What are different solar panel technologies such as thin film and crystalline?

According to NREL, 90% of photovoltaics in the world in 2011 was silicon-based. Different silicon-based photovoltaic (PV) cells can be categorized monocrystalline (mono-Si), polycrystalline (p-Si) and thin film solar cells (also called amorphous silicon cells).


Crystalline Silicon Solar Cells

Monocrystalline Silicon (mono-Si) Polycrystalline Silicon (p-Si)
Efficiency (of the panel, not the individual cells) Made out of pure silicon (i.e. perfectly aligned silicon molecules), so have higher efficiencies of 15–20% Not as pure. Have lower efficiencies of 13–16%
Space efficiency Higher panel efficiency translates to higher space efficiency: lesser space is required for the same output. Lower space efficiency.
Looks Has uniform color and look because of pure silicon. Isn’t as aesthetic; has a speckled blue color.
  • Most expensive Si-based solar cell.
  • Live the longest and will usually have a 25-year warranty; performance better than a similarly rated p-Si panels.
Has a simple manufacturing process with less wastage of silicon, so has a lower cost.
Negatives Performance decreases with temperature; particularly imp. for India. Slightly worse compared to mono-Si in performance with increasing temperature.
Selection b/w mono-Si and p-SI Cost and space-efficiency are deciding factors in selection. From a pure financial standpoint, it could be better to go with polycrystalline panels. When space is a constraint, it is best to go with modules giving highest output, which could be a higher efficiency monocrystalline panels. Notwithstanding these, each application needs a professional assessment of the panels as well the individual requirements for the correct choice.  Recent improvements in p-Si tech. have also resulted in the development of modules equal to or better than many mono-Si brands in terms of efficiency and heat tolerance. Currently, polycrystalline panels are the most popular in home solar installations.

Thin film cells are cheaper than the above two technologies. However, they have the least efficiencies: only about 9% in operation. Owing to the resulting larger space requirements, they are not suitable for rooftop applications. However, an important advantage with this technology is that temperature and humidity has less of an impact on their performance. Therefore, thin film technology (both silicon based and non-silicon) comprise a significant chunk of the ground-mounted solar plants. Another advantage of think film cells is that they are flexible.

What are the sub-components of a module and why should I know about these?

  • Aluminium frames
  • Cells
  • Glass
  • Encapsulant
  • Backsheet
  • Connectors


Why they are important?

Aluminium Frames Should be electrically compatible with the rest of the panel
Cells  Mainstay of PV technology that produces the power
Glass The glass should have high transmissivity and also be durable
Encapsulant Encapsulant used should have high resistance to UV and moisture-induced delamination
Backsheet Backsheet protects the active elements in the panel from environmental influence, especially from moisture, temperature fluctuations, chemicals and mechanical damages.

It protects the environment from the active electrical elements in the panels by acting as an insulator.

Connectors In addition to aiding electrical connections in PV solar arrays, connectors must meet the voltage and current requirements for their service while providing a low resistance point of contact.

What does a cell grade (grade A, B etc.) indicate?

This is what the different grades mean:

  • Grade A cells don’t have any visible defects, and their electrical performance are as per the listed specifications. Grade B solar cells have visible but tiny defects, but their performance isn’t affected. As an example, for Grade A solar cells, a slight bend of <=2.0 mm is permitted
  • Grade B cells will have a slight deviation of 2–5 mm.
  • Grade C solar cells give a performance off their specification, while Grade D solar cells are pretty much useless.

In India, you will find both Grade A and Grade B being made available by an Engineering, Procurement and Construction (EPC) companies, with the latter at a significantly less price.

What are the different sizes of solar modules?

The size for the solar panels will depend on the output (in watts) rating. Modules sizes usually used in solar plants are 250 W and 300–310 W. 250 panels have a size of about 65” by 40”.

How much do modules weigh and why is this important?

  • A typical solar panel weighs around 1–2 kg per square foot with the mounting structures. This is usually within acceptable limits of roof loading.
  • On a wattage level, a 250 W crystalline panel typically has a weight of 20 kg and 300 W panel has a weight of 22.5 kg.
  • Weight of the modules is important because it has to match the load bearing capacity of the roof.

The weight per square footing (100 sq ft) for some materials is given below:


Roofing Material Weight per 100 sq ft
Asphalt Shingle 85–110
Metal 35–65
Plastic polymer 30–135
Clay tile 270–815
Concrete 250–450
Slate 365–450
Wood 90–165


How are modules for rooftop application different from ground-mounted application?

  • High-efficiency (thus having better space efficiency) modules are more important for rooftops because of space is the main constraint in this case.
  • The key differences between rooftop and ground-mounted installation are the size of the plant and the mounting structures employed. Panels themselves are not much different.

Cost for import or taxes for the import

  • There is no basic customs duty for solar cells (and other components used in module assembly) and modules as against an import duty of 26–29% applicable to most goods.
  • As solar modules are often procured directly by the project developers, there is also no additional local tax.

The standard import duty for inverters in India is around 28%, but it is only around 5.15 for use in solar projects.


Why are Indian panels costly?

Indian panels are not costly; but Chinese panels can come at cheaper rates. The following are the reasons:

  • The larger scale of Chinese solar PV industry gives manufacturers an access to cheaper raw materials giving them an MSPs that are lower by >20%. (Minimum sustainable price (MSP) is the minimum price at which a company can sell its products while also getting adequate returns for the company to sustain.)
  • The cost of power is low.
  • Low-interest capital and subsidies provided by the Chinese Government also helps the manufacturers to sell the panels at very low price.

How do Chinese and Indian modules compare?

According to this Bijlibachao page, prices for good quality imported and Indian panels are similar. For bulk transactions, a good quality imported panels will cost Rs. 30–35 per watt versus Rs. 30–32 for good quality Indian panels. Note that majority of solar panels imported in India are Chinese, 70% in the financial year 2014–15. One of the reasons for such large share of Chinese modules is that unlike US and Europe, India hasn’t imposed any anti-dumping duties.

What about, say, German and Japanese modules?

More than 2/3rds of PV panels imported to India are Chinese, and this share has had an upward trend. In a comparison with the Chinese modules, German modules have no advantage in terms of performance. However, they will cost higher. Japanese modules are similarly costlier.

What are the warranties and guarantees provided by panel manufacturer?

Most mono-Si panels come with a warranty of 25 years. Good quality p-Si panels will also come with 25 years warranty. Thin films, as they degrade faster, come with a shorter warranty.

Manufacturers will usually guarantee a minimum performance for crystalline silicon panels as follows:

  • 90% of the rated output for around first half of 25 years, and
  • 80% of the rated output for the remaining of the 25 years.

Better that this guarantee, some panel manufacturer provide a linear performance guarantee. Under linear performance guarantee, usually a maximum degradation of 2.5% is guaranteed in the first year, and some value in the range of 0.5–0.7%/y thereafter.

  • Over 25 years of operation, a linear performance guarantee can increase cumulative generation of power by more than 5%, at the cost of a slight increase in the price of panels.

Responsible for panel’s warranty (EPC/Manufacturer)

  • Panel Manufacturer is responsible for panel’s warranty. EPC helps you to apply for the warranty and get it from manufacturer.

Insurance for the modules

  • Property Risk Insurance
    This insurance covers material damages due to external causes such as fire, theft, vandalism, sabotage, hail damage, snow load, lightning strike, overload, operational mistakes, clumsiness and negligence and animal bite.
  • Public liability
    Provides cover for any damage caused to third party property during installation of the panels. Essential for businesses engaged in Construction and Installation of solar panels and solar farms

What is the actual lifetime of a module? What determines the lifetime?

High-quality manufacturers provide a 25-year warranty on their solar panels. Good quality solar panels degrade by less than one percentage each year. So typically at the end of 25 years, the panels are still giving more than 80 % of rated output. Beyond 25 years, the panels will keep giving reasonable performance of >60% to 40–45 years, if they are well maintained!


What are the parameters for selecting a suitable panel?

For selecting a solar panel, you need to think about a lot more than just the quoted price as these panels will be giving you returns for a very long time.

  • Consider the parameters that will affect the field performance of the solar panel; these include positive tolerance, temperature co-efficient rating, PID and LID resistance and efficiency.
  • Compare the warranties and performance guarantees the panel manufacturer is providing, as it is an indicator of quality.
  • Look at the certifications the panel has to ensure the quality it claims and that it adheres to certain minimum production safety and testing requirements. This page lists the different Ministry of New and Renewable Resources (MNRE) certifications.
  • You will finally want to consider what kind of cells were used to manufacture the solar panel and select the one that best fits your application: monocrystalline, polycrystalline or amorphous. This is considered more in question 5.

Every panel needs to be judged on its own merit, based on these factors. Other than that, factors such as the country of manufacture and where the company is headquartered aren’t of significance.

What are the typical problems that arise if I go for low quality modules?

Because of lower efficiency, faster degradation, lack of features like anti-PID and low temperature coefficient, can give up to 30% lower output, adversely affecting investment returns.

Should I go for very high efficiency modules or compromise on efficiency for a lower cost?

It can make economic sense to go for high efficiency modules if area is the major constraint. High efficiency modules will generate more units over their lifetime from the same area. If land is not the major constraint, you could go for panels with a lower efficiency in the range of 15 to 17% while saving on the initial investment.

Why should modules be cleaned regularly and are there are other types of maintenance to be undertaken?

Solar panels need to be cleaned regularly as the dust can significantly reduce the power output. Irregular maintenance of your solar panels will also void any manufacturer/installer warranty. Cleaning a solar panel is not very different from a windshield, and you should do it once every 3 weeks for a healthy life of the panels.

 How to crosscheck that you got the modules from your EPC that you asked for?

  • The back label of the panels contains specifications like the power output and voltage. You should check them to be sure you got what you were promised.
  • You should also crosscheck with the manufacturer’s datasheet for parameters like efficiency, warranty, temperature coefficient and anti-PID feature.