Tip:
Highlight text to annotate it
X
♪ [music playing-- no dialogue] ♪♪.
Thank you, I'm not sure if I can see this under here.
I may have to wander out there.
Well, we'll try it.
I've got to point out a few pictures here because every one
of these pictures uses photovoltaics, and has been
a focus of NASA programs in all of these cases.
The space station which you see right there will have
the largest solar powered ever in space by the time
of its final construction.
That has 262,000 single crystal silicon solar cells that look
just like this.
And I'll pass this around so you get a chance to see it.
They're laid out on a little plastic blanket
with copper interconnects.
And if you use a little imagination here you'll find
you can match up the back side contacts with the pattern
on this capton polyimage structure.
You have four laser drilled holes through this, so if you
hold it up to the light you'll see the four holes
and the contacts are wrapped through those holes in the cell
to the back side.
So you've got essentially when this is in sunshine, you've got
the equivalent of a battery with a plus side and a minus side.
And we are going to talk a little bit more about that
as the day progresses.
Now you might wonder a little bit about what a blimp
is doing there.
It's an airship and there is a lot of interest currently
in NASA in looking at these kinds of powered airships
for upper atmospheric studies.
Now it's a lot of real-estate.
This thing is huge.
Just imagine rolling out a solar cell blanket on top of it
to use as power for the airship.
And we've done a lot of work actually looking
at the application for that particular case.
And believe it or not we've actually flown this.
It's an entirely electric aircraft.
It is powered by cells on the top wings and these
are electric motors that actually provide the thrust
necessary for the aircraft.
The motivation for that, well there's several motivations
for that.
Again, upper atmospheric research where they can have
this stay up.
If you use it in conjunction with a fuel cell, for example,
where you have some storage you can envision leaving it up
for quite a long time.
We are now at NASA, according to the President's program
as he announced it in 2004, we are going back to the moon.
Of course the President is changing, who knows what
the next one will do.
But we've been investigating how we would power our cells if
we established a base on the moon.
Now of course you know that the moon has a few problems
with solar power.
It's dark half the time, right?
So what you can do is in fact, you can put things at the poles
where you can get sunlight for the entire time.
And last but not least, we'd like to go back to Mars.
And I will spend a little bit of time talking about that.
We have some studies that our group is doing
on the Mars rovers.
Previously on the Pathfinder rover that landed in 1997,
and also one of our scientists is working with the current
Mars exploration rovers, Spirit and Opportunity, that are still
believe it or not roaming the planet four years after their
landing in 2004 and what was theoretically a 90 day mission.
Okay, so they got that one wrong.
We'll come back to why they got that one wrong in a few minutes.
What is the more recent is our departure into
the terrestrial world.
We now have, and this is under construction as we speak,
a concentrated system.
This is the photovoltaic research building right behind
this picture here.
This will be a 900x concentration.
It has vertical junction silicon solar cells on this little bar
here that will power it.
It is water cooled and the cooling water will theoretically
run back in to the buildings heat power.
This is grid interconnected with the building, and so whatever
electricity we generate we will either use or essentially
sell back to the grid.
This array, look at the top one, that's a bonnet array,
it's only been at Glenn Research Center now for a little
over a year.
It is a two kilowatt polycrystalline silicon cell
array, and it is just grid tied into the building behind it
to provide power again for the building, and if there is
excess back to the utility.
The bottom arrays here, this was a photovoltaic test bed that
was built in the 1970s.
These are arco solar panels, crystalline silicon.
Each of these panels, just take one little slice here,
is 4.3 watts.
These panels are 20 watts.
And I guess I've got to touch it and wake it back up again.
Come back, come back.
It's sleepy.
(male speaker). Strange.
(Dr. Bailey). Yes, well,
interesting arrangement.
There it is, it came back.
These terrestrial rays are a result of
a Presidential mandate.
Mind you another one of those federally unfunded mandates
that they put out often to the educational world,
they have now put out for NASA.
NASA is the single largest, well the government I guess,
not just NASA, but the government as a whole,
is the single largest user of electricity in the country,
and so there has been an edict given by the President
that we will turn green, right.
Of course the problem is we have no way to fund these systems,
so little by little we're putting them up when we can
get the resources to do so.
So this 2-kilowatt array represents an effort that NASA
is making as an agency to become a little more green
and environmentally conscious.
So having said all that, let's go more specifically
to the solar cell.
Now it won't hurt you, it's a little bit of math,
but if you look at a solar cell, if you look at it in the dark,
it acts like a diode.
If you look at it in the light, what you have is the interaction
of the light with the semiconductor such that excitons
are formed.
Excitons are bound electron and whole pairs.
Now, there is an asymmetry in the construction of this
PN diode, if you will, and that is quite simply the fact that
if you look at silicon here on the chart, you will see that if
you put a little bit of boron in silicon, boron has one less
electron than silicon, and you can make a p-type semiconductor.
If you put one more electron by using phosphorous in silicon,
you can make an n-type semiconductor.