Silent Flight: PV Powered Blimps

[Bret Cahill]

It's surprising there aren't more solar powered blimps for tours of
canyons. The forest service could use them to count big horn sheep and
other lildlife. If the weather was fair, wouldn't you like to take a
quiet ride in an airship? Maybe sneak up on a mule deer . . .

There's no question conventional PV would get a blimp going over 25
mph. Boeing's new 40% efficient PV would move an airship at 30 - 35
mph.

The first PV airship should be named the "Pronghorn."


Bret Cahill

[Orval Fairbairn]

In article . com>,
"Bret Cahill" > wrote:

> It's surprising there aren't more solar powered blimps for tours of
> canyons. The forest service could use them to count big horn sheep and
> other lildlife. If the weather was fair, wouldn't you like to take a
> quiet ride in an airship? Maybe sneak up on a mule deer . . .
>
> There's no question conventional PV would get a blimp going over 25
> mph. Boeing's new 40% efficient PV would move an airship at 30 - 35
> mph.
>
> The first PV airship should be named the "Pronghorn."
>
>
> Bret Cahill

The solar cells to power it would consume a lot of its payload.

[Vaughn Simon]

"Bret Cahill" > wrote in message
oups.com...
> It's surprising there aren't more solar powered blimps for tours of
> canyons. The forest service could use them to count big horn sheep and
> other lildlife. If the weather was fair, wouldn't you like to take a
> quiet ride in an airship? Maybe sneak up on a mule deer . . .
>
> There's no question conventional PV would get a blimp going over 25
> mph.

There is considerable question (in my mind at least) that conventional PV
could get a blimp going at that speed, you are talking several hundred HP yes?
How many square yards of PV would that take? Remember that only a portion of
the cells would be receiving full sunlight, so multiply the PV area you need by
at least two. Remember that PV cells have significant weight, would the thing
fly?

>Boeing's new 40% efficient PV would move an airship at 30 - 35
> mph.

There is a little problem here, you would need to figure out how to place a
giant lense over your blimp. Those are concentrating solar cells. From the
article: "Using concentrated sunlight, Spectrolab demonstrated the ability of a
photovoltaic cell to convert 40.7 percent of the sun's energy into electricity."

Vaughn



>
> The first PV airship should be named the "Pronghorn."
>
>
> Bret Cahill
>

[Don Tuite]

Seen this site?

http://www.lockheedmartin.com/wms/findPage.do?dsp=fec&ci=14477

Don

[Jim Logajan]

Orval Fairbairn > wrote:
> The solar cells to power it would consume a lot of its payload.

In the text "Airship Technology" Edited by Khoury and Gillett, Chapter 16,
"Solar Power" deals with design issues of solar powered airship proposals.

Using thin-film PV arrays and brushless DC motors, it states that:
"Potentially, the solar power system could weigh less than 10% of the gross
lift of the 22 tonne airship and would then be competitive in weight with
the conventional airship."

[Kyle Boatright]

"Bret Cahill" > wrote in message
oups.com...
> It's surprising there aren't more solar powered blimps for tours of
> canyons.

The last time I checked, a canyon is about the worst place in the world for
a blimp. First, it is a confined space. Blimps are not particularly
maneuverable, and a confined space requires maneuverability. Second, canyons
have swirling winds. Blimps are pretty tough to control in those conditions.
Third, canyons have walls, which cast shadows. Shadows put a damper on solar
cells.

>The forest service could use them to count big horn sheep and
> other lildlife. If the weather was fair, wouldn't you like to take a
> quiet ride in an airship? Maybe sneak up on a mule deer . . .
>
> There's no question conventional PV would get a blimp going over 25
> mph. Boeing's new 40% efficient PV would move an airship at 30 - 35
> mph.

Right. Until a cloud blew over (or you flew into the shadow of a canyon
wall). Then you'd need a hell of a lot of battery capacity (and weight) to
power your blimp.

>
> The first PV airship should be named the "Pronghorn."
>
>
> Bret Cahill

[Bret Cahill]

> Seen this site?

> http://www.lockheedmartin.com/wms/findPage.do?dsp=fec&ci=14477

Not until just now.

They need to apply that technology to something fun. It would be like
those hot air balloon rides except you could go to more places faster
more often and with greater safety.

You could have conventional power backup for emergencies or getting
across town but most of the time you'ld be very quiet.

This is the best way for most people to see charismatic wild animals.

Most animals scatter when a hiker is even a mile away.


Bret Cahill

[Stubby]

Jim Logajan wrote:
> Orval Fairbairn > wrote:
>> The solar cells to power it would consume a lot of its payload.
>
> In the text "Airship Technology" Edited by Khoury and Gillett, Chapter 16,
> "Solar Power" deals with design issues of solar powered airship proposals.
>
> Using thin-film PV arrays and brushless DC motors, it states that:
> "Potentially, the solar power system could weigh less than 10% of the gross
> lift of the 22 tonne airship and would then be competitive in weight with
> the conventional airship."

And if something other than silicon solar cells are used, the efficiency
can be much high. In 1981 I heard a talk by one John Fan who was
launching a company to make galium arsinide cells. I believe he could
get 10% conversion efficiency rather than 1 to 2% for Si .

[[email protected]]

Bret Cahill > wrote:
> There's no question conventional PV would get a blimp going over 25
> mph.

Maybe. Per http://www.goodyearblimp.com/faqs/faqs_construction.html :

"The GZ-20A size blimps (Spirit of Goodyear; Spirit of Innovation; Spirit
of America) are 192 feet long, 55 feet in diameter, and 59.5 feet high,
with 202,700 cubic feet of helium and a gross weight of 12,840 lbs."

"The GZ-20's carry two fuel injected Continental I0-360's, producing 210
horsepower each."

"The usual cruising speed is thirty-five miles per hour in a zero wind
condition; all-out top speed is fifty-three miles per hour on the
GZ20."

Jane's "Encyclopedia of Aviation" (ISBN 0-517-10316-8), p. 425, says
that the Goodyear "Mayflower" (built 1978) has a gross volume of
202,700 ft^2, so I am assuming it's the same size as the current blimps.
Jane's also says that the Mayflower has "an envelope surface area of
2,006 m^2 (21,600 sq ft)". Jane's also cites the twin 210 hp IO-360
engines.

So, 420 hp is 313 kw. If your motors are 90% efficient, you need to
deliver 345 kw to the motors. If you covered the entire surface of the
envelope with solar cells, you'd need to _average_ 0.172 kW / m^2 to get
that much power. If you assume that everything is great and you're
getting 1 kW / m^2 coming in, that's 17.2% efficiency. I would guess
that at most half of the solar cells would actually be illuminated, so
that means you need to average 0.344 kW / m^2 or 34.4% to get that much
power. As has been noted, the "40%" cells require a concentrator (lens)
in front of them to get that efficiency. Spectrolab claims their TASC
cells ( http://www.spectrolab.com/prd/terres/tasc-main.htm ), which
don't need a concentrator, are up to 30% efficient.

On the weight side... Googling around says that a Continental IO-360
weighs something like 300 lbs. I have no idea what the fuel burn is
like in a blimp, but for grins let's say there is at least enough fuel
for two hours at 10 gal/hr/engine, or 240 lbs. So dropping all of that
stuff gains you 840 lbs.

Spectrolab says one of their cells is 2.277 cm^2 and weighs 0.234 g.
To cover the entire skin of the blimp, you'd need about 8.8 million
of these cells, or about 2060 kg or 4050 lbs. So you're up about
3210 lbs (25% over gross) and you haven't even strapped on any
electric motors yet.

You might be able to make it work with a smaller blimp - you'd need less
power, but you'd also have less surface area for mounting the cells.

Matt Roberds

[Don Tuite]

On Sat, 13 Jan 2007 22:10:25 -0500, Stubby
> wrote:

>Jim Logajan wrote:
>> Orval Fairbairn > wrote:
>>> The solar cells to power it would consume a lot of its payload.
>>
>> In the text "Airship Technology" Edited by Khoury and Gillett, Chapter 16,
>> "Solar Power" deals with design issues of solar powered airship proposals.
>>
>> Using thin-film PV arrays and brushless DC motors, it states that:
>> "Potentially, the solar power system could weigh less than 10% of the gross
>> lift of the 22 tonne airship and would then be competitive in weight with
>> the conventional airship."
>
>And if something other than silicon solar cells are used, the efficiency
>can be much high. In 1981 I heard a talk by one John Fan who was
>launching a company to make galium arsinide cells. I believe he could
>get 10% conversion efficiency rather than 1 to 2% for Si .

We're up to about 18% for 3-bandgap Si, although SunPower's getting
21% with special wafers that have a long enough minority-carrier
lifetime to allow the collection grid to be placed on the backside of
the wafer. Amorphous panels produced using a web-printing process
seem to be getting around 15%, enough for one of the oil companies to
be using them to power one of their oilfields on the patch down by
Bakersfield.

Don

[Bret Cahill]

Even with a pv-solar situation where you only realize 50 watts/m^2 the
blimp would still go 17 mph which allows for a lot of options not
possible with a balloon.

In the summer vacation season in the Grand Canyon or some other SW
desert area, the airship would go considerably faster.

There are no economies of scale as far as speed is concerned.
Increasing size only increases lift.

The cost might not be prohibitive. Covering half a 30 m dia sphere
with 1400 m^2 of $300/m^2 pv would cost half a million dollars, but
would displace 14 tons of air.

A lot of recreation related industries can spend that.

The only other alternative for silent flight is to have something like
a hybrid electric vehicle drive train with a good sized battery.

Economies of scale would definitely allow for a heavy battery in a
larger blimp with a longer range.

When you approach the area of interest kill the engine and use the
battery to power the motor for awhile.

Maybe get a police dept to replace a helicopter with an electric hybrid
electric blimp. Not only does the noise wake everyone up but it alerts
the criminals.


Bret Cahill

[Bret Cahill]

> >Even with a pv-solar situation where you only realize 50 watts/m^2 the
> >blimp would still go 17 mph which allows for a lot of options not
> >possible with a balloon.

> Yeah - but travel by balloon is pretty rare.

This thread was never about commercial aviation but scenic tours. Hot
air balloon tours are quite popular. One got tangled in a high voltage
power line near Phoenix just last year.

Blimp tours with their greater range, flexibility and safety should be
even more popular.

> If you have a blimp that
> can do 17 mph, you're facing a lot of days where you can only fly
> downwind.

What's the point of quiet propulsion on windy days?

> >The only other alternative for silent flight is to have something like
> >a hybrid electric vehicle drive train with a good sized battery.

> Or a really good muffler on a regular, internal combustion engine. Can
> you tell if a Lexus is running from 200 feet away?

Some might want to get closer to a charismatic animal than 200 feet. I
was thinking of flight where you could only hear your own breathing.

> The other thing
> you need is a large, slow moving prop.

A large slow moving prop is quiet.

Have you ever seen the props on ballistic subs? They are a unique
design that is supposed to be ultra quiet, but I've never seen them on
trolling motors. DoD takes forever to declassify technology.

Anyway we need the compressible flow equivalent. In fact, the quietest
low rpm large diameter air prop is probably has pretty much the same
size and shape as a ballistic sub prop.

> A LOT of the noise from an
> airplane is from the prop.

Heavier than air aircraft generally require higher speed propulsion
which is inherently noisy.

> Most of the work that's made helicopters
> quieter has been with the tail rotor.

Still way too loud. Hikers complain about choppers in the Grand
Canyon.

> >Maybe get a police dept to replace a helicopter with an electric hybrid
> >electric blimp. Not only does the noise wake everyone up but it alerts
> >the criminals.

> But they want something that can fly faster than a criminal can
> run/drive.

Give those meth heads a real workout!


Bret Cahill

[[email protected]]

Richard Riley > wrote:
> On Sun, 14 Jan 2007 04:27:40 GMT, wrote:
>> If you covered the entire surface of the envelope with solar cells,
>> you'd need to _average_ 0.172 kW / m^2 to get that much power. If
>> you assume that everything is great and you're getting 1 kW / m^2
>> coming in, that's 17.2% efficiency.
>
> Total solar flux of 1 kw/m2 assumes noon on a clear day at the
> equator.

That's part of what I meant, but didn't make explicit, when I said
"everything is great".

> Average flux in North America throughout the year is between
> 125 and 375 w/m2 depending on where exactly you are.

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. 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.

Matt Roberds

[[email protected]]

Bret Cahill > wrote:
> Even with a pv-solar situation where you only realize 50 watts/m^2 the
> blimp would still go 17 mph which allows for a lot of options not
> possible with a balloon.

How do you figure on the 17 mph? Looking at the Aztec, NM profiler data
at http://www.profiler.noaa.gov/npn/profiler.jsp?options=full , it does
appear that in the summer, the winds aloft don't often get over 15
knots, which is about 17 mph. But they also seem to regularly be around
10 knots, or about 11.5 mph, so if you're flying into the wind, you're
only making about 5.5 mph. I've piloted an aircraft where the wind was
greater than the available thrust; going backwards is about four different
kinds of no fun.

> The cost might not be prohibitive. Covering half a 30 m dia sphere

That's a volume of about 14,100 m^3 or 499,000 ft^3. That's over twice
as big as the current Goodyear blimps. Do we know how to build blimps
that big?

> with 1400 m^2 of $300/m^2 pv would cost half a million dollars, but
> would displace 14 tons of air. A lot of recreation related industries
> can spend that.

I guess the blimp itself is free and so is getting it certificated to
fly.

> The only other alternative for silent flight is to have something like
> a hybrid electric vehicle drive train with a good sized battery.

Maybe. I haven't run any numbers, but you might be able to make this
work if you charged the battery on the ground before takeoff (plug-in
hybrid). Batteries are really heavy, though. In a nearby thread, I
figured that to get the same mechanical work out of 1 kg of gasoline,
you'd need 20 to 27 kg of Li-ion batteries.

Matt Roberds

[Bret Cahill]

> 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.


Bret Cahill

[Kyle Boatright]

"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
>

[Bret Cahill]

> > Even with a pv-solar situation where you only realize 50 watts/m^2 the
> > blimp would still go 17 mph which allows for a lot of options not

> How do you figure on the 17 mph?

Drag calculators.

Power = drag X velocity.

> Looking at the Aztec, NM profiler data
> at http://www.profiler.noaa.gov/npn/profiler.jsp?options=full , it does
> appear that in the summer, the winds aloft don't often get over 15
> knots, which is about 17 mph. But they also seem to regularly be around
> 10 knots, or about 11.5 mph, so if you're flying into the wind, you're
> only making about 5.5 mph. I've piloted an aircraft where the wind was
> greater than the available thrust; going backwards is about four different
> kinds of no fun.

It was better than being in a balloon, wasn't it?

Most mornings at this time of year I look out at the mountains and a
balloon is going over them. Apparently the balloonists have figured
out the morning wind.

> > The cost might not be prohibitive. Covering half a 30 m dia sphere

> That's a volume of about 14,100 m^3 or 499,000 ft^3. That's over twice
> as big as the current Goodyear blimps. Do we know how to build blimps
> that big?

Make it any size that will hold one or more people.

> > with 1400 m^2 of $300/m^2 pv would cost half a million dollars, but
> > would displace 14 tons of air. A lot of recreation related industries
> > can spend that.

> I guess the blimp itself is free and so is getting it certificated to
> fly.

There is a new ultra thin [light weight] copper alloy PV that
supposedly will cost only $1/watt and has a somewhat higher efficiency
than conventional Si PV. Some even believe it will be cheap enough to
shut down the grid, even in the Pacific NW. The Google guys -- we
really need to stop calling them the "Google guys" and get their names
-- are building a big plant in downtown S.F. to produce dozens of
megawatts/year.

Then the real cost will be in the envelope, gondola, He, hanger,
insurance, parachutes, etc., not the PV.

> > The only other alternative for silent flight is to have something like
> > a hybrid electric vehicle drive train with a good sized battery.

> Maybe. I haven't run any numbers, but you might be able to make this
> work if you charged the battery on the ground before takeoff (plug-in
> hybrid). Batteries are really heavy, though.

Hybrids just don't go very far on battery only power. A Tesla will go
240 miles but it doesn't have the drag of a blimp.

> In a nearby thread, I
> figured that to get the same mechanical work out of 1 kg of gasoline,
> you'd need 20 to 27 kg of Li-ion batteries.

A blimp is just _begging_ to be solar powered.


Bret Cahill

[Bret Cahill]

> >> 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?

Depends on the situation. If it's just a small owner - operator - one
person craft then the extra weight and cost of aux power might not be
justified or even possible. Moreover it's not such a big deal if a
weekend hobbiest listens to the the wrong weatherman and crashes his
home made into the wash during a microburst. He'll probably just cell
phone for help to recover the PV and motor.

A commercial tour operation is different. The goal is to get a lot of
people onboard a large airship for as many days as possible. Crashing
into the Colorado River is not acceptable and the heavy lift of large
displacement allows for fuel power backup.


Bret Cahill

[Larry Dighera]

On 14 Jan 2007 19:39:23 -0800, "Bret Cahill" >
wrote in . com>:

>There is a new ultra thin [light weight] copper alloy PV that
>supposedly will cost only $1/watt and has a somewhat higher efficiency
>than conventional Si PV. Some even believe it will be cheap enough to
>shut down the grid, even in the Pacific NW. The Google guys -- we
>really need to stop calling them the "Google guys" and get their names
>-- are building a big plant in downtown S.F. to produce dozens of
>megawatts/year.


http://www.nanosolar.com/history.htm
May 2002: Nanosolar is founded by Martin Roscheisen and Brian
Sager to make solar electricity much more cost-efficient through
much better technology. The approach taken is to develop
medium-efficient but ten times less costly solar cells -- and do
so with a Silicon Valley style team of the best and brightest
engineers. The company is incorporated in Palo Alto, California,
and receives initial financing from the founders. Initial
laboratory work commences focused on technology to produce much
thinner (100x) solar cells with much simpler (printing) processes.



http://www.informationweek.com/industries/showArticle.jhtml?articleID=193303376
The project [the solar electrification of the entire Google
corporate campus] will involve 9,212 solar panels provided by
Sharp Electronics. A majority will be placed on the rooftops of
some of the buildings in the "Googleplex" and parking lots. The
solar energy will be used to power several of Google's Mountain
View office facilities.

Google has a strong interest in solar. A startup originally funded
by Google in June announced a $100 million financing package and
set plans to build what the company claims as the world's largest
solar-cell manufacturing facility in California.

Presently in pilot production in its Palo Alto, Calif.-based
facility, the solar-cell startup — Nanosolar — has started
ordering volume production equipment for use in a factory said to
have a total annual cell output of 430-megawatts (MW) once fully
built out, or approximately 200 million cells per year.



http://www.nanosolar.com/
Nanosolar has developed proprietary technology that makes it
possible to simply roll-print solar cells that require only
1/100th as thick an absorber as a silicon-wafer cell (yet deliver
similar performance and durability). Watch the CNN video.

[Bret Cahill]

A blimp has one advantage over other applications of PV on cloudy days:
The option of dumping some ballast and floating above the clouds.

Balloons can change level as well but it doesn't increase their thrust.


Bret Cahill