Smart Clothing: PV-Powered Future Fabrics

** From NanoMarkets LC ** Just in time for the holidays, for that technophile-slash-fashonista in your life: Tommy Hilfiger’s new $599 solar panel jacket, which combines a removable solar pack with “prestigious Abraham Moon wool for a traditional twist,” the designer proclaims. The jacket incorporates several snap-off amorphous silicon (a-Si) solar panels on its back (from supplier Pvilion), hooked to a battery pack in the front pocket with a double USB port.

The companies claim the solar panels can fully charge this battery, which itself can fully charge a standard 1500 mAh mobile device up to four times. Rather importantly they don’t say how long that would take, though the battery also can be charged by laptop or external outlet.

So far the general Internet response to the solar-powered jacket has largely been head-scratching curiosity and “what won’t they dream up next.” Nevertheless, a month into their trial debut the jackets appear to be in demand with limited remaining availability. More broadly, we see this as one of the more visible recent examples of the next trend in consumer electronic devices: truly wearable electronics, or “smart clothing.”

Wearable Electronics and Smart Clothing

The two earliest types of wearable computing concepts have been smart watches and smart glasses, both of which basically move smartphone functionalities into a wearable context. Most of the smart glasses being developed arguably go a step further to mesh communications capabilities with additional visual and other sensual enhancements (including augmented reality), and in a much more visible profile.

Ultimately, true wearable computing will evolve to be more than a device worn or strapped to (or even someday implanted within) the body — it will be integrated into clothing itself. Thus, “smart clothing” blurs the lines between fabrics and electronics with items that merge with the body of the wearer in both form and functionality. These incorporate various computing devices and sensors and energy harvesting — and even fabrics that incorporate some of those capabilities themselves — for various kinds of applications, from fitness metrics to pregnancy monitoring, even biochemical hazard protection.

The Hilfiger jacket isn’t the only solar-powered clothing we’ve seen. Other examples include:

• Pauline van Dongen created wearable solar clothing in 2013: a dress with 72 flexible solar cells and a coat with 48 rigid solar cells. Each was said to be capable of charging a smartphone to 50% over an hour in full sunshine.
• LLBean’s Solar PowerCap has a solar panel in the brim to charge a (non-replaceable) NIMH battery and power four LED lights, “even if it’s not in direct sunlight.” A full charge is said to provide more than 21 hours of light.
• The ILLUM cycling jacket concept incorporates printed electroluminescent ink and printed photovoltaic technology, with the functional parts placed outside the jacket and into several ergonomic panels.

Solar: Powering the Smart Clothing Revolution

Those sensing functionalities, plus the connectivity to collect and consolidate data to make sense of it all, involve some fairly significant power consumption. Energy to power smart clothing could come from a variety of sources: a small solar panel, an antenna that collects ambient radio wave energy, a thermoelectric material that absorbs body heat, or piezoelectric devices that collect energy from movement.

Thus NanoMarkets sees energy harvesting and power generation technologies combined with energy storage systems as the next step in developing practical wearable electronics, complementing one another and demonstrating ways to charge smart textiles without having to “plug in” the garment.

A key factor in any “smart clothing” is that the technology lends itself to wearability, i.e. flexible and lightweight. Also (and rather obviously) the small area afforded by clothing presents a challenge for any kind of energy generation.

Thus this is a market for alternative solar PV technologies to shine. NanoMarkets suggests that organic PV ultimately is a prime material choice for PV on fabric, as it can be produced on large-area, low-cost plastic planar substrates. Dye-sensitized solar cells (DSC) also are emerging as a contender.

The formfactor lends best to flexible lightweight thin-film technologies which by their nature have lower efficiencies, and in a small available surface area. In the past, research efforts have attempted to bridge these gaps:

• Sefar (Switzerland) has developed a transparent front electrode on a fabric base for flexible solar cells. The synthetic fabric is coated on one side with a gas-tight, transparent layer; it offers light transmittance of over 85%, and can be processed using the roll-to-roll method. The conductivity in the fabric is created by means of woven-in metal wires (R < 1 Ω/sq).
• The EU-funded research project Dephotex (2008-2011) worked to demonstrate flexible solar cells that can be readily integrated into fabrics, identifying suitable materials for the solar cells and different techniques for implanting them into the fabric. Despite needed improvements to conversion efficiency and flexibility, a number of companies are said to have expressed interest in collaborating with Dephotex to commercialize photovoltaic fabrics.
• Researchers at Beijing National Laboratory for Molecular Sciences (January 2013) have integrated power fiber for energy conversion and storage, utilizing a highly flexible solar cell fiber and pseudocapacitive fiber employing redox polyaniline that converts and stores solar energy in one device.
• China’s Fudan University has developed a new method to produce flexible, wearable DSC textiles by stacking two textile electrodes.
• PowerFilm Solar uses fabric (among other materials) as non-traditional backing for solar panels, from portable chargers up to a canopy-size foldable shelter.
• The U.S. Army and MC10 have collaborated to scale up stretchable solar panel prototypes and assess their efficiency as functional battery chargers, including flexible solar energy harvesters sewn into uniforms and backpacks.

Remember the Consumer

Before planning your wardrobe around powered “smart clothing,” we urge everyone to remember the biggest question about this sector: end-market appeal. While the current generation of smart glasses do seem to be gaining momentum in some industrial use cases, the general consensus so far (especially about Google Glass) is that they look strange when they are worn — meaning they’re a non-starter for consumer market appeal. Newer entrants are promising more understated styles much closer to “normal” glasses as possible, even if it means reducing their functionality (and price-point).

The lesson: any hope to blend electronics functionality into a truly wearable context, targeting beyond niche applications such as military into the large volumes (and large revenues) promised with broad consumer adoption, must demonstrate a clear usage case on top of style considerations. Solar-powered fabrics are not easy to wear; they must incorporate a robust design (perhaps Hilfiger’s choice of wool helps here), and the purpose of integrating PV has to be clearly highlighted in the product’s design. Bulky, unattractive clothing won’t be appealing to anyone in a mass-market context. As a counterexample, we recall the proposed Solar Coterie “solar bikini” design that incorporated strips of flexible solar cells. This would seem not only difficult to wear, but rather counterintuitive to combine electricity with clothing meant to be immersed in water!

Fashion designers are key to the success of any fashionable clothing, and their interest in smart clothing is very important for the introduction and success of the smart fashion sector. For now, we observe that fashion designers prefer illuminated clothing and sound-reactive products in their offerings, which represents a very niche and smaller market. However, we are starting to see indications that designers would prefer clothing that incorporates energy storage and health sensing, which will result in greater penetration of smart clothing in fashion.

NanoMarkets does see a bright future for smart clothing with built-in energy harvesting and storage, particularly solar. Although it’s in infancy at the moment, we see this gradually growing in time.