Da' Blimp
Read on or save yourself somewhat <g> and read below my dotted line------ <g>
The articles on the Lockheed blimp usually mention 10kW of power but I’ve seen a couple that mention 15kW....hmmmmmm.
Then there is the geostationary orbit at 70,000 feet, with the blimp
capable of speeds up to 80mph (interesting map of seasonal winds vs altitude over Iowa from Amateur Radio Group’s high altitude balloon launch website
users.crosspaths.net note the lower wind variability at 80,000 feet and the extremes in July & December ,note that the blimp will likely be working hard to maintainstationary position during the shorter, lowest insolation days of the year)
Lockheed airship ~500 feet long, 160 feet in diameter, cigar shaped
Prototype uses batteries for nighttime power
but production models will use
lightweight fuel cells… so I wonder and speculate about
? PEM ? 40% efficiency from H2
H2 derived from electrolyzer, so I wonder and speculate about
80% efficiency
10kW ('dissing the 15kW figures) needs 240kWh/day to run at full power (modified below for direct PV supply
during strong daylight hours)…
during sunlight hours a power controller could deliver the power directly
to the electric plants on board (propeller engines, communications, surveillance equipment) and the electrolyser avoiding the losses in electrolysis>H2 generation>PEM fuel cell conversion process speculated on below.
But with 40% PEM efficiency it needs in terms of H2 energy
2.5x 240kWh or 600kWh
And backing up to the production of this H2 there is, let us use, an assumed 80%
electrolyzer efficiency so the blimp would need 600kWh/.8 of dc power
or
750kWh/day
assuming no dc transmission losses from the PV panels.
Now assume the design takes into account and requires adequate dc output on the worst
Shortest winter days e.g. winter solstice in the northern hemisphere at the northernmost latitude of the coastal continental US, Portland, Maine 43.6 degrees, Tacoma at 47.2 degrees, so let’s use 45 degrees. (http://www.uwsp.edu/geo/faculty/lemke/geog101/lab_answers/01_Earth_Sun_Geometry.pdf
Sun’s angle will be ~22 degrees at noon at this latitude on December 22nd
Traditional optimal angle would be to set the panels on earth upright at 68 degrees to
Align normal to the sun’s noon rays… but this is a curved cigar-shaped blimp!
I’m assuming that only one side of the Blimp’s PVs can be
oriented towards the sun but the side will have an array of thin-film PV, as Lockheed has stated, but it will be mounted on the CURVING surface of the blimp’s main body.
So if I assume that during shorter winter day’s ½ of the blimp’s PVs still have to produce 750kWh, then how many watts have to be put on the curved surface of the blimp, adjusting somewhat (20% boost??) for higher insolation
(less atmospheric path and blockage) at the blimp’s 70,000 foot altitude
plus
there is the potential for a boost from 2D tracking if the blimp is via ground control constantly oriented towards the sun to boost solar insolation from sunrise to sunset during the winter months.
For ease of calculation, I am assuming the thin film PV panels are covering the top half of a regular cylinder. Guesstimating from the drawings on the web can we say that as much as 250-300 feet of the 500 ft blimp length are clad in PV? And ½ the circumference (here I’m stretching the sketches that sometimes show less than the top ½ of the circumference but what the hell!) or 3.14 x 160 feet or ~500 ft (502.4ft) and so we could guesstimate a
Total top half thin-film PV clad surface area of 250 feet half circle that is 250 to 300 feet long. Let’s assume 300 foot length yielding a total surface area of 75,000 square feet but essentially only half of this or 37,500 square feet producing power during December.
The best figures I’ve seen for terrestrial insolation with tracking (positioning blimp!) for
these latitudes have been 3-4 hours/day so I will assume that this curved body (huge assumption and those with real differential math please weigh in) will only receive/be exposed to ½, (probably only 1/3 if 68degrees is optimal), of that
(again I invite those better at mathematics to weigh in on the differential sunlight exposure over my already hypothetical ¼ of a cylinder extending from the blimp fuselage’s mideline upward to its peak line)
In the absence of good math analysis of this ¼ exposed cylinder of PV’s insolation
, I will just resort to using half of those December insolation figures for the blimp… 1.5 to 2 hours equivalent of full solar insolation that are being absorbed and converted by ½ the PV panels that the blimps is clad with… if orientation is being done well by ground control
That equals 1.5 to 2 hours equivalent of full solar insolation to the blimp PVs in late December and only being exposed/absorbed by ½ the PV panels that the blimp is clad with at best (orientation issues in the midst of winds at 70,000 feet).
Back to the 750kWh, maybe substracting for direct power during 8.5 daylight hours with nil efficiency loss, we still have weak sun for ¾ of the 24 hour day. I’m going to pick 18 hours as primary hours for PEM fuel cell predominance vs. solar cell predominance as a power source…. Go ahead and scratch your armpits, etc. on this one too <g>
New figures become, 6 hours direct at 10kWh x 6 hours = 60kWh
Plus 18 hours via electrolysis/H2/PEM fuel cell>power using units= 562kWh
Total reduced from 750kWh to 622kWh.
PV at optimal angles will receive 2 hours of solar insolation and therefore would have to generate 311kw per hour over those equivalent full solar insolation hours to convert H.
But they aren’t optimally angled because they are sitting on a floating cigar that is being buffeted by winds that are being read remotely by some poor bastard at ground control
And who has to fly this blimp constantly from some game controller.
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MY BEST GUESS on amount of thin clad PV needed per ‘production’ blimp is at least
500 kW and up to 1MW. This would require PV efficiency on a 300 ft long x 250 ft arc
PV cladding for the blimp of from (using 10 square feet/square meter approximation)
13.3% to 26.6%. The lower figure is near
where we are in space projects as this quote from a few years ago says: United Solar has been testing and evaluating the suitability of its technology and products under space conditions. NASA Lewis Center has measured a 12% beginning-of-life conversion efficiency for UNI-SOLAR® cells.
Our competition is CIGs with its higher efficiency IMO but this is counterbalanced by Stan’s “promise”
of twice the power density for Unisolar’s PV. If you are Lockheed, who you gonna’ call? The promised lighter PV or the promised higher efficiency PV to satisfy all the design criteria?
Lockheed, et al, speak of 11 blimps as sufficient to guard the coast which means (using my
Wild-ass approximations)
5.5 to 11 MW of thin film, I figure kapton PV, which is “promised”
(cough…cough) as high margin PV stuff
and unless someone gives it away
I would guess the price at $20/watt or above.
Lucky indeed if any announcement comes this year of the PV supplier chosen
as only the battery prototype
Blimp is being launched first for evaluation
If you made it this far then thanks for reading my stumbling thoughts and
Goodnight,
Al
PS Any calculus on summation of total insolation on a 1/4 cylinder much appreciated with the sun at 22degrees at noon only, etc. etc. etc. |
