Electricity From the Desert

I think that the article's numbers might be a trifle optimistic. Solar thermal energy is about the same efficiency and any other thermal power plant, but the problem remains, what do you do when the sun isn't shining? Storage on that scale has just not yet been developed. Though I suppose it's possible.

The facts still remain. The best possible output we can hope for from surface based solar is about 1.8KWH/m², which is to say 150 watts per square for 12 hours a day, and we still have to work out mega-scale storage and extreme long distance transmission.

The best way to do solar power is to place solar power stations in orbit, where we can reasonably expect 700 watts per square meter for 24 hours of every day without interruption. Here are the numbers.

1.4KW/m² solar flux at our orbit. Approximately 50% conversion efficiency to electricity. Microwave transmission promises 75% efficiency. So, we get 12.6 kilowatt-hours per square meter from a powersat, as opposed to 1.8 from surface based facility, and no worries about storage.

Am I missing something??

and another thing: no sandstorms in space. kinda crowded up there though - what do you think the space junk issues will be like in, say, twenty years?

I wonder what kind of animals or plants might flourish in the shade of a Sahara array. If it's not engulfed in sand.

The 'space junk' issue is a lot less of an issue at GSO than at LEO. It also makes a lot more sense to place these powersats in a geosync orbit than low Earth orbit because of the facts that rectenna design is a heck of a lot simpler, and there are a lot fewer chances for the satellite to pass through Earth's shadow. And since these things are likely to be pretty big, putting them further out makes them a great deal less obtrusive in the night sky, even though they are still likely to be fairly bright objects even so.

Another important fact is that microwave rectennas do not block out the sun. Thus, they can be placed just about anywhere, whereas no plant life that relies on photosynthesis can live under a surface-based solar collector.

I can't read the complete article but the thermal efficiencies published by the Desertec consortium are not to optimistic.

The heat in the collector of a solar tower goes readily over 800°C.

The salt, used to store the heat, is over 600°C in the newest systems. (in Spain) I know this for sure as I had to solve some technical issues resulting from these temperatures.

Modern turbines work with superheated steam.

On this side of the water we are continuously developing techniques to improve the thermal efficiency and the total efficiency of the system.

We really believe that there is no option for the future: solve the technical issues or watch television in the dark.

Yes, but what happens when someone or something gets in the path of the transmission?

Have some fun today,

PAPADOC

RMFR

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -Richard Feynman

These basic ideas may be sound, but there is intermixing of KW vs KWH in this description, making it harder to evaluate.

I personally cannot see a space station to collect energy. Getting the energy down to ground level needs to be solved first as well as the high costs of putting even 1Kg into space....

Some major problems need to be solved on costs, not least that for probably 35-40 minutes or so on each orbit, the earth will obscure the sun, and in a geostationary orbit 8-10 of 24 hours aproximately......

I still feel that "earthbound" will still work best for many years to come especially as the efficiencies of solar cells, though improving every year, are still too low for space (a further reason not to go into space!)

Andy,

These issues have already been pretty much worked out. First of all are the high boost costs. Absolutely agreed, boost costs are astronomical. However, they are slowly coming down, and with the advent of private enterprise entering into it, you can expect them to begin coming down a lot faster. Furthermore, with private enterprise, you can expect to begin seeing new technologies as companies seek to lower their costs to increase profits.

Also, the obvious way to build these things is in space, with space-based materials and energy. In terms of delta V, it's easier to haul materials up from the moon or the asteroids than to drag them up from Earth surface. This might be a nice way to deal with some of these NEOs. And we do know for a fact that Lunar regolith is made up of lots of useful materials such as aluminum, titanium, silicon, oxygen, etc.

Second is that beaming power down to Earth surface is already pretty much worked out, using microwave transmission. There are numerous articles on the subject available on the internet, but microwave transmission of power has been a proven concept for decades. Efficiencies look to be around 75%, and while the rectifying antenna assemblies, or rectennas, will have to be fairly big, they are simple, minimalistic structures which don't block out sunlight, so that farming could easily go on right underneath them, for example. And, they are still small enough that they could easily be situated close to points of use, such as Frankfurt.

Third, in a geosynchronous orbit, the satellite might never be occluded but for a few minutes in a month. First off, remember that the Earth's rotational axis is tilted 21 degrees from it's plane of orbit, which means that GSO is at the same inclination. Second, remember that GSO is almost 36,000Km above mean sea level, at which distance the Earth subtends a rather small angle. Further, orbital velocity is still 11,000Kph, which means that if and when a powersat enters the Earths shadow, it just isn't going to take very long to cross it.

So in reality, the largest problem with building solar power satellites is developing the space-based infrastructure to actually build them in space. I absolutely agree that building them on Earth and then lofting them into place would be absurdly expensive, but as we develop the orbital infrastructure, they will just get cheaper and cheaper to build. And the spin-offs from such an effort would be fantastic.

Some good points and some (scientific) dreams. Sorry......

Let us wait and see, but I do not expect to see anything (other than relatively small experiments) worth talking about till the middle of this century or later!! Which I certainly will not be around for!!!

Energy of the type needed for a rocket may become even more expensive.....

Time will tell us all......but don't hold your breath........

I do hope that you are right as that would be best for mankind generally......but I also believe that in the next 30 years or so, Fusion will become completely viable, then we will not need to shoot rockets or the like to harvest sun power.....

Such pessimism. As I recall, people have said similar things over and over throughout history. But the fact is that we have gone ahead and done the impossible, over and over again.

Furthermore, space is the most supremely important of things. It is, at the risk of sounding cliche, the final frontier which if embraced will prosper us in ways beyond imagining, and from which turning away will spell our ultimate doom as a species.

I am actually the complete opposite of a pessimist character wise, a true dyed in the wool optimist, but I am also a realist!!!

The more you REALLY know about this subject, the more you realise just what a lot of work is still there to be done......

Lets all hope that it happens far sooner than I believe......

I'm with you Dr Moose.

You'll see it when you believe it.

Every technology, every idea, every invention began with a thought. A thought coupled with vision and perseverance prevailed where the thought manifested into reality.

Henry Ford proposed The car (horseless carriage)
"The horse is here to stay but the automobile is only a novelty, a fad" said the president of the Michigan Savings Bank advising Henry Ford's lawyer not to invest in the Ford Motor Co, in 1903

Wright brothers-Airplanes
"Flight by machines heavier than air is unpractical (sic) and insignificant, If not utterly impossible" said Simon Newcomb; The Wright Brothers flew at Kittyhawk 18 months later.

Radio
"The wireless music box has no imaginable commercial value. Who would pay for a message sent to no one in particular" Associates of David and Sarnoff responding to a call for investment in the radio in 1921.

Power from space proposed by DrMoose:

"I personally cannot see a space station to collect energy" Andy Germany; February 2009

"5 years later a revolutionary energy space station transports energy to the earth and greatly reduces mankind's dependence on fossil fuels." szwasta

What I actually wrote was the following, this time in full and not out of context:-

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I personally cannot see a space station to collect energy. Getting the energy down to ground level needs to be solved first as well as the high costs of putting even 1Kg into space....

Some major problems need to be solved on costs, not least that for probably 35-40 minutes or so on each orbit, the earth will obscure the sun, and in a geostationary orbit 8-10 of 24 hours aproximately......

I still feel that "earthbound" will still work best for many years to come especially as the efficiencies of solar cells, though improving every year, are still too low for space (a further reason not to go into space!)

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As I said before:-

"Don't hold your breath!" and I would also like to be completely wrong, but until I am wrong, don't forget YOU ARE!!

We need so many seriously HUGE breakthroughs, just to achieve the space station idea.....I know it will come one day, but what I am querying is the time scale that appears to be the "mode" here with some people.....I will state again " I HOPE I AM WRONG! "

So sorry,but you appear to be missing the fine detail (small print?).....that is ALWAYS very important in this life!!!

You also missed/misunderstood what I was saying/posting......read my post again CAREFULLY this time..."I personally cannot see a space station to collect energy".

I should have expanded this for you to include ...."in my lifetime"....

I never said NEVER......all I question is the euphoric ideas over WHEN, that is quite a lot of difference.....

If you want to place a bet on the 5 years you mentioned with me, be my guest.

I will even allow you the same bet and 10 years for the space station, are you still ready to put your money where your mouth is???????

My bet is at least 50 years (me long gone!), probably a lot more......for anything really big enough to make any difference (lets say a minimum of 10%?) of the world's energy needs. I do expect experiments to take place and tests to be made from space.....in a relatively short time scale say 5 to 10 years!!!

My personal take is more people will tend to go at least partially "Offline" and generate as much power for their needs as they can with their own Solar/Wind power collection. Using the grid when its not enough.

Generally speaking, energy in any form will get more and more expensive, this has always been true, it is unlikely to change and get cheaper.....I would even bet against that happening in any long term...

The houses will get better and better insulated, all expelled air will be used to warm the incoming air in winter and to cool it in summer, many house outside surfaces will collect energy in one form or another (its already being done, but not enough....).

Deep drilling to use geothermal energy for new houses (its already in use here...!)

Better and better heat pumps to recover heat before its a loss.......

Rainwater will be gathered by more households in large underground tanks and filtered for drinking. That is already done now in many households here, though theoretically, the drinking of rainwater is banned, believe it or not.....it may only be used for toilets, washing of clothes and the garden....

The modern cliche is "carbon footprint", this is really up to date and fully correct. If you can reduce your CF, then you reduce your costs AND you help save the environment/planet. Its a "Win Win" situation for us all.

Let the scientists get on with the things you mentioned as we will need those developments, sooner rather than later......I am all for them.....

Have a great day anyway......

The largest problem in the energy question for the world are stories like this one: people tend to postpone the immediate action as perhaps in 20 or 100 years they will find the real solution.

The same is valid for nuclear fusion: it might work but it will take another £€$ 100.000.000.000 and 20 to 50 years for the first power station to supply the grid.

With this amount of money the desertec project would have been executed to supply Europe and Africa with "free" solar power.

Yes, the mirrors need to be cleaned almost every day, nice job of local low educated people.