Before my trip to Morocco back in March I decided to buy a solar charger backpack. I knew I was going to be making heavy use of several portable electronic devices (iPhone, camera, GPS) during my trip and would be in places where power would be hard to find. Much of the time I’d be on foot, so I wasn’t sure I could count on using the 24V charger in the truck, and since I didn’t know if I’d have access to a good power supply at the bivouac every evening, I didn’t think a battery pack would be the right choice. I needed something else. Sunlight seemed like the perfect solution, and it would give me a good excuse to test a new technology with the liberating promise of independent power.
The local outdoors store I shop at didn’t offer a solar charger backpack. Although they had solar base stations and stationary models for campsites, I thought a backpack would be more practical since I wouldn’t have to worry about remaining in a single place or having it stolen. Additionally, since I didn’t really know how mature this technology was, I figured if it didn’t work very well as a charger, at least it wouldn’t be a complete waste; it could still be useful as a plain old backpack.
So I turned to the Internet. I did a few searches to see what product info I could find. I did find a few reviews, but most of them seemed to be summaries written from the available product literature. None of them gave much detailed information, and none contained firsthand accounts of actual use. Unfortunately, I didn’t look carefully enough at the bags from Voltaic Systems. With hindsight, they’re the only ones that seem to have accurate product information, as well as an easy solution for charging camera batteries.
Having missed that, and without any objective criteria to evaluate the product info I found online, I decided to go with the one model I already knew something about: the Eco Traveler by Traveler’s Choice which uses a Power Plastics solar panel manufactured by Konarka. I had heard a talk by Dr. Markus Scharber of Konarka at the Swiss @-print Conference in December, and I liked by the idea of organic photovoltaics (OPV) both in terms of their efficiency in sub-optimal sunlight conditions, their lightness and flexibility, as well as their manufacturing process, which seemed more environmentally sustainable than most Silicon-based PV modules. Konarka had announced 8.3% efficiency for their OPV, and while substantially less than that of competing technologies, they claimed their material had a substantial advantage in low-light conditions. The person I spoke with during the break said an A4-size sheet of Power Plastic could provide enough energy to charge an iPhone completely during about 7 hours of sunlight. That was sufficient for my purposes. (I’ve made the pdf case study of this bag from Konarka’s website available here via GoogleDocs.)
Once I’d made my decision, I went straight to Amazon and was happy to see they had this product in stock. The bag seemed well-made and reasonably stylish. It had a large front pocket for carrying gear and a laptop compartment on the back big enough for my 13′ MacBook. So I was all set until I clicked “proceed to checkout” and got a message that the bag was only available to North American customers and Amazon would not ship it to me in Switzerland. I checked Amazon France, but they didn’t have this model and didn’t have a large choice of alternatives. Now I was intent on finding another supplier.
I didn’t find one right away, and by the time I did (Luggage Pros) it was only about 2 weeks until I was scheduled to leave for Morocco. The international shipping info said my order would be delivered in 10 working days, so although it would be close, I thought the package would arrive in time. It didn’t. Fortunately, I didn’t have too much trouble finding places to charge up during my trip. Unfortunately, although my bag was waiting for me when I got home, the weather turned cold and rainy. I wasn’t able to find enough sunshine to do any real tests for almost four weeks.
That changed at the end of April, and now I have the results of my first experiments.
The first thing to note is that the backpack didn’t come with a lot of instructions. Having gotten used to the customary step-by-step “Getting Started” User Guide that now comes with most electronic appliances, I was surprised to find the instructions simply said to expose the bag to sunlight and plug the solar bag output miniUSB cable to the rechargeable Lithium-ion battery until the LED turned green, then charge electronic devices with the fully charged battery using the appropriate connector. Rather summary, but there was a little more information in the guide. It said that the battery has an “intellectual protection chip” that protects against overcharge, over discharge, overload and short-circuit. When its LED turns red, the charge is too low, and the battery must be recharged.
There were six different connectors for charging most of the major phone models, and a wall charger for using it in the absence of sunlight. The weather wasn’t cooperating, but I was impatient, so I first tried plugging the battery to the bag and leaving it by the window on the west side of the apartment where it would get some rays of sunshine at the end of the day. There wasn’t enough sun during those first weeks to do much of anything though. It occurred to me a week or so later that it might be a good idea to run the battery through a few cycles by charging it via the wall socket and emptying it into my iPhone before trying to charge it fully in the sun.
I tried this twice and managed to charge my iPhone 3GS from 3-4% to 70% battery status before the red alarm LED turned on. The battery’s alarm feature is rather annoying. When the alarm is triggered, the red LED blinks on and off, while the iPhone alternates rapidly between charge and battery modes, beeping each time the mode changes. A similar test with my BlackBerry produced the same effect.
According to the Eco Traveler specs, the rechargeable battery has a capacity of: 3.7V 1000mAh. Apple doesn’t list the capacity of their internal batteries, but according to iFixit, the 3GS battery capacity is 3.7V, 4.51 Wh, or 1219mAh, so the maximum charge it could get from the recharger is about 82%. My tests were well under that.
The next challenge was to find enough sun to test the Power Plastic solar panel. I managed to do so by charging the battery over several weeks whenever I had a chance to expose it to sunlight. This was mostly on weekends, and I almost never had the luxury of placing it in sunlight for a full day.
I kept a log of the exposure time. The battery has a white LED that glows pink when the battery is being charged, so I could tell the panel was working, but there was no way to know how much energy was being transferred to the battery. After 4 weekends, I had exposed the panel to sunlight for a total of 10 hours and 10 minutes, but the green LED still hadn’t lit up, and I was beginning to wonder if it ever would.
Then it happened! On the fifth day of charging, during a three-hour charge period under filtered sunlight, the LED turned green:
28 April 16:00-18:00 Clear (2 hours)
6 May 2012 14:00-14:55 bright sunny then clouded over (55 min)
17 May 2012 9:45-11:55 sunny with high stratus, thinly veiled at first then mostly clear (2h 10 min)
26 May 14:27-19:32 clear, no clouds (5h 5m)
27 May 12:40-15:35 sun with some clouds/haze, mostly full sun until around 2:40 then veiled/cloudy (2h 55m)
I unplugged the battery from the solar panel and plugged it into my iPhone. Within an hour the alarm LED came on. My iPhone had only been charged to 59% as you can just barely make out in the video below.
This was quite different from the product information from the reviews, which said that the bag would charge a cell phone completely in two hours.
Konarka’s own Travelers Choice case study document gives the same information. Of course it’s hard to compare since most of the time I was charging the backpack late in the day when the solar irradiance was low, but my bag was in full sun just after midday during several hours and the green LED didn’t turn on.
Overall, I’m rather disappointed with the charge time: over 10 hours of sunlight to charge my iPhone to 59%. However, the bag could still come in handy in extreme situations, and when the weather is good. Unfortunately it’s only useful for a smart phones or PDAs, because there’s no connector that’s compatible with most camera battery chargers. The only backpack I’ve seen so far that has a solution for camera batteries is the one from Voltaic Systems.
I’ve already started running a second test, but the weather still isn’t cooperating (image from meteoblue.com)
Since I haven’t seen any hands-on reviews of solar chargers, I thought I’d write this one, although this bag is soon destined to become a collector’s item since Konarka filed for bankruptcy last week. It’s still not clear to me whether Konarka’s failure was primarily due to a problem with the technology or whether it was simply a question of falling solar panel prices that reduced the company’s attractiveness to investors.
Nevertheless, I found the experiment very instructive. I’d have thought that solar panel providers would have learned a thing or two from Apple about making their product easy to understand for non-technical people. The products I found are poorly documented, or include information that is just plain misleading. I suspect the error regarding the iPhone charge time in the product review comes from an error in the Power Plastic panel specs. Konarka has several different series of panels, with charge times for an iPhone 3GS ranging from 1-8 hours.
As long as solar chargers remain technical products designed for technically inclined users, and don’t take into account the context in which consumers will be using them, they’re not going to take off. I think we’ve got a way to go before this technology is ready for mainstream.
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