Microwave/laser heating on small atmospere area

[AncientCoder]

Background: I been reading some articles about creating massive solar farms in space, on the moon, etc. and sending the energy down to Earth by microwaves or laser.

Question: Wouldn't this EM radiation create a kind of thermal "column" and some nasty weather because of the constant hot spot?

 

[Bobbywhy]

AncientCoder: Microwave and laser energy both pass through the atmosphere with little or no absorption…no absorption, no heating. So there would not be a “thermal column” if large amounts of energy were beamed from space down to the surface of our earth.

 

[AncientCoder]

THX

I thought there might be some effect though at those high energies.

 

[wildwohl]

Also, it is a crime to do so anyways.
http://en.wikipedia.org/wiki/Outer_Space_Treaty

 

[geo101]

Not if the system is used for peaceful purposes (in its original function it is not a weapon) and the relevant governments do not claim sovereignty of the "land" on which the equipment is based.

I'm not too sure about commercial exploitation though, but I don't think there is anything covering that.

 

[AlexLAV]

I think hot spots will be in any case since conversion efficiency of laser light or microwaves into electricity in not 100 %. But such hot spots exist around modern power plants also.

Powerful laser radiation or microwaves can be dangerous for birds. And what about influence of clouds on the laser light propagation?

On the other hand there are many empty places on Earth well illuminated by Sun where solar plants may be constructed.

 

[AncientCoder]

I've been doing a little reading and apparently there is some absorption depending on the wavelength used versus the specific chemicals(?) in the atmosphere!

Water vapour absorbs this frequency!
Oxygen absorbs that frequency!
et al

So if they are pumping down mega-watts or giga-watts, we are looking at some fraction which would still be lots of heat being added to the atmosphere in a very narrow defined area!

So much so that one proposal suggested beaming the energy down to a high altitude platform as laser for coherence, and then converting to microwave to pass through the lower atmospere/clouds with less absorption/blocking!

 

[AncientCoder]

Another little number I ran across on a different subject(AGW) at physorg!

Katrina was about a 150kj/cm2 TCHP hurricane.

If you heat the Gulf by 2C, that would ADD an additional 84kj/cm2 to TCHP...

Not sure how much these numbers apply, but I don't think I would like to see the results!

THX all!

 

[Bobbywhy]

While you are correct that there is some absorption of energy at various frequencies of microwaves and also of lasers, it makes logical sense that the systems engineers who design the system would avoid using them. They would choose those wavelengths that pass through the atmosphere with minimum absorption.

Second thought: Good idea to consider hybrid systems, too, if they would be more efficient.

 

[Dr Lots-o'watts]

You think it would affect the weather any more than irreversibly bringing up innumerable tons of fossil fuel gases? You might find a cheap KFC-style joint nearby the receiving end though.

 

[AlexLAV]

So much so that one proposal suggested beaming the energy down to a high altitude platform as laser for coherence, and then converting to microwave to pass through the lower atmospere/clouds with less absorption/blocking!

Please could you answer some questions:

1. How do you imagine realization of the high altitude platform?

2. What is the efficiency of conversion of laser beam power to microwave one, and how much heat must be removed from the convertor? As far as I know maximum to-date convertion efficiency of laser light to electricity is about 60 %. I don't know what is the efficiency of the microwave generators. An any case I suppose the total heat power to be removed from the platform must be rather high. What is supposed mechanism of the cooling?

3. As I can estimate efficiency of the total energetic chain from solar light to the final consumer on Earth is very low. My estimation: solar light to electricity - about 40 % (maximum to-date value), electricity to laser light - 60 %, laser light to electricity - 60 %. So, the total efficiency without microwave link is not higher 15 %. Wouldn't it better to use solar energy by another way? For example, using Earth-based solar power station, or reflect solar light by huge orbital mirrors to Earth.

 

[Bobbywhy]

Proposals for space-based solar power collection systems have been around for forty-four years (since 1968). Anyone who is interested in reading up on this technique may find this overview useful:

http://en.wikipedia.org/wiki/Space-based_solar_power

The Wiki article does include the possible losses due to absorption of microwaves or laser transmission by the atmosphere.

 

[AncientCoder]

Sorry AlexLAV not my field, as the "AncientCoder" nick is from 40 years in computers.

I'm basically just asking if people have considered that "beaming" this much power through the atmosphere have considered the effects of how much energy would be absorbed!


THX Bobbywhy!

From the Wiki post:

Only about half the power generated by the SSP would be delivered to the grid, once all losses are factored in. These losses are on the same order as modern fossil fuel plants.

So it still looks like a lot of energy would be absorbed when transmitting gigawatts within a confined area which would create a pretty good localized thermal updraft!

I will leave it to the weather gurus to figure out what that does!

 

[Bobbywhy]

Sorry AlexLAV not my field, as the "AncientCoder" nick is from 40 years in computers.

I'm basically just asking if people have considered that "beaming" this much power through the atmosphere have considered the effects of how much energy would be absorbed!


THX Bobbywhy!

From the Wiki post:



So it still looks like a lot of energy would be absorbed when transmitting gigawatts within a confined area which would create a pretty good localized thermal updraft!

I will leave it to the weather gurus to figure out what that does!

Please don't be too hasty in assuming there would be hot columns in the atmosphere. True, as the wiki article states, around one-half the total energy would be lost. It does NOT say all those losses will be due to absortion. Remember there is a "loss budget" which would include conversion efficiencies at both ends, beam spillovers, etc. We would need to know those in more detail, I think, to reach the conclusion you have.