Back to Homepage Contact Sunlight Electric
 
Infinite Menus, Copyright 2006, OpenCube Inc. All Rights Reserved.
Photovoltaics Modules 101 from Sunlight Electric
Photovoltaics Modules 101 from Sunlight Electric
Crystalline Silicon PV Module
Crystalline Silicon PV Module

The heart of every PV system is the array of photovoltaic modules. Today, the overwhelming majority of PV modules (more than 95%) are crystalline silicon, made from the second most abundant element on earth.

But despite the fact that most PV modules utilize similar technology, there can be considerable variations in performance. As such, we consider understanding four key differences critical to making a smart decision between different proposals. So here we go...

1. Nameplate Ratings versus Real-World Performance (or STC v. PTC...WTF?)

It would seem obvious that a "224" module is better than a "215", right? Not so fast grasshopper. What if the so-called 224 only really put out 192.6 watts while the "215" put out 195.5 watts, or even 199.6 watts? Confused yet?

Manufacturer

Module

Nameplate
Rating

(Watts)

CEC/PTC
(Watts)

Sunpower Corp

SPR-315E

315

290.0

Sunpower Corp

SPR-305-WHT

305

280.6

Suntech

STP270-24/Vb-1

270

236.9

Yingli Solar

YL230P-29b

230

203.7

Sharp Electronics

ND-U230C1

230

198.0

Sunpower Corp

SPR-225-BLK

225

202.9

Sharp Electronics

ND-224U

224

192.6

Sanyo Electric Co

HIP-215N

215

199.6

Sunpower Corp

SPR-215-BLK

215

195.5

Kyocera Solar, Inc.

KD-215GX

215

189.1

Sanyo Electric Co

HIP-210N

210

194.9

Sunpower Corp

SPR-210-BLK

210

188.9

Kyocera Solar, Inc.

KD-210GX

210

184.6

Suntech

STP210-18/UB-1

210

180.3

Evergreen

ES-A 205

205

185.4

GE Energy

GEPVp-200-M

200

173.1

BP Solar

SX3195B

195

170.5

The explanation lies in the manufacturers' use of the "Nameplate rating" in the model number and how they derive those figures. For example, Sharp's ND-224U module has a nameplate rating of 224 watts, and this comes from the testing protocol used by Sharp and every other PV manufacturer. In the factory, PV manufacturers use Standard Test Conditions (STC) which keep the PV test temperature at a nice constant 78 degrees F. In the real world, even a chilly day can see hotter PV cell temperatures since dark surfaces absorb light and heat. On a hot summer day, PV modules can heat up to over 150 degrees F. And there's the rub.

So the industry came up with a better testing protocol -- called "Photovoltaics for Utility Scale Applications" (PV-USA) or PVUSA Test Conditions (PTC), and were widely adopted by the California Energy Commission, so are sometimes referred to as CEC ratings. 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 can heat up to 20 degrees C. above ambient 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/CEC 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 Solar California web site).

2. Watts Are Important, but So Are Inches and Feet

Now that you know about the difference between STC and PTC watts, you can simply just make sure you buy the highest PTC rating available, right? Alas, it's not that simple. What probably matters more than the wattage of a PV module is the watts generated per square foot. The wide range of PV technologies available today range from 5 watts per square foot to over 16 watts per square foot ("WPSF"), and over 300% improvement versus the bottom end of the range!

Manufacturer

Module

Nameplate
Rating

(Watts)

PTC/CEC
(Watts)

PTC/CEC
(Watts/Sq. Ft.)

Sunpower Corp

SPR-315E

315

290.0

16.5

Sunpower Corp

SPR-305-WHT

305

280.6

16.0

Sunpower Corp

SPR-225-BLK

225

202.9

15.1

Sanyo Electric Co

HIP-215N

215

199.6

14.7

Sanyo Electric Co

HIP-210N

210

194.9

14.4

Sunpower Corp

SPR-210-BLK

210

188.9

14.1

Kyocera Solar, Inc.

KD-215GX

215

189.1

11.7

Yingli Solar

YL230P-29b

230

203.7

11.6

Kyocera Solar, Inc.

KD-210GX

210

184.6

11.5

Suntech

STP210

210

180.3

11.4

Sharp Electronics

ND-U230C1

230

198.0

11.3

BP Solar

SX3195B

195

170.5

11.3

Evergreen

ES-A 205

205

185.4

11.2

Sharp Electronics

ND-224U

224

192.6

11.0

GE Energy

GEPVp-200-M

200

173.1

11.0

As the above chart shows, many common modules are in the 11 WPSF range but even the difference between 11.0 and 11.9 is nearly 10%, so it makes sense to only get as space-efficient product as you need. If products in the 11 WPSF range won't generate enough power in the space you have available, then paying a modest premium for higher efficiency products like Sunpower could be a smart investment.

While there is a lot of discussion lately about "thin film" solar products (~5% of the market) such as amorphous (non-crystalline) Silicon, CdTe (Cadmium Telluride) and CIGS (Copper, Indium, Gallium and a form of Selenium), these materials usually yield from 5-9 WPSF, typically ruling them out for most applications due to lack of space.

3. Some Like it Hot, Others... Well, Not So Much

Manufacturer

Module

Temperature
Coefficient of
Power

(%/°C)

Sanyo Electric Co

HIP-205BA3

-0.29

Sunpower Corp

SPR-220

-0.38

Sanyo Electric Co

HIP-200BA3

-0.29

Sanyo Electric Co

HIP-195BA3

-0.30

Sunpower Corp

SPR-210

-0.38

Sunpower Corp

SPR-200

-0.38

Kyocera Solar Inc

KC-200GT

n/a

Conergy

230P

-0.45

BP Solar

SX3195B

-0.50

GE Energy

GEPVp-200-M

-0.50

Kyocera Solar Inc

KC175G

n/a

Conergy

C175M

-0.50

Mitsubishi Electric Corp

PV-MF170EB3

-0.48

Sharp Electronics

ND-208U1

n/a

Sharp Electronics

ND-200U1

n/a

The next thing that anyone considering an investment in solar power needs to know is the degree to which hot temperatures will degrade the performance of their system. Photovoltaic modules perform best at cooler temperatures, and some lose less production as temperature rises than others, due to the materials and technologies used. In the field, due to their light-absorbing properties, solar cells will average about 20 degrees Celcius above ambient temperature, or (all in Fahrenheit) 106 degrees on a 70 degree day, or 136 degrees on a 100 degree day.

Temperature Coefficient of Power ("TCoP") is expressed at the percentage loss with each one degree increase in temperature Celsius. The closer to zero (the less negative the number is), the better the hot weather performance. If a PV module has a TCoP of -0.50%, then that module will lose 10% of it's output with a 20 degree Celcius increase in cell temperature -- a truly amazing stat. (Aren't you glad you know this now?) You may note that some manufacturers don't publish this data ("n/a"). We think that it's not good business to withhold important information from a customer and our policy is that we won't sell any products for which we cannot verify these key performance metrics.

4. In This Case, Being Intolerant is a Good Thing

As the manufacturing process for making PV modules includes a lot of variables, each and every PV module is tested at the end of the manufacturing line to determine its performance and nearly every manufacturer take some latitude in allowing modules that fall slightly short of their intended rating. For example, if Company X was looking to make 200-watt modules (STC), and one tests at 191 watts, then they might label it as a "200" and note a "tolerance" of +/- 5%. Because these products are priced on a per-watt basis, then Company X selling this module as a "200-watt" yields 4.7% more revenue for the manufacturer while giving the customer 4.5% less output. Pretty shocking, isn't it?

Manufacturer

Module

Manufacturing
(AKA Power)
Tolerance

Kyocera Solar, Inc

KD-215GX

-0W/+5W

Evergreen

ES-A-200

-0W/+5W

Sanyo Electric Co

HIT-215N

-0%/+10%

Schott Solar

POLY220

-0%

BP Solar

BP 3215B

-3%/+5%

Suntech

STP-210

+/- 3%

Solarworld

SW230

+/- 3%

Yingli Solar

YL 235 P

+/- 3%

Mitsubishi Electric Corp

PV-TD190

+/- 3%

Trina Solar

TSMDA05-220

+/- 3%

Hyundai Solar

HiS-M215SG

+/- 3%

Sharp Electronics

ND-224U

-5%/+10%

Sunpower Corp

SPR-315E

+/- 5%

First Solar

FS-270

+/- 5%

GE Energy

GEPVp-200-M

+/- 5%

As a result of this practice, you can see there's not much incentive to ever sell a module in the "plus" range (e.g., a module intended as a "200" that tests at 209 watts), because they will simply sell it as a "220", assuming the same +/-5% tolerance.

For the US market, the most common tolerance is +/-3% and there are some manufacturers that sell at +/-5% and there are some that actually sell at +/-0%.

As you can see, every PV module varies in important ways. At Sunlight Electric, we believe there can be a place in the market for each and every one of these products, as getting more of one thing usually involves trading off another. We believe it's our job to educate our customers as to the trade-offs and make recommendations on the best fit with their needs.

Back to Top
Nameplate Ratings
Watts per Square Foot
Temperature Tolerance
Manufacturing Tolerances



1.866.GET.SOLAR