Short Circuit PV Panel

What you need is micro thermal dynamic technology from...

http://scirustechnologies.com/winter_solutions_5.html

Quote:

>>>>The micro thermal dynamic filament array is virtually invisible to the human eye. Thanks to the high light transmitability and low power requirements to operate, an increase in power production of 15%- 40% on average can be expected.<<<<

Can be expected:??? 15% to 40% of ???

I am hanging around in the sub tropics, where one snowball is a once in 50 years surprise, only for a few minutes. So is ice. The weather is about the same as where you are.

Solar production as reference, in July was close to 30 kWh/day, the last week it has been cloudy and there is 4 to 6kWh/day left. Some ice and/or snow on top of the panels will take the production about down to a figure that you will need backup power to get these defrosted, what their solution will need.

I rather would have read some economics about their "patented application", because I doubt if there will be any "win" situation for the user in it. You can compare it with the invisible wires in the glass of a car rear window. Takes quite some energy.

This would be a little bit north of your location, and mine, in Canada.....The 15% increase is compared to manual cleaning of collectors, and the 40% increase is no clearing of ice and snow....the details of the testing are at this link ↓↓

http://scirustechnologies.com/performance_3.html

...or a black roof... ?
Del

Hey! ,,,is that a black roof up there?... I don't know,, but those look like pvc sidings....

Solar panels are at best around 20% efficient. The other 80% is either reflected or more likely absorbed and then emitted at longer wavelengths, i.e. heat. As dvmdsc commented, you need to get light to the panel first. Certainly, if you get sunlight to the panel it will warm it up. At temperatures just below freezing it will do the same thing as sunlight on asphalt; it will melt it. Keep in mind, though, that at really low temperatures, it's not going to melt much ice.

yes it would heat up......as in burn up

No it won't.

If you short circuit the panel, its terminal voltage will immediately drop to zero, and Ohms law tells us that watts equals volts x amps, so if one of those is zero, then no power will be produced or dissipated.

No power equals no heat.

It can be different if you have other panels in the array, as they may well dissipate their power in the short circuited panel.

This is why bypass diodes are used extensively in solar arrays.

The panels have internal resistance. If you S/C the panel, the voltage generates current according to the resistance of the panel, therefore heat.

Try shorting the output of a linear variable voltage supply. You get zero volts at the output, but the current rises to the maximum the PSU allows. Again Volts x Amps internally = Watts. Touch the heatsinks and you will find proof, I've done it.

Phaddy,

You are right with your power theory. Shorted panels in sunlight produce current. That is how I test them out of the box. They come with a female and male connector and I just shorten connect them and they produce between 2 and 4 amps for a 125 Watts panel. The question here is: how much light do the panels receive when covered with ice or snow.

At night that same 125 Watts doesn't produce more than 5 milliamperes when it is full moon. D.

A PV cell is a totally different animal to a linear power supply.

I suggest you do some research on solar panel I/V curves. You will see that under both open circuit and short circuit conditions, a solar panel produces no power.

No power equates to no heat generated.

This link is just one of thousands that you can check if you need further information. Below is an excerpt from that site for the lazy ones among us.

"The power available from a photovoltaic device at any point along the curve is just the product of Current (I) in Amps (A) and Voltage (V) in Volts (V) at that point and is expressed in Watts. At the short circuit current point, the power output is zero, since the voltage is zero. At the open circuit voltage point, the power output is also zero, but this time it is because the current is zero".

A P/V curve is different from a I/V curve when it comes to solar cells. You start referring to the I/V curve and this shows that the panels produces power. The P/V curve does not.

A short circuited Solar array produces current in light. Of course where you connect the two wires from the solar panel, you will have no voltage. And that goes for the whole length of the wire. While measuring 0 volts, a current is generated in the panel by recombination of the junctions, the internal resistance of this current source is the sum of all the series cells, (and the Schottky's in the box)

Obviously you choose to ignore the link provided that supports my statement, so there's no point me wasting any more time on this.

A short circuited solar panel will produce ABSOLUTELY NO power, that is a plain and simple fact.

Try googling it.

I suggest that you read up on the topic if you really want to be educated.

In the meantime, keep the off topics coming, it's always a good way to cover up your lack of knowledge.

Dear bwilko:

Thank you for your answer. It will give the forum more depth for this OP.

As far as I understand, the OP asks if the solar panel will produce enough heat when shorted and covered with snow and/or ice. IMHO this is not a regular use for solar panels.

I have read the link more than once before I answered, and I am happy that you give me the opportunity to thank you for providing it.

My conclusion is that we should read everything else in the link too and just not take something out of the context to prove what is not the issue. The following quote is also an excerpt from your same link:

quote>>>

A Solar (PV) Cell or a Panel / Module produces its maximum current when there is no resistance in the circuit, i.e. when there is a short circuit between its Positive and Negative terminals. This maximum current is known as the Short Circuit Current and is abbreviated as Isc. When the Cell / Panel (Module) is shorted, the voltage in the circuit is zero.

>>>>>>

The voltage in the circuit is zero indeed, because the + and - terminals are connected together (what shortens the circuit). In the panel however, the current is dissipated in its own internal resistance which is not zero but relatively low. From there the high(est) current on this (close to) 0 volts point.

The statement in your link is correct for power, emitted to the circuit, i.e. the load, and this is the problem point of discussion (or slight disagreement): Once you put a ampere meter in the circuit your short creates a slightly higher resistance and perhaps they have the equipment to measure the voltage over your shunt.

I find that the example of Phaddy is not bad. I would have compared a solar panel with a battery (that only stops providing current when it becomes dark - strictly hypothetical).

When you short the battery, the voltage will also drop to about zero, and probably heat up or melt the wire where you make the shortcut with. (because of the low internal resistance of the battery)

The solar panel is limited in current because of all the physical properties and the behavior of the junctions in the cells. The panel itself warms up a little internally, but not comparable to a full sunlight heat (15%) and not enough to heat up the wires (typical min. 4 mm2), because the power is easier dissipated in the panel surface.

In one of my earlier posts here I stated that I test the panels out of the box with making a short between + and - while measuring the current with a clamp -on hall DC current clamp. (Measuring the voltage with a DVM is not error free)

I really do not have to be convinced. Just read this and make your conclusions. This is a science zone where black, or white just can be grey, depending just on staying on the surface or digging deep into the situation. If English were my native tongue, I probably could have given a more distinguished reply. I try to be clear:

My standpoint and goal is to give the OP a good answer and discuss the wrong answers for his specific situation. He is asking if the panel will generate heat when short and covered with ice and/or snow and I answer no, because the panel is darkened and not able to produce a significant amount of power under those conditions. (the I/V and P/V curve is not appropriate for his question)

Generally spoken, to generate power into an external load you are right. But this situation needs a different interpretation and examination.

Always willing to learn I appreciate your comments. Regards. D

Some common sense issues.

Note the ice itself blocks lot of light energy reaching the solar cells. Efficiency of PV panel is just about 15 % at the most at today's technology level. It will further go down- if ice contains other dust particles etc. Many others have given other view points of why ice will not melt. A PV panel covered with ice- will it generate electricity at all is doubtful.

This is all doublethink with a dose of catch 22.

A) If a roof is covered with thick snow or ice, a solar panel or a black roof won't work.

B) If it's night time a solar panel or black roof won't work.

C) If it's a nice sunny day the black roof will get hot and melt any snow landing on it. A solar panel will generate power which could conceivably be used to warm the roof.
Thus a black roof is as good as the solar panel... it doesn't matter how many amusing pictures get posted...
Neither is much good... but a black roof is a damn site cheaper.
Del

You should know by now that your thoughts are incorrect.

As already posted, they are at best around 15% effective IN SUNLIGHT! Covered in ice of snow, at night = no power.

Modern good panels also have a water jacket (with antifreeze) to both cool the solar cell, which reduces aging and slightly improves efficiency of the cells. This water jacket, if fitted, can also be used to assist both central heating and hot water.

Some companies sell units to cool already installed panels at a far lower cost, just click them on under the solar cells....

Such units, if fitted, could be easily connected to the hot water system on winter mornings for a few minutes (at what energy cost I have no idea!), to easily and quickly get rid of ice and snow, but is it really worth it? Only if you have very cheap hot water I would guess...

Such units, are probably not in use for hot water making in winter time I would think, but I do not know for sure, as in winter, the solar cells may be cooled enough, as the water cooling was designed more for summer weather I believe.

Maybe someone here has such water cooled units on his house and give some tips/thoughts....

Solar DHW panels will self-clean if even a corner of a flat panel or the top of the tubes can receive light. In a few hours the panel is clear of snow. Perhaps a smallish DHW collector could be the source of heat for heat tracing the PV panels- keeping the tracer line outside the weather envelope of the PV panel (of course).

Even after a real 'snow-dump', the owner would only have to clean the DHW panel/array to get defrost started.

I have a friend who has collectors for heating air for his home. The contractor installed the collectors vertically and I wondered why at first. The reason is that the collectors collect no snow and work great in the winter. Not the ideal angle but they work well. In the summer the vertical orientation means that they produce no heat. If a electrical solar cell was oriented more steeply and the bottom was above the normal snow level, then the snow would more easily slide off and would not block the collector. I know that down the block, there are solar collectors mounted at a steep angle that stick out over the edge of the house. They have a flat roof like mine. I didn't notice this until this discussion. I don't know whether it is the same in the summer or not, but I'm going over to talk to the owner this afternoon and find out. If the collector was at the right angle, it would easily shed snow and still be withing the power producing orientation to the sun. Changing the angle twice a year wouldn't be too bad since I have to go up and clean the gutters anyway. I am starting to look at solar possibilities because those who did it earlier had a very short payback (5-6 years) at the higher costs of solar back then and the increased costs of electricity since. With the lower costs of solar now a conservative calculation shows the interest on an investment at over 20% currently. Where else can you find a secure investment that will likely increase percentage right now that will pay at that rate? I have plenty in the market now and don't really want to put more in. I am doing better than that on the market, but don't want all my funds at risk. Banks are out of the question.

this is what you want.a panel with a solar tracker, always has the optimal angle if the sun is out

We were talking about snow buildup, not optimum angle to the sun. A steep angle is better for the snow, but since my location is quite southern, it is not optimum for sun. You are correct that a few more panels are usually cheaper than trackers, but that is a different case altogether. I have talked to the neighbor and he does change his in the fall and spring. It takes him more time setting up the ladder than changing the panels. His panels are steep enough to clear snow and he only losses about 10% from ideal. He had data to prove it. He supplies all his needs with a grid tie inverter. He does have gas heat, but that is cheap here.

Just know what to do. I had a client who loaded his tracker with too many panels so that he could not handle it anymore. Need to calculate snow load, but also wind load.

Try 23.4°, which is the axial tilt of the earth to the Sun....which gives us summer and winter as we revolve around it!!

There are some good articles on the internet. For example:-

http://en.wikipedia.org/wiki/Axial_tilt

I hope this helps.

Gee you two guys are good.

You purport to know all about this subject yet fail to possess even the basic knowledge that most primary school students have.

Whilst the earth's axial tilt to the vertical is indeed 23.4°, the apparent movement of the sun's path North to South across the sky from winter solstice to summer solstice covers 46.8°.

Maybe this is another subject that requires a bit more study on your part.

Glad you're not installing solar panels for my company.

What I wrote was 100% accurate:-

Try 23.4°, which is the axial tilt of the earth to the Sun....which gives us summer and winter as we revolve around it!!

What you appear to have understood was not accurate as you appear to have misread what I wrote. (Here you join a large number of others here, slow to understand and quick to post!!), and you were rude and unfriendly as well. Not a good start....

The Wiki link I posted is accurate in the same manner as I wrote, or perhaps you need to "correct" the Wiki link!!

It must be obvious to most here that this means a doubling of the effective value as a perceived Sun movement over the year. Not really Einstein was it!!

Was ANYONE here made wiser from your comment? I seriously doubt it. Come on Guys, own up, who is now better informed? Anyone? One?

I do believe the poster I originally replied to was talking about 12° of inclination, which has absolutely no truth to it at all!!!

Maybe you intended to post to him?

Have a great day, post slower and read better!!!

The tilt really depends on the latitude. There is a lot of false info on the internet. A study was made here at Los Alamos by LANL which actually tested the angle of different panels. It turned out that pointing directly towards the sun was not the best for all panels. They came up with a calculation that was latitude plus a value that was close to the average of the different cell constuctions. Some of the contributors to the study even disagreed with it's conclusion. To state a simple value without taking into account the latitude location is naive.

If you are questioning the 23.4°, then you are on the wrong steamer, that value is fixed, as stated in the Wiki article I posted.

Did I misunderstand your position? (pun intended!)

The earth revolving around the sun changes the relative angle of course and there are tables to allow easy working out of the correct angle to set to.....but that 23.4° is as far as I am aware fixed......just saying its not is simply wrong!

Though I have read that the earth has a slight wobble, but whether it changes the angle by even a minute or two I would never believe! e.g. For us, its fixed in stone!!!

Where you are on the earth affects only the basic angle used in setting fixed Solar units. Trackers may also need to be "helped" possibly.

In the tropics it is much higher angle than at the poles. That is what they were talking about.....probably a simple calculation to use the local latitude to get the right angle of positioning.

Good try at covering your ass Andy.

Dvmdsc said :- " Roughly the sun shifts about 12 degrees between winter/summer".

No way any person with an understanding of the seasons could have misunderstood that to mean angle of inclination as you suggest.

You then corrected him be saying :- "Try 23.4°, which is the axial tilt of the earth to the Sun....which gives us summer and winter as we revolve around it!"

Which was a clear indication that you were stating that the true shift between summer and winter is 23.4°.

Clearly incorrect, but don't let that faze you.

You speak of others rudeness, but you display an inordinate arrogance even for a German.

I have put this first answer off topic, because the interpretation of the 12 degrees is not correct. I should have written 2 X 12 degrees. My panels are about horizontal with just the little inclination, needed to have no puddles on the glass (alu board of the frames, where the glass fits in)

Horizontal because I need the noon period sun the most.

In my specific case, I have 12 degrees less at sunrise and also 12 degrees at sunset.

I refer to calculators on the internet because each place on earth needs a different optimal set up. The theory I let you guys discuss in peace. Regards. D.

OP here! Very interesting exchange of ideas and info, thanks to all. My system is up here in MN and sometimes gets a thin coat of ice and partial snow coverage. The ambient temp can stay well below freezing for months and I sometimes take a hot water hose to the panels to clean them. I wondered if it would be safe to short the panels, and if that would increase temp of the panels to speed melting of the ice. One respondent shorts panels to test them, so that seems safe. I wonder how much power/heat a 250w panel would dissipate assuming of course light can penetrate the ice. Would it be 250w? Or maybe depend on the internal resistance or other factors particular to the panel? I'll see if the seller knows and post any answer here. Of course most panels are made in China and tech expertise may be hard to find.

Hi SSCpal,

I test the panels indeed with shorting them, but that is for a very short period, just to check if they deliver enough power when they come straight out of the box. They have traveled a long way and sometimes screws in the contact box come loose. With a DVM, even when one cell has bad connections and has passed the QI test it would turn out good while it is actually bad.

I also do not put the panels in full sunlight when unpacking. The panels we use produce an Isc of 8-9 Amperes (shorted)

I don't think shorting the panels for a long period is good. They are laminated in a vacuum thermo- oven and the consistency of the films and sandwich could be endangered.

Solar panels are still too expensive for these experiments.

To answer your question: when exposed to sun and short, they will heat warm up. How much, is your task to come back with a figure. I have no ice here.

Also shorten solar panels can be easily done when a low voltage inverter is applied. When using strings of 200 - 600 Volts DC, disconnecting the panels can be deadly when touched. I also see not a lot of panel users in this forum with in depth experience participate in the discussions. Regards. D.

Have you understood nothing from the previous posts?

Found this....

"Montréal firm TN Conseil has developed a passive technology that melts snow and ice from

the face of a PV panel. This technology

consists of a black absorber foil bonded to the

rear of the panel, a one cm air cavity which

insulates against heat loss, and a clear Lexan

back cover sheet. The absorber foil collects

the solar radiation that is incident on the rear

face of the panel, and in combination with the

back cover, elevates the temperature of the

panel, promoting snow and ice removal. In

this way, the technology is somewhat like a

solar thermal stagnating air collector, utilizing

the radiation which is reflected off the

snowcover on the ground behind the panel. "

http://www.rerinfo.ca/documents/trPVSnowandRime.pdf

Why did you think of using solar PV panel? If your objective is to melt snow- Solar thermal heat pipes could be considered with a oil circulation (was being made in Germany long ago) in the heat pipes. PV panel is certainly not a practical proposition.

See #25

Most of the heating will be a simple conversion, light > heat and only a small portion by joule effect light > electricity > heat, so shorting will NOT have any noticeable effect on ice layer. Now if you expect a dramatic power increase as a reult of de-icing by other method, don't be too optimistic. Ice, i.e. low env temp means both lower incoming solar power per surface AND better panel efficiency, all other things being equal, so a panel clean from ice will not give much more power. Now if your needs are marginally higher than available, maybe... S.M.