Sharp 170, SolarWorld 175 or Evergreen 190 -can't decide

Re: Sharp 170, SolarWorld 175 or Evergreen 190 -can't decide

Solar Guppy or one of the other designers here can probably give you more accurate information--but the basics:

If you are looking at voltage drop as the temperature increases--make sure you divide the drop by the panel voltage--so that all drops are "normallized". The voltage drop is bascially on a per silicon wafer basis. So a 26 volt panel will have more drop per degree C vs a 12 volt panel--when the specifications per cell are actually the same. (the % voltage drop per C is the same).

Looking at panel Vmp voltage is OK--but also look at string voltage. You may put 4 lower voltage panels or 5 higher voltage panels in series and have the same string voltage and current.

Mono vs Poly-silicon--pretty much shop on price ($/watt) and surface area... You will get a tiny bit more power from Mono crystalline silicon per square foot vs Poly. But if you have the room to mount--it may not be worth the price difference (be sure to include the costs of the wiring and frame work too). If you have astetic issues--the Mono Crystalline panels don't have that "fractured purpley glass" look--if that is important to you (or your wife).

For me, a good place for a quick lookup of any solar panel specs. is the Xantrex GT design web site... They have hundreds of solar panels and list the basic specifications when you choose one to model.

Sharp NE-170U1
Max Power Voltage - Vmp 34.8 Vdc
Open Circuit Voltage - Voc 43.2 Vdc
Voltage Temp Coeff - Vtoc -0.144 V/°C
STC Rating - Pmp 170 Wstcdc
Max Power Current - Imp 4.9 Adc
PTC Rating 149.9 Wptc

Solar World SW175
Max Power Voltage - Vmp 35.4 Vdc
Open Circuit Voltage - Voc 44.6 Vdc
Voltage Temp Coeff - Vtoc -0.145 V/°C
STC Rating - Pmp 175 Wstcdc
Max Power Current - Imp 4.95 Adc
PTC Rating 162.7 Wptc

Evergreen ES-190-RL
Max Power Voltage - Vmp 26.7 Vdc
Open Circuit Voltage - Voc 32.8 Vdc
Voltage Temp Coeff - Vtoc -0.1148 V/°C
STC Rating - Pmp 190 Wstcdc
Max Power Current - Imp 7.12 Adc
PTC Rating 167.2 Wptc

Hmmm... I wonder if there is an error in the Xantrex Data base or not... Look at the PTC rating for all of the panels (probably what you should be basing your $$/Watt calculations on--PTC is the rating from the California Energy Commission and should be the most accurate when comparing across brands/models). The Wptc are not tracking the Manufacturer's STC ratings that closely...

Evergreen "190" which is supposed to have the tightest power spec. ratings is hardly 6.5 watts more power than the Solarworld "175" should be closer to a 15 watt delta. And the the Sharp "170" is almost 13 watts less than the Solarworld "175" -- which should have only been a 5 watt difference.

Note that the V/°C for the Evergreen is less than the other two panels--but that is because it is also a lower voltage panel:

Evergreen:
-0.1148 V/°C / 26.7v = -0.43%/°C

Solar World:
-0.145 V/°C / 35.4v = -0.41 %/°C

Evergreen's V/°C drop is slightly more than the Solar World when normalized. (5% difference between brands is probably not a significant difference in voltage drop for most installations).

-Bill

Re: Sharp 170, SolarWorld 175 or Evergreen 190 -can't decide

Here is a nice link that shows how to compare solar panels against each other (do a little spec. hunting and spreadsheet analysis)... This site is biased towards the Sanyo HIT hybrid panels--which I would suggest careful scrutiny about before buying...

I am not sure I would toss the PTC spec. away as being completely useless... It is based on several actual panel parameters--and can be "adjusted" by the manufacturer if they believe the numbers are in their favor:

So the industry came up with a better testing protocol -- called "Photovoltaics for Utility Scale Applications" (PV-USA) or PVUSA Test Conditions (PTC). PTC were developed at the PV USA test site in Davis, California and represent a more real life condition of 20 degrees C. ambient temperature (68 F.), 10 meters above ground level, and wind speed of 1 meter per second. As PV cells average about 20 degrees C. above ambient temperature in the real world (104 F.) and cell voltage drops as temperature increases, a PV module's power output in real life conditions will always be lower than the power measured at the factory where cell temperature is maintained at a controlled 77 degrees F. (25 C). But since there are differences in technology and manufacturing processes, the ratio of PTC to STC can vary dramatically. So the first lesson in evaluating PV modules is to ignore the nameplate rating and go right for the PTC ratings. But some manufacturers don't publish these data on their spec sheet. (!) Don't worry, you can look up any module sold in California here (The CA Energy Commission's web site), and here are some of the best selling ones.

Given that, at least in California, PTC=$$$ (cash rebates), manufacturers of current products have every reason to "tweak" their specs. to the California Solar Program's rebate program's requirements.

As I understand Solar Guppy, and looking at a few sites yesterday and today--for example Xantrex uses a different Vmppt range when listing the CEC ratings vs the their "real ratings" to get a 1% better number. Another Mfg. was pointed out yesterday (SMA?) appeared to be doing the same thing too.

GT4.0N:
MPPT voltage range (CEC & CSA): 240 - 480 Vdc
MPPT operating range: 235 Vdc - 550 Vdc

Not that this is really wrong (and who is going to really be able to accurately measure 0.5-1.0% differences with a home installed inverter).

Perhaps, as SG says, PTC numbers are not worth using when comparing panels--but the generically available PTC numbers are usually much closer to predicting actual array output vs the STC numbers in my sample size of 1.



-Bill