What are the different Solar PV Technologies?

*Jambo,?habari?

Currently on the market in many countries across Africa, they are a number of solar panels that are on sale from different manufacturers. They come in various appearances and perform differently. So do you understand how to differentiate them? Do you have an idea of their performances? Would you know which ones to install on your company’s premises (or domestic) roof? In this section, we will be talking about PV technologies commercially available, their module degradation and the certification process.

?Solar PV Technologies

Solar PV technologies have evolved over the time and exist in 3 classes:

• Crystalline silicon modules (80% of total global market)

Crystalline silicon (c-Si)?modules consist of PV cells connected together and encapsulated between a transparent front (usually glass) and a backing material (plastic or glass). They are 2 types here.

Mono crystalline wafers?are cut from a big crystal ingot in an expensive process and?multi-crystalline wafers?(cheaper) are made from a variety of methods.

• Thin Film modules (17% of total global market)

These modules are made with a thin-film deposition of a semiconductor on a substrate. The desire to reduce cost of cells led to the research and development on thin-films. Consequently, they are less efficient and less expensive than crystalline silicon modules. There are various types:

Amorphous silicon (a-Si)?is the non-crystalline form of silicon. It can be deposited onto a variety of flexible substrates. Its low cost makes it suitable for applications where low cost is more important than efficiency (I can see big smiles here, lol).

Cadmium Telluride (CdTe), the compound of cadmium and tellurium, consists of a semiconductor film stack deposited on a transparent conducting oxide-coated glass.

Copper Indium Selenide (CIS)?consists of a compound of copper, indium and selenium.

• Advanced Concepts (3% of total global market)

There some advanced concepts that are currently developed, combining the different types mentioned above with other materials.

?Degradation of the modules

One thing that has for sure been experienced by owners of solar systems is that the performance of a PV module will decrease over time. Over the 25-30 years of their useful life, solar panels output will actually gradually decrease. Multiple factors affect the degree of degradation and some of them are listed below:

• From first time they are used, crystalline modules suffer irreversible?light-induced degradation (LID). This initial degradation occurs due to defects that are activated on initial exposure to light. Depending on the wafer and cell quality, the LID can vary from 0.5 % to 2 %.

Amorphous silicon (a-Si) cells degrade on a similar light process and could lose between 10%?and 30% percent in the power output of the module in the first six months. Thereafter, the degradation will stabilise at a much slower rate.

• Humidity?is another factor. The moisture from the environment may lead to electrochemical reactions that can result in corrosion, causing significant losses in PV module performance. This phenomenon most particularly monitored in tropical regions, for instance Gabon and Cameroon. Arid areas like countries of southern Africa will not suffer too much from this problem.
• We mentioned on an earlier post that the?temperature?does have an impact on the modules. For many cities and rural places, operating conditions above 25 °C (Temperature at which manufacturers rate their module), the solar modules are losing, depending of the type, around 0.3% to 0.5% of power for every degree increment.
• Other environment factors like?pollution and dust, common across all the major African cities, do cause?soiling?of modules, impacting their performances.
• The?material quality?and the?manufacturing process?do matter. Certainly for the African manager in a business agglomeration of Cotonou or the customer in the streets of Lomé, you will not be able to assess accurately these criterions, but you should make an effort to check that panels are coming from a reputable module manufacturer. From pictures provided above, I am hoping you could at least make the difference from their appearance.

Once they settle, altogether you could expect PV modules to have a long-term power output degradation rate of between 0.3% and 1 % per annum. Their efficiency is covered by the table below:

?With that in mind, I would expect everybody now to have an idea of the kind of performances you could expect from the different Solar panels you will encounter on the local or international markets.?And yes you guess it right, the more efficient a panel is, the more expensive it will be in general.

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PLEASE DO YOURSELF (AND THE PLANET) A FAVOUR, DON’T JUST LOOK AT THE PRICE,?THINK ABOUT THE PERFORMANCE AS WELL!!

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Certification

To ensure good quality, solar panels should normally go through certification. The?International Electrotechnical Commission (IEC)?has produced commonly accepted standards. Standards IEC 61215 (for crystalline silicon modules) and IEC 61646 (for thin film modules) include tests for thermal cycling, humidity and freezing, mechanical stress, hail resistance and performance under some fixed test conditions.

I hope you’ll be able to differentiate solar panels and pay more attention when making a purchase. I want you to get value for your precious money!

As usual enjoy yourself and look after our planet…Switch this device off when you’re done!!

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*?Jambo,?habari:?“Hello, how’s it going?” in Swahili, national language spoken in Kenya, Tanzania, Uganda

?Summary

Notions to remember

• Cristalline Silicon Modules
• Mono crystalline Module
• Multi-crystalline Module
• Thin-film Modules
• Amorphous Silicon Modules
• Cadmium Telluride
• Copper Indium Selenide
• Advanced Concepts
• Module degradation factors
• Light
• Humidity
• Temperature
• Pollution and Dust
• Material quality
• Manufacturing process
• Certification
• Standards IEC 61215 for crystalline silicon modules
• Standards IEC 61646 (for thin film modules)

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Sources:

1. Energy Science, Principles, Technologies, and Impacts, 2nd?Edition – John Andrews, Nick Jelley
2. Photovoltaic Solar Power Course – Prof John I B Wilson, Heriott Watt University
3. Sustainable Energy – Without the hot air – David JV MacKay
4. Utility-Scale Solar Photovoltaic Power Plants – A Project Developper Guide – IFC 2015
5. Utility Scale Solar Power Plants – A Guide For Developers and Investors – IFC 2012