Hi Marty‹I¹m listening‹very thoughtful analysis of the space solar approach.
On the Monterey meeting, it is not for a sequence of presentations of geoengineering (or alternative) approaches, but for working toward some guidelines for experimenting with various geoengineering approaches. Now, the guidelines for any of the ideas would seem likely to include consideration about whether the approach will make any sense compared to alternative approaches‹so your comments about space solar requiring so much less area of space, requiring a space shuttle launch per 10 MW (ratio for the Solaren approach per your calculations, or less for other approaches) and GEO orbit being closer that L1 are pertinent to thinking about space based geoengineering might will be part of the discussion‹though the response is likely to suggest that the mass per W/m2 for deflection may be a good deal less than the capture and transmission of a W/m2‹or whatever the comparison should be. And it may well be that space power would do better with a clean stratosphere and troposphere than one loaded with sulfates, etc., so I would think that those types of tradeoffs would come up (so, space based energy versus causing more scattering of radiation). We are still working on the program and breakout groups seeking to structure them to lead to interesting discussions of various issues relating to consideration of proceeding with research on geoengineering. Now, for the 2011 Melbourne meeting of IUGG, I (along with Alan Robock and likely others) are expecting to be co-convenors of the geoengineering symposium, and it might well be worth there having a number of talks on tradeoffs‹space geoengineering versus space power. That might well be a valuable way to organize at least part of the program. Best, Mike On 11/26/09 4:44 PM, "Martin Hoffert" <[email protected]> wrote: > Ken & Joe et al.: > > Let's give Solaren the benefit of the doubt in every way: > > Savvy space-based solar power people know that microwave-based space solar > power doesn't make sense for power levels much below 1 GW transmitted to Earth > from geostationary orbit (GEO) 36,000 kilometers up because you have to have > big transmitting and receiving antennas to capture the beam in light of the > (impossible to beat because it is constrained by physics) diffraction or > spreading of the beam , which is proportional to (wavelength)/(aperture). To > make those big structures cost-effective you have to beam a lot of power > through them. To cut to the chase, let's forget about cost and safety issues > for now. > > Solaren says it it wants to deliver 200 MW by microwave beaming to the > California Gas and Electric grid by 2016, let's say with an overall DC-to-DC > transmission efficiency of 50% which is pushing it -- but maybe doable. > > That means making 400 MW in space from PV arrays So Solaren has to lift a PV > array capable of generating 400 MW to GEO. That is heavy lifting. If you > include structure, beaming antenna, power conditioning, etc. and push the > technology as hard as you can, you might get 1 kilowatt of output in space per > kilogram of mass with current technology. So, to get 400 MW (400,000 > kilowatts) out of the PV array, you have to lift 400,000 kilograms or 400 > metric tons (1 t = 1000 kg). The space shuttle has a payload capacity of about > 20 metric tons to GEO. So 400 tonnes/20 tonnes means the equivalent of 20 > shuttle flights by 2016 starting say two years from now (5 flights/year). Huh? > NASA hasn't been able to manage anything more than 130 shuttle flights in the > 30 years they've been flying -- an average of 4.3 flights/year. Yeah, I know, > Solaren's would likely be unmanned flights. And privatization of access to > orbit might do better than NASA's launch army, but not that much better that > fast, to do something no one has never done. Not to mention that you need > in-space assembly of those large arrays, as we did for ISS. If these aren't > crewed flights, where are the robots that will assemble the components? They > don't exist. The worst part of this idea is that you need a huge capital > investment just to demonstrate and measure efficient space power beaming by > microwave. If it flops, that could be the end of space solar for a long time. > > Hey, I am a strong advocate of space-based solar for base load electricity. > But Solaren has made a ludicrous claim on the face of it. It's one thing to > dream big. But their proposal simply cannot be accomplished in the time frame > set forth with private sector funding. Certainly not without massive money > from government. It's the wrong approach anyway. Premature optimism has > already happened many times with fusion. We don't need this. Too many space > power guys have been silent perhaps to not give comfort to opponents. But > scientists should not do this. Anyone can make a mistake. Maybe the Wall > Street Journal can be easily fooled. But Mother Nature will not be fooled. > > Space based solar is a good idea mainly because satellites in GEO can beam the > energy 24/7 and get 7 times more solar flux per unit area than the long-time > flux at earth's surface, and the massive storage needed for major market > penetration of terrestrial solar is destined to be a major issue. The way to > go now is beaming the power by laser which can also penetrate the atmosphere, > but has 100,000 times shorter wavelength than microwaves. At least do this in > parallel with testing microwaves, as the Japanese Space Agency is doing. > Lasers permit a demonstration of order a few hundred kilowatts in space with a > mass to orbit of a few metric tons, similar to hundreds of communication > satellites already in GEO. And even before this a series of demonstrations > from the ISS can be done. A laser system can also grow in a modular way and > will not encounter electromagnetic frequency allocation problems like a > microwave system will. > > A bonus is that space-based solar requires far less real estate in space to > power the earth than the sun shields or solar parasols proposed by some > geoengineers to compensate for global warming from the fossil fuel greenhouse. > The reason is that the radiative forcing from CO2 doubling, about 4 watts per > square meter, is fifty times less than humankind's energy use per unit surface > area of the earth. It's why we have to worry about global warming with it > physics amplification from the fossil fuel greenhouse long before we have to > worry about heating the planet from the second law heat dump from our energy > use. It's too bad this stuff is not understood. > > Against my better judgement, I may write a paper on with my #1 son Eric for > submission to Science or Nature. Unfortunately, there are so many wonderful > distractions going on at the same time and who knows if they will even take > it? Maybe I'll ask Mike MacCracken if I can present these ideas at his > Geoengineering meeting next year in Monterey. Mike, are you listening? > > Happy Thanksgiving to all, including any native American descendants who > survived the bacteriological holocaust of European settlers in the 17th, 18th > and 19th centuries. > > Marty Hoffert > Professor Emeritus of Physics > Andre and Bella Meyer Hall of Physics > 4 Washington Place > New York University > New York, NY 10003-6621 > > NYU Phone: 212-998-3747 > NYU Fax: 212-995-4016 > Home Phone: 516-466-9418 > Home Fax: 516-487-0734 > Cellphone: 516-972-4779 > Email: [email protected] > Web page: http://www.physics.nyu.edu/people/hoffert.martin.html > > > > > > > At 8:07 PM -0800 11/25/09, Ken Caldeira wrote: >> Joe, >> >> I would talk to Marty Hoffert about this: "Marty Hoffert" >> <[email protected]> >> >> Something weird must be going on. >> My understanding is that this makes no sense from a technological point of >> view -- and that comes from space solar advocates >> >> It would be interesting to find out what is behind this and what their game >> is. >> >> Best, >> Ken >> >> >> ---------- Forwarded message ---------- >> From: None <[email protected]> >> Date: Wed, Nov 25, 2009 at 7:50 PM >> Subject: California regulators have recommended approving Solaren's long-term >> SSP contract with PG&E. >> To: alternative energy action <[email protected]> >> >> >> California regulators have recommended approving Solaren's long- >> term SSP contract with PG&E that would beam 200 megawatts of SSP to >> California. Long ways to go, but we are moving. >> >> http://online.wsj.com/article/BT-CO-20091120-713779.html >> >> -- >> >> You received this message because you are subscribed to the Google Groups >> "alternative energy action" group. >> To post to this group, send email to >> [email protected] >> <mailto:[email protected]> . >> To unsubscribe from this group, send email to >> [email protected] >> <mailto:alternative_energy_action%[email protected]> . >> For more options, visit this group at >> http://groups.google.com/group/alternative_energy_action?hl=en >> <http://groups.google.com/group/alternative_energy_action?hl=en> . > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
