We live in 21st-century Gadgetopia. GPS units, digital cameras, iPods, cell phones, laptops— all light and portable enough to carry to off-the-grid locations. So why not bring the grid along as well? An array of lightweight, compact solar chargers are available that can recharge your electronics anywhere you hike or travel. Well, sort of. Eventually. Pint-sized solar panels work—you just need to understand their limitations. So let’s illuminate the topic. 

HAVE A GOOD LATITUDE  The basics of solar power aren’t complex. Direct sunlight contains more energy than indirect, low-angle light that travels farther through the energy-sapping atmosphere. Consider this: On winter solstice in Boston, when daylight is short and the sun peaks at 25 degrees above the horizon, the sun provides only a quarter of the total energy available on summer solstice, when the day is long and the sun reaches 71 degrees above the horizon. The amount of usable solar energy drops off significantly when the sun is obscured by clouds or haze, or when its rays strike a solar panel at an oblique angle. When manufacturers talk about charge time, they are talking good, direct, middle-of-the day, high-in-the-sky sunlight conditions. For low-angle, indirect, and wintertime sun, charge times will be much longer. 

KNOW YOUR FLOW  Under a perfect sun, portable solar panels have a maximum potential output of energy, usually listed in watts. (Actual output will be less, sometimes much less, depending on conditions.) The amount of energy produced closely correlates to the total surface area of the panels; double their size and you’ll roughly double the wattage. Portable solar chargers are, by definition, small. Therefore the energy produced is low; most pocket-sized devices ($50-$150) produce somewhere between 0.5 and five watts (think a very dim light bulb). Some manufacturers —Brunton, PowerFilm, Sunlinq—produce larger, foldable, or rollable arrays of panels that produce significantly more wattage. They can also be plugged together in series to increase overall output. More juice costs more money—expect to pay from $200- $300 (6-18 watts) to $400 and up (25 watts or more)—and will weigh more, ranging from the pocket sized (4-6 ounces) to 56 watts (3 pounds). 

CHARGE!  To maximize sun savings, many portable solar chargers feature an integrated battery that accumulates power anytime the panels are catching rays.

DID YOU KNOW?
Each hour, the sun strikes Earth with more energy than the world's people use in a year.

The charge can then be transferred to your device whenever it’s needed. (These built-in batteries can also be pre-charged before you leave on a trip via a USB port on your computer or by plugging them into a wall.) Electronic devices require a minimum amount of power to recharge in a reasonable time frame. For most small items—iPods, digital cameras, cell phones—the necessary threshold is rarely a problem for even the smallest solar chargers, especially those with internal batteries. Laptop computers are more problematic; you need a minimum of roughly 10 watts to charge them, 50-plus watts to run them. Always make sure you’ve got the proper adapter to charge your chosen device; most portable solar chargers come with a wide selection. 

GOOD CHEMISTRY  Solar panels are not that efficient; most convert only 10-15 percent of the sun’s total energy to electricity. Efficiency can be improved by the chemical structure of the photovoltaic cell, which varies depending on the model. Multi-junction panels capture more of the spectrum of sunlight, increasing efficiency. Amorphous silicon panels are more efficient in low and indirect light. CIGS (copper indium gallium diselenide) panels are more efficient in good, direct sun but less so in low light conditions. 

FACE REALITY  Combine all of the above and here’s the power check. Small solar chargers (5 watts or less) require a lot of high-quality sunshine to charge even the smallest device: cell phones and iPods (4-8 hours), digital cameras (4-10 hours), or the solar charger’s own battery (6-10 hours). Higher wattage panels decrease charge time significantly; a 52-watt panel can re-boost your iPod in 60 minutes or your laptop in under three hours. Just remember, the world is rarely as sunny as we want it to be—plan accordingly.