2012 PV Module Guide

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

Modules are similar in technology, warranty, and price, but some will prove a better choice than others. Module prices have steadily decreased (see “...and Cost” sidebar), making them a smaller percentage of overall installed system cost—but modules are still expensive. And, as a long-term investment, reliable energy production is critical.

Unfortunately, there isn’t any national board that certifies PV module quality and performance ratings. Though modules must meet Underwriters Laboratories (UL) 1703 standards for quality to be installed in systems subject to inspection, most of the performance data is provided by the manufacturers themselves. The California Energy Commission (CEC) attempts to fill this void through its list of approved equipment eligible to receive rebates.

We have reviewed the CEC database for compliant modules, collected their module data sheets, and verified the information with the module manufacturers. The result is a list of more than 830 modules from more than 50 manufacturers (available in its entirety at www.homepower.com). Manufacturers excluded were those without U.S. sales and distribution offices (customer service is important); those that only make thin-film modules (found mainly in large commercial and utility-scale systems); and modules smaller than 175 W (since larger modules are dominating the residential market).

For more details on deciphering module spec sheets, see “Understanding Module Specifications” in HP145. Keep in mind that specifications are subject to change—consult the manufacturer for the latest data.

The following information will help you make an informed decision about which module is right for your system. This is not an article about the “best module,” nor even a “top 10” of modules, but rather a discussion of the features and specs of many modules that can work for different applications. Which module to select will depend upon the priorities of installers and end users, specific installation considerations, system applications, and expectations.

STC & Rated Power

Module model names typically correspond to their rated power at standard test conditions (STC)—their output under 1,000 W/m2 of sun intensity and a 25ºC cell temperature. If there is a “225” in the model name, the module most likely has a nameplate rating of 225 W. 

Module rated power has steadily increased over the years. Fifty-five W (and smaller) modules were once common; they gave way to 85, 110, and then 150 W modules. The trend continues, with most of the modules on our list rated at 200 W or greater (the average size of all the modules on the list is 236 W); only 30 on the list are rated at 300 W or more, and only three are rated at 400 W or more—all three are made by the same manufacturer, Grape Solar. 

PV cell size determines the cell’s amperage—the larger the cell, the more photons of sunlight it can intercept and the more current it can produce. Square 6-inch cells are the largest used in normal commercial production of crystalline silicon modules. Each cell can produce 8 amps or more, and each operates at about 0.5 Vmp. Wiring 96 of these cells together in series in one module produces approximately 48 V (96 × 0.5 VDC = 48 V), resulting in a 384 W module (8 A × 48 VDC = 384 W). The highest-power module listed on the table is 410 W, the result of 96, 8.15 A, 0.524 V cells wired in series for a module voltage of 50.3 Vmp. 

Larger modules mean fewer modules to install for the same power output. Instead of 20, 200 W modules, 10, 400 W modules can be used. Fewer connections required between modules can improve system reliability. However, higher-voltage modules also can constrict system design options in residential applications, where arrays are limited to 600 VDC (see Methods in this issue).

Larger modules are a handful—the six largest modules on our list each measure 6 feet 5 inches by 4 feet 3.5 inches, weigh more than 78 pounds, and require two people to move. This compares to a typical 230 W module, which may be about 5.5 by 3.25 feet, and weighs about 45 pounds.

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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 !

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