On Wed, Nov 3, 2010 at 11:00 AM, <brin-l-requ...@mccmedia.com> wrote:
snip > I looked at the articles you provided, and I noted, without surprise, that > they omitted a very key detail: laser efficiency. In typical everyday > usage, lasers are not very efficient. Even in high tech uses, such as > inertia fusion, particle beams are much more efficient: about 12% vs. about > 1%, back when inertia fusion was big back in the '80s. Solid state diodes of the kind in the Wikipedia picture are hitting 50% now with research projects that expect to raise it to 65% and eventually to 85%. That's not coherent so there is a further loss of perhaps ten percent pumping a coherent laser medium. Even today you can get 20-35% out of a green laser pointer. "Green DPSS lasers are usually around 20% efficient, although some lasers have been reported to be 35% efficient. In other words, a green DPSS laser using a 2.5 W pump diode would be expected to output around 500 mW of 532 nm light." http://en.wikipedia.org/wiki/Diode-pumped_solid-state_laser Try this in google solid state laser diodes efficiency "105 kW" > These are the kind of omissions that are tell-tale to me. It's an > absolutely critical piece of information, which isn't mentioned. I've seen > it probably literally thousands of times in the writings of true believers. > I use it as a measure of a serious engineering or science project. Real > practical engineers are very excited when they talk about key technical > challenges. True believers don't talk about them. Want a copy of "Beamed Energy and the Economics of Space Based Solar Power" ? Paper I gave last year at a conference. It's a bit out of date since I now think CW lasers and hydrogen heaters are a better near term prospect than laser ablation. > So, tell me, how are the lasers going to get the power to energize the fuel, > and what is the efficiency and weight of the lasers involved? Since the lasers stay on the ground the weight isn't very important. Figured at 50% efficient and $10 per watt, 6 GW output will draw 12 GW from the power grid and cost $60 B. That's a lot but there are places it could be done, South Texas was one I looked at, and more recently California near the southern end of the Pacific Intertie. Keith _______________________________________________ http://box535.bluehost.com/mailman/listinfo/brin-l_mccmedia.com
