Avoid Solar Disappointment This Holiday Season

I just completed an important comment on a review I read of the Bushnell SolarWrap Mini on Trailspace. The review lacked performance numbers & prompted me to write a bit more about pocket solar chargers. Here is a link to the review (my comment follows)...
Bushnell SolarWrap Mini Review

The Problem With Pocket Solar Chargers...

In attempting to reduce size, weight, & cost, manufacturers are prone to eliminating performance to any reasonable level.

In brief, I don't recommend any solar charger under 2 Watts (solar cell peak power), and all solar/back-up battery packs should be at least 2500 mAHr.
And, if the product doesn't state these specs clearly, you should smell a rat.

The Explanation...

The typical electronics-equipped trekker is taking a smartphone & camera into the wild. Often, the camera is a dSLR with a larger battery pack than the iPhone. Sometimes there is a need to charge AA or AAA batteries for headlamps or GPS receivers.
Let's run a scenario with the basics: iPhone & dSLR.

The Smartphone's power budget...

The iPhone 6 now packs a battery size of 1800mAHr (up from the iPhone 5's 1500mAhr). The iPhone 6 'plus' is up to the 2900mAHr range. The Samsung Galaxy S5 packs a battery in the 2,800mAHr range these days.
What does this mean?
It will take at least 9 Watt-Hours of power to fully recharge the iPhone 5, and at least 15 Watt-Hours to sully recharge the latest iPhone 6 or Samsung Galaxy S5.

Now the camera...

Most point & shoot camera batteries are in the 1,000 mAHr range, while the bigger dSLR batteries are in the 1800-2000mAHr range. Let's take the case of the popular Canon LP-E6 battery which is used in the 5D, 60D, 7D camera models.
The LP-E6 battery is 1800mAHr @ 7.4V which means it will take at least 18 Watt-Hours to fully charge it.

The other issue is the battery's voltage. Charging a 7.4V battery from a 5V USB source requires a special charger. 12V charger cradles are available, but let's keep the cost & size of the system down by choosing to stay in the USB realm.

Total Power Budget...

Let's assume that you are taking your Canon 5D Mark II camera, and your fancy new iPhone 6 into the bush for a week of trekking. You are planning to drain both the camera each day, but the iPhone should last 2 days.
By the numbers, you will need to replace 18 + 8 = 26 Watt-Hours of power each day. 18 for a full LP-E6, and half of the iPhone 6's 15 WHrs.

Attaching a solar charger to a backpack means less than ideal exposure to the sky (except during stops), so allowing for that, plus occasional tree cover, you would need a solar panel of at least 10 Watts to keep up with your power needs.

A solar storage battery should ideally be twice your anticipated demand, which puts us at 52 Watt-Hours in our example (or 14,000mAHr in a USB battery).

Your Options...

If you look around the market, you'll see PowerMonkey products in the 3-4W range, and Goal Zero in the 3-7 Watt range. These will not keep up with the demands of our scenario. And you can certainly forget the little chinese clamshell chargers in the 0.5-1.5 Watt range!

Look for the components you need...
Waterproof solar panels for kayaking & canoeing. Sensitive thinfilm panels if you are going north or expect tree cover or questionable weather, or crystalline panels if you are at altitude or tropical latitudes. You're not going to purchase a separate system for each (probably), so consider what trekking you plan to do most.
The battery should be thin & light, and able to support all your electronics. Keep it safe & dry. Please don't believe that you can trek properly with an AC inverter... too much added weight, cost, & complexity. Stick to USB or 12V.

What About Just The Smartphone?

If you're considering a gift of solar this holiday season, stick to solar chargers that have a solar panel of at least 2 Watts. This will give you up to 50% of a typical smartphone charge each summer day. That is a level of performance most people can live with. Combine that with an internal boost battery in the same range as the smartphone (2500 mAHr or more), and you will have a satisfied trekker!

Need Any Help?

Send me a note! I can help evaluate any products you are interested in.