Space Solar Power

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Comment by Michael, Houston on November 1, 2008 at 7:47am

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Comment by neil cox on October 9, 2008 at 9:51pm

The size of the rectenna or light receiving site is mostly determined by how tight the beam can be made. The size of the illuminated spot is mostly determined by how long the beam is. From solar L1 (over a million miles) the illuminated spot might cover all of Texas. From a balloon ten kilometers away one square meter may be possible. In theory we can make the beam narrower by making the transmitting antenna or laser array bigger. The Arecibo radio telescope is the largest humans have built so far, for both transmitting and receiving. The last I heard they have a 445,000 watt transmitter that can send command signals to space probes up to about 50 billion kilometers away = 1/2% of a light year. We could say that space solar power has been demonstrated over huge distances, except nearly all the power missed the receiving antenna because the illuminated spot was much larger than the receiving antenna. Transmitting antennas up to 5 kilometers have been suggested for sending power 36,000 kilometers from GEO orbit. Likely that will work, but Arecibo is much smaller, so we may be surprised when we build a 5 kilometer or bigger transmitting array. Sometimes things do not scale up as the math suggests.
A very high power density a laser beam (or microwave beam) has additional spread because it is heating the air. I think HAARP found that the air heating effect was negligible even at ten million watts or more, but laser studies have shown considerable beam spreading due to the beam heating the air. Much of the data is secret, but Department of Defence is seriously considering space solar power, so they can likely access the secret data produced by HAARP www.spacesolarpower.wordpress.com. Another concern is the effect of the beam on humans and other life forms. Typically we have erred on the side of caution. Casualties and sickness from intense beams of electromagnetic radiation (radio to light) have rarely been documented other than the damage from radio heating as in diathermy. Above light frequency ionizing radiation, as in sun burn and gamma are well known dangers, but I have not heard any proposals to use these very short wave lengths for Space solar power other than in science fiction. We do have avoid human exposure to high density electromagnetic beams, but there is little evidence to suggest that 1/10 watt per square centimeter is dangerous, below the ionizing frequencies of ultraviolet light. Neil

Comment by neil cox on October 9, 2008 at 8:30pm

The estimates for space solar power have a wide range, partly because we have not agreed on the details. We might put up some solar synchronous satellites (someone suggested altitude 600 nautical miles) These would likely stay perhaps 100 miles East of sun set as they circled the Earth. I think they can be semi polar, so they would occasionally pass over most of the countries of Earth, instead of favoring the countries in the tropic zone. Typically they would deliver the energy to solar sites in greatest need who might be willing to pay as much as 30 cents per kilowatt hour for enough electricity to avoid rolling blackouts near by. Instead of microwaves, the satellite would have perhaps 2 million 1/2 watt laser diodes. The solar panels on the satellite would need to produce about 2 million watts as the diodes are presently about 50% efficient. About 1/2 of the beam energy would be lost passing though Earth's atmosphere and about 20% of the received 500,000 watts would be converted to electricity = 100,000 watts = enough for at least 50 homes. If the illuminated spot is 1000 square meters (we likely cannot get the spot that small at present, but likely can by 2012 when the satellite is ready to launch. With microwaves we may never be able to get the spot that small) the average power density is 1000 watts per square meter = 1/10 th watt per square centimeter = the maximum allowable leakage from microwave ovens. Even if the beam falls on a city for a year, few to no human casualties are likely. The system will be designed so that no likely group of failures can cause even 1/10th second exposure of a city. The hazard will be far down the list of hazards most likely to afflict average humans. We can, and perhaps will have to, reduce the average beam density to perhaps 100 watts per per square meter, because we cannot get the spot size smaller than 10,000 square meters. Not many solar receiving sites are presently as large as 10,000 square meters, and the illuminated spot will be elliptical unless the satellite is directly over head. That will occur rarely and briefly, so the larger illuminated spot will often fall partly outside the solar receiving site, wasting part of the beam's energy and producing a hazard in some people's mind.
Perhaps 200,000 watts is delivered to square kilometer size rectennas by microwave (starting with 2 million watts of photovoltaic cells in the same orbit) but we have not built a rectenna nearly that large, so some surprises are likely, and rectenna cost projection are likely optimistic. We possibly can launch the entire laser satellite including the 200,000 watts of photovoltaic cells, with a single launch. Sending the same equipment to GEO stationary orbit (altitude 36,000 kilometers) would require perhaps ten launches and assembly in space. The feasibility of assembly in space has not been demonstrated except by repairs to the Hubble space telescope, and the construction of ISS = the international space station. Neil

Comment by Jim Martin on October 8, 2008 at 3:31pm

There is a version of Space Solar Power that might be economical sooner than the GEO-microwave system usually considered. Placing reflectors in a sun-synchronous low orbit, perhaps 600 nmi, could reflect sunlight to Earth. Fields of photo-voltaic cells could use normal sunlight during the day. In the morning and evening, the reflected light would provide an additional boost of output. New, low-cost PV cells are being developed.

The reflected sunlight could also be used with the Solar Updraft Tower concept. See:

http://push.pickensplan.com/group/solarupdrafttower

A new concept, the Solar Windmill, is similar to the Updraft Tower. Adding 1-way valves allows capture of wind energy also. See:

http://push.pickensplan.com/forum/topic/show?id=2187034%3ATopic%3A259129

Comment by Jim Martin on October 3, 2008 at 1:43pm

Attached is a paper by Dr. Dana Andrews presented at a recent IAF conference. It shows how other options have a better chance that Space Solar Power in the near term. Dana gave me permission to put a copy here.

Space_and_the_Green_Energy_Options.pdf

Comment by neil cox on September 24, 2008 at 2:46am

The details of Ridgcrest project appear to be correct science, so the prankster was very skilled, if this is fake.
30 times 500 megawatts = 15 gigawatts which is much less than the total peak demand of Arizona, new Mexico, Nevada and Southern California, but perhaps 1/2 of the energy was produced by coal fired plants even in 1983.
The first number in the box on the picture appears to be :OCCC on my computer monitor. If this is 10000, that agrees with the 70,000 mentioned in the same box. Apparently only two of the 7 towers are shown and perhaps not all of the heliostats. The shadow of the center tower is about the correct length for December 22 at noon when the shadow would point North. The out of round, however; is incorrect (unless this is South of the Equator- I'm confusing myself) In the North Temperate zone, Heliostats located North of the tower have the angle of incident to reflected angle smaller and thus are more efficient. Heliostats due South of the tower won't work at all in late fall and early winter, unless the beam can reach another tower in a different direction. The out of round may be due to taking advantage of the land contors, to keep tower height cost reasonable. This site may be one of the old copper mines, which happens to have near optimum elevation variations.
I continue to be concerned about the length of the reflected beam, but perhaps 7 towers lets this be under 2 km most of the time.
500 megawatts seems difficult, if under 2 km beam length is a constraint, even with 7 towers. I'll think more on that latter. Neil

Comment by Dr. Paul A. Curto on September 12, 2008 at 4:45pm

Here is an artist concept of the Ridgecrest design --

Comment by Dr. Paul A. Curto on September 12, 2008 at 1:20pm

I was stunned to find this link online. It appears that the Ridgecrest Project has been revived, or someone is pulling our leg. The details are in the flyer and a pdf on the site.

http://www.goldenstateenergy.com/about4.html

Comment by Dr. Paul A. Curto on September 12, 2008 at 7:50am

When we designed the Ridgecrest Project in '82, which was killed by the loss of the solar tax credits, we had been in negotiation with GM to buy the largest assembly plant in North America at the time, in Fremont, CA to make heliostats. I met Roger Smith at the time (of the famous Roger and Me film by Michael Moore). The plan was to build at least 30 500 MW class power plants using a combined cycle gas turbine topped steam cycle to replace all of the oil and gas fired utility power plants in the Southwest. Each plant would be co-located with the existing plants in six states (CA, AZ, NM, TX, NV, and UT). The idea was known at the time as Solar Thermal Repowering. Look it up on Google for details.

From memory, the towers were to be made from slip-formed reinforced concrete and were 250m high. On top, a downward-facing cavity with four openings housed a huge air heat exchanger made of Inconel and insulated with alumina blankets. Turbine inlet temperature was maintained at about 800 C, and was controlled by a variable speed split shaft turbine so that the exhaust temperature was pegged at 427 C, and was piped to a thermal storage unit and in parallel directly to the steam generators on the ground. The thermal storage utilized iron orthosilicate, aka copper slag, recovered as waste product from dozens of old copper smelters peppered around the region. The steam system ran 24/7 at 100 MWe, while the gas turbine output varied from 50 to 460 MWe depending on the solar insolation.
We had good enough data to calculate that the average daily solar to electricity efficiency would be about 19%.
The total insolation at Ridgecrest is the highest in the US, at 5.90 kWh/m2/day. That means we expected over 400 kWhe/m2 of heliostat surface each year.
The estimated cost of the plant, in mass production, was about $1500 per kWe in 1983 dollars. That's 840 million dollars per plant in 1983. Maybe 2 billion today? Who knows?

GM used Fremont to build the Geo and later sold it to Toyota.

Comment by neil cox on September 11, 2008 at 8:46pm

Hi Dr. Curto: Is anyone making 100 or more heliostats per day? What is the cost for 25 square meters of reflecting area 5 meters by 5 meters on a ten meter pole? I think big is better. I think your 20% load factor and/or one kw/square meter is optimistic by a factor of four. What percentage of a 2 kilometer beam from a heliostat can we expect to enter the receiver window in the tower? Remember, the Sun is not a point source, so the beam spreads. How high does a heliostat 2 kilometer East or West of the power tower need to mounted to avoid the beam hitting the backs of closer heliostats,when the sun is approximately East or West of the tower between Sept. and March, assuming the ground is flat? I'm thinking two towers 2.3 kilometers apart, for 8 square kilometers near the SE and SW corners of the 2 by 4 kilometer solar farm. Heliostats South of a tower will only have favorable angles early morning and late afternoon, perhaps never in late December. What percentage of the delivered heat is carried off by a 20 kilometer per hour wind? If the tower turbine is designed to produce 20 megawatts, what is it's efficiency when producing 10 megawatts? If the power towers/heliostats are so great, why don't we have several under construction, or do we? Neil

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