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INTRODUCTION:

Solar panels account for more than 60% of the solar power plant cost. There are hundreds of companies making solar panels. Of those hundreds, many companies are considered to be top solar panel makers.

Each company claims their product is the best because: 

A) They offer monocrystalline panels (Mono vs Polycrystalline – Which is The Best?)
B) They offer high-efficiency solar panels in the market. 
C) They make both solar cells and panels. 
D) Their market share is high.
E) Their panels are used by the best companies in the world.

Should you select panels based on the above information? Looking at selected parameters such as efficiency may lead to an improper selection. A comprehensive comparison of guaranteed technical parameters, materials used to make panels and results from independent lab tests would help to pick the best option.

This article explains how and what to look for while selecting solar panels

The best way to select a solar panel is based on the performance data of panels for 25 years. However, more than 90% of solar installations across the world are less than 6 years old. In the absence of the performance data, the following steps will help you to arrive at a decision.

Shortlist Top Solar Companies

As there are hundreds of companies manufacturing solar panels of different grades, shortlisting tier-1 or top companies would help. Some of the parameters that could help to shortlist the companies are market shares of solar cell and panel makers (2015, 2016, 2017), production capacity, top names you hear in the market etc. This could result in a list of about 20-25 companies.

Compare on important Technical Parameters and Warranties

Before going into comparison, select the same type of module from products of the shortlisted companies e.g: 72 cells, 320 Wp standard module.

To select the best panels, one of the things you could do is compare the shortlisted panels on guaranteed technical parameters. The parameters’ values are mentioned at STC (standard test conditions) in product datasheets. The performance in the field may be different from STC conditions. However, STC data would give indications on quality.

The parameters could be categorized as: 

1. Electrical Parameters
2. Mechanical Parameters
3. Thermal Parameters
4. Warranties

Electrical Parameters

Module Efficiency

It is the conversion efficiency of solar light into electricity. Please note, module efficiency is different from cell efficiency, which is higher.

Low Light Performance

All parameters mentioned in datasheet are at STC conditions. Under STC condition, solar radiation is 1000 W/m2. However, in reality, radiation values would be lower and module efficiency falls in low light conditions (e.g. at 100 W/m2). Therefore, the comparison of efficiency in low light conditions is important.

PID (Potential Induced Degradation)

Performance of a solar panel decreases with time. One of the factors that influence the degradation is PID. Therefore, it should be checked whether a module is PID resistant or not.

Mechanical Parameters

Wind, Hail and Snow Load Capacity

As the terms explain, these parameters indicate the withstand capacity of a module when exposed to high wind speeds, hails or snow loads. These could cause very minor cracks in modules and affect performance over time.

Dimensions & Weight

The lighter and the slimmer is always the best. Especially, when roofs have to carry the panels for more than 25 years.

Thermal Parameters

Temperature Coefficients for Power

Performance of solar panels varies with temperature. Power produced by a panel decreases with increase in temperature and vice versa. The change is captured in the temperature coefficient for power.

Compare on Materials they use

For the best panels, STC conditions of modules would be more or less the same. Yet, there would be differences in quality and costs. Therefore, a comparison of material specifications could help to decide on quality vs cost.

Components of solar panels are:

A) Solar Cell
B) Encapsulation
C) Backsheet 
D) Junction Box 
E) Tempered Glass 
F) Frame

Frames give strength to the module and they should not corrode. Generally, anodized aluminum is used to protect from corrosion.

Quality of tempered glass dictates strength and transmission of light to solar cells. Low iron content in glass and anti-reflective coating on glass help to transmit more light. Therefore the thickness of glass and transmission efficiency (or low iron level and presence of anti-reflective coating) should be checked.

Poor backsheet material can result in yellowing, delamination over time. Poly Vinyl Flouride (PVF) material is considered the best material for backsheet. Other materials used for the backsheet are Polyethylene Terephthalate (PET), Fluoroethylene and Vinyl Ether polymer (FEVE) and Polyvinylidene Fluoride (PVDF) may result in some problems according to a study by DUPont.

Encapsulation is done by Ethylene Vinyl Acetate (EVA). In order to reduce costs, some times a low-quality EVA is used.

Comparison of these materials used by solar panel makers will help to select the best of top solar companies. Comparison of materials used is a bit tricky as the information is not shared in datasheets or website. It is suggested to request the data from manufacturers for comparison.

Validate Performance from Reliable Independent Testers

In addition to the comparison on parameters and materials, results independent tests validate the selection. Some of the reliable indicators from independent testers are: 

1. PTC rating
2. PV reliability scorecard form DNV GL

PTC rating indicates performance close to real conditions. You can find the PTC ratings here.

As module performance depends on real-world conditions, DNV GL developed rigors test standards. Based on them, it evaluates modules and publishes PV Reliability Scorecard reports every year.

CONCLUSION

Comparison of technical parameters filter out top 20 – 25 companies and arrive at 5 -7 good products. Comparison of materials used and inputs from independent lab tests help to select the best module.

To make your job easy, we have created a comparison table for selected solar modules. We keep updating the list and/or data. You can download them here.