Looking for “the One”: How to check the quality of a solar panel

There are over 350 manufacturers in the market of photovoltaics. Some make panels better than others, straight up. The panels from LG or Panasonic are likely to be higher quality than panels from a company that you can’t even google. Look for brands with a name and a good reputation on the market.

A good way to ensure that a solar panel is of high quality is to look for certification from organizations such as the International Electrotechnical Commission (IEC) or Underwriters Laboratories (UL). They test solar panels to ensure that they meet certain standards for safety, performance, and durability. Many manufacturers will list certifications and awards on their websites. This information can usually be found on the About us or Certifications page.

The datasheet contains all the technical specifications of a panel. Here is what you want to pay attention to.

Each brand has something special about them. REC half-cut cells design massively improved the shading resistance of panels. Panasonic HJT technology makes its panels outstanding in hot climates. Hanwha Q CELLS Q.UANTUM innovation raised cell performance in low light conditions and so on.

Sometimes the strong sides of a panel are mentioned on the first page of a datasheet. You can also check out our solar reviews to get a picture of what manufacturers are capable of.

Production numbers in the datasheet come from testing solar panels at standard test conditions (STC) to measure their performance. STC includes an irradiance of 1000 W/m², a cell temperature of 25°C (77°F), and an air mass of 1.5. Using STC allows for a fair and easy comparison between different solar panels. Note that STC numbers don’t always reflect how well a panel performs in the real world — a roof is not a lab after all.

The tolerance is the range of solar panel’s production. A smaller tolerance means that the solar panel is more consistent in its output. It’s best when panels have a positive tolerance. This means that the panel performs at STC just as well as the numbers in the datasheet say, or even better.

The temperature coefficient measures how much a solar panel's output drops when it gets hotter than 25°C (77°F) at which it is tested. Usually, it varies between −0.3%/°C and −0.5%/°C. A lower temperature coefficient means that the solar panel is less affected by hot weather.

Efficiency or conversion rate stands for the percent of the sunlight that gets converted to electricity. It is calculated from the ratio of size of a module to its power. The most efficient panel provides maximum energy for a minimum size. In 2022 the best panels were just shy of 23% and we’ll probably cross this threshold in 2023.

Previously we’ve covered what efficiency depends on and how manufacturers try to increase it. By itself, efficiency is not the most important metric but its role grows when you deal with limited space.

The data sheet lists the dimensions, weight, and resistance to environmental factors such as humidity, salt mist, UV radiation and mechanical stress. Mechanical tolerance becomes important when you live in places where extreme weather conditions are common. For example, it makes sense to pick sturdy panels for a home in Tornado Valley. Floridians also prefer panels with high durability, given how often hurricanes hit them.

Mechanical tolerance is measured in pascals (Pa). For example, 2400 Pa maximum load is equivalent to 140 mph wind which is a Category 4 hurricane on the Saffir-Simpson hurricane wind scale.

Solar panels usually come with a product warranty that ranges from 10 to 25 years. There is also an output warranty for 25 years which ensures that the output of a panel won’t fall below a certain level. You can expect a panel to retain 80-90% of its production by the end of year 25. Top manufacturers, like REC and LG, also add in workmanship warranty if their panels are installed by certified contractors.

Bifacial panels usually get a 30-year performance warranty. A few brands go above and beyond 25 years. For example, Silfab and Aptos Solar issue 30-year output guarantees for their panels. Sometimes warranty is not mentioned in the datasheet and instead comes in a separate PDF on the brand's website.

Despite their durability, solar panels may arrive damaged because of careless delivery. A visual inspection of your solar panels can reveal obvious defects.

Remember that the risk of damage increases when panels have to travel a long way, so choose options which are not farther than 1,000 miles from you. Small quantities are also more subject to damage. If you want to get less than 10 panels, consider picking them up from the nearest fulfillment center.

Some defects can’t be detected with the naked eye, but they can cause quite a few problems throughout the lifespan of a module.

Microcracks can occur during the manufacturing process or because of careless shipping or installation. The effect of microcracks on a panel can vary. Sometimes they barely affect production. Sometimes they cause electrical separation inside a panel and bring the output down by a third.

Delamination — separation of the layers of a solar panel — starts at one side of the panel and then spreads across the whole thing. Most often It happens in tropical climates and leads to corrosion and eventually to the failure of a PV module. Delamination can be caused by poor workmanship, manufacturing negligence or high temperatures. Some try to patch the panel with sealant and duct tape but it only delays the inevitable.

After installing your solar panels, you would want to see how they perform, wouldn’t you? You can check their output at home via a few different methods:

1. Multimeter. A multimeter can be used to measure the voltage and current produced by a solar panel. This can give you an idea of the panel's power output. An alternative standalone device would be a solar power monitor.
2. Inverter. Inverter collects data about the production of your array daily. With modern inverters, you can check the numbers using a mobile app.
3. Monitoring system. You can purchase a separate monitoring system for your installation that can be accessed online or through a mobile app.

If the performance of your array seems suspiciously low, contact your installer right away. If he can’t figure out the problem, discuss the issue with the manufacturer.