I do not think it is feasible. In a geosynchronous orbit it would indeed have the sun most of the peak useage day, but at 22,400 miles, the antenna(rectenna) farm would be quite large. I suppose it can be placed in a desert area.

200 MW = 200,000 KW, or about the insolation at noon of a square 450 meters on a side of 1 KW/square meter. Working back to a rectenna efficiency of 40% means that about 2.5 KW/Meter squared of microwave energy would impinge on this area, and they would have to transmit a bit over 1000 MW, which means it would consume about 2000MW at microwave efficiency of 50% , and at peak solar efficiency of about 20% the array would gather 10000 MW, more or less which is a collecting and focussing area of about 100 Kilometers square.

That startup has no hope. Higher efficiency solar cells, NASA grade, would help, but that cost would kill the project. Higher efficiency conversion to RF would help and higher efficiency rectennas would help.

It could be used along the Rio Grande, as a night light, as well as a cooking zone, to reduce immigration?

Could one walk through a microwave flux of 2500 watts per square meter and live?

The big dishes that track Geostationary satellites have to work a figure 8 pattern to stay on a satellite due to earth wobble and quantum forces of a mis-shapen planet.

If the collector is converting it's juice to radio waves to be narrow beamed to earth, the aiming of the transmitter will have to be doing a pattern to stay on the earth target.

What microwave frequencies are harmful to man? High powered 900 and 2450 MegaHz can make your brain explode. 2450 MegaHz is the frequency of your microwave oven that water reacts to. 900 MegaHz is reserved for cellphones so you can chat it up and melt the wax out of your ears. NOT!!!

San Francisco is 121 square Kilometers to give an idea of area.

There are so many alternative energy experiments going on!!

Your assumptions for solar energy density seem based on measurements on Earth at sea level. Without atmosphere, energy density is likely to be over 30% higher. Specific spectrum ranges may be significantly higher on a relative basis, possibly providing opportunities for more efficient conversion of solar energy. Large area inflatable reflectors may be relatively inexpensive. Just some things to consider.

On a clear day the radiation at the equator at noon is about 1000 watts per square meter. days vary and on dark, cloudy days lots less. In orbit it will be a constant~1370 watts,.

Even so there are many complex aspects that govern the final efficiency of a system that works like this:-

1370 watts in

sun to electricity 30% = 411 watts

- electricity to uwave 55% = 226 watts

- beamed to earth 85% = 192 watts

- intercepted 85% = 163 watts

- rectified to DC 95% = 155 watts

- turned into AC 95% = 147 watts

- delivered 200 miles away. 95% = 140 watts

That is 7 stages and the end efficiency is the product of each net efficiency.

so ~10% reaches the ground to sell. True you have a limitless resource, but has a cost effectiveness study be done with realistic efficiency factors?. My factors are estimates from a non EE, so I invite any EE to change a term to suit reality.

Solar Constant

Describes the Solar Radiation that falls on an area above the atmosphere at a vertical angle: s = 1.37 kW / m².

In space, solar radiation is practically constant; on earth it varies with the time of day and year as well as with the latitude and weather. The maximum value on earth is between 0.8 and 1.0 kW / m². In Germany, the average annual amount of insolation varies between 950 and 1100 kWh / m², depending on the region.

this link shows the concept spoken about.

http://www.technologyreview.com/blog/energy/23381/

If the solar array was in an equatorial orbit it would be in the sun even when the earth collector is in the darkness of the morning and evening hours. In the middle of the night when most folks are using little power the array would go through the earth's shadow.

If the array orbited so that it was north or south of the equator on the night side it would be in the light 24 / 7. It would have to work more to stay locked on target.

Jon

The problem with collecting energy off-the-planet and beaming it down, is what to do with all the waste heat after the energy has been used to do something useful. The planet's surface area is more-or-less fixed, so how does it radiate away into space without increasing global temperatures <rhetorical question>?

No - the way to harvest sunlight sustainably is to install the collectors in highly-insolated deserts. First.

PW,

Microwave heating only occurs at certain frequencies like 900 and 2450 megaHz as in industrial heating and cooking. They may have their eye on a frequency most suited to Microwave energy transfer without drastic side effects.

Kind of like living under high tension lines.

Jon

Interesting, how about lasering the power down, or are they concernd about atmospheric losses?

Conversion on laser light can climb up to 45% with solar panels.

I think its worth having a go at. Better technologies will follow in the future, this is just about paving the first few steps in the way!

I remember years ago when they talked about microwaving energy from a collector in space. now we have a rerun of that.

But now it is more possible than the dream that it was then.

Maybe the solar wind will blow it away and spoil the dream.

Yes, With the laser we can play burn-the-ants, or is that milit-ants?

When I first heard of this sort of plan to beam down via microwave there was some mention of the possibility of burning a hole in the ozone layer.

Sometimes I wonder if the experiment was tried by the Russians over Antartitca, but I wonder lots of things, and am absolutely certain no group of scientists would ever do anything that would endanger our planet.

What is the hertz that is most efficient? Could it burn a hole in the Ozone layer?

Sometimes I have wondered if it would be possible, and at all practical, to drop cable into the atmosphere at high altitude, with solar collectors on the extreme end as a way to collect power.

As I have thought of the Space Elevator concept, I have come to wonder if part of the flaw of it is the idea that it needs to go all the way to the surface, and have come to wonder if it would be enough to just get it to dangle in the upper atmosphere.

Now it is said that only carbon nanotubes will enable the Space Elevator concept, and I used the word cable loosely, without adjective.

Further I really myself ought to know what the most efficient wavelength is, but I don't.

Now without a doubt either the space elevator, or solar sails beaming down electric energy sounds like an incredibly expensive bit of engineering.

You still have to ask yourself though, is this the sort of Long Term Planning we really need to embrace? Should we go, "Yeah, sure it will cost gazillions of money to make this work, but hey, we'll have all the "free electricity" we'll ever need, and it will work forever!"

Who exactly is this "Start Up"?, by the way?

What experiments do we commonly know about that prove the viability of this concept?

Are the successes secret?

Should I buy stock in PG&E, with the expectation they will corner the market on future energy supply?

How are the family fortunes based on investments in AT&Ts laying of telegraph and telephone cable from North America, to Europe doing?

Permanent solutions to permanent problems are worth whatever they cost, whereas expensive temporary solutions, to permanent problems, aren't worth as much.

Guys,

I am old enough to remember this discussion the last time around. 20 to 40 years ago?

At the time I was a satcom engineer so was interested in the downlink issues, performance, safety etc.

I have never believed that this was a feasible concept from a safety point of view and I would expect that we have a long, long way to go before the performance issues are anywhere close to what is needed..

From a peformance perspective one needs to keep the numbers high to make the concept semi feasible.

Large ultra efficient solar arrays coupled to highly efficient power supplies coupled to highly efficient microwave power generators, Highly efficient radio antennae at both ends, highly efficient Rf to Dc conversion and highly efficient DC combination before the distribution network.

Each of these stages has to be >>90% efficient otherwise there will be almost no output.

We need high efficincy from all stages otherwise it all collapses, and high magnitude powers are neccesary in order to make the numbers and finance acceptable.

On the safety front , who wants to live close to a solar arrray farm receiving large amounts of Microwave power, with the problems of satellite wander, as stated earlier a Geostationery satellite descibes a figure of eight in the sky - this can be minimised by very accurate empalcement in orbit and by accurate station keeping of the whole bird or by expensive consumption of energy to keep the beam accurately pointed. The level of accuracy required is a non trivial problem.

Another non trivial problem, the current concern about microwave radiation associated with the cell phone industry is completely trivial compared with this technology.

Frequency cooordination will not be at all easy, the use for 2450MHz was originally proposed and is sensible from the technology perspective but is not good from a safety aspect; who wants large tracts of land turned into effective microwave cookers?

And can we live with large harmonics of the fundamental frequency swamping the air waves? Let alone any incidental modulation of the fundamental with power supply and control circuit components?

Now I have lost the original system budgets and I would be grateful for anyone posting any early material or even what is being proposed currently so that we can take a proper, sober look at the proposal and its impact on the planet.

I cannot see this as a going concern, but , hey, I can be wrong!

Sleepy

What is orbital dynamics?

What effect does cross-section have on orbital lifespan? Why is ballistic coefficient a factor in geocentric orbits when there is no aerodynamic drag?

What is Lentz's Law? What possible factor would it play in orbital lifespan?

Why would the space shuttle tether experiments have relevance to this issue?

Gavilan

A. As has been amply explained by others, the overall efficiency of delivering space-based energy to earth will always be lower than just leaving the same solar cells on earth. Getting another 30-40% insolation won't make up for that. It would be more cost effective to just put big inflatable mirrors in orbit and shine the light down, then convert it on earth. But still...

B. The safety problems are real. Don't forget that we are also making a large chunk of property into a "no-fly" zone. Pouring additional heat into the earth from space-based sources would also increase global temperatures. Can we adjust the focus of the beam antenna to increase the power density and move the hot spot around? Yikes! It's better than nukes in space. That's the real reason it might actually get built, despite the incredible cost.

C. Here's the real deal-killer. If you think PVs are expensive at $5/W now, just wait until you spend $25,000/pound to ship them into orbit. That 200W panel that you paid $1000 for just cost $1,000,000 to put into orbit. This is why NASA uses the highest-efficiency multi-junction cells on their satellites; the actual cost of the cells is trivial compared to the cost of transporting them. By doubling the efficiency, you reduce the weight shipped by 2X.

Has anyone considered looking at this from another point of view? How about an orbiting reflector(s) to send down the solar energy as is and convert on the ground?

This could be done in isolated locations and once converted to electriciy tranfered on ground via power lines. One other thing to consider is if there was someway to use these solar reflectors to alter weather patters i.e. storms by selectively warming an area and take the punxh out of a storm system to turn a hurricane into a mild summer storm, additional revenue could be generated from reduced insurance payoff due to storms let alone saving llives.

California PG&E Use solar array at geo-synchronous orbit and transmit the energy back as microwave is old concept. Yes, there will be energy loss through transmitting process. But, why don't we use high altitude blimp to test the idea to see how efficient it is first? Then, move to the next step to build an on-orbit solar arrays!

Now, another even bolder idea! Can we directly use the transmitted microwave to burn seawater so that desalination and hydrogen generation are done the same time. I believe we can pinpoint certain sea coast area with least population, and put infrastructure cost as part of this grand project expense.

Since burning seawater by radio wave is not a secret now, the method inventor should start thinking about my idea. The reason is that if we want to turn microwave back to electricity and invert on grid to redistribute electricity to nearby desalination system will cost more $ to do it!

I don't think is will actually be possible, especially in that timeline. I'm just going to chalk this one up to the current green fad that is going on in the US right now.