Guide to Solar Backpacks and Portable Solar Panels — Slowly Getting Better


fwave flexible solar panel

As yet, flexible solar panels such as the F-Wave are better suited to curved surfaces on buildings than the backs of backpacks. Photo by Marufish at flickr.com; CC 2.0 License.

The concept of a solar panel backpack hasn’t changed. Ideally, the panel becomes part of the pack fabric, as flexible and tough as ripstop nylon. As you hike, sunlight activates the hidden power cells, and by the time you reach camp the charging system rebuilds the daily juice your personal electronics require. At camp, panels integrated into the roof of your lightweight tent power lanterns, heat the tent floor and even hook you up to the internet.

As yet, no one builds those things. The current devices available at consumer level do often include solar cells and charging systems far better than those of five years ago. Solar panel manufacturers at first built for the DIY technician and experimenter and provided very little support for the amateur consumer. If you bought solar panels, you needed to learn how to set up a charging station and battery bank and convert the DC to power appropriate for your uses. Charging stations prevent overcharging damage by converting the output voltage of a bank of solar cells to a level appropriate for the battery you use for storage. Today, many portable solar panel systems include charging stations and storage batteries, as well as an array of connectors for cell phones, laptops, personal entertainment electronics and sometimes even adapters that will charge a dead car battery. Solar panels can still confuse anyone new to the technology, but many manufacturers have realized their main customers don’t do DIY.

catalyst solar computer bag

Holds a laptop. Includes a small solar panel and connectors for charging small electronics, slowly.

Potential for Confusion: You might think that the  Catalyst Solar Computer Backpack would charge a laptop computer with the built-in solar panel. If so, you’d be disappointed, since the small panel only outputs enough power for smaller devices such as cell phones and Blackberries. Even for those low-power products you’ll need many hours of direct sunlight and proper panel orientation to the sun to build a useful charge. The Catalyst Solar Computer Backpack does include the necessary connectors to charge iPods, iPhones and other small electronics. The pack’s laptop compartment will hold a laptop.

The flexibility of modern solar panels greatly increases the durability of what was once a fragile technology. Fabric-type flexible panels even function after being riddled with bullet holes, and roll into somewhat convenient shapes for storage. If a bullet hit one of the main output wires, you’d still be out of luck. Flexible solar cells don’t survive crumpling and creasing well, and you can’t find a solar tent you can stuff carelessly into a sack as yet. Fabric panels weigh more than ordinary ripstop nylon, and if you take one along with enough power to run more than a cell phone you’ll add several pounds to your gear. You’re still better off taking fresh batteries if you simply want to save weight. Panels only make sense if you’ll be out for a long trip. For a panel large enough to efficiently power small devices, you have two choices: panels that roll up, and panels that fold up along dividing seams. Folding panels take up less space than rolls.

voltaic solar power backpack

The Voltaic 1010 solar panel bag provides two selectable voltage outputs, plus common connectors and a storage battery.

Minimum Solar System: Voltaic’s 1010 OffGrid Solar Backpack includes the basics you’ll need for practical solar charging of small consumer electronics devices. The dual panel system switches from 6 to 12 Volts at 4 Watts. If your device uses 4 Watts or less, it can run directly from the solar panel. The 11 Watt storage battery included in the bag stores extra energy for “jump-starting” rechargeable devices independently of the solar panel. You can also cheat by using the AC wall adapter to fill the battery or charge devices while on the grid. Voltaic suggests a solar charge time of about 5 hours for a typical cell phone. Although it’s possible to charge a laptop this way, expect a charging time of days, not hours.

As a basic guideline, just look at the size of the panel. Efficiency does vary, but a panel 3 inches by 6 inches will take many hours to charge a cell phone and is useless for anything as power-hungry as a laptop. For a panel this small to be of any use you’ll have to devote much of your daylight time to it, orienting it towards the sun while it takes all day to charge the phone.

folding solar panel

To recharge laptop batteries and quickly recharge smaller devices, you'll need panels too large to ride on the back of a backpack. Photo by Beige Alert at flickr.com: CC 2.0 License.

A solar panel about a foot square, the size that fits on the back of a backpack conveniently, can charge a cell phone in about half a day and will do some good while you’re traveling. Panels work best when facing the sun, of course, and output drops in cloudy weather and ambient light. You’ll have much better luck setting the pack down in a sunny spot at camp than you will by walking a twisting trail.

A solar panel about a yard square provides considerable useful power and can run small devices like cell phones without waiting for charge to build. If a large panel provides 60 Watts of power, it generates enough juice to do the equivalent of lighting a 60 Watt light bulb. It won’t actually light a bulb, because this requires conversion circuitry that changes the DC output of the panel to an AC voltage. Every step in the conversion uses power and most would be lost in that process. The panel needs the proper DC converters and connectors to directly power personal electronics, or it’s useless to you. If a panel outputs 18 DC Volts, you can’t just hard-wire it to a device that needs 6 DC Volts. You need a converter to drop that 18 Volts to 6 Volts so you don’t torch electronic components designed to operate at the lower voltage.

PowerFilm F15-1800 30w Folding Solar Panel Charger

Powerfilm's basic package includes the solar panel and one connector. You'll need other accessories for many charging tasks.

Accessories Not Optional: PowerFilm’s F15-1800 30w Folding Solar Panel Charger provides enough energy to run a small television, but the essential adapters, charger and storage battery come extra. Powerfilm provides a full line of accessories and you might not require all of them. The panel folds into an 11 inch by 10 inch by .75 inch flat package weighing 1.8 pounds. Unfolded, it captures solar energy from a area 40.5 inches long by 30.5 inches wide.

Converters that drop the voltage output also drop the power output. The simplest 6 Volt converter wastes two thirds of the energy received from the 18 Volt panel. Useful energy at the device end of the system is always less than at the output of the panel. “Smart” devices include this basic circuitry and only need a raw voltage input. “Smart” devices also cease charging when the battery reaches peak level. Not all electronics includes smart power conversion, so check the specs on your device before deciding on a solar power system. One user of the Brunton Solar Panel who reviewed the product on Amazon noted that after purchasing the proper car charger adapter, the only way it would connect to the laptop he wanted to charge, he could find no evidence of any actual charging happening even though the panel and charger seemed to be working. What might have happened was that the car charger dropped the voltage down to about 6 DC Volts, wasting most of the power the solar panel provided. The resulting combination might trickle charge the laptop battery over a period of several days, if no one used the laptop. Turn the computer on briefly to see what a few hours of charging has accomplished, and you’ve canceled out the power gain made by a low-wattage solar panel.

brunton solar panel in canoe

The Brunton solar panel stows away in a neat hard plastic tube. Extra connectors may be required. Photo by KeithD at Amazon.com.

Roll-Up Convenience: Brunton Outdoors, the manufacturer of the Brunton SolarRoll Flexible Solar Panel, provides a very helpful FAQ page with information that applies to any portable solar panel system and with specifics for matching a Brunton panel to your personal electronics. The Brunton panel rolls into a neat package, protecting by a hard plastic carrying tube. The largest Brunton panel unrolls to nearly six feet in length.

Solar cells can combine in series strings or in parallel banks, outputting a wide range of voltages and power levels depending upon that physical layout. The most efficient layout would produce a voltage and power output matched to the electronics you intend to power with it. Many high-power folding panels were designed to meet a wide range of needs. The lightest and simplest are best matched to low-power devices. If it’s good enough to run your highest-wattage toy, you won’t need to worry about the wasted energy when you’re charging something less. The panel will make more electricity than needed for a low-wattage device.

If you want dependable emergency power on demand, to charge a cell phone or a GPS, take a hand-cranked charger instead of a solar panel. It requires a little time and effort, but crank chargers work even in the dark. Crank generators weigh ounces instead of pounds, making them a good emergency backup for ultralight travelers who won’t leave the cell at home.

gosolar solar panel

Available in three power ranges and with appropriate connectors. Sensible accessories are either included with the panels or available separately.

Excellent Customer Support: I recently reviewed the GoSolar! folding solar panels on The Marked Tree and was very impressed by their quick and honest reply to my questions. I had estimated how long it might take to charge a car battery with one of their panels and emailed with that same question. You ought to be on the road again in four or five days with their 24 Watt kit, maybe even sooner if it’s perfect weather and you don’t play the radio. The GoSolar! 42 Watt Portable Folding Solar Charger Kit trickle-charges a car battery in about half that time. GoSolar’s products power a wide range of devices and meet several levels of need. Expect technical support you can understand.

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