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.
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.