You’ve heard of photovoltaic (PV) solar panels. You might have heard of concentrated solar power (CSP). But what about flexible solar panels?

In my experience as an energy consultant, clients often lament the slowing growth of solar capacity in Germany. As the government phases out subsidies for solar, households simply do not want to pay the high cost of purchasing and installing conventional panels. Flexible solar panels could help to provide them with an affordable alternative, and they offer serious upside.

In this case, “flexible” doesn’t refer to a power system’s ability to modify electricity consumption or production in response to variability. The term actually refers to physical flexibility. As in, solar panels that can be mounted on curved surfaces.

At first glance, this seems like a significant advantage over conventional solar. If we increase the amount of surfaces on which solar panels can be mounted, we should be able to expand solar capacity dramatically, and everyone should head over to Amazon and pick up a flexible solar panel ASAP. Not so fast. Before you conclude that we’ve solved climate change or you decide to go out and buy your own flexible solar panel, there are a few factors to consider.

A brief introduction to solar panels

A couple definitions up front: photovoltaic (PV) solar panels use sunlight through the photovoltaic effect in order to directly generate electricity. PV systems are not a new technology. Bell Labs demonstrated the first practical use of PV in 1954. I won’t get into the weeds about how this works. In short, PV cells are typically made of two thin slices of silicon. Each slice is seeded with either a positive or negative charge, establishing an electric field in between. When a photon of sunlight hits the cell, it knocks an electron free. This electron is then transferred to wires, along which it can flow like any other source of electricity. 

You might have heard that solar power cannot be stored without a separate storage (battery) system. This is mostly true for PV systems – even the most advanced batteries still have a hard time storing the power they generate. Thus, the electricity from PV is typically used immediately by the producer or fed into the power grid and transmitted to the consumers who need it. This brings us to the main criticism of PV: without adequate storage technology, solar power can only be used when the sun is shining. 

On the other hand, concentrated solar power (CSP) uses thermal energy from the sun. CSP makes use of mirrors or lenses to focus sunlight onto a small area (like burning something with a magnifying glass). The heat is then used to drive an engine as part of an electricity generator connected to the grid. Compared to PV, CSP generates much less electricity in cloudy conditions. However, CSP can utilize storage at a much greater level than PV, which is why solar farms typically are built using CSP. Moreover, similar technology can be used for heating and cooling. Due to divergence in costs over the past decade, CSP now represents less than 5% of total global solar capacity. However, the IEA estimates that global CSP capacity will double by 2022, from about 5 GW to 10 GW.

Flexible solar panels use PV technology. Unlike conventional panels, in which the silicon slices are typically housed between slates of glass, the PV cells in flexible solar panels are sandwiched between two pliable, insulated layers. These are what affords them their flexibility, but also, as we’ll discuss below, what makes them less durable.

(Photo from Md Juremi, Nor Rashidah & Mustafa, Ubaidillah & Agam, Mohd & Nur, Hadi & Hashim, Abdul Manaf & K. Arora, Vijay. (2011). Nanosphere Lithography: Fabrication of Periodic Arrays of Nanoholes. AIP Conference Proceedings. 1341. 296-300. 10.1063/1.3587005.)

The first flexible solar panels started hitting the market in the mid-2000s. Today, there are a variety of flexible panels available for a wide range of purposes, as we’ll revisit later in this post.

Use cases for flexible solar panels

The advantages of flexible solar panels can be summarized as follows: they are lightweight, flexible (obviously), and portable. Furthermore, they are relatively inexpensive and often do not need to be installed. These attributes lend themselves to a variety of unique use cases.

The most obvious use case for flexible solar panels is rooftop power generation. Presently, conventional solar panels are more efficient than their flexible counterparts at generating electricity on rooftops. However, irregularities like curved surfaces and chimneys often prevent them from being built in the first place. Moreover, certain roofs cannot bear the heavy load that conventional solar panels require. This is where flexible solar panels make a lot of sense. 

Theoretically, we could dramatically increase the proportion of sun-facing rooftop surfaces that generate electricity by employing a combination of conventional and flexible solar panels. Just check out Google’s Project Sunroof for estimates of potential rooftop solar generation. The model analyzes roof shapes in order to estimate savings via installation of conventional PV. Importantly, the model excludes roof shapes that are not amenable to rigid panels. Using flexible solar panels, a wider range of roof shapes could be exploited to generate green electricity.

While flexible solar panels would supplement conventional generation on household, commercial, and other building rooftops, they represent the only viable option for car rooftops. This is due to their curvature, which makes the use of conventional panels impractical. Furthermore, the lightweight, flat structure of flexible panels allows them to be installed on cars without significantly affecting aerodynamics or weight. The Lightyear One represents the first car to integrate solar panels directly:

As some of the panels are portable, they make for a great source of generation for people on the go. Hiking, camping, hunting, or sailing for several days at a time all represent activities where electricity might be useful but is not often readily available.

The downsides

While flexible solar panels are promising, they include several downsides compared to conventional solar. In fact, as we stand in 2019, flexible solar panels unequivocally should not be employed in any setting where conventional would be practical. The reasons for this are as follows:

Firstly, the most modern flexible solar panels are not as efficient as their conventional counterparts. Classic PV panels can convert up to 20% of incoming light energy into electricity, while the thin solar film in flexible panels can only muster 3-15%. This is why, as the current technology stands, flexible panels should be seen as a supplement to conventional solar wherever possible, rather than a replacement.

Next, as you might imagine, flexible solar panels are not as durable. While conventional panels typically last around 20 years, flexible models tend to survive around 5 years at the most. It is not difficult to find reviews of flexible panels that do not even last that long. Due to their thin structure, the solar cells are typically more susceptible to damage from heat and the elements. In general, the surface scratches more easily as it is not made of glass. Furthermore, if the cells are not generally of high quality to begin with, they will not last very long (although the same can be said for conventional panels). Due to this difference in useful life, flexible solar panels often come with much shorter warranties.

Finally, conventional panels sometimes offer the advantage of a sun-tracking system. This is one attribute that flexible panels give up in order to gain flexibility. Again, these panels should be used for a fundamentally different purpose than conventional.

Which flexible solar panel should you buy?

While flexible solar panels clearly offer some promise, understandably, potential buyers might have a bit of unease when doing their research. I searched “flexible solar panels” on Amazon and took a screen grab of the first few results:

The first thing you might notice is that one can expect to spend a few hundred euros/dollars on a flexible solar panel. The second thing I noticed is that there aren’t a ton of reviews for any of the products listed. “Amazon’s Choice” only has 38 reviews, and they aren’t great. When I do my online shopping, I tend to trust Amazon, but in this case, there just is not enough information available to be comfortable making a decision.

In my opinion, the key to finding a reliable solar panel would be to find one with a reliable solar cell manufacturer. Unfortunately, the big players in the solar industry with proven track records (SunTech, Trina Solar, and Motech Industries to name a few) have not dipped their toes into the flexible solar market. Some Google searching indicates that Giaride, Kingsolar, and Renogy seem to be popular options, but I cannot personally comment on their reliability. Sunpower, a more reliable, well-known brand, has flexible products on offer, but it is difficult to find consensus regarding their reliability.

With these factors in mind, I cannot in good conscience make a concrete purchase recommendation. There are indications that future innovations in this space will produce more reliable and efficient options, but at present, I can only conclude that purchasing a flexible solar panel is somewhat risky, although the price is significantly lower than conventional.

Future outlook

In this final section, I’ll highlight some of the most interesting areas of research regarding flexible solar cells.

  • For the past ten years or so, there has been ongoing research into the potential of printing solar cells onto paper. Here is a recent review of the literature demonstrating 9-13% efficiencies. Paper is not only significantly cheaper than other materials, but it is also recyclable and biocompatible. 
  • Sunflare, a manufacturer of solar panels since 2009, uses copper indium gallium selenide (CIGS) rather than silicon PV. Sunflare has come up with an innovative cell-by-cell manufacturing process. The company claims that this method, as opposed to traditional mass production of solar cells, ensures a higher level of reliability. While pricing information on Sunflare’s panels is limited, we can assume they are more expensive than other flexible panels given their novel production process. However, while the panels are designed for rooftop use, they are so lightweight that they can be installed with an industrial glue. Furthermore, Sunflare recently debuted a line of residential solar shingles. Time will tell if these are able to withstand more extreme temperatures.
  • Perovskite-based solar cells have been gaining traction as a potential cheap alternative to silicon in the future. Unlike other types of solar cells, this novel type of cell allows an electrical current to flow throughout the solar panel despite dead zones. This research is in its very early stages and the cells currently have a much shorter useful life than even other flexible solar cells.

Conclusion

While there are definitive advantages to flexible solar panels, the technology remains in its infant stages. Furthermore, the relatively thin market for these products makes research and consumer recommendations difficult.

In sum, flexible solar panels represent a small but positive development in renewable energy generation. While they won’t drastically reduce carbon emissions in the short-term, they could play an important role in harnessing as much of the sun’s energy as possible in the years to come.