PV Purchasing

Top 10 Considerations
Beginner

Inside this Article

Installation of a PV Array
Ready to invest in a PV system? Check out our top 10 tips for choosing the best module.
Siemens Module
This Siemens module is still covered under warranty, even though the module line has twice been transferred, first to Shell Solar and then to SolarWorld.
Ningbo Solar Module
If there’s plenty of room, then lower power-density modules, like this NBsolar 165 (12.9% efficiency), can be less expensive per watt.
SunPower E-19 318-watt Module
At 19.5% efficiency, the SunPower E-19 318-watt module offers one of the highest power densities available.
Module Layout
Module sizes and dimensions need to be carefully considered to maximize roof space, while meeting local fire safety setbacks. The illustrations at left show the importance of comparing different module options. Both rooftops are the same size; both have arrays that use 185 W modules, but the modules have different dimensions. This results in the top left array having 27% more rated capacity. (Note: If modules were arranged in landscape orientation, the bottom array could accommodate 24 modules instead of 22.)
Scheuten Multisol P6-54 Module
Pay close attention to power tolerance ratings: Some modules have both positive and negative ratings; others, like this Scheuten Multisol P6-54, rated at 0 to +10%, have positive-only power tolerances.
Fronius' Online String-Sizing Tool
Online string-sizing tools will determine how many PV modules and strings are needed to meet inverter capacity and voltage range.
Sanyo HIT Modules
Some modules, like Sanyo’s HITs, allow light to pass through the backsheet for underside lighting, as well as power generation from reflected light.
SunPower Modules
Manufacturers now offer more module options—like black frames and backsheets—to suit homeowners’ aesthetic preferences.
SolarWorld Module
Some modules, such as this one from SolarWorld, are made entirely in North America, which means less embodied energy from transportation, as well as creating jobs stateside.
Installation of a PV Array
Siemens Module
Ningbo Solar Module
SunPower E-19 318-watt Module
Module Layout
Scheuten Multisol P6-54 Module
Fronius' Online String-Sizing Tool
Sanyo HIT Modules
SunPower Modules
SolarWorld Module

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.

Comments (3)

rdrcfo's picture

In regards to installer preference or disfavor with installing PV modules purchased outside does it mean they markup the modules costs as part of the instllation?

Michael Welch's picture

Hi there. Yes, sort of. Like in any other trade, they buy at wholesale and sell at retail to the end consumer. But it is part of the package. If you buy your own equipment, you may not find a reputable installer to put it in. If you do, you are likely to pay a higher installation labor cost for a couple of reasons. First, the seller hasn't made a dime on the equipment, and second because they may not be used to the equipment the customer purchased on their own. But here is the worst of it under this scenario. You probably will not get system support from the installer, your support would need to come from wherever you purchased the equipment, or from the manufacturer if they are willing.

rdrcfo's picture

Thanks Michael your comment was helpful and certainly makes sense.

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