Famous eng-tips member interviewed about hydrogen on the ABC

[GregLocock]

Good realistic look at why hydrogen electrolysis projects are struggling worldwide. Since it was on the ABC I was expecting the usual boosterism. Nah, basic line was you can't subsidise bad physics to success. https://www.abc.net.au/listen/programs/the-radio-national-hour/the-radio-national-hour/104837476

There was one mistake - we often have days at a time with little solar and no wind, right across the grid. Hence your facility will be shut down arbitrarily.

 

[dik]

we often have days at a time with little solar and no wind, right across the grid.

That's why the Chinese are planning to put a solar panel grid in space. Active 24/7.

 

[GregLocock]

Did you know the Earth casts a shadow?

 

[dik]

Did you know the Earth casts a shadow?

If you locate it properly, it can cast a shadow on the earth... nearly total 24/7.

 

[GregLocock]

Please demonstrate with a plausible example.

 

[TugboatEng]

If you locate it properly, it can cast a shadow on the earth... nearly total 24/7.

That sounds like a weapon.

 

[dik]

That sounds like a weapon.

Tiny shadow...

 

[GregLocock]

Can't find an orbit that gives solar 24/7? Because there isn't one that's usable. As usual you have been, at best, misled.

 

[dik]

What if it was located over one of the poles?

 

[JoshPlumSE]

The poles definitely wouldn't work..... But, I suppose it's technically possible to put a satellite orbit that follows the rotation of the earth so that it would be in daylight almost all the time. However, what would be the frigging point? You cannot send that power down to earth in any sort of cost effective way. Right?

Dik: That's why the Chinese are planning to put a solar panel grid in space. Active 24/7.

Again, what would be the point of this? Maybe link to an article about this (if one exists).

Maybe to create "shake" to reduce the energy input from the sun? Just off the top of my head this sound like a truly preposterous "solution" that can't have any basis in actual reality.

How much CO2 would be produced in the manufacturing of the rockets and such required to put enough material to create "shade" significant enough to make any impact?!

 

[btrueblood]

There are possible orbits that get full sun (L1 orbit for instance), but the earth still rotates underneath, so beaming the power down (typical studies use microwave beams targeting large (like 1/2 of Nevada size) antenna fields) is problematic. People might not like the extra warmth of those microwaves beaming down on their heads in an already hot area (maybe only a problem at the edge of the antenna grid?), or they might be unhappy with a large wire grid network spanning thousands of square miles overhead.. Cost effectiveness has never really been studied, the cost to lift enough panels to make it worthwhile has been too high historically. It might become cost effective if a lunar base ever gets established. Then you need to consider the maintenance, solar cells degrade in space due to mechanisms not found on earth - i.e. solar radiation ion damage and micrometeorite ablation.

From memory, it was awhile ago I worked with colleagues studying the problem for comsats, but it is theoretically possible to get about 90% of 24/7 power in a geosynchronous orbit, since Earth's full shadow zone is only a few hours of the orbit, and that only in the parts of the year when the axial tilt of the satellite orbit is aligned with the earth's orbit around the sun. So, 24/7 with battery storage on orbit...or multiple satellites so you can have 2 out of 3 beaming at "night".

"The poles definitely wouldn't work". Um, no Josh. There are a couple ways to make a near-stationary polar orbiter, one that might work for a power satellite is one of R, L. Forward's statites. Again, not been demonstrated, and certainly more expensive than a geosynchronous satellite, but not impossible. Orbital dynamics is a fun subject.

 

[GregLocock]

Solar from space has been studied in some depth. One estimate is that it would be 100000 times more expensive than terrestrial solar.

Polar orbits are very expensive to get to, about double the deltaV required for an equatorial orbit. The earth would spin underneath you so you can't beam the energy down continuously.

Another option would be a lagrange point, again you have problems with deltaV and the spinning earth.

The only way round the spinning earth issue is a geosynchronous equatorial orbit, which is in darkness for just over an hour a day. Typical beam intensity at the earth's surface would microwave a mouse to death in a minute. Clouds are still an issue.

 

[btrueblood]

"Polar orbits are very expensive to get to, about double the deltaV required for an equatorial orbit. The earth would spin underneath you so you can't beam the energy down continuously."

Well, unless you had an antenna covering the pole, and you steer the beam to it. Probably not realistic for a north polar satellite, but we aren't really talking "realistic" anyway.

Again, at GS orbit you aren't in darkness every orbit, only twice a year does the SC orbit intercept the sun-earth line at earth's ecliptic. Earth's rotation axis is the SC orbit plane, is tilted at 23.5 degrees relative to its orbital plane, and these two planes then have to intercept sun-earth line of sight.

And yeah, clouds might intercept some of the microwaves, but a lot will get through - comsats operate on microwave frequencies, so do aircraft radars, and they don't have any significant problems with signal attenuation. edit: you might be able to have beachfront property owners pay you to locate your antenna grid nearby, and have the continuous microwave beams boil off clouds that form. 24/7 beach weather, woo hoo!

Basically it's down to launch costs vs. return on investment. Oh, and: adding intercepted radiant solar power (that otherwise would have missed the earth entirely) into earth's existing solar power budget will definitely cause global warming. Like a coffee cup in a microwave oven kinda thing.

 

[GregLocock]

In summer, in Australia, to hit net zero we need about 4 times as much windpower, on average. In winter more like 10x, on average. However, since Australia a monolithic blob of land set in some big oceans our wind patterns are often very simple, such that the entire continent sees similar windspeeds. We often get a high over the whole country, with little wind, for days at time.

 

[hokie66]

Another solar energy boondoggle. Hopefully, President Trump's team can prevent this stuff for a few years.

Energy experts blast failed billion-dollar DOE project as 'financial boondoggle,' 'disaster'

Energy experts are sounding the alarm over a failed green energy "boondoggle" after the Ivanpah Solar Power Facility signals its road to closure.

www.foxnews.com

 

[GregLocock]

The pin is being pulled on several hydrogen projects globally, including BP's in Western Australia and the one in Queensland. The economics of the latter were hilarious , $12.5B to make $1.6M of hydrogen a year, eventually.

 

[dgeesaman]

That sounds like a weapon.

"That's no moon"