Do you dream of hiking the Appalachian Trail, cycling from coast to coast, or just spending the weekend in the wilderness? Now how about without a cell phone, GPS, or iPod? That's what I thought. Welcome to the world of portable solar panels. Solar is the way (and the only way) to bring your electronic toys and play with them too.
Now harnessing the power of the sun isn't new. We've been doing it for decades. Solar panels have been used to power RVs, homes, businesses, even communities. But these solar panels have always been too big and too heavy to throw into a backpack before hitting the trail.
Things have changed. Recent technological advances have made solar panels more portable than ever. So portable that you can bring solar power with you anywhere you walk. By throwing a few ounces of technological wonder in your backpack, you can keep your portable electronics running anywhere under the sun.
Go camping, backpacking, biking, kayaking, you name it - for as long as you like and still call home to Mom. Free energy from the sun is turned into an electrical outlet, that can be taken anywhere.
This is your guide to choosing the best portable solar solution available. We'll answer questions like...
Now let's harness the power of the sun...
The most important question to ask yourself when considering a portable solar panel is "Can I plug my device in and charge it?".
Here are the most common types of connections:
"On a long journey, even a straw weighs heavy" - Spanish proverb
Just how lightweight should a portable solar panel be? Like the Spanish proverb, it depends on the length of the journey, but it also depends on how you'll be transporting it.
For hiking, backpacking, climbing, and cycling I personally wouldn't go over 1lb. There's no reason to either, unless you'll be hauling a laptop, which will require a bit more solar power...but then I'd have to seriously ask myself "why am I hauling a laptop!". A lightweight solar panel that's small, foldable, or rollable will be easy to stow in or outside your pack.
Unfortunately determining what a portable solar panel weighs isn't always easy. Some manufacturers list the weight of just the panel, while others include the weight of all the accessories and adapters too. Contacting the manufacturer may be the only way to know for certain just how much weight you'll be carrying on your journeys.
If you're RV boondocking, car camping, or boating weight and size isn't of much concern. You could even go with something like the foldable and still portable Mars100-Watt Solar-powered 12V Battery Charger matched with a 12-volt deep cycle battery and inverter. This setup would power just about anything you would want to bring along on a camping trip.
Like the full-size solar panels used for homes and RVs, portable solar panels are also quite durable and resistant to nasty weather. Many are designed to take abuse while camping and hiking and some, like the Solar Joos Orange, can even be submerged in water.
Even though most portable solar panels are not completely waterproof, most are weather resistant and will survive a rain shower. But don't expect the panel to keep charging during a rain, as most won't.
How much solar power are you going to need? The nitty gritty answer requires some simple math. But if all you're going to charge is a cell phone, it's hard to go wrong. Choose a portable solar panel that won't weigh you down and that's compatible with your device.
These guidelines will give you an idea of what it's going to take to keep you powered up. Keep in mind these are only guidelines. For the nitty gritty answer calculate your daily power consumption below.
The watt rating isn't the only thing to consider when choosing a solar panel. You also need to look at the output power rating. A solar panel with a higher watt rating than another, but a lower output power rating will take longer to charge your phone or other device.
The USB port on portable solar panels provides 5 volts of power, just like the USB port on your computer, so this number will not change. But the amp and watt rating will. Some manufacturers provide the USB output rating in Amps only, so to get the Watt rating take Amps x 5 (for 5 volts). By comparing numbers you'll see which panels give you the fastest charging times.
You'll find that many panels have different output ratings for the USB port and the 12-volt port. Often the 12-volt output rating will be higher than the USB rating. For example the Goal Zero Nomad 7 has a USB output of 2.5 watts, but the 12-volt output is 3 watts. If you have the option, connecting your device to the 12-volt port would provide a faster charge with this particular solar panel.
As the temperature goes up, voltage drops. A portable solar panel with a higher peak voltage will perform better in hot weather than a panel with a lower voltage rating. It will also perform better in conditions that are less than ideal such as on cloudy days or in the shade.
If you have several devices to charge then choosing the right portable solar panel will require a little addition and multiplication. Not to worry though. It all boils down to how much power those gizmos use, and how long they're used each day.
Let's say we have a smartphone with a 8 Wh lithium-ion battery. "Wh" stands for watt-hour. If we drain this battery each day, we'll need a little more than 8 watt-hours of power to charge it back up again. I say a "little more" because charging a battery is not 100% efficient. To account for this inefficiency we'll take 8 x 1.2 to get 9.6 watt-hours. It will take 9.6 watt-hours to charge our 8 Wh battery.
Now we'll have to decide how much sunlight we can count on having each day. I'm in sunny California where 10+ hours is common, but we'll figure in some partly cloudy weather and go with 6 hours for this example.
Now we take 9.6 (watt-hours needed to charge our battery) divided by 6 (hours of sunlight) and get 1.6. Here's the equation...
So in this example a solar panel with an output power rating of 1.6 watts would work. A panel with 1.6 watts of output power produces 1.6 watts each hour under ideal conditions.
Of course conditions can be far from ideal, so choosing a panel with a few extra watts is best. Also keep in mind that things like backpacking through a forest, camping in the Pacific Northwest, or traveling to Alaska will all reduce the amount of sunlight you and your solar panel will receive. So be realistic about how much sunshine will be in your forecast.
If you've got AC or 12-volt DC devices you'll need to add up the power consumption for them too. 12-volt DC devices are usually rated in amps and AC appliances in watts. To make things easier we'll convert everything to Watts, so for 12-volt devices take the amp rating and convert it to watts like this...
Amps x 12 (for 12 volts) = Watts
Next use this equation to calculate the total watt-hours for both AC and DC devices...
Device Power Draw (Watts) x Hours Used Each Day = Watt Hours
For example, we have a laptop computer rated at 60 watts and we use it for 2 hours each day. This adds up to 120 watt-hours (60x2=120).
With AC devices, we'll be using an inverter. Since an inverter is not 100% efficient, there will be some wasted energy. We'll need to multiply our AC watt-hours by 1.2 to account for this loss. Since we're running our laptop with the AC power supply, we'll take 120 (AC watt-hours) x 1.2 and get 144 watt-hours.
Lastly, we'll add up the watt-hours for all devices to get our grand total daily power consumption. Once we have this number we'll use the same sunlight equation as above...
(Watt Hours Consumed x 1.2) ÷ (Hours of Sunlight) = Recommended Minimum Solar Panel Output Rating in Watts
So with our laptop example we would take 144 watt-hours divided by 6 (hours of sunlight we expect) and get 24 watts. We'd want a solar panel with at least 24 watts of output power.
By using these steps you can add up all the power your mobile office consumes, throw in a few watts for a rainy day, and choose a portable solar panel with enough output power to do the job.
Many portable solar panels come with an internal battery. The solar panel charges the battery and the battery charges your device. So why doesn't the solar panel charge your gadgets directly? Without an internal battery a small solar panel may suddenly stop charging your device due to clouds or an object passing in front of the panel. You could lay out the panel, plug in your phone, and come back 5 hours later to discover your phone barely received a charge...all because you walked in front of the panel soon after laying it out.
The Suntactics sCharger-5 works around this problem. It incorporates what Suntactics calls "Auto-Retry Technology" which re-starts charging in the event the panel is temporarily blocked from the sun. No battery is needed, saving some weight.
Another reason batteries are used is that many small solar panels aren't capable of charging cell phones or other devices directly. There are exceptions like the Instapark Mercury 10. Thanks to its stable circuitry, it can charge most USB devices without an internal battery.
Omitting the battery does shave some weight off your pack, but a battery does have a few advantages which can make up for its weight. For one, you'll be able to leave the solar panel out to charge the battery, then use the battery to charge your device later, even at night. A battery also provides reserve power in case you experience several cloudy days in a row.
If the portable solar panel you choose comes without an internal battery, you can buy a lithium-ion battery for around $20-$40 should you decide you need one. The Anker Astro Mini 2600mAh is a popular one that weighs only 2.7 ounces. Portable external batteries like these have a USB port for connecting and charging your phone or other USB device, and the battery itself can be charged with either the USB port on your portable solar panel, or your computer's USB port.
Here are a few more popular lithium-ion battery packs that can be charged via the USB port on portable solar panels...
Need to charge AA, AAA, C, or D batteries for your flashlight, camera, or other camping gear? Solutions include the Goal Zero Guide 10 Plus which features a AA/AAA battery charger matched with the Nomad 7 portable solar panel. The AA/AAA battery charger also doubles as a USB charger for your cell phone or other portable device. The charger, with the included AA batteries, can be used to charge your phone anytime, even without the solar panel. You can also purchase the Guide 10 Plus Charger separately and use it with any portable solar panel that has a USB port.
Here are a few more solid options for charging AA, AAA, C, or D sized batteries with solar power...
Another option is to use a battery charger that includes a 12-volt car adapter like the Alpha Power AA/AAA Battery Charger. The car adapter can be connected to any portable solar panel with a 12-volt port.
If you need a more powerful battery and weight is of no concern, then a 12-volt deep cycle battery is the way to go. These are often called marine batteries and they're found in boats as well as RVs.
The two most common types of 12-volt batteries are wet cell and AGM. Wet cell batteries are the cheapest, but they do require some maintenance and they must be kept in a well ventilated area. AGM batteries on the other hand are sealed, require no maintenance, and can be stored anywhere. They also have a much longer lifespan.
Weighing 30-80 lbs and up, 12-volt deep cycle batteries aren't so portable, but they work well for car camping, boating, and RVing.
When charging a 12-volt battery with solar, a charge controller is necessary to regulate the voltage going to the battery. Without one you risk overcharging the battery. The only exception is if you're using a very low wattage panel for trickle charging. Portable solar panels with built-in charge controllers are available. For solar panels that don't include a charge controller, one will have to be purchased separately.
To get the most life out of a deep cycle battery it's important that it not be discharged by more than 50%. This means you'll need at least double the capacity you plan on consuming.
For more information about setting up a solar panel system to charge 12-volt batteries see my Guide to RV Solar Panels.
This chart will give you an idea of what size solar panel and battery is best for the device you can't leave home without.
Keep in mind that these are only guidelines. In order to fine tune your choices you'll need to calculate your daily power consumption as shown above.
Best Battery Size
Since 2010 I've relied on solar power for every electronic device I own. It really is amazing if you stop to think about it. Solar panels silently turn light into electrical energy and require no fuel or maintenance to do it. It's like magic.
Portable solar panels have now brought that magic to the masses. Now anyone can reap the benefits of free energy from the sun, and at the same time reduce their dependence on filthy fossil fuels.
Now that you've seen the light, might as well use it. After all, it's free!
Here's a few helpful conversions and formulas we used in this article.
1 Amp = 1000 mAh
Watts = Amps x Volts
Calculate Daily Watt-Hours or Amp-hours Consumed
Device Power Draw (Watts) x Hours Used = Watt Hours (Wh)
Device Power Draw (Amps) x Hours Used = Amp Hours (Ah)
AC Appliances: Account for Wasted Energy With Inverter
AC Watt Hours x 1.2
Calculate Recommended Minimum Solar Panel Output Power in Watts
(Daily Watt Hours Consumed x 1.2) ÷ Hours of Sunlight
If you'd like to learn about setting up a larger solar power system for RVing, car camping, or boating click on an article here to continue.
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