How to buy a Solar Panel

When most people get ready to buy a solar PV system, the first thing they shop for is the Solar Module. And for good reason since it is the most costly component of a grid interactive system. So what should you look for when making this important decision? There are now countless manufacturers on the market and their products all appear to be the same these days. But glossy advert pictures can be deceiving. A closer look at a product’s data sheet may be required to make a good choice, and of course reading product reviews in such magazines like Home Power or Solar Pro. You should consider and compare frame, PTC rating, warranty, manufacture longevity and of course, cost.

PV Module frames have evolved greatly over the years. Thickness is important to keeping the frame from flexing in the wind or when subjected to snow loads. It’s true all modules will have a little flex and it is true that when attached to a mounting structure they gain rigidity. But if a module is too flexible to begin with, damage could occur to the solar cells and wire traces causing “hot spots” of resistance. This damage isn’t usually visible to the naked eye either. This type of damage, or “micro-fracture” is usually only detectible with a microscope. The damage could occur during shipping and handling, or during a rough wind storm, or due to heavy snow loads. Most manufacturers have taken the step to move towards a 2” frame to help strengthen against micro-fracturing. Some have even added cross-bracing in the middle of the frame. Whatever you buy, keep in mind that a flimsy module may lead to a poor investment.

The PTC rating, or Photovoltaic USA Test Condition rating (measured in watts), is a good measure of a PV module’s performance under real conditions. Take two modules both having the same manufacturer’s nameplate rating (based on Standard Test Condition, also known as in the laboratory conditions) of 240 watts. When installed under PTC conditions they could have totally different results. The typical PTC rating of a 240 watt module can vary as much as 7 watts, from around 211-218 watts. A module that underperforms in this result can mean fewer dollars in your pocket over its lifetime. To find a complete list of PTC ratings, go to www.gosolarcalifornia.ca.gov.

Note that I am not referring to a module’s “Solar Efficiency.” Solar efficiency is only the measure of how much power per square foot a module can produce. There is a lot of buzz in the media about Solar Efficiency because someday we all hope to power our house from a PV cell the size of a Cliff Bar. But if that cell costs more than the house, no one would buy it. So given today’s modules, is efficiency beneficial? Sort of. A high efficient module may be 20% smaller than its lower efficient equivalent, but you may pay 30% more in cost. Not a great indicator of financial performance. Instead, PTC ratings can tell you how well a module performs in the real world.

Warranties display a commitment from the manufacturer to quality and ultimately keeping your money in your wallet. There are two types of warranties offered by the manufacturer: workmanship and performance. Performance warranties ensure that you will receive a guaranteed minimum production over the life of the module. Thanks to legislation begun in California, performance warranties are 20 years at a minimum, some are as long as 25. But performance warranties aren’t all the same. Usually they are stair-stepped. For instance, you may only be covered for 90% from day one to year 10, then 80% from year 10 to year 20. To be competitive, some companies pro-rate your performance over 20 years based on years in service (e.g. 97% at year three). Workmanship warranties have no real guideline so they vary from 3 to 10 years.

So will the manufacturer be around in 20 years to support their warranty? Great question. Since solar really started to take off in 2005, there are more start-up companies selling modules than there are grains of silicone in a PV cell. Will they be around in 20 years? Probably not. A good question to ask is how long have they been around? Do they produce anything else besides solar? Is their name a recognizable brand name? These are easy ways to tell if a company is likely to be around to cover your warranty.

The good news is that many brand name modules are well made and indeed available at a good price. Of course it’s always important to price shop. You are making a long term investment. It may be appealing to purchase the cheapest module on the market to keep your up-front cost low, but it could lead to financial risk later on. At the same time you probably want someone to help you make an informed decision. Industry magazines are very helpful. But so is a reputable sales company. Every reputable company is going to have one or two of these “best buys” at a great price. As you make your purchasing decision, listen to your salesperson. They should be able to help you make the best long term financial decision. Ask questions. They should help you invest correctly today, and they should also be there to help protect your investment down the road.