Different sizes of panels

Badar

I have three different types of branded/unbranded panels.

One brand is "CanadianSolar"
Other is "Suntech Solar"
Unbranded panels are from China unbranded, Off course.

For example
I have 110 watt panel of Suntech (36.5V-Multi Crystalline)
I have 170 watt panel of Canadian Solar (36.5V- Mono Crystalline)
I have 150 Watt of Unbranded, low grade looking cheap panel (19.5V-Multi Crystalline)

Surprisingly,
CanadianSolar panel(170W Mono) and Suntech(110W Poly) have exactly same sizes.
On Other hand china unbranded cheap panels(150W Poly) have much smaller size than above two good quality panels. Even a china unbranded sheet of 90W poly has visibly smaller size than that of 100w suntech.

I want to know
1: reason behind this difference in sizes is (36v vs 19v) configuration?
2: or, it might be the difference in configuration?

Further I want to know
3: Is it possible to check" if "canadiansolar" panels I own (or going to purchase in future) are original one? A national level company here claims that they are authorised dealer of "CanadianSolar" in Pakistan. I Emailed CanadianSolar for confirmation of their dealership/check of warranty of panels I own, but have not received any reply from them since last two months. Although I was not expecting such negligence from them, as I emailed Schneider with a question. they replied me in much detailed and positive manners. I was expecting same thing from CanadianSolar, but disappointed.

BB.

Re: Different sizes of panels

You need the full specifications for the panels to understand them electrically...

Vmp = Voltage maximum power (the "ideal voltage" to maximize the Pmp=Vmp*Imp) (used to plan power production)
Voc = Voltage open circuit (nothing connected but volt meter) (used to size array vs maximum rated input voltage for controller)
Imp = Current maximum power (again Pmp=Vmp*Imp) (used to plan power production)
Isc = Current short circuit (used to size wiring and fuses/breakers for protection--Typically around 1.25x Imp)

The Voc of a panel is pretty easy to measure with a volt meter... Just place panel in any sort of direct sun (morning/evening/middle of day) and read the meter. Voc is temperature dependent--So it will read higher when the cells are cold and lower when the panel is hot (after setting in full noon time sun for a few minutes). Just the physics of the solar cell (silicon has one curve, other types have other curves).

Isc of a panel is pretty much relative to the amount of sunlight reaching the face of the panel. In fact, you can use a solar panel plus current meter (near dead short) to measure the amount of sunlight (accurate to within ~5% error). The "standard" for full sun at sea level is ~1,000 Watts per Square Meter. Of course, dust/humidity/clouds reduce the amount of sunlight. And high altitude and clear weather increases solar irradiation. Current rises very slightly rises with cold temperatures (around 1/5 or 1/10 of Voltage vs Temperature) and is usually ignored.

Remember that power is:

• Power = Voltage * Current (and = V²R = I²R )

If you have a graph of Current vs Voltage for a solar panel and also plot Voltage*Current you will see a "peak" where the maximum power is located. That is defined by Vmp*Imp.

http://lib.store.yahoo.net/lib/wind-sun/SPM085P-specifications.pdf (~90 watt panel)

Each of the curves is at different amounts of solar irradiation:

Attachment not found.
Note that the current curves are relatively flat from zero to near Imp... At that point the current starts falling as the voltage nears Voc. (it is getting more difficult to find these curves--vendors are leaving out these charts now).

So--We need to know the "four ratings" (Vmp, Imp, Voc, Isc--And really at least Vmp/Imp) to understand how to use a panel in a system.

Regarding comparing panels. The output current is proportional to the area of the panel and its efficiency. You can take two different panels and point them at the sun and measure the Isc output of the two panels can be directly compared (identical available solar energy to both panels at same time). Use a meter set to 10 amps (typical maximum current for most hand held digital multi-meters) and connect to panel. It may be better to place a piece of cardboard or dark blanket over panel before connecting meter--MC4 connectors do not like "arcs" as it can ruin their small connection surface.

And you can compare panels in any sunlight by using the Isc of a known good panel (i.e., Isc=5 amps) and measuring Isc at that time of day/weather condition... If you measure Isc-actual=2.5 amps, then that moment of sun is around:

• Solar Irradiation = 1,000 W/Square Meter * 2.5 amps measured / 5.0 amp Isc = 500 W/M² or ~1/2 of standard sun

Next you measure the Voc (open circuit voltage) of the panel. You can also count the number of cells on a panel and guess that each cell is ~0.5 volts Vmp... A 36 cell panel would be ~18 volts Vmp and ~22 volts Voc.

Voc of a good panel is pretty much based on the cell temperature (basically in weak morning direct sun or stronger).

It is a dance to pick panels that are available to you locally and the same questions about which charge controller--And MPPT (maximum power point tracking--full buck mode switching power supply/power converter) vs PWM (pulse width modulated--basically just an "on/off" switch).

MPPT controllers can take a wide range of input voltages (a typical "expensive" MPPT controller in the US will take ~Vmp-array of 17.5 to 100 VDC).

An PWM controller needs to be "matched" between array and battery bank for optimum operation (typically 12 volt battery needs Vmp~17.5-18.6 volts).

So--here are are stuck at price of solar panels (18 volt Vmp vs panels with Vmp of 30 volt or more) and prices of charge controllers (MPPT controllers cost 2-5x more than similar quality PWM controllers). And secondary questions of how far the solar array is from the battery bank+charge controller (longer wire runs should have higher operating voltage--or the copper costs will kill you due to high voltage drops from high current)...

Sorry, I have to stop here (very complicated set of questions/answers with lots of "grey" answers--not black or white)--Have things to do right now. Ask your questions and I will be back.

-Bill

Badar

Re: Different sizes of panels

Since there is a great chance of world war-1 between me and my wife for being too much late. It is therefore, a good idea to read this useful post tomorrow, so that peace of bedroom could be ensured.

see ya tomorrow.