looking at less than 70 W/m^2. For comparison, the solar constant [1] is more than 1300 W/m^2. So, no cooking. Also, the receivers would be microwave antennas on poles, i.e. they wouldn't monopolize the land they stand on. There is concept art from the 70s showing cows grazing between/under them. [1] https://en.wikipedia.org/wiki/Solar_constant https://en.wikipedia.org/wiki/Solar_constant
- nbadg 5y ago
  > 70 W/m^2 For reference, according to wikipedia [1] the US federal limit on microwave oven emissions (outside of the enclosure, ie, what you would experience if you smushed your face against the glass while watching your oatmeal cook) is 50 W/m^2, which is "far below the exposure level currently considered to be harmful to human health". [1] https://en.wikipedia.org/wiki/Microwave_oven#Direct_microwave_exposure https://en.wikipedia.org/wiki/Microwave_oven#Direct_microwav...

by xt00 5y ago

evgen 5y ago

The receiving rectenna would be large, but from what I know it would basically consist of a spaced array of small vertical antennas. The sat does not need to be in geostationary orbit and in fact a better solution is to have a constellation at lower orbits. This also eliminates the last problem you posed because if something goes wrong with the sat you just de-orbit it before you had planned and write it off. If you fly through the beam or walk through it you would not know. Do you feel a slight warming when you put your hand on top of your wifi antenna? There are problems with space-based solar and beaming energy, but none of your objections make the list.

xt00 5y ago
The non-geostationary design in low-earth orbit is mentioned with not much detail in this article and would generate far less power for a particular receiving location since it only periodically receives power -- so there are various objections to that approach as well. In the case of the geostationary energy being sent through the atmosphere to the receiver -- they mentioned 2000MW of power being delivered -- assuming you use the area of a house (as viewed from top down) as an area to compare against, by some rough calculations roughly 10KW would be impinging upon a house surface that is roughly 1500sqmeters -- so 10KW of microwave energy directed into a house area -- that is non-trivial, so I assume your comparison between wifi antenna's was in reference to the low earth orbit solution -- the geo stationary solution referenced in the article is very powerful and would be in a totally different class from the approx sub 1W range coming from your wifi antennas. So I would be worried to walk through it.
senectus1 5y ago
>in fact a better solution is to have a constellation at lower orbits only that this turns the cost of something that is already very very expensive into something that is hideously ridiculously expensive.
- evgen 5y ago
  No it doesn’t. The major cost is not the satellite structure, it is getting up there. Low orbit costs significantly less.

deleted 5y ago

[deleted]

jeffbee 5y ago

30 sq km isn't even a lot less than the land you'd need for a simple terrestrial PV station of the same capacity. NREL said in 2012 that the total space needed for PV is 8 acres per MW, so 2000 MW would occupy 65 sq km.

T-A 5y ago
Are you comparing peak power? Keep in mind that space-based solar can work around the clock, while ground-based hits peak power only around noon and does nothing at all at night, so it needs to (1) be complemented with something else for baseload and (2) be oversized by some multiple to deliver enough power through the day.

T-A 5y ago

> if you flew an airplane through that 30 sq km area what happens, or various wildlife like birds fly through that area? 30 square kilometers is 3e7 m^2. 2000 MW is 2e9 W. So you're looking at less than 70 W/m^2. For comparison, the solar constant [1] is more than 1300 W/m^2. So, no cooking. Also, the receivers would be microwave antennas on poles, i.e. they wouldn't monopolize the land they stand on. There is concept art from the 70s showing cows grazing between/under them. [1] https://en.wikipedia.org/wiki/Solar_constant https://en.wikipedia.org/wiki/Solar_constant

nbadg 5y ago
> 70 W/m^2 For reference, according to wikipedia [1] the US federal limit on microwave oven emissions (outside of the enclosure, ie, what you would experience if you smushed your face against the glass while watching your oatmeal cook) is 50 W/m^2, which is "far below the exposure level currently considered to be harmful to human health". [1] https://en.wikipedia.org/wiki/Microwave_oven#Direct_microwave_exposure https://en.wikipedia.org/wiki/Microwave_oven#Direct_microwav...