Originally published 3-5-2019
When you think of solar panels you might picture large expansive solar fields or an array of solar panels installed on a home near where you live.
While “solar farms” and building-integrated solar are large segments of the overall solar market, there are portable options as well.
Today’s post focuses on portable solar technologies, comparing flexibility, durability, portability, power/weight ratio, temperature coefficient, variable/low-light performance, efficiency, and cost.
We’re going to review three specific technologies in detail, Crystalline (c-Si), as designed for portable applications, amorphous silicon (a-Si), and copper indium gallium selenide (CIGS). We will also address two other solar technologies organic (OPV), an emerging technology in the commercial space, and gallium arsenide (GaAs), a highly efficient but costly solar technology.
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Before we begin, let’s define these categories:
Flexibility: Ability to be flexed (important in design integration), up to and including rolling or folding for storage.
Durability: Resistance to damage from dropping, physical impacts, rough handling, and exposure to elements.
Portability: The ability to easily transport the solar panel.
Power/Weight Ratio: Power generated per lb/kg (important for weight-constrained designs and portable applications).
Temperature Coefficient: How each technology is affected by heat.
Variable/Low-Light: Ability to harvest energy when partially shaded or in indoor or low-light environments.
Efficiency: A laboratory measurement of how solar technology converts light to energy in specific environmental conditions, called Standard Test Conditions (STC, 25C with 1000 W/m2 at 1.5 AU).
Cost: The expense of the technology relative to other solar options.
Crystalline: Portable panels are commonly backed on fiberglass and are semi-flexible to a degree before cracks and damage occur.
Amorphous Silicon: Incredibly flexible and can be rolled or flexed without damage.
CIGS: Can be manufactured on a flexible plastic substrate.
Crystalline: Can be quite brittle but more resilient with the proper encapsulation. Crystalline technology is susceptible to damage when dropped or handled roughly, even with an ideal encapsulation.
Amorphous Silicon: Very resilient to damage due to a monolithic construction. If a portion of the panel is damaged, that particular area shuts down, but the remainder will continue collecting energy. The performance of this material when damaged is superior to any other technology.
CIGS: Impacts can deteriorate encapsulation layers leading to moisture ingress, shortening the panel’s lifetime.
Learn more about amorphous silicon’s extreme durability.
Crystalline Silicon: Portable to a point due to their weight and lack of flexibility. Smaller panels can be taken with you, but often crystalline panels are designed for static installations.
Amorphous Silicon: Incredibly portable and ideal to be folded, rolled, and provide power for those on the go.
CIGS: Although lightweight and rollable, panels degrade during long-term storage. This doesn’t suit portable applications where panels may be stored for long periods between uses.
Crystalline: Semi-flexible crystalline panels have higher power-to-weight ratios than traditional rigid framed panels.
Amorphous Silicon: Achieves exceptionally high power to weight ratios using ultra-lightweight substrates and encapsulants.
CIGS: While not the highest, CIGS solar technology is quite efficient when it comes to power/weight.
Crystalline: Most affected by heat and degrades 0.40% per degree C over 25C. (1)
Amorphous Silicon: Amorphous is affected less by heat than other technologies and degrades 0.16% per degree C over 25C. (1)
CIGS: CIGS, much like crystalline, is greatly affected by heat and degrades 0.30% per degree C over 25C. (1)
Learn more about how temperature affects different solar technologies.
Crystalline: High-quality whole cells, like the Sunpower wafer we use in Soltronix products, have excellent low light performance while low quality and laser-cut cells have poor performance.
Amorphous: Amorphous has great low-light or indoor performance collecting more energy in lower light situations than other technologies. PowerFilm Indoor Solar material performance is guaranteed in indoor light down to 200 lux and will work below that light level.
Learn more about how shade affects different solar technologies.
Crystalline: 18-22% and up to 23%+ at the very top end. More commonly in the 15-18% range for mass-produced cells, a value that can drop to 8-15% once cells get cut to make small,
Amorphous Silicon: A real-world performance average of 6% with lab results up to 12%.
CIGS: 12% is common, with higher efficiencies possible in lab conditions.
Crystalline: Due to an ever-increasing scale, the cost of crystalline solar panels continues to drop, making it the least expensive solar technology.
Amorphous Silicon: Medium
Crystalline: Depending on the manufacturer, crystalline solar panels can be quite efficient and cost-effective, making them an ideal solar technology for static or relatively static installations with full sun exposure that don’t require extreme durability or flexibility.
Amorphous: Amorphous is ultra-thin, lightweight and highly durable, flexible, and portable. It is ideal for applications that require extreme durability and flexibility. a-Si is the perfect technology for custom projects and can be integrated into designs more easily than rigid technologies.
CIGS: Flexibility, medium cost, and moderate efficiency.
Crystalline: As a rigid solar technology, crystalline is not ideal for portable applications where panels are constantly moving and can’t always be handled with care. Cells are prone to cracking, and entire panels can stop functioning. Expert design, materials, and construction are required to ensure crystalline panels can withstand demanding portable applications.
Amorphous Silicon: Due to manufacturing scale, amorphous is more expensive than other technologies and requires more area to generate the same power (important for space-constrained applications).
CIGS: CIGS panels require “sun-soaking” before reaching their rated output. Long-term storage can permanently damage these panels since CIGS material degrades when not exposed to
light. Additionally, CIGS technology is prone to damage from impacts.
Gallium arsenide (GaAs)
Gallium arsenide, while exceedingly expensive, can be made in a flexible, portable, and high power/weight ratio format. This technology is only viable for applications where costs are not a driver, and someone is looking for a lightweight solution with the most power possible in a given area.
Organic PV is a known quantity in the solar field but has yet to become a manufacturable technology in a commercially viable way. It promises to be very flexible, portable, and low-cost, but at this time, those promises are yet to be fully realized.
Solar Comparison Chart
Solar is more than a single technology. Each technology comes with its own set of strengths and drawbacks.
Depending on the application, any number of solar technologies can satisfy your particular needs.
PowerFilm Solar has been developing and honing manufacturing of amorphous silicon for nearly 35 years and offers a host of custom crystalline solar solutions as well.
We would love to hear more about your power needs, suggest solutions we can create, and help determine what is best for you.
Contact us today and let’s start a conversation.
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(1) Outdoor performance of organic photovoltaics: Diurnal analysis, dependence on temperature, irradiance, and degradation p.9
(2) Outdoor Performance of a Thin-Film Gallium-Arsenide Photovoltaic Module p.4
(3) National Renewable Energy Laboratory
(4) Ruiz Raga, Sonia & Fabregat-Santiago, Francisco. (2013).Temperature effects in dye-sensitized solar cells (p.2333)
(5) Franhofer ISE Photovoltaics Report p.26