Editorial Feature

Solar (PV) Panel Comparison for Efficiency, Material, Voltage

Topics Covered

Introduction
Monocrystalline Panels
     Pros and Cons of Monocrystalline Solar Panels
     Applications of Monocrystalline Solar Panels
     Key Products
Polycrystalline or Multicrystalline Panels
     Pros and Cons of Multicrystalline Solar Panels
     Applications of Polycrystalline Solar Panels
     Key Products
HIT (Heterojunction with Intrinsic Thin layer) Solar Cells
     Panasonic HIT™
Alternatives
     Thin Film Solar Panels
     Dye-Sensitized Solar Panels

Introduction

Solar panels are a renewable technology that generates heat or electricity using sunlight as a source of energy. They can be utilized as an element of a larger photovoltaic system for electricity generation and supply in residential and commercial applications. Every module is rated based on its DC output power under normal test conditions, typically with a value of 100-320 W.

The solar panel market has shifted from trial stage to early adopter stage. According to ResearchMoz, the global market for solar panels is expected to reach US$180.7 billion by 2021. The Chinese government’s significant investment in solar PV is the major driving factor. China was the market leader in terms of the installed capacity as of 2015, having a total capacity of 43.530 MW. Germany, Japan, and the United States were holding the second, third, and fourth place, respectively.

With increasing pressure on fossil fuels and the significant developments in the solar energy industry, solar panels are expected to play a major role to address the energy demand. A number of research activities have been carried out all over the world to increase the efficiency of solar panels in order to handle this energy crisis.

For instance, a coating developed by the researchers at University of California Riverside could increase the efficiency of solar panels by 30% or more. In another research, Stanford engineers developed “invisible wires”  that could improve the efficiency of traditional solar cells from 20% to 22%. This article discusses the different types of solar panels as well as the commercially available solar panel products offered by major manufacturers.

Monocrystalline Panels

Image Credit: Martin D. Vonka | Shutterstock.com

Monocrystalline or single crystal solar PV panels are one of the oldest, most reliable, and most efficient ways to generate electricity from solar energy. Here, each PV module is fabricated from a single silicon crystal. The silicon is purified, melted, and then crystallized into ingots, which are then cut into thin wafers to produce individual cells. The typical color of monocrystalline PV module is black or iridescent blue.

Pros and Cons of Monocrystalline Solar Panels

The following are the key benefits of the monocrystalline solar PV panels:

  • Longevity
  • Efficiency is high in the range of 15-24% as they are fabricated from the highest grade silicon, making them cost effective in the long term
  • Lower installation costs
  • Space-efficient
  • Non-hazardous to environment
  • Greater heat resistance
  • More electricity
  • Embodied energy

High initial cost and fragility are the major drawbacks of monocrystalline solar panels. The monocrystalline silicon is produced using the Czochralski process, which involves significant silicon wastage.

Applications of Monocrystalline Solar Panels

Monocrystalline solar panels are generally utilized for large scale solar applications, such as commercial and residential solar installations. They can also be employed for smaller scale applications, and the size of the panel is based on the type of application. Smaller monocrystalline solar panels (5, 10, 25 W) can be used to charge laptops, digital cameras, phones etc., while larger panels (40, 80, 130 W) panels can be used to power appliances such as microwaves or fridges, gardening features or outdoor lighting systems, or integrated into a solar array to power houses located in remote areas.

Key Products

Mitsubishi Electric offers a wide range of high-performance single crystal PV modules for various applications. The company’s monocrystalline range includes the following products:

  • PV-MLT Series
    • PV-MLT265HC, 265 Wp
    • PV-MLT260HC, 260 Wp
    • PV-MLT255HC, 255 Wp
  • PV-MLE Series
    • PV-MLE265HD, 265 Wp
    • PV-MLE260HD, 260 Wp
    • PV-MLE255HD, 255 Wp
  • PV-MJT Series
    • PV-MJT250GB, 250 Wp
    • PV-MJT245GB, 245 Wp
  • PV-MDT Series
    • PV-MDT205HB, 205 Wp
    • PV-MDT200HB, 200 Wp
    • PV-MDT195HB, 195 Wp

Yingli Solar’s PANDA technology is ideally suited for residential and commercial projects where energy input is required. The company offers high power density solar modules featuring n-type silicon-based high-efficiency solar cells. These modules are 8% to 18% more efficient compared to traditional p-type modules.

Yingli Solar’s PANDA 60 Cell Series comprises the following module types:

  • YL300C-30b, with peak power of 300 W
  • YL295C-30b, with peak power of 295 W
  • YL290C-30b, with peak power of 290 W
  • YL285C-30b, with peak power of 285 W
  • YL280C-30b, with peak power of 280 W
  • YL275C-30b, with peak power of 275 W

Panda 60 Cell Black and PANDA 54 Cell 250 W are the other products offered by Yingli Solar.

Suntech Power Co., Ltd. also manufactures a wide range of monocrystalline PV modules:

  • STP275S-20/Web - 60-cell all-black 4-busbar monocrystalline solar module with performance efficiency of up to 16.9%
  • STP280S-20/Wem - 4-busbar monocrystalline 60-cell solar module with performance efficiency of up to 17.2%
  • STP280S-20/Wew - 4-busbar monocrystalline 60-cell solar module with performance efficiency of up to 17.2%
  • STP290S-20/Web – A combination of advanced cell and module technology with conversion efficiency of up to 17.8%
  • STP295S-20/Wew - A combination of advanced cell and module technology with conversion efficiency of up to 18.1%
  • STP330S-24/Vem - 72-cell Vem module specially developed for large scale projects and achieves a conversion efficiency of 17%

Polycrystalline or Multicrystalline Panels

Image Credit: France DC | Shutterstock.com

Polycrystalline or multicrystalline panels use solar cells that are made from multifaceted silicon crystals. The appearance of polycrystalline cells is not as uniform as the monocrystalline solar cells. They have a surface with a random pattern of crystal borders rather than the solid color of single-crystal cells. Since a low-cost silicon is used to fabricate polycrystalline cells, their efficiency is typically in the range of 12%-14%, a value slightly less than the monocrystalline cells, but much higher than solar technologies such as thinfilm.

Pros and Cons of Multicrystalline Solar Panels

The following are key advantages of the multicrystalline panels:

  • The production process is simple, cost-effective, and reduces silicon waste compared to single crystal panels
  • Heat tolerance is slightly lower than single crystal panels
  • Temperature co-efficient is higher than single crystal panels, meaning that the panel output will drop with increasing temperature; however these variations are minimal practically

The disadvantages of the polycrystalline panels are as follows:

  • Lower conversion efficiency compared to monocrystalline panels due to the use of low purity silicon
  • Lower space-efficiency
  • Less aesthetically pleasing compared to single crystal and thinfilm panels

Applications of Polycrystalline Solar Panels

Polycrystalline solar panels are the most used PV panels on the Earth. They are offered in a wide range of power ratings, from 5 W to 250 W or more, for use in both residential and commercial installations.

Key Products

Sharp is one of the companies that provide high-performance, highly reliable polycrystalline PV modules. The company offers a wide variety of products that fulfill the conditions for various installation locations.

Yingli Solar is another company operating in this field, offering high-performance polycrystalline solar panels with an outstanding efficiency rating of up to 16%. YGE 60 Cell Series and YGE 72 Cell Series are the two products offered by Yingli Solar.

The following module types are covered in the YGE 60 Cell Series:

  • YL275P-29b, with peak power of 275 W
  • YL270P-29b, with peak power of 270 W
  • YL265P-29b, with peak power of 265 W
  • YL260P-29b, with peak power of 260 W
  • YL255P-29b, with peak power of 255 W
  • YL250P-29b, with peak power of 250 W

The following are the module types covered in the YGE 72 Cell Series:

  • YL325P-35b, with peak power of 325 W
  • YL320P-35b, with peak power of 320 W
  • YL315P-35b, with peak power of 315 W
  • YL310P-35b, with peak power of 310 W
  • YL305P-35b, with peak power of 305 W
  • YL300P-35b, with peak power of 300 W

Another key player operating in this field is Suntech Power, who supplies multicrystalline solar PV modules to meet the requirements of commercial, residential, or utility scale solar projects worldwide. The STP265-20/Wem and STP320-24/Vem are the polycrystalline solar panel products offered by Suntech Power. The STP265-20/Wem is a cost optimized PV module with 60 polycrystalline solar cells. The STP320-24/Vem is a PV module featuring 72 multicrystalline solar cells, with a proven performance efficiency of up to 16.5%.

Mitsubishi Electric also supplies a wide range of polycrystalline PV modules for various applications:

  • PV-TD Series
    • PV-TD195HA6, 195 Wp
    • PV-TD190HA6, 190 Wp
    • PV-TD185HA6, 185 Wp
    • PV-TD180HA6, 180 Wp
  • PV-TJ Series
    • PV-TJ235GA6, 235 Wp
    • PV-TJ230GA6, 230 Wp
    • PV-TJ225GA6, 225 Wp
    • PV-TJ220GA6, 220 Wp
    • PV-TJ210GA6, 210 Wp
  • PV-UJ Series
    • PV-UJ235GA6, 235 Wp
    • PV-UJ230GA6, 230 Wp
    • PV-UJ225GA6, 225 Wp
    • PV-UJ220GA6, 220 Wp
    • PV-UJ210GA6, 210 Wp

HIT (Heterojunction with Intrinsic Thin layer) Solar Cells

HIT solar cell has become the subject of intense research within the photovoltaic research community, due to its low process temperature in comparison with crystalline silicon (c-Si) solar cell and comparatively high efficiency (η). This solar cell structure uses thin intrinsic amorphous silicon layers as a surface passivator and also as a buffer layer at the top and bottom surfaces of n-type crystalline silicon (c-Si) wafer. A highly doped n+-type bottom layer acts as a back surface field, while a thin p-type a-Si top layer is used as an emitter. Sanyo Electric Company, a Japan-based company and part of Panasonic, invented the crystalline silicon wafer–based hetero-junction solar cell concept.

Panasonic HIT™

The photovoltaic module HIT™ solar cell is the original hetero-junction type, comprising of amorphous and monocrystalline silicon layers. The presence of amorphous layers in the cell avoids electron recombination, reducing the associated power loss and delivering industry-leading performance. The unique structure of Panasonic HIT™ allows it to maintain high conversion efficiency and performance even at hot temperatures, generating more energy throughout the day.

Key Features

The key features of the Panasonic HIT™ are as follows:

  • High temperature stability
  • High efficiency, roughly 27% more power when compared to 260 W competitor panels
  • Maximum use of available roof space
  • Generates higher power for the same system size
  • More power per area
  • RoHS complaint
  • PID resistant

Key Products

Panasonic offers the following HIT PV modules:

  • HIT 330 (UL)
  • HIT 330 (IEC)
  • HIT 325 (UL)
  • HIT 325 (IEC)
  • HIT 320 (IEC)
  • HIT 294 (IEC)
  • HIT 240 (IEC)
  • HIT 240 (UL)
  • HIT Double 225 (IEC)

Alternatives

Thin Film Solar Panels

Image Credit: Science Photo | Shutterstock.com

Thin film solar panels are mainly produced by applying thin layers of semiconductor material onto different types of surfaces, like glass. When compared to silicon module solar cells, thin film solar cells are durable, simpler, lighter, and easier to develop. Rather than molding or slicing crystalline silicon, the silicon material used in thin film panels does not have a crystalline structure. As such, there are four major types of thin films: amorphous silicon; copper, indium, gallium, selenide (CIGS); cadmium telluride (CdTe); and organic photovoltaic cells (OPC).

Energy conversion efficiency of thin film solar cells is much lower than the crystal silicon PV cells. A volume-produced PV module based on the tandem model of stacked microcrystalline and amorphous silicon layers exhibits an energy conversion efficiency of roughly 8.5%. A triple-layer cell consisting of two types of microcrystalline and amorphous silicon can achieve a conversion rate of 10%. Sharp is involved in the mass production of Lumiwall Illuminating Solar Panel, which is a thin-film solar cell with integrated LEDs. Lumiwall Illuminating Solar Panels were deployed in the portico and corridor of the Yodoyabashi Redevelopment Building situated in Chuo Ward, Osaka, Japan. The solar panels produce power during the daytime and the integrated LEDs render beautiful light at night.

Pros and Cons of Thin Film Solar Panels

The following are the key advantages of the thin film solar panels:

  • Low manufacturing costs
  • Versatile
  • Can be produced at industrial scale, making them more economical than crystalline-based solar cells
  • Have a uniform appearance
  • Can be made flexible
  • Shading and high temperatures do not have any major effect on performance.
  • Can be used in situations where space is not a constraint

The drawbacks of the thin film solar panels are as follows:

  • Low efficiency
  • Degrade faster than mono- and polycrystalline solar panels
  • Not suitable in most residential situations
  • Require plenty of space

Applications of Thin Film Solar Panels

Thin film solar panels are mainly used in electronic powering circuits, home light applications, and in solar fields. As it is possible to make the cell transparent, building products for architectural applications like skylights and windows that use these cells can be designed.

Dye-Sensitized Solar Panels

Based on nanometer and molecular-scale components, dye-sensitized solar cells (DSC) are next-generation solar cells that offer an economically and technically viable option to existing p–n junction PV devices compared to traditional systems. DSCs make it possible to design unique solar cells with a large flexibility in color, shape, and transparency, and can be manufactured at a lower cost than that of traditional devices.

As DSC cells can be fabricated using a simple process of heating curing and coating, extensive research is going on in this field. Sharp  had attained the record-breaking conversion rate of 11.1%.

Pros and Cons of Dye-Sensitized Solar Panels

The following are key advantages of the dye-sensitized solar panels:

  • Low cost
  • Good price/performance ratio
  • Operate in low light and at wider angles
  • Operate at lower internal temperatures
  • Long life
  • Mechanical robustness

The drawbacks of the dye-sensitized solar panels are as follows:

  • Cannot be used for large-scale deployments where higher-cost and higher-efficiency cells are more practical
  • Liquid electrolyte is not stable at variable temperatures and can freeze at low temperatures, cutting power generation and causing potential physical damage
  • Electrolyte solution contains volatile organic solvents

Applications of Dye-Sensitized Solar Panels

Dye-sensitized solar panels are suitable for outdoor applications like window systems as well as in rooftop solar collectors.

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