Whether you are a homeowner wanting to install your own PV system or a professional installer, one challenge will be choosing, among hundreds of options, which module will be the best fit.
Selecting modules requires an understanding of module attributes and specifications. Once you are familiar with those, the job becomes ranking modules based on your criteria. You will find that the most important module characteristics depend on the site and your system goals.
This article discusses the top module considerations: module efficiency, price, aesthetics, reliability, manufacturing location, and integrated features. Then, we consider some common scenarios and how module attributes fit them.
Module efficiency is a function of power output per square foot (W/ft.2). The higher this value, the more energy a specific footprint can produce. Module outputs range from about 11 to 19 watts per square foot. For example, let’s say the usable shade-free area on your rooftop measures 240 square feet (20 by 12 feet). Using modules that produce 15 W per square foot yields a 3.6 kW array.
Module dimensions also come into play when determining actual array wattage. Common 60-cell modules are about 65 by 39 inches wide. For our example, we could fit two rows of six modules in a portrait configuration. If the module wattage is 265 watts (with an efficiency of about 15 W/ft.2), our array will be 3.18 kW.
Module price is a factor for most folks. The good news is that module prices have dropped dramatically over the last few years. In 2008, modules were approximately $4 per watt; it is now common to find them for less than $1 per watt. Total system costs followed the same trend—in 2008, they hovered around $8 per watt; now, the average cost is less than $4 per watt (before incentives; assuming professional installation).
Once you factor in any local incentives and the 30% uncapped residential federal tax credit (currently set to expire at the end of 2016), it is no wonder we are seeing so much growth in the PV industry. In fact, in the first quarter of 2014, 74% of new electrical generation in the United States came from solar. Residential PV installations exceeded commercial installations for the first time since 2002, and more than one-third of the residential PV systems came online without any state incentives.