The return on investment of the solar system depends on the quality of solar panels you use.
There are a number of solar panel types and brands available which makes it difficult to choose the right one. However, there are the right set of parameters that you must check before choosing the solar panels.
In this blog we will explore how to choose the best solar panels so that you get maximum ROI.
Efficiency and Performance Ratio (PR)
Efficiency of the solar panel defines how effectively it converts sunlight into electricity. For example, if a panel has 21% efficiency, that means it can convert 21% of sunlight into electricity. Therefore, efficiency is the main factor that decides the ROI of the solar installations.
The top performing modules such as monocrystalline PERC or TOPCon give efficiency of about 20-22%.
Here are different types of solar panels and their efficiencies-
Type of Solar Panel | Technology Description | Typical Efficiency Range |
Monocrystalline (Mono-Si) | Made from a single crystal structure of silicon; uniform dark appearance. | 20–23% |
Polycrystalline (Poly-Si) | Made from multiple silicon crystals melted together; bluish hue. | 16–18% |
PERC (Passivated Emitter Rear Cell) | Improved mono/poly cells with rear surface passivation for better light capture. | 19–22% |
TOPCon (Tunnel Oxide Passivated Contact) | Next-gen mono technology enhancing electron flow through a tunnel oxide layer. | 21–23.5% |
Bifacial Panels | Capture sunlight from both front and rear surfaces using transparent backsheets. | 20–24% (effective) |
Thin-Film (a-Si, CdTe, CIGS) | Lightweight layers of photovoltaic materials deposited on glass or plastic. | 10–13% |
Heterojunction (HJT) | Combines crystalline silicon with thin-film layers for hybrid efficiency. | 22–24% |
Alongside the efficiency performance ratio is one of the most important factors that should be considered who chooses the best solar panels.
The performance ratio (PR) assesses how well a solar plant can convert sunlight into actual electricity. A healthy PR range is between 80-85%.
Degradation Rate and Warranty
While choosing the best solar panels consider the degradation rate and warranty. Choose solar panels that have an annual degradation rate of ≤ 0.5% and the performance warranty of more than 25 years.
The degradation rate depends on the material quality of the panel, the process of manufacturing, UV exposure, and the cleaning methods used. Other external factors such as humidity, dust abrasion and the thermal stresses can also accelerate the degradation of the solar panels.
Manufacturers provide two types of warranties- product and performance warranty. Product warranty covers manufacturing defects and premature failures. The performance warranty guarantees that the panel will deliver certain performance after a set period. The typical performance warranty of different types of solar panel is as follows.
Panel Type | Initial Efficiency (Approx.) | Annual Degradation Rate | Power Output After 10 Years | Power Output After 25 Years | Typical Performance Warranty |
Monocrystalline (Mono-Si) | 20–23% | 0.45–0.6% / year | 94–95% | 84–87% | 25 years |
Polycrystalline (Poly-Si) | 16–18% | 0.7–1.0% / year | 90–93% | 75–82% | 25 years |
PERC (Mono/Poly) | 19–22% | 0.45–0.6% / year | 94–95% | 84–87% | 25–30 years |
TOPCon (Tunnel Oxide Passivated Contact) | 21–23.5% | 0.3–0.4% / year | 96–97% | 89–92% | 30 years |
HJT (Heterojunction) | 22–24% | 0.25–0.35% / year | 97–98% | 90–93% | 30 years |
Bifacial (Glass–Glass) | 20–24% (effective) | 0.3–0.45% / year | 96–97% | 88–90% | 30 years |
Thin-Film (CdTe, a-Si, CIGS) | 10–13% | 0.8–1.0% / year | 90–92% | 75–80% | 20–25 years |
Temperature Coefficient
Heat is the critical parameter for the performance of the solar panels. Solar panels do not perform well in high heat.
Each solar module is tested under standard test conditions at 25°C cell temperature and 1,000 W/m² irradiance.
The temperature coefficient indicates how much solar panels output is decreased for every Celsius rise above 25°C.
The temperature coefficient for the maximum power ($\mathbf{P_{max}}$) of commercial solar panels typically falls in the range of -0.5%/°C to -0.26%/°C
Panel Technology | Typical Pmax Temperature Coefficient Range | Power Loss Indication |
|---|---|---|
Polycrystalline Silicon | −0.45%/°C to −0.50%/°C | Higher temperature sensitivity; greater power loss in hot conditions |
Monocrystalline Silicon | −0.35%/°C to −0.45%/°C | Moderate temperature sensitivity |
High-Efficiency (PERC, IBC, N-Type/TOPCon, HJT) | −0.26%/°C to −0.35%/°C | Lower temperature sensitivity; better performance in heat |
Thin-Film (Cadmium Telluride, CIGS) | −0.20%/°C to −0.30%/°C | Generally the lowest sensitivity; best performance in extreme heat |
Build Quality and Certifications
Solar panel build quality decides how solar panels will withstand the harsh environmental conditions and maintain its performance over the given lifespan.
The high quality solar panels are made from premium grade silicon cells and UV resistance encapsulant materials.
Choosing the sub standard solar panels often develop microcracks, hotspots and moisture ingress.
Also to ensure the long term stability, ensure the solar panels you use have the international certification standards. Ensure the solar panels have IEC 61215, IEC 61646, IEC 61730, and UL 1703 certifications.
Standard | Focus/Purpose | Key Tests |
IEC 61215 | Design Qualification & Type Approval for Crystalline Silicon PV Modules. This is the fundamental performance benchmark. | Thermal Cycling (-40°C to +85°C), Damp Heat (1000 hours at 85°C/85% humidity), Mechanical Load (wind/snow pressure). |
IEC 61646 | Equivalent standard for Thin-Film PV Modules. | Similar durability tests with additional checks for light-induced degradation |
Standard | Focus/Purpose | Key Tests |
IEC 61730 | PV Module Safety Qualification. Assesses the mechanical and electrical construction to prevent fire, shock, and personal injury. | Construction requirements (insulation, clearance, creepage distances), Fire Resistance, Wet Leakage Current Test. |
UL 1703 | Safety Standard for Flat-Plate PV Modules. The primary safety standard required for the North American market. | Covers fire, electrical, and mechanical safety, often merging with IEC 61730 in newer standards (UL 61730). |
Key Takeaways on How to Choose Best Solar Panels
Choose panels with high-efficiency of 20–23% and strong performance ratio
Prefer the solar panels with a low degradation rate (≤0.5% per year)
Ensure long warranties of 25–30 years for better lifetime returns
Opt for modules with a temperature coefficient of -0.35%/°C or lower
Prefer panels certified under IEC 61215, IEC 61730, and UL 1703
FAQs
1. What factors should you consider when choosing the best solar panels?
The best solar panels should be selected based on efficiency, performance ratio (PR), degradation rate, warranty, temperature coefficient, build quality, and certifications. High-efficiency panels with low degradation and strong thermal performance generally deliver better long-term ROI.
2. Which type of solar panel gives the highest efficiency?
High-efficiency technologies such as TOPCon, HJT, and bifacial solar panels typically offer the highest efficiency, ranging between 21% and 24%. These panels generate more electricity from the same roof area, making them ideal for maximizing energy output.
3. What is a good degradation rate for solar panels?
A good solar panel degradation rate is 0.5% per year or lower. Lower degradation means the panel retains more of its original power output over time, improving long-term performance and return on investment.
4. Why is the temperature coefficient important in solar panels?
The temperature coefficient determines how much power a solar panel loses as temperatures rise above 25°C. Panels with a lower temperature coefficient (such as −0.35%/°C or better) perform more efficiently in hot climates and maintain higher energy generation.
5. What certifications should solar panels have for long-term reliability?
Reliable solar panels should have certifications such as IEC 61215, IEC 61730, and UL 1703/UL 61730. These standards ensure the panels are tested for durability, safety, thermal performance, and resistance to harsh environmental conditions.
