Guide for Selecting Solar Backpacks and Bags: Taking Civilization into the Wilderness
Category: Solar Outdoors
In today's constantly connected culture, being days away from civilization on a hiking trip isn't considered an excuse for missing a conference call. If you get lost, you just pull up your GPS app. Want to order a bag of tacos twenty miles into the Grand Tetons and have it be delivered to your campsite by drone helicopter? Well, you can't... at least not until TacoCopter formally opens for business.
Americans are becoming an ever more connected people, even when we try to get away and commune with nature. Unfortunately, nature doesn't come with a grid system and power outlets, and most devices aren't designed for multiple days of off-grid use. Luckily, your iPhone doesn't need to have an adversarial relationship with fresh air and sunlight: given the right equipment, you can use that sunshine to keep your devices running!
As solar panels have become lighter and more efficient, a whole product range of solar backpacks and charging cases has sprung up to give the connected nature lover portable power generation capacity. Even the US Army has taken to using them in the field. These products can be a great addition to your outdoor gear, but there are a few things you need to consider in order to avoid buyer's remorse and get the most out of your gear.
The first thing that you should do as you are reading this guide is to browse solar backpacks and solar bags in the Outdoors Section of the SolarTown store. And you should also look at portable solar modules that generally provide a little more power for your needs in remote areas.
1) Device voltage: check the devices you need to charge
Voltage is for power what elevation is for water - power flows from higher voltage to lower voltage. In order to charge your device, you need a power source that provides a high enough voltage that the power it generates will flow into your device from the power source. Choose a power source whose voltage is significantly lower than that of the battery you are trying to charge, and you can actually end up draining your battery into the power source!
Before you purchase a solar powered bag or case, make sure you know the voltage requirements of all the devices you plan to use with it. Most devices will list their voltage rating either on their charger or in their manual, with the notably frequent exception of USB-powered devices, which require 5V to charge.
2) Device usage: you can't charge and discharge the battery at the same time
Unless the solar bag you choose allows for direct DC charging of devices and has a compatible connector for your device, you will most likely be using a built in battery as an intermediary power source. The DC current from the solar cells will charge the battery, which will in turn charge your device's battery. The only problem is that with most solar bags you can't charge and discharge the battery at the same time, meaning that you will need to choose between charging your device and collecting solar power.
- You will probably be charging your device at night, not during the day.
- If your device requires recharging during the day, bring a spare battery.
3) Device power demand
If you want to fully charge your device, you'll need to make sure that your solar bag's battery can store that much power. Because battery charging and discharging are not 100% efficient, these are not necessarily the same thing. You will likely not be able to get a full 3,000 milliamp-hours out of a solar bag's 3,000 milliamp-hour battery, but you will need to collect that full 3,000 milliamp-hours to fully charge the solar bag's battery.
You should also make sure the solar bag can provide enough power to fill your device's battery. This isn't as straightforward as checking the voltage, as most batteries list their capacity in hours of use rather than in stored current capacity, so you'll need to do some back-of-the-envelope math.
To determine how much power your battery will need to charge, follow these steps:
- Fully discharge your device
- Time how long it takes to charge it back to full charge from the grid.
- Divide the charger's wattage by the charger's voltage.
- Multiply the watts/volts by the number of hours it took to fully charge the device.
This will provide you with a measure of the total amount of current in amp-hours, which can be converted into milliamp-hours by multiplying by 1,000.
mAmp-hours = (Charger Wattage)/(Charger Voltage) * (Charging time in hours) * 1000
Make sure that your solar bag has the capacity to store 5-10% more than this much power, and you can rest easy that your device will be fully charged at the end of the day.
Example: The MacBook on which this article was written is charged by a 60W, 16.5V charger. It takes roughly three hours to charge from a fully drained (and somewhat old) battery. By plugging these numbers into the formula above, we end up with 11 amp-Hours, or 11,000 milliamp-hours, of power capacity. To make sure I could fully charge the battery, I would want a bag with a capacity of 12,100 milliamp-hours, ten percent more storage capacity than the laptop's battery capacity. The 3,000 milliamp-hour battery of my Voltaic Fuse Solar Bag Charger which you can find in our solar bags section wouldn't be up to the task of recharging the MacBook in one sitting. A product like the Voltaic Generator Solar Laptop charger with its 16,000 milliamp-hour battery capacity would be a better choice.
4) Access to the sun: you need sunshine to charge the battery
It goes without saying that your solar bag can only produce electricity if it has sun shining on its solar panels. If you are planning to hike out in the open or are taking a boat trip, this shouldn't be too much of a problem. However, if you're hiking through valleys or forests, you need to be aware that the reduced exposure to the sun will not only reduce power output but may fail to create enough voltage to move the power generated by those panels into the bag's battery. If you are planning this kind of expedition, you might be better off looking into solar blankets or portable solar modules that can be set up at camp.
For those who want to maximize their on-trail power production in an optimal environment, adjustability can be key. If you are hiking south the solar panels your backpack will be pointing north, away from the sun if you are hiking in the northern hemisphere. A satchel such as the Voltaic Switch Solar Bag will allow you to adjust your load so that the panels will always be facing the southern sun.
These five easy tips will allow you to select the right solar bag or backpack for your particular needs. Once you have the right solar bag, you will be able to bring a little bit of civilization to areas far off the beaten path.