"Timm Simpkins" wrote in message ...
"Rod Speed" wrote in message
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"Timm Simpkins" wrote in message
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Rod Speed wrote
Anthony Matonak wrote
News wrote
How much heat do PV cells emit on the back and front of the
cells?
You could think of it this way. Typical PV panels are
around 12% efficient at converting sunlight into electricity.
This means that the other 88% is converted into heat.
Well, maybe 16 and 84%, eg 0.84x800 = 672 W/m^2 in AM2 sun.
...that would only be true if they were a perfect
black body absorber of all energy that falls on them.
But they are better than that.
Nope. Not even possible.
Rich Komp says the silicon is almost transparent to IR, and the
aluminum contact beneath is shiny, so PVs are a selective
surface.
Waffle, the fact remains that all of what doesnt get turned
into electricity does not end up as heat. Plenty gets reflected.
The maximum efficiency ratings they are getting now are approaching
30%.
In
normal production they are around 23%. The average cell is about
12%
efficient. Also, no matter what misguided brain fart you're having
now
Rod,
the rest of the sun's energy that is absorbed by the panel IS
converted
to
heat. In fact, the efficiency of solar cells decreases as the heat
increases so there are many people experimenting with methods, both
passive
and active, to remove that heat and somehow convert that heat to
electricity
as well. The measure of efficiency is not measured by the amount of
energy
available, it's measured by the amount of energy produced compared
to
the
amount of energy used.
Here's a link discussing the heat loss:
http://www.nasatech.com/Briefs/Apr99/NPO20284.html
Now Rod, don't complain to me about how wrong you are now. You can
complain
to the guys at Nasa about it.
You can measure the efficiency by taking the wattage being wasted as
heat
and compare that to the wattage being output by the solar cell. If
the
rays
are reflected and have no impact on the process, they cannot be
measured,
so
the measurement is totally what is absorbed by the panel.
I don't understand why you wouldn't know how efficiency rates are
calculated. It's been common science for quite a long time now. It
would
not be a true calculation of efficiency if they were to calculate
the
efficiency by the total energy available. That's like calculating
the
efficiency of a motor by calculating how much energy is output
compared
to
the amount of energy available in the entire gas tank when you only
used
a
quarter of a tank.
That is interesting, but frankly it seems like a poor way to state
efficiency for a solar collector. How does one determine the
amount of energy absorbed and not reflected in the collector?
Since solar insolence is readily available for an area, it would seem
more proper to use useful energy out divided by solar energy insolent.
This would account for energy reflected away from the collector as well
as energy converted to non-usable forms (for example, heat in a PV
cell).
Measuring efficiency like what you're saying, I could have a
1 m^2 cell that is 80% efficient produce less electricity than
a 1 m^2 cell that is only 15% efficient. Just 'accidently' have
a highly reflective coating on the first cell. Would run much
cooler, and have higher 'efficiency', but not very useful.
Makes the 'efficiency' number useless to compare cells.
Would have to revert to just electric output 'in full sun'. And *that*
leaves a lot to be desired (define 'full sun' for every location??)
When you buy solar cells, you don't purchase
efficiency ratings, you purchase wattage ratings.
Irrelevant waffle.
I don't agree with your assesment that you can lower
the efficiency of a solar cell by reflecting the sun's rays
He didnt even say that.
Here are a few quotes:
"How does one determine the amount of energy
absorbed and not reflected in the collector?"
Nothing like that bit you claimed you didnt agree with.
"Measuring efficiency like what you're saying, I could have
a 1 m^2 cell that is 80% efficient produce less electricity
than a 1 m^2 cell that is only 15% efficient. Just 'accidently'
have a highly reflective coating on the first cell."
Nothing like that bit you claimed you didnt agree with.
He very well did say that.
Nope, that is saying something quite different. That isnt
even 'lower the efficiency of a solar cell by reflecting the
sun's rays' its just rubbing your nose in the fact that the
efficiency of solar cells aint measured the way you claim it is.
By adding a highly reflective surface to the collector,
you are reflecting the rays away from the collector.
Duh.
He claims that the lack of those rays would lower the efficiency,
Nope, he aint saying anything like that.
and that simply is not true.
Having fun thrashing that straw man are you ?
If you took a theoretical motor
Hasnt got any relevance what so ever to HOW THE EFFICIENCY
OF SOLAR CELLS IS ACTUALLY MEASURED.
since the heat increase in the solar panel should be
lower as well and so the ratio's should be similar.
Not a clue.
No you don't have a clue.
Pathetic, really.
That reflected energy is not taken into
account in calculations of efficiency.
Irrelevant to the original claim being discussed.
It is completely relevant to the original claim I was having an issue with.
Nope.
It can't be since it's almost impossible to measure.
Complete and utter pig ignorant drivel. Its completely trivial
to measure the amount of energy falling on the PV system.
That's exactly what I'm saying. If you measure that energy you're not
measuring the amount of energy being consumed, but the amount available.
Pity about how the efficiency of solar cells is actually measured.
You can measure temperature differentials and output. A solar cell
that puts out 12 volts at 6 amps is putting out 72 watts of power.
Its actually more complicated than that too, because it isnt a
simple pair of numbers, depends on the load being driven too.
We're talking theory here.
Nope.
The numbers I'm putting out are the theoretical maximum
outputs available from the solar panel, and that should be obvious.
Even you should be able to bull**** your way out of
your predicament better than that pathetic effort.
And is completely irrelevant to the original claim anyway.
At 20% efficiency, that means for every 72
watts of power you loose 1440 watts to heat.
Not a clue.
If you measure the heat difference in the solar panel
Whatever that waffle is supposed to mean.
and convert that to watts,
Not even possible.
It's entirely possible to convert heat to watts.
You were talking about a HEAT DIFFERENCE.
The measure of heat is done in joules. You can convert joules to watts.
the conversion is k=0.0002780752 * j where w = watts and j=joules.
Nothing like your previous pig ignorant claim.
you can compare that to the electrical output
and that's where you get your efficiency rating.
Not a clue.
If you're inhibiting the path of the sun,
you aren't lowering the efficiency rating
You can be when PV systems dont necessarily
work at the same efficiency with different light levels.
Irrelevant when we're not talking about anything but theory.
Even you should be able to bull**** your way out of
your predicament better than that pathetic effort.
That may likely be true,
Corse its true.
but the fact is that if you reflect that light away from
the solar panel you can't use it in your measurements.
Pity about how the efficiency of solar cells is actually measured.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
Temperature of the PV system in spades.
because you're restricting the solar panel's fuel. Fuel that doesn't get to
the panel cannot be consumed and cannot count toward the efficiency.
Pathetic, really.
Your link doesn't really explain what you are saying about calculating
cell efficiency. It discusses that cells get warm and have to be cooled.
And that heat can be used to keep batteries warm in cold weather.
I was referring to the statement that says that the
energy that doesn't produce power produces heat.
It doesnt even say that as absolutely as the original claim being discussed.
It JUST says that a lot of heat is generated as well
as the electricity. NOT that ALL the energy that falls
on the PV system ends up as electricity or heat.
"most of the solar radiation focused by solar concentrators
onto solar photovoltaic cells is converted to heat."
Nothing like the claim that all the energy falling
on the PV system ends up as heat or electricity.
That is what it says,
Pity its nothing like the claim that all the energy falling
on the PV system ends up as heat or electricity.
and I am giving the proof that
Nope, just flaunting your complete pig ignorance of
how the efficiency of solar cells is actually measured.
the theory that the efficiency rating of solar cells has anything
to do with anything besides power output and heat. FUEL
NOT USED CAN'T BE USED TO CALCULATE EFFICIENCY.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
What is REFLECTED clearly doesnt end up as either in the PV system.
You claimed that in a 12% efficient system
that the other 88% was not converted to heat.
I ACTUALLY said that the other 88% wasnt ALL converted
to heat IN THE PV system, a different matter entirely.
That is completely false.
Fraid not.
Here's what was said:
QUOTE
You could think of it this way. Typical PV panels are
around 12% efficient at converting sunlight into electricity.
This means that the other 88% is converted into heat.
Nope, that would only be true if they were a perfect
black body absorber of all energy that falls on them.
In practice quite a bit is just reflected off them.
END QUOTE
Which was correct when I said it and is still correct.
All you have ever done is flaunt your complete pig ignorance
of how the efficiency of PV systems is actually measured.
I wasn't using that to bolster efficiency ratings arguments.
More irrelevant waffle.
But I don't see any discussion about calculating the efficiency of
a solar cell in the manner you described. I think you're wrong in
this and PV cell efficiency is calculated as (electric-energy-out) /
(solar-energy-flux*area-of-collector). A much more logical method.
Do you have another NASA link that explains your point better?
I don't, but I can give you plenty of links on how to measure efficiency.
Irrelevant to the original claim being discussed.
And you cant with the PV SYSTEMS BEING DISCUSSED ANYWAY.
You are saying that just because there is a certain amount of energy in
a given area of light that that energy is being consumed in the reaction.
Nope, he aint saying anything like that either.
If he's not saying that, then why is he talking
about the energy in a given area of light?
Concentrate on the word CONSUMED.
It has no relevance if he's not trying to take it into account.
Separate issue entirely.
That is not how efficiency ratings are made.
Wrong again.
Then how are efficiency ratings made?
Basically be MEASURING the amount of solar energy that falls
on the PC system and measuring the amount of electrical energy
it produces, and that is the efficiency, at the particular set of
conditions on solar energy level and temperature and load etc.
You dont approve ? Your problem.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised WHEN they laugh in your face.
I'll put it simply for you. The amount of energy consumed
in a system compared to the amount of usable energy
output by the system is how you get efficiency ratings.
Pity about how the efficiency of PV systems is actually measured.
If I am wrong,
No if about it.
I'm waiting to be educated,
Not even possible.
even though I know you can't.
Nothing like a completely closed mind eh ?
You only measure the potential energy of the
amount of fuel, in this case sunlight and divide
that by the amount of energy output in the reaction.
Wrong again. The only energy output that matters with efficiency
is the electrical energy, and that is precisely what he just said.
That is correct, I should have said the amount of useable energy.
Doesnt help.
Pity about how the efficiency of PV systems is actually measured.
Since nothing is done with the heat, that figure
must be thrown out. He did not say that though.
Yep, he's pointing out to you that you havent got a clue
about how the efficiency of PV systems is actually measured.
Since it's impossible to measure the exact
amount of fuel being consumed by a solar cell,
What matters is the TOTAL SOLAR
ENERGY FALLING ON THE SOLAR CELL.
No sir!
Yes cur!!
What matters is the TOTAL SOLAR ENERGY CONSUMED BY THE SOLAR CELL.
Pity about how the efficiency of PV systems is actually measured.
The fact that it falls on the solar cell does not guarantee that it will be used.
Pity about how the efficiency of PV systems is actually measured.
The fact is, you guys are arguing that reflected
solar energy has some part in the calculation
of the efficiency of a solar panel in creating power.
And that is the way THE ENTIRE INDUSTRY DOES IT.
That is simply not true.
Fraid so.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised WHEN they laugh in your face.
That is completely trivial to measure.
you need to measure the heat.
Nope.
How else do you find out how much fuel is being consumed?
There is no 'fuel'.
The industry measures the amount of solar energy falling on the PV system.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised WHEN they laugh in your face.
If you can't measure the exact amount of solar energy consumed,
'consumed' isnt even relevant.
you have to measure the total power created by the system.
Power isnt even being created.
That means not only measuring the amount of energy
that was converted to electricity, but the amount of
energy converted to heat. When you add those
together, you get the total amount of energy input.
Pity about how the efficiency of PV systems is actually measured.
Now, in a system where there is fuel being burned,
Completely and utterly irrelevant to how the
efficiency of PV systems is actually measured.
you must also take into account fuel that does not get
burned unless you are calculating how efficient the system
is at burning fuel. Fuel that does not get burned has not
been used and would skew any true efficiency figures.
Completely and utterly irrelevant to how the
efficiency of PV systems is actually measured.
Now, I admit that my theory that you have to measure the
heat may be flawed since I have never measured efficiency
of solar panels, and have never talked to anyone that has,
And are so stupid that you cant even manage to look up
how the efficiency of solar panels is actually measured either.
Apparently neither can you. If you had, and I were
wrong, you would be shoving it down my throat.
That is precisely what I have been doing, stupid.
but as far as the way to measure efficiency, I know for a
fact that you cannot use the amount of fuel available as the
determining factor of the efficiency since there is no possible
way that reflected energy can be consumed in the reaction.
Pathetic really.
Have a look at how solar cell efficiency is actually measured some time.
If you were to blow air into a turbine and measure the power produced,
you could not take into account the energy in the air that was not taken
in by the turbine. That would give you a false reading of efficiency.
Completely and utterly irrelevant to how
solar cell efficiency is actually measured.
Efficiency is efficiency is efficiency.
Pathetic, really.
It is completely relevant.
Completely and utterly irrelevant TO HOW SOLAR
CELL EFFICIENCY IS ACTUALLY MEASURED.
You on the otherhand aren't.
Pathetic, really.
Using solar insolence in the denominator would be similar to
measuring power out of the motor divided by the fuel-flow-rate
(to use your analogy). That method *does* make a lot of sense.
It even accounts for fuel losses through evaporation or leakage
(analogous to reflection from the surface of a PV cell)
Fuel losses are only applicable if they
enter into the system in the first place.
Not with solar cells.
Solar cell efficiency is the percentage of the solar energy
available to the PV system that ends up in electrical energy.
If the fuel isn't used, how do you count it in efficiency?
Pity about how the efficiency of solar cells is actually measured.
It must be introduced into the system in order for a measurement to be made.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
Calculating reflected energy is as relevant to calculating actual
efficiency of a system as calculating how many hairs you loose to
the sewer every time you take a shower. No relevance whatsoever.
Pity about how the efficiency of solar cells is actually measured.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
You are talking about reflected fuel, and that
cannot have entered into the system at all.
Completely and utterly irrelevant to how
solar cell efficiency is actually measured.
I will admit to some lack of knowledge of solar cells,
And complete pig ignorance about how
solar cell efficiency is actually measured.
but in my studies of fluid dynamics I have had many
occasions to calculate efficiency of different systems.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
We had to take special care not to
calculate the fuel not used in the reaction.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
Also, you cannot use the power available if you don't
have a system that is designed to consume that power.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
Therefore, unused fuel must be removed from the equation.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
An example would be if you were to run your system on
hydrogen. If you were pumping the hydrogen through a
turbine, but not burning it, you could not take the energy
potential in the hydrogen itself into account. If you were
burning the hydrogen, but not splitting the individual atom,
you could not take the atomic energy into account.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
There is so much energy in everything, but if that
energy is not consumed in the reaction, you are
calculating for something that can never exist.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
This is the same with solar energy.
Nope.
If you are calculating efficiency for a fuel that has no possibility
of giving you power because it doesn't enter into the system,
you are calculating efficiency for something that cannot exist.
All completely and utterly irrelevant to how
solar cell efficiency is actually measured.
Thanks for that completely superfluous proof that you have never
had a clue about how solar cell efficiency is actually measured.
Rod, you make a good argument for abortion, but
you don't make much of an argument against my facts.
You havent even presented a SINGLE fact relevant to HOW
THE EFFICIENCY OF PV SYSTEMS IS ACTUALLY MEASURE.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
If you are talking about how efficient of a collector of solar
energy it is, that is one thing, but if you are talking about how
efficient of an electricity producer it is, that is another entirely.
Pity about how the efficiency of solar cells is actually measured.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
A solar collector for heating water should be calculated
the way you are suggesting, because the less solar
radiation it collects, the less efficient it is. A photovoltaic
cell on the other hand is measured totally differently.
Pity about how the efficiency of solar cells is actually measured.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
You are either arguing a point you know nothing about, or are
getting confused about the system we are talking about measuring.
Or I actually understand how the efficiency
of solar cells is actually measured.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
Measuring the efficiency of a fuel pump
is not the same thing as measuring the
efficiency of an internal combustion engine.
Pity about how the efficiency of solar cells is actually measured.
Try telling the industry that they havent got a clue about how to
measure it. Dont be too surprised when they laugh in your face.
Totally apples and triangles.
Yep, all your crap about fuel and engines and showers is that in spades.