Oh yeah, forgot to address this issue. Your analysis is faulty because it doesn't consider all the energy in the cell, only the electrical energy.
In the shorted cell photons create electrical current which is then dissipa ted in the internal resistance of the cell. When the cell output is open t he photons continue to fall on the cell and dislodge electrons, but with no place to go those electrons recombine with holes and generate heat directl y without external current flow. So the same heat is generated in both cas es.
No. However, I have no idea what the OP is using or doing and prefer to assume the worst possible situation. There are plenty of warning labels on consumer products that have little or no connection to probability and reality. Think of my warning about shorting the panel as this type of warning.
Very dangerous. My might ingest the silicon and choke, or cut yourself with the glass. If the glass is a drinking glass, and you drink enough dihydrogen monoxide to drown, it can be fatal.
I left my driving glasses on my car seat one hot afternoon. When I returned to the car, there was a smoldering hole melted into the upholstery. I don't believe they teach such things to architects: However, I don't think the OP's solar cell phone charger would be using any optics capable of concentrating the light sufficiently to do any damage.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
The impedance of a solar cell is not constant. The impedance that must be matched is the dynamic impedance which is dV/dI rather than V/I.
Consider the open circuit output voltage of the solar cell. In the case yo u describe the output voltage at MPP would be half the open circuit voltage . It is more like 90+% so that there is much less heating from the electri cal current in the cell than there is in the load.
Remember, solar cells are not 100% electrical. Much of there operation is in the physics, not entirely unlike batteries.
Ok, I'm wrong (again). The consensus seems to be that the cell becomes slightly warmer in an open circuit than in short circuit but with some conditions as to the type of cell and construction:
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Sorry. I should have added some annotations to the spreadsheet to indicate credits, refund, and discounts. In Aug 2016, I signed up for the PG&E CARE program, which amazingly declared me to be impoverished and worthy of being subsidized by a reduction in rate of about $20/month. The large drop in cost in Sept 2018 was due to Santa Cruz joining the Monterey Community Power Cooperative, which buys bulk power and resells it to member counties at discounted prices: No clue how long that will last. There was also a "generation credit" and "conservation incentive credit" which further reduced the monthly billing.
I like to draw my conclusions first, and then fabricate the evidence to prove it. If I remove that credits, subsidies, programs, politics, and such from my billing, it would show a fairly constant billing rate over the 11 year period. My reduction in electricity usage hasn't been a straight line decrease (because I'm spending more time at home these days), but at least up to about 2015, does show that no matter how much I decrease my usage, the monthly costs are about the same. Therefore, conservation doesn't pay.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
But, but, but, the graphs *do* show monthly costs varying with the monthly usage. I can see virtually every feature in the usage curve reflected in t he cost curve. I'd like to see the correlation coefficient of the two curv es.
As you say, you drew a trend line that supports your premise, but did you c onsider any other lines? I see a fourth order polynomial produces interest ing results. In particular it shows your costs going down the last few yea rs with no real change in the usage trendline. Seems to me maintaining the status quo in usage gives the best results in costs. Whatever you did in Aug this year gave the absolute best results over the entire graph. Keep d oing THAT!
Same energy in (full sunlight minus that reflected), same electrical energy out (nil). Therfore same amount of heating. With the open circuit panel it's conduction through the diode junctions of each cell (hole-electron recombination at the junction) that produces the same heat energy as the resistive heating in the shorted panel, If you want to reduce the self-heating of a panel electrically you connect it to a load (preferably MPPT)
Maybe they do change colour, the hole-electron thing could make infared light...
Those coatings would also block some visible and near IR light that could have been used by the solar cells, they would also trap more of the heat produced by the visible light that isn't converted to electric current and any heat produced by I^2*R losses. I can seen them possibly being useful on thermal solar panels (but ordinary glass is already pretty good at blocking thermal inrared), but I am not convinced they'd help photoelectric solar panels.
Well, no. Generator impedance is mostly not resistive in origin. electrically generators are like low K (gapped) current transformers; primary frequency represents shaft speed and primary current represents rotor magnetisation.
Just apply the laws of thermodynamics. At MPP the most power is being extracted from the panel. removing power means less of the input power remains to be converted to heat inside the panel. OTOH the difference between 850W of heating and 1000W of heating may not be particularly significant.
Agreed. However if the MPPT charge controller is operating at the MPP, and I fix those variables that don't change very rapidly (solar irradiance, position of the sun, static load, etc), I believer that I can assume that the resistance, ESR, and impedances are reasonably constant.
Ummm... the solar panels deliver DC. Neither inductance or capacitance matter with DC. However, if you're talking about the interface between the MPPT charge controller and the load, then yes, inductive and capacitive reactances have an effect. The MPPT controller is a DC to DC regulator that feeds either a battery charger, DC to AC inverter, or both. It can operate at any frequency with only the slow response and hold times changing. With both the input and output of the MPPT charge controller as DC, there's no dV/dI which would require AC output.
The voltage at the MPP is more like 75-80% of the open circuit voltage. See the tables at:
The MPP in watts for maximum power transfer is closer 50% of the product of the maximum open circuit voltage times the maximum short circuit current. Let's see how it works with the sample specs for the SW295 panel from above URL at: Maximum Power Pmax 295 W Open circuit voltage Voc 40.0 V Max power point voltage Vmpp 31.5 V Short circuit current Isc 10.10 A Max power point current Impp 9.45 A
Ok, it's not 50% and not 90+% but more like 75%. That's higher than what I expected. It also doesn't explain why I'm finding numerous web pages like the one's I cited claiming something like "MPPT is when the solar cell source impedance is matched to the load impedance". Time for me to search for data that supports my assertions.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
I was under the impression (apparently false) that a cells internal resistance was lowest at the MPP and increases on either side, which reduces the efficiency of the cell at either extreme (open and short circuit). Therefore the self heating would be at maximum at the MPP and less with an open or short circuit. I guess that's not true, although right now, I can't see why.
That would be interesting. Thermochromic solar panels, where I could actually see the hot spots and failed cells without having to borrow an expensive FLIR camera.
IR reflective coatings are getting better. Here's one that changes the color of the incoming IR to boost the panels output:
About 70% reflectivity at middle and far IR for TiN coatings. See Fig 4: You're right about trapping the heat inside, but as the coatings become better at reflecting far IR, the problem will probably become insignificant (I hope).
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
I'm not talking about reactive components or properties. The impedance of the solar cell simply is not well modeled as a fixed resistance. The MPPT provides the maximum power output, but the analogy to a fixed impedance is faulty.
I remember a friend thinking the impedance of the source had to match the i mpedance of the load in order to maximize power output. That is not correc t. No matter what the impedance of the load is, I can get more power into the load by lowering the impedance of the source when working with a voltag e source.
Like my friend you are mixing apples and oranges.
You really aren't getting the impedance thing. You can't take the V/I as t he impedance. It has to be the tangent to the curve, in other words dV/dI. The load doesn't give a rat's ass about where you are on the curve. What matters is where you will be for a small change in voltage or current.
Maybe I don't really get it. I've always said, if you can't explain someth ing clearly, you don't understand it.
The thing about matching impedance only applies when you are varying the lo ad impedance. That much I know for sure. It's simple math. Check it out. Pick a load impedance. Then calculate load power with a matched source i mpedance and a zero source impedance.
You are thinking of MPPT curve as being controlled by some active circuit. The curve is drawn by varying the load resistance with everything else con stant. So in that case the MPP *is* the point of matched impedance. The a ctive circuit is needed because the load is the load (usually not resistive ) and the other factors vary.
at lower current you get less power out because P=VI and reducing I reduces P
at higher current increasing the voltage available available because you can't exceed the cell's quantum efficiency, the cell just runs out of available electrons.
I dont know if they would be visible to a silicon photoelectric image sensor or not it seems the photons would be near the quantum threshold.
The same thing will happen if the panel or cell is open-circuited, yes? Then are you saying that the cell will cool down at the maximum power out point?
Yes, that is not only right, but absolutely correct!
That is cooler relative to a cell in the shorted state, not relative to the environment. But then if the environment is being blasted with the same sunlight, I guess it would get cooler than the environment as well.
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