Cost. In the last few years, PV module prices have steadily declined. According to Solar Buzz, as of August 2010, the average retail price per watt was at $4.17. However, finding lower-cost, unblemished, UL-listed modules is fairly easy—we found modules as low as $2.50 per W from various online retailers.
While cost is an important consideration, shopping online and purchasing the lowest-cost modules may not be the best approach. Purchasing modules from an experienced and qualified PV designer/installer, while likely more expensive, will help ensure that a system is designed to meet your specific requirements and/or expectations, as well as a professional installation and support afterward. In fact, most reputable installers will only install the brands they are familiar with, and may not install systems purchased from an outside source. Additionally, some incentive programs require the system to be installed by a licensed/certified PV installer.
Module cost represents about 50% of the overall cost of a residential grid-tied PV system, which ranges from $5 to $8 per installed W. Economies of scale influence the cost as well. For example, the full cost of a 1 kW PV system might be at the upper end of that scale ($8,000), while a 10 kW system would be toward the lower end ($50,000).
Warranty. Twenty- to 25-year power output warranties are standard in the PV industry, and material warranties range from two to 10 years. Material warranties often cover problems such as clouding or discoloration of the glass cover, delamination, poor solder connections, and failed bypass diodes.
Power warranties cover module power loss and are generally offered for 25 years. (Some of the items covered under material warranty are also covered under power warranty if those failures reduce power output.) Not all power output warranties are the same. For example, SolarWorld offers a “25-year linear performance guarantee.” If during the first year, module output falls below 97% of rated output under standard test conditions (STC; 25°C cell temperature, 1,000 watts per m2 irradiance), the company will replace the module. In subsequent years, if modules show a decrease of more than 0.7% per year (until the module is 25 years old), the company will also offer replacement. Often, other module power output warranties require that output fall below 90% within the first 10 years, or below 80% after year 10, to be considered for a warranty claim.
On the flip side, sending in a module for a warranty claim has drawbacks, including shipping costs and the potential for system downtime. When module shopping, ask the supplier how warranty claims are handled, what the typical shipping costs are and who pays for them, and if you have access to replacement/substitute modules to keep your system running should you need to return your modules.
Manufacturer History. Another factor to consider is the manufacturer’s history in the business—how long have they been producing PV modules. Manufacturer longevity can be some indication of whether the manufacturer will be around for the duration of the warranty. While the future of PV module manufacturers is impossible to predict, manufacturers with longevity in the PV manufacturing business have worked out a lot of their production and design issues.
Be aware that shifts in the industry can have various outcomes. For example, the module line first produced by Astropower in Newark, Delaware, was taken over by GE Energy, and most recently bought by Motech. Unfortunately, GE Energy would not cover Astropower modules after it purchased the module line. Thankfully, Motech will honor GE module warranties, but Astropower module owners are still out of luck. In contrast, Arco’s module line, acquired by Siemens, then Shell Solar, and now SolarWorld, has survived all these transitions with the company’s warranty intact.