"Bret Cahill" wrote in message
ups.com...
I found those same numbers at http://en.wikipedia.org/wiki/Solar_power ,
which cites http://www.nrel.gov/gis/solar.html . But that apparently
also includes night and cloudy days, so what's actually coming in on a
sunny day will be more than that.

In May and June in Arizona before the monsoon season when r. h. is 8%,
you are guaranteed 800 + watts/m^2 during the day.

You _will_ be going 25 mph with conventional PV.

I agree that it won't get all the way
up to 1 kW / m^2. Since the proposed blimp will apparently be day VFR
only, using the higher daytime insolation should be OK. What happens
when clouds blow in or you stay out too late is left as an exercise for
the student.

Even on a cloudy day the speed wouldn't drop off all that much because
of the propeller rule in propulsion, power ~ u^3. If the power drops
off by a factor of 8, the speed only falls by 50%.

But "just in case" have some good old fashioned fuel engine backup.

Remember, we're talking about a lighter than air (or at least neutral
buoyancy) craft here. You can't afford to have the "belt and suspenders"
approach of redundant propulsion systems. You do want to carry a payload,
right?



Bret Cahill