2012 PV Module Guide: Page 2 of 4

Intermediate

Inside this Article

Choosing Solar-Electric Modules
Comparative Module Size
Module size is creeping up, with both pros and cons: A 96-cell, 410 W Grape Solar module (left) is almost 6.5 feet tall and more than 27.5 square feet, compared to a more common 72-cell, 230 W module (right) at about 17.5 square feet.
SunPower Solar-Electric Module
SunPower’s 318-watt module offers 19.5% efficiency—top of the industry, but at a premium price.
Sanyo Solar-Electric Module
Sanyo’s HIT series offers a +10% (no minus) power tolerance.
Day4 Solar-Electric Module
Day4 Energy is one of four manufacturers that have modules rated at a low NOCT of 43°C.
Sun Earth Solar-Electric Module
Sun Earth Solar Power (Nbsolar) represents one of the three manufacturers that have modules with a PTC-to-STC ratio of 0.92 or better.
Silicon Energy Solar-Electric Array
Silicon Energy’s power warranty is 15 years at 90% of rated output, and 30 years at 80%.
SolarWorld Solar-Electric Module
SolarWorld and other companies offer linear warranties that allow a yearly percentage decrease in output over the warranty period.
Choosing Solar-Electric Modules
Comparative Module Size
SunPower Solar-Electric Module
Sanyo Solar-Electric Module
Day4 Solar-Electric Module
Sun Earth Solar-Electric Module
Silicon Energy Solar-Electric Array
SolarWorld Solar-Electric Module

Module Efficiency

When two modules of the same dimensions are exposed to the same sunlight intensity, the more-efficient one will yield more watts per square foot. Thus, module efficiency and rated power per square foot are closely related. 

Watts per square foot is easy to calculate—divide the module’s rated power by its dimensions in square feet. For example, a 250 W module that measures 40 inches by 65 inches (18.06 ft.2, 40 in. × 65 in. ÷ 144 in.2/ft.2) produces 13.84 W per square foot (250 W ÷ 18.06 ft.2).

Efficiency is calculated based on the nameplate power rating of a module, which what it produces when subject to 1,000 W per m2, called “full sun.” Calculating the module size in square meters means a ratio can be made to calculate efficiency (1 ft.2 = 0.0929 m2). The 250 W module that makes 13.84 W per ft.2 is just a little less than 15% efficient:

18.06 ft.2 × 0.0929 = 1.678 m2

250 W ÷ 1.678 m2 = 149 W per m2

149 W per m2 ÷ 1,000 W per m2 = 0.149 = 14.9% efficient 

More than 530 of the modules on our list are at least 14% efficient; the field narrows to about 140 modules that boast at least a 15% efficiency rating; only 20 modules have an efficiency of 16% or more.

No matter how you slice it, SunPower modules are tops in both efficiency and watts per square foot. The company’s monocrystalline silicon modules feature high-efficiency cells and use back contacts, eliminating the traces and conductors between cells that appear on the front of most modules and which block photons from sunlight. This translates to more surface area, more current, and more power per square foot.

Using efficient modules can be particularly effective when space is limited. However, if it costs too much, the bit of extra efficiency may not be worth it. Selecting modules based on cost—“dollars per watt”—frequently trumps efficiency when there is enough space for the array.

Power Tolerance

Unfortunately, the saying, “you get what you pay for” doesn’t necessarily hold true when you’re paying dollars per watt for PV modules. That’s why you need to pay attention to power tolerance, the percentage that the actual power output of a module can vary from its STC rating.

For example, a 200 W module with a +/-5% power tolerance may produce anywhere from 190 to 210 W at STC. Product lines that are often differentiated in 10 W increments become blurred when the 210 W version of the same module may test between 200 W and 220 W. About 400 modules on our list have the most common power tolerance of +/-3%.

More than 350 of the modules listed have positive-only power tolerance, which means that the module will produce at least its rated power at STC, if not a little bit more. Nearly 75 on the list have a power tolerance of +5/-0% or better, including modules by Kyocera, Perlight Solar, Schüco, Solon, Suntech, Sanyo (+10/-0%), and Schueten Solar.

Comments (2)

jenniferwoods's picture

I was actually searching for the most reliable one. Now as it is said about Sunpower, this must be considered seriously.

Jim and Elaine Stack's picture

check Sunpower panels before you get any. All are good and you can't go wrong but Sunpower are also twice as good as any I have seen. The local ASU TUV PTL labs test panels from all over the world. Sunpower really stands out above all others.

PS I don't sell or work for Sunpower, I just wish I did !

Show or Hide All Comments

Advertisement

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading