How to compare solar panels

• Monocrystalline panels have the highest efficiency ratings, which typically range from 18% to 23%.

• The higher the efficiency rating of a solar panel, the fewer panels you’ll need to reach a specific output.

• The average lifespan of a solar panel is between 25 and 30 years, so be sure to look for product and performance warranties that last at least 25 years

Once you’ve decided to buy solar panels, you’ll need to shop around to determine the right kind of panels for your system. In this article, we’ll outline the factors you should consider when comparing solar panels, including efficiency ratings, degradation rates, and more. Once you know what you’re looking for, you’ll know the right questions to ask solar companies for more information, and you’ll have a better idea about how to choose a solar installer for the array you need.

Reading through the elements you’ll need to compare may also turn you off of going solar, and that’s okay, too. Solar isn’t best for everyone, but it’s worth learning before making your final decision.

How to compare solar panels: Overview

There are three types of solar panels to choose from: monocrystalline silicon (Mono-Si), polycrystalline silicon (Poly-Si), and thin-film (CdTe, CIGS, a-Si). Here are some quick facts on each type:

• Monocrystalline panels are the most popular type of panel for rooftop installations. They offer the longest lifespan and have the highest efficiency ratings, which typically range from 18% to 23%.

• Polycrystalline panels are less expensive but require more space, making them less popular for residential installations. Poly-si panels are also less efficient than mono-si panels, performing worse in high-heat and low-light conditions.

• Thin-film panels are the most affordable solar panels on the market as they’re much easier to manufacture. They weigh less and install faster, but degrade faster and have the lowest efficiency ratings. There are three types of thin-film panels: amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium selenide (CIGS), with CdTe being the most commonly used.

If you live in a place with low light, like the Pacific Northwest or Upper Midwest, you may want to explore Passivated Emitter and Rear Contact (PERC) enhanced solar cells. These cells are optimized to capture the greatest number of photons without altering the functionality of a solar cell. In other words, PERC-enhanced cells can give you better energy output in places that don’t get as much sun.

Factors to use when comparing solar panel models

When comparing different solar panels, you’ll want to look at several factors. The table below breaks down the various features you should pay attention to, why they matter, and what you should look for when reading specs.

Assess efficiency based on cell type and design

Efficiency is the most important factor you’ll need to consider when comparing solar panels. Depending on the type and technology of the panel, efficiency ranges from 13% to 24%. The higher the efficiency rating, the fewer panels you’ll need to reach a specific output. 

To make sure you’re getting the best performance from your solar energy system, look for panels that use heterojunction technology. You can also choose tandem cells for premium performance.

Use the temperature coefficient to judge hot weather performance

If you live in a hotter part of the country, you’ll want to purchase solar panels that work well in higher temperatures. All solar panels lose power as temperature increases, but some are optimized to have a higher heat tolerance. 

These panels have lower temperature coefficients, which is the percentage decrease in output for every 1-degree Celsius (°C). For example, panels that decrease by 0.26% per 1-degree Celsius have a temperature coefficient of -0.26%/°C.

The lower the temperature coefficient, the better the performance in hot climates. These panels are ideal for rooftops with poor airflow or for desert installations.

Compare panel wattage to understand output potential

Panels have different output potentials, so you’ll want to look at panel wattage to determine which panels make sense for your needs. Wattage tends to vary from 250W to 450W per panel. It’s important to note that larger wattage panels are cheaper to install, as they reduce racking and labor costs.

You should also compare the Standard Test Conditions (STC) and Nominal Operating Cell Temperature (NOCT) ratings for each. The STC rating is based on standardized conditions for performance, whereas the NOCT rating takes into account the real-world conditions of the climate where you’ll install the panels.

Review product warranty and durability ratings

When putting together a home solar panel system, you’ll want to feel confident in your panels’ longevity. The average lifespan of a solar panel is between 25 and 30 years, so be sure to look for product and performance warranties that last at least 25 years. Product warranties protect you from defects due to poor workmanship or material quality, whereas performance warranties offer a guarantee of energy output for the duration of the warranty.

You’ll also notice that some panels have specific certifications that relate to durability and safety. The International Electrotechnical Commission (IEC) certifications are the most widely recognized in the solar industry, but IEC 61215 and 61730 are also important. The 61215 certification relates to durability, meaning a panel can withstand harsh climates and mechanical stresses like heavy snowfall or hail. The 61730 certification refers to safety, and panels with this certification meet international safety standards.

Corrosion can be a real issue, so if you live in a humid climate, look for panels with anodized aluminum frames. These frames resist corrosion well, extending your panel’s lifespan.

Examine long-term degradation rates

It’s essential to pay attention to degradation rates, as well. A good solar panel retains 85% to 90% of its original output after 25 years. The less your panels degrade over time, the better your return on investment. High-end panels should have long-term degradation rates of 0.5% or less. A degradation rate over 0.5% will shorten the lifespan of your panel and ultimately be less cost-efficient.

Consider brand reputation and manufacturing tier

Manufacturing tiers are financial classifications for solar panels. Tier 1 manufacturers are large and reliable, with solid financial backbones and a high degree of vertical integration. Tier 2 refers to any manufacturer that isn’t in Tier 1. You can still find decent Tier 2 solar panels, but you can more easily trust the performance and durability of Tier 1.

Before you decide on a brand of solar panel, do some quick market research. Check independent lab tests on brands and read customer feedback on independent review sites. Brands like SunPower and REC tend to rank highly for panel quality and customer service, and customers give Qcells high ratings for price point.

Calculate cost per watt for true value

Determining a panel’s cost per watt will help you get a ballpark estimate of what it will cost to add a solar energy system to your home. For example, if a 6 kW (6,000-watt) solar system costs $15,000 installed, divide $15,000 by 6,000 watts to get $2.50 per watt. Our data shows the average price per watt is $3.56.

Cost per watt normalizes pricing across panel sizes because it includes factors like hardware, installation, and inverter costs. Don’t base your entire decision on the lowest cost per watt, however, as a lower cost doesn’t always translate to better quality.

Choose a visual design that suits your application

If you’re installing solar panels on or next to your home, you’ll want them to be visually appealing, or at least not distracting. All-black panels have a cleaner look but may run hotter in higher temperatures.

 Both frameless and glass-glass designs are resilient and present a streamlined aesthetic. Busbar-free panels, which don’t have the copper or aluminum strip between cells, offer a sleek, uniform surface. Be sure to look at each design to learn what fits with your home’s style.

Bottom line: choosing the right solar panels

When choosing solar panels, start by comparing their efficiency and wattage to ensure you get the highest output from your system. Your budgetary restrictions, brand preferences, and environmental conditions will help you narrow down the panels to choose from. Finally, you should use the cost per watt and the panels’ degradation rate to project the system’s long-term value.

FAQ About Comparing Solar Panels

Below are a few frequently asked questions about comparing solar panels:

How do you compare solar panels?

When comparing solar panels, you’ll want to consider several factors, including the cost, efficiency, degradation rate, and brand reputation.

How many solar panels will I need for a 1,200 square foot house?

To power a 1,200 square foot house, you’ll need between 12 and 14 standard 375-watt panels.

How long do solar panels last?

Most solar panels have a lifespan of between 25 and 30 years. They’ll continue to create electricity beyond that, but at lower efficiency.

Which type of solar panel is the most efficient?

Monocrystalline solar panels have the highest efficiency ratings, ranging from 18% to 23%.