More fuel for thought

Jim Logajan wrote:
wrote:
Andrew Sarangan wrote:
There is 30 horsepower of solar radiation falling on a Cessna 172's
wing that we are simply throwing away.

Unless I dropped a decimal somewhere, there is about 16 M^2 of wing
area on a C-172.

At ~1000W/m^2 insolation, that yields an "ideal" max power of ~16,000 W.

30 HP is 22.4 kW; there isn't that much energy in sunlight.

Since there are ~746 W/HP, by my reckoning the sunlight power on a C-172
wing is ~21 HP. Still not bad, though not sure where Andrew got 30 HP.

He's using 1.4 kW, which is about the max you'll ever get.

Both of you are ignoring the fact that you get that only if the angle
beteen the sun and your collector is 90 degrees, otherwise you have
to multiply by the sine of the angle to get the real energy per unit
area.

The challenge is extracting the full solar spectrum and storing it.
But there are no fundamental scientific reasons why this is not
achievable.

You mean other than we haven't a clue how to do it in the real world?

There are no fundamental scientific reasons why we can't:

Convert light into electricity with 90% efficiency.

Real world system efficiencies of 40% should be possible today - using
solar thermal (e.g. solar troughs).

Lab efficiencies are already around 40%.

Using collectors or concentrators doesn't change the overall efficiency,
it only makes the area of the converter required for a given amount
of energy smaller; the total area remains the same.

And for photocells, it runs the temperature up which plays hell with
the usefull life and reliability.

Cure cancer.

That is already being done for some forms of cancer. Next time try "Cure
the common cold." (And strictly speaking the body does that on its own - it
just makes you feel miserable while it goes about it!)

Cure cancer as in take these pills twice a day for a week, not irradiate
or cut out a chunk of the body and hope there isn't too much collateral
damage to the body, though with stuff like proton therapy the irradiation
stuff is getting pretty good.

Produce sustainable fusion.

Always 30 years off.... ;-)

Convert junk mail and coffee grounds into 100 LL.

An interesting idea. :-)

Mr. Fusion; I forgot about the banana peels.

--
Jim Pennino

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In article Andrew Sarangan writes:

On a clear day, the average solar power incident on the earth's
surface is 1400Wm^2. http://hypertextbook.com/facts/1998/...utbundit.shtml

No, that is the solar power at the top of the atmosphere.

By the time it gets through the atmosphere, the accepted figure is
1000 watts per square meter.

Consumer solar cells are available claiming about 20% efficienty now.
If they can do as their ads claim, the 16 sq meters of the top of the 172
will get 3.2 kW under direct solar radiation, and perhaps 70% of that on a
typical mid-day for most of us due to the sun angle being lower than
directly overhead. That 2.25 kW would give 3 horsepower if the conversion
were 100 percent efficient (it isn't).


As for 100 percent efficient solar cells, you say:

We are already doing it, for specialized applications. Internal
quantum efficiencies of certain semiconductor materials have
approached nearly 100% within a narrow spectral range.The challenge is
how to translate that to match the broad solar spectrum. The know-how
exists, but there isn't enough investment to make it happen.

If you believe that, you should be out convincing investors that you
can make them very rich. Don't tell us. Show us.

Convince those that point out that the laws of thermodynamics
setting limits apply to solar cells too.


Had we spent all the post-911 terrorist-aversion expenditures on
something like this, we could be declaring independence from the
middle east.

Speculation, with no facts in evidence.


I know that we spent several millions erecting a metal fence around
our small GA airport. All it did was screw up the localizer signal and
trap the deer population. I don't think even the administrators
believed there was a terrorism threat here.

Yes, the whole security paranoia over aircraft has not gone away.


On the other hand, NSF (National Science Foundation) budget has barely
kept up with inflation in the past 10 years. This is where we count on
for fundamental break throughs in discovery.

Last I checked, the NSF didn't do research. Universities do some, but
putting things into production is done by businesses.



Now, if I had the cash, I would be inclined to see if that 3 horsepower
could be fed to a reasonably efficient prop to drive an ultralight around.
It might be difficult to stay ultralight with all the solar power weight,
but it would be fun if it could be made to work.


Alan

Phil J wrote:
On Apr 15, 11:52 am, Gig 601Xl Builder
wrote:
While I agree that alternate forms of energy are a very good thing for
very many reasons there is no reason to do anything at this point that
will trash the world economy because there is still several metric
butt-loads of crude out there.

I don't know of anyone who is suggesting that we trash the world
economy.

There are lot's of Greens out there that would do exactly that and if
the truth were known they would be happy about it. These are the same
people that were pro-USSR prior to the 90s. They are watermelons. Green
on the outside and red on the inside. That is a friend of mine's
favorite saying. He probably got it from Rush but it is a pretty good
description.

wrote:
Both of you are ignoring the fact that you get that only if the angle
beteen the sun and your collector is 90 degrees, otherwise you have
to multiply by the sine of the angle to get the real energy per unit
area.

I didn't ignore that aspect out of ignorance or oversight. I'm not
trying to write a treatise on the subject after all. And anyway, we also
"ignored" clouds, fog, smoke, bug splatter, and night too. It didn't
seem relevant to the underlying point. Which I took to be the amount of
power in sunlight. (Solar powered aircraft have been built and set
records, after all.)

Jim Logajan wrote:
Real world system efficiencies of 40% should be possible today -
using solar thermal (e.g. solar troughs).

Lab efficiencies are already around 40%.

Real-world heat engine efficiencies of 36% have been observed in power
plants:

http://en.wikipedia.org/wiki/Heat_en..._performa nce

(Alan) wrote:
Now, if I had the cash, I would be inclined to see if that 3 horsepower
could be fed to a reasonably efficient prop to drive an ultralight
around. It might be difficult to stay ultralight with all the solar
power weight, but it would be fun if it could be made to work.

You are about 28 years too late - it was demonstrated in 1980. Here's a
brief history of solar powered flight:

http://www.nasa.gov/centers/dryden/n...-054-DFRC.html

Jim Logajan wrote:
wrote:
Both of you are ignoring the fact that you get that only if the angle
beteen the sun and your collector is 90 degrees, otherwise you have
to multiply by the sine of the angle to get the real energy per unit
area.

I didn't ignore that aspect out of ignorance or oversight. I'm not
trying to write a treatise on the subject after all. And anyway, we also
"ignored" clouds, fog, smoke, bug splatter, and night too. It didn't
seem relevant to the underlying point. Which I took to be the amount of
power in sunlight. (Solar powered aircraft have been built and set
records, after all.)

I can make a solar motor out of 4 cigarette lighter flints, a magnifying
glass, and a refrigerator magnet; that doesn't mean it is usefull
for anything other than a physics demonstration.

There is a big difference between the amount of power in sunlight
and the incident power in sunlight, and the incident power is what
there is to work with.

Jim Logajan wrote:
Real world system efficiencies of 40% should be possible today -
using solar thermal (e.g. solar troughs).

Lab efficiencies are already around 40%.

Real-world heat engine efficiencies of 36% have been observed in power
plants:

http://en.wikipedia.org/wiki/Heat_en..._performa nce

Yeah, and bejeezus huge solar boilers have been build in sunny climates
with some sucess.

None of that has anything to do with running a practical airplane.


--
Jim Pennino

Remove .spam.sux to reply.

On Apr 15, 2:47*pm, Gig 601Xl Builder
wrote:

I don't know of anyone who is suggesting that we trash the world
economy.

There are lot's of Greens out there that would do exactly that and if
the truth were known they would be happy about it. These are the same
people that were pro-USSR prior to the 90s. They are watermelons. Green
on the outside and red on the inside. That is a friend of mine's
favorite saying. He probably got it from Rush but it is a pretty good
description.

Really? How many Communist Greens have you met that wanted to trash
the world's economy?

Phil

On Tue, 15 Apr 2008 11:58:25 -0500, Gig 601Xl Builder wrote:

Dan Luke wrote:
......a self made dooms day scenario so to speak.

Oil is $110/bbl and climbing. Gasoline is on a similar path. Those facts
alone are already starting to give serious economic impetus to alternative
energy development.


Oil is at an all time high because the dollar is at an all time low.

That's not the only reason. Demand is at an all-time high and growing
fast. Crude is getting more expensive to extract.


All
the money both foreign and domestic is moving into hard commodities.
Gold and oil just happen to be the most popular two. If the dollar
wasn't in the hole so badly the resent find off the coast of Brazil
would have really depressed the oil futures market.

Hmmm...

"...could contain as much as 33 billion barrels!"

That's a pig-in-a-poke until the reserves are proven.

That's why it didn't depress prices--not even a smidgen.

On Tue, 15 Apr 2008 10:43:01 -0700 (PDT), Phil J wrote:

I don't know of anyone who is suggesting that we trash the world
economy.


Talk radio "environmentalist" strawmen say it all the time.

That's why it shows up here.


But I think now is the time to devote some serious resources
to find alternative, sustainable ways to keep our societies running.
If we wait until the end is clearly in sight, we probably won't be
able to afford to spend the resources it will take to solve the
problem.

If you want to get some good perspective on this kind of thing, read
the book Collapse by Jared Diamond. It's a very clear-eyed, down-to-
earth analysis of why past societies have flourished, but then
ultimately collapsed. Over and over again in human history, societies
have over-used their natural resources until they suffered a
catastrophic collapse. This is the rule, not the exception. It is
very rare in human history for a society to live in a way that is
sustainable over the long term. Clearly, our current society is not
sustainable, and if we ignore history we will be condemned to repeat
it.


You're just one of those whacko alarmists.

Everything will be fine if we just keep doing things the same way we
always have.

Don't worry; be happy!

On Tue, 15 Apr 2008 16:55:04 GMT, wrote:


The challenge is extracting the full solar spectrum and storing it.
But there are no fundamental scientific reasons why this is not
achievable.

You mean other than we haven't a clue how to do it in the real world?

There are no fundamental scientific reasons why we can't:

Convert light into electricity with 90% efficiency.

Cure cancer.

Produce sustainable fusion.

Convert junk mail and coffee grounds into 100 LL.

You're just a happy little ray of sunshine, aren't you?

Yeah, you're right: we don't know how to do any of this stuff.

Might as well give up on all of it.