Comparing Portable Solar Technologies
Posted on 03/05/2019 at 11:08 AM by Seth Hansen
Today we are going to focus 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 six specific technologies. Crystalline (c-Si), as designed for portable applications, three thin film technologies, including amorphous silicon (a-Si), copper indium gallium selenide (CIGS), organic (OPV) which is an emerging technology in the commercial space and gallium arsenide (GaAs) which is a very high-end choice.
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 each 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.
Flexibility: Crystalline is entirely rigid when framed in glass. Some portable panels can be backed on fiberglass and are semi-flexible but only to a degree before cracks and damage occur.
Durability: Crystalline can be quite brittle but more resilient with the proper encapsulation. Even with the ideal encapsulation crystalline technology is susceptible to damage when dropped or handled roughly.
Portability: Due to the weight and lack of flexibility, crystalline panels are only portable to a point. Smaller panels can be taken with you, but most crystalline panels are designed for static installations.
Power/Weight Ratio: Crystalline panels are quite heavy when compared to thin film solar technologies.
Temperature Coefficient: Crystalline is the technology most affected by heat and degrades 0.40% per degree C over 25C. (1)
Variable/Low-Light: While some manufacturers’ variations are better than others, as a whole, crystalline solar technology’s variable/low-light performance is poor.
Efficiency: 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, sub-25W panels.
Cost: Due to an ever-increasing scale, the cost of crystalline solar panels continues to drop making it the least expensive solar technology.
General Advantages: 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.
General Disadvantages: As a rigid solar technology crystalline is not ideal for portable applications or those where panels are constantly on the move and can’t always be handled with care. Cells are prone to cracking and entire panels can stop functioning. These issues can be mitigated somewhat by the encapsulation, but a crystalline solar panel will never be as durable as a flexible panel.
Copper indium gallium selenide (CIGS)
Flexibility: Can be manufactured on a flexible plastic substrate.
Durability: Impacts can deteriorate encapsulation layers leading to moisture ingress shortening the panel’s lifetime.
Portability: Although lightweight and rollable, CIGS panels degrade during long term storage. This doesn’t suit portable applications where panels may be stored for long periods between uses.
Power/Weight Ratio: While not the highest, CIGS solar technology is quite efficient when it comes to power/weight.
Temperature Coefficient: CIGS, much like crystalline, is greatly affected by heat and degrades 0.30% per degree C over 25C. (1)
Efficiency: 12% is common with higher efficiencies possible in lab conditions.
General Advantages: Flexibility, medium cost and moderate efficiency.
General Disadvantages: CIGS panels require “sun soaking” before they reach their rated output. Long term storage can permanently damage these panels since CIGS material degrades when not exposed to light. CIGS technology is prone to damage from impacts.
Amorphous silicon (a-Si)
Flexibility: Amorphous is incredibly flexible and can be rolled or flexed without damage.
Durability: Due to a monolithic construction, amorphous panels are very resilient to damage. If a portion of the panel is damaged that individual area shuts down, but the remainder will continue collecting energy. The performance of this material when damaged is superior to any other technology.
Portability: Amorphous panels are incredibly portable and ideal to be folded, rolled and provide power for those on the go.
Power/Weight Ratio: Amorphous is a very efficient power/weight technology.
Temperature Coefficient: Amorphous is affected less by heat than other technologies and degrades 0.16% per degree C over 25C. (1)
Variable/Low-Light: 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.
Efficiency: A real-world performance average of 6% with lab results up to 12%.
General Advantages: Amorphous is ultra-thin, lightweight, extremely durable, flexible and portable. It is the perfect technology for custom projects and can be integrated into designs more easily than rigid technologies.
General Disadvantages: 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).
Gallium arsenide (GaAs)
Flexibility: Epitaxial Lift-Off (ELO) GaAs can be mounted to flexible plastic substrates.
Durability: Not as fragile as glass but still very breakable. ELO GaAs panels are more durable because they are thinner and don’t have a sheet of glass but still less durable than other technologies. ELO GaAs panels don’t feature the same cell connection redundancy as other technologies (amorphous) and can’t be flexed too frequently without damage.
Portability: Can be manufactured in highly portable formats.
Power/Weight Ratio: ELO GaAs has the highest power/weight ratio. Rigid GaAs variations have power/weight ratios similar to crystalline.
Temperature Coefficient: GaAs is affected the least by heat and degrades 0.1% per degree C over 25C. (2)
Variable/Low-Light: Single junction GaAs solar cells have great low-light performance.
Efficiency: 27% efficiency with some cells 30+% efficient. (3)
Cost: Very high
General Advantages: High efficiency, lightweight, low-light performance.
General Disadvantages: Very high cost.
Flexibility: Organic solar panels are very flexible and can be rolled or flexed without damage.
Durability: OPV solar technology has been hindered by major short and long-term stability issues which prevent their practical use.
Portability: Can be manufactured in lightweight and portable formats.
Power/Weight Ratio: High
Temperature Coefficient: Dye-sensitized organics degrade 0.37% per degree C over 25C. (4)
Variable/Low-Light Performance: Medium
Efficiency: Range between 2-3% with perovskite organic variations at 11.6% or higher. (5)
General Advantages: Compatible with roll-to-roll printing and uses inexpensive, abundant materials.
General Disadvantages: Low realized panel efficiency. Panels degrade quickly, leading to a short panel lifetime. Perovskite organic variations degrade more rapidly and are not commercially viable due to harmful components such as lead.
Solar Comparison Chart
Solar is more than a single technology each method has its own set of strengths and drawbacks.
PowerFilm Solar has been developing and honing manufacturing of amorphous silicon for over 30 years and is now offering custom crystalline and gallium arsenide solar solutions as well.
We would love to hear more about your power needs, the different solutions we can create and help determine what is best for you.
Contact us today and let’s start a conversation.
Categories: Solar Education