Several gigawatts of power!!! But because the area of the receiving antenna array (lots of poles joined by wire, rather than a big dish, much like that weird radio telescopey place on the West edge of the M1 in the Midlands I presume) is over several kilometres, the power intensity is reasonably low. Intensity low. Total power - huge![/quote]
If it’s 1GW per km^2, that’s 1kw/m^2. If you lie down, you’re covering an area of about .75m^2, so are receiving power at 750W. This is your average microwave oven, and would make you toasty warm and kill you. Would you sit in a microwave oven?[/quote]
Hee hee. Only if it was unplugged.
Just make the antenna a bigger to get the intensity down. Remember, nobody said the antenna would be small.
The intensities they are talking about in the Wiki are more of the order of a mobile phone than a microwave. Whether that’s realistic or not I don’t know, but we’re certainly not talking an intensity that’s positively dangerous. (but since people suspect mobile phones are dangerous… there’s still something to think about). It’s all in that link.
But if you make a massive antenna, the problem is that then the power has to travel down lots of cables. Which depletes it all the while.
Even super conductors where power loss is minimal in the conductor generally requires lots of power to maintain the optimum temperatures for superconductitivity.
Big antenna (lots of resistance/attenuation) + low power = project failure.
The whole point of this is to some how increase the power available from the sun, so if you need a massive antenna why not just put lots of solar panals on the roofs of houses?
This is already done in many places, in individual houses in London there is a project where your solar cells on the roof can power your house, and feed the national grid when you aren’t using the power. You get the satisfying site of your meter going backwards. When you need more power your house is supplemented by the grid.
If you need massive collectors then this whole scheme is a non-starter.
Especially when you take into account the massive R + D costs and of course the lifting of the matierials into space.
Presumably there is far less loss of microwave energy to atmosphere beaming it from an efficient panel in space than there is loss of solar energy to atmosphere with a panel on the ground. More to the point, the panel, being in a geostationary orbit (which is rather high) doesn’t suffer from that thing known as “night” so much and is illuminated 99% of the time. So you almost double your efficiency straight off even neglecting the lack of atmospheric losses.
The people who dream up these things are clever people and issues such as losses in the receiving antenna will probably be covered. In case you haven’t read the link yet here’s what they have to say about the downlink.
The Earth-based receiver antenna (“rectenna”) is also key to the concept. It consists of a series of short dipole antennas, connected with a diode. Microwaves broadcast from the SPS are received in the dipoles with about 85% efficiency. With a conventional microwave antenna the reception is even better, but the cost and complexity is considerably greater. Rectennas would be multiple km across. Crops and farm animals may be raised underneath the rectenna, the thin wires used only slightly reduce sunlight, so the rectennas are not as expensive in terms of land as might be supposed.
For best efficiency the satellite antenna must be between 1 and 1.5 kilometers in diameter and the ground rectenna around 14 kilometers by 10 kilometers. For the desired microwave intensity this allows transfer of between 5 and 10 gigawatts of power. To be cost effective it needs to operate at maximum capacity. To collect and convert that much power the satellite needs between 50 and 100 square kilometers of collector area using standard ~14% efficiency silicon polymer solar cells, state of the art and expensive triple junction gallium arsenide solar cells with a max efficiency of 28% could reduce the power area by ~50%, but in both case the solar stations structure would be several kilometers wide as most designs are based on a rectangular grid, making it much larger than most man-made structures here on Earth. While certainly not beyond current engineering capabilities, building structures of this size in orbit has never been attempted before.
Notice my bold - they’re scaling the antenna’s for a desired intensity which is presumably that which would be safest without compromising working efficiency. It certainly seems that the problems do not lie in the Physics of this idea, but more the practicalities.
It’s getting the panel up there that’s the first big problem. Firstly this means driving down the “per area” mass of the panel, then how to construct it and then the real biggie: we we don’t have a fleet of reliable, truly reusable launch vehicles that can each make a flight say, once a week, and we therefore don’t have a cat in hell’s chance of getting all the components up there to assemble.
But that’s another “Here’s what is possible” space story…
The lecturer who first introduced me to this seemingly crackpot solar panel idea is a firm believer that we should be investigating in space infrastructure such as a truly reusable launch vehicle, so that we can try these crackpot ideas and possibly rescue humanity from our own man-made doom that environmentalists predict. I hate to say it, but I agree with him. :?
