What's the best solar panels to buy？

Choose SunPower Maxeon 6 panels (22.8% efficiency, 25-year linear warranty) or REC Alpha Pure-R (22.3%). Prioritize low temp coefficients (-0.24%/°C), 25-year performance guarantees, and certified local installers for maximum ROI.

Cost and Value

While you can find panels for as little as $0.35 per watt from budget manufacturers, premium panels from brands like REC or SunPower typically range from $0.80 to $1.20 per watt. This initial 60% to 70% price difference is significant, but it doesn't tell the whole story. The key metric is the Levelized Cost of Energy (LCOE), which calculates the total installation cost divided by the total electricity generated over the panel's life. A cheaper panel with a lower efficiency rating (like 18.5%) might produce less power over time on a limited roof space compared to a higher-priced panel with 22.5% efficiency.

A premium panel with a lower annual degradation rate, such as 0.25% per year versus a standard panel's 0.55%, will generate substantially more electricity in years 15 through 25. For a 10 kW system, that difference in degradation can mean an extra 2,000 to 3,000 kWh of electricity produced over its lifetime. If your utility charges $0.15 per kWh, that's an additional $300 to $450 in savings, directly offsetting the higher initial cost.

Furthermore, higher efficiency panels often have a higher power output rating per panel. For example, a premium panel might output 400 watts compared to a standard 350-watt panel. If your roof space is limited, you can install fewer of the 400-watt panels to achieve the same system size, which can reduce balance-of-system costs like racking and labor, shrinking the overall price gap.

Your local climate and electricity rates are critical factors. If you have high electricity costs (above $0.20 per kWh) and a good net metering policy, the return on investment for a more efficient, durable panel will be much faster, often cutting the payback period by 1 to 3 years. The federal Investment Tax Credit (ITC), which currently offers a 30% tax credit on the total system cost, also applies to the more expensive, high-quality equipment, amplifying the value of your investment.

Quality and Testing

They track metrics like power output degradation, which for a high-quality panel should be no more than 0.25% to 0.35% per year. This means after 25 years, the panel should still be operating at at least 90% of its original output, compared to cheaper models that may degrade at 0.5% or more, dropping to 85% efficiency or lower. This 5% difference in performance over time can equate to thousands of kilowatt-hours of lost energy generation.

Low-quality EVA can yellow and become opaque under intense UV light, reducing light transmission to the cells and causing a power loss of 3% to 8% within the first few years. The back sheet, a multilayer polymer film, must be robust to prevent moisture ingress and electrical insulation failure. Inferior back sheets can crack, leading to a failure rate that can be 5 to 10 times higher than panels with proven, brand-name back sheet materials. The frame, typically aluminum, should have a corrosion-resistant coating with a thickness of at least 15 to 25 micrometers to withstand coastal salt spray or industrial pollution without pitting.

The quality of the junction box seal is also critical; a poor seal can allow humidity to reach 85% inside the box, leading to corrosion and potential hot spots. To ensure these modules work together, independent laboratories certify panels to international standards, the most important being IEC 61215 for performance and IEC 61730 for safety. These tests are exhaustive. For example, the Mechanical Load Test applies a static pressure of 5,400 Pascals (equivalent to a heavy snow load or high wind) to the panel's surface to check for microcracks in the cells.

The Damp Heat test subjects panels to a temperature of 85°C and 85% relative humidity for 1,000 hours to accelerate the effects of long-term outdoor exposure. Panels that pass these tests with minimal power loss, typically less than 2% to 5% for the entire test sequence, demonstrate superior build quality.

Look and Feel

The most common panel has a grid of 5 to 10 thin silver bus bars on a light blue background, but the trend is toward a more uniform, all-black appearance. This "esthetic premium" can influence the final system cost by 3% to 8%, but for many homeowners, the improved curb appeal is a worthwhile investment.

Standard panels use silver bus bars that are 1-2 mm wide to collect electricity from the silicon cells, creating a visible grid. The all-black esthetic is achieved primarily by using black-back sheets and frames, along with shingling or hiding the bus bars. Shingled-cell technology, where small cell strips overlap, eliminates the 2-3 mm gap between cells, creating a smooth, continuous surface. This not only looks better but can also increase the panel's active area, boosting its power output by 5 to 20 watts for a similarly sized standard panel. The silicon cells themselves can be monocrystalline (typically darker black) or polycrystalline (lighter blue); monocrystalline cells now dominate the market, with efficiencies ranging from 20% to 23%, and offer a more consistent color.

Most panels use anti-reflective coated glass, which increases light transmission by 2% to 3% compared to uncoated glass, giving the panel a darker, less mirror-like appearance. A less common but visually striking option is the frameless panel, which eliminates the 35-45 mm wide aluminum border for a completely flat profile. However, this design can complicate installation and may not be suitable for all racking systems. The weight of a standard panel is around 40-50 lbs, while larger, high-output panels can weigh over 60 lbs, a factor your installer must account for regarding roof load. When planning your array, consider the spacing between panels. A 0.5 to 1-inch gap is standard for thermal expansion and maintenance, but a tighter layout can be requested for a more integrated look.

Power and Performance

A panel with a 22.5% efficiency rating will indeed produce more power per square foot than one rated at 20.0%, but the key metrics that predict long-term energy harvest are the power temperature coefficient, the degradation rate, and performance in low-light. For instance, two panels both rated at 400 watts at Standard Test Conditions (STC) can have an annual energy output difference of over 3% based solely on how they handle heat.

This number, typically between -0.20%/°C and -0.35%/°C, indicates how much power the panel loses for every degree Celsius its temperature rises above the standard testing temperature of 25°C (77°F). On a sunny day, a solar panel's surface can easily reach 65°C (149°F). A panel with a coefficient of -0.26%/°C will experience a power loss of -10.4% at that temperature, while a panel with a poorer coefficient of -0.34%/°C will lose -13.6% of its output. This 3.2% difference compounds over thousands of hours of operation, meaning the better panel will generate significantly more energy during the hot summer months when you might need it most for air conditioning.

The second critical factor is the annual degradation rate. A panel guaranteed to degrade at only 0.25% per year will still be producing at 92.5% of its original output after 25 years. A standard panel degrading at 0.55% per year will only be at 85% output. For a 10 kW system, that 7.5% difference in Year 25 translates to 750 watts of lost capacity, which could mean 1,000 kWh or more of unrealized electricity production annually, depending on your location.

Warranty and Support

A standard warranty might guarantee 90% output in the first decade and 80% by year 25. However, a superior warranty, often from tier-one manufacturers, guarantees a much slower degradation, such as 97% retention in year 1, falling to 92% in year 12, and finally to 85% or even 87% in year 25.

When dissecting a solar warranty, you are actually evaluating two distinct agreements: the product warranty and the performance warranty.

l Product/Materials Warranty: A standard period is 10 to 12 years, but leading manufacturers now offer 15 to 20-year full product warranties, with some extending limited coverage to 25 or 30 years.

l Performance/Power Output Warranty: A commitment of 85% after 25 years is average, but a guarantee of 87% or 90% indicates a more robust product. Pay close attention to the claimed tolerance. Panels are sold with a power tolerance, typically 0 to +5%. This means a 400W panel is guaranteed to produce at least 400W (or more) when new.

A reputable company should initiate a claim review within 30 to 60 business days of notification. Ask if they have a network of pre-approved installers for replacements or if you must coordinate with your original installer, which can add weeks or months of delay. A significant but often hidden cost is the labor for replacement. Some warranties only cover the cost of the new panel, leaving you responsible for a labor fee that can range from $300 to $800 per panel for a certified technician's time. The best warranties explicitly include labor coverage for at least the first 5 to 10 years.

Installation and Fit

While a standard residential panel typically measures around 68 inches by 40 inches and weighs 40 to 50 pounds, newer high-wattage panels can be over 80 inches long and weigh more than 60 pounds. This 20% increase in size and weight may require additional structural supports on some roofs, adding 5% to 10% to the installation labor cost.

Furthermore, the type of cell technology directly influences installation complexity. Panels with half-cut or shingled cells are inherently more resistant to shading; if a small section of a panel is shaded, a half-cut cell design can lose only 30% to 50% of its power, compared to a standard panel which might lose 80% to 100%.

l Roof Assessment and Compatibility: The installation begins with a thorough roof evaluation. The roof's pitch, typically between 15 and 45 degrees, affects the optimal tilt angle for energy production. A deviation of 10 degrees from your local latitude can result in a 1-2% loss in annual energy yield.

l Panel Size and System Layout: The physical size of the panels you choose determines how many can fit on your available roof space. Using larger, higher-wattage panels (e.g., 450W instead of 370W) can reduce the number of panels, racking points, and labor hours by 10% to 15% for the same total system size.

l Electrical Configuration and Modules: Modern string inverters have a wide operating voltage range, often from 150V to 1000V, but the total voltage of your panel string must fall within this range, typically between 300V and 600V for optimal efficiency. Micro inverters or DC power optimizers, which are attached to each panel, add $0.10 to $0.15 per watt to the system cost but can boost overall energy production by 5% to 25% on roofs with complex shading, and simplify the system design by allowing each panel to operate independently.

l The ultimate goal of installation is not just to secure panels to the roof, but to create a unified system where the sum of the parts works at peak efficiency for decades. This requires precise alignment of physical mounting, electrical wiring, and local environmental factors to ensure every kilowatt-hour of potential generation is captured.