RE: Energy projects was Underwater mortgages and the economy

On Wed, Nov 3, 2010 at 11:00 AM,  <brin-l-request-r0TUnz/JSrZWk0Htik3J/[email protected]> 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  It's a bit out of
date since I now think CW lasers and hydrogen heaters are a better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