The sun has got its pack on
Smartphones are essential tools for modern life, but they all suffer from one big problem: every so often you have to plug them in and charge them up.
And it seems like keeping our phones powered up is becoming increasingly challenging, with handsets demanding more and more precious battery life for their increasingly sophisticated features and whizzy graphics.
This means life can often feel like a constant hunt for USB ports and plug sockets. And, while keeping your phone juiced is just about doable when you're at home or in the office, what if you're going for a hike?
The good news is that there's an alternative source of energy available wherever you are: the sun. And technology is starting to harness its power, with solar-powered bags becoming increasingly common.
Yes, the idea of lugging a solar-powered bag around with you might seem a little lame – but you'll be the one laughing when you're able to Periscope your friends' misery at not being able to check Facebook.
Here's our pick of solar bags we've found on the web…
Glory Solar Cycling Backpack
Price: $85.50 (around £60, AU$110)
Glory Solar's Cycling Backpack is perfect for outdoor pursuits. It's made from durable, lightweight fabric that's weather-resistant, so it should be able to cope with whatever you put it through.
Its maker says the solar panels are super-high-efficiency, with a transfer rate of 22%. It also includes a power bank for when the clouds go in. And the best news? It isn't too heavy at just three pounds (1.36kg).
Price: Starting at $249 (around £175, AU$320)
If you're looking for the sort of solar bag that you can take into a business meeting, SunnyBAG's Business Class Collection is stylish, genuine leather option.
The solar panels are built into the satchel's flap, and are used to charge up a power bar within – you can then plug whatever USB device you like into this.
The panel is also flexible, so if your bag twists a little nothing will break, and it's resistant to water and dust. Best of all, it weighs less than 2kg. There are a number of subtly different models available in both black and brandy colours.
Voltaic Systems Array
Price: $379 (around £265, AU$485)
The Voltaic Systems Array is one of the beefier bags in this round-up. It contains three solar panels on the rear, and the built-in battery will charge your smartphone seven times, or a laptop once.
Helpfully, the Voltaic website even tells you how long it'll take the Array's 10W cells to charge up: 1.5 hours in the sun will charge your phone, and 11 hours will charge your laptop (there's a built-in slider on the battery unit that enables you to select the voltage you need for the device you want to charge).
The bag is mostly black, but it's available with three different colour accents: orange, silver and charcoal.
Price: $100 (around £70, AU$130)
The Birksun Boost has a built-in 3W solar panel that takes up the top half of the rear of the bag. The panel is waterproof, so there's no need to worry about getting caught in a shower, and the whole bag weighs just 2.3 pounds (1.04kg).
It's available in a wide range of colours including California Blue, Tahoe Navy, Festival Pink, Crimson Red and Popsicle Orange, and with different patterns printed on the fabric. There's also a built-in laptop sleeve for laptops up to 15 inches in size.
The Bugout Solar Backpack
Price: $239.99 (around £165, AU$310)
If you're planning on embarking on some paramilitary misadventures, yet still want to be able to reliably check in on Foursquare when you reach the enemy base, then Escape Solar Gear has you covered.
Its Bugout Solar Packpack contains a 4W solar panel that can output to either a USB port or a 12V auto socket, into which you plug in your gear. There are concealed pockets, and quick-release shoulder straps, should you find yourself in what the official description calls 'tight situations'.
If things get really 'tight' the main cavity even houses an optional Kevlar bulletproof Class IIIA panel. And the bag is fully MOLLE-compatible, should you wish to integrate it with the rest of your military gear.
Price: $249 (around £175, AU$320)
The Lifepack is much more than just a solar-charging bag. Sure, there's a solar cell built in that can recharge an iPhone 6 up to 12 times, but there's also an integrated lock that be extended on a cord, so you can clip your bag to a table or similar to prevent thefts.
The focus on security is also evident in the four concealed pockets for storing important documents such as your passport, and the laptop sleeve is reinforced with air cells, so if you drop your bag your computer won't take much of a hit.
There's even a built-in bluetooth speaker, so you can be the life and soul of the party wherever you go – or you can just annoy the hell out of everyone on the top deck of the bus if you want to.
The Lifepack launched on Kickstarter a few weeks ago aiming for a mere $20,000, and has already obliterated that target, reaching $440,000. It's due to start shipping in October.
Custom Solar Powered Duffel Bag
Price: £78 (around $110, AU$145)
One type of bag we haven't shown you yet in this round-up is a gym bag – so here you go. This bag, designed by one Etsy user, can charge your phone while you work out.
The Adidas bag has been modified to take a 6W solar panel, which can be clipped on or off as needed. There's also a built-in 2600mAh battery, to hold the charge for when you're out of the sun.
It also comes with a three-LED solar flashlight, just in case you need to find your way home in the dark after a late session at the gym. It's currently listed as unavailable on Etsy, but we're hoping it gets reinstated soon.
Price: $479 (around £335, AU$615)
GoPlug's bag appears similar to others on our list, comprising solar panels and power bank – but this power bank is significantly more advanced.
Not only can you set the power bank to charge your phone on a timer, you can even do it based on location. So if it detects that you're wandering into the wilderness it can power you up to ensure you're able to call for help should you need it.
It also has a proximity sensor, and will tell you if your phone moves a certain distance from you, alerting you to theft or misplacement. And it can push alerts to your phone in the form of notifications.
All this comes at a price, though. When the bag ships in October (it's another Kickstarter success story), it'll cost a massive $479, including the bag and power bank.
Eceen 7Watts Messenger Bag
Price: £59.99 (around $85, AU$110)
If you prefer a messenger-style bag rather than a backpack, Eceen's solar bag packs a 22%-efficient solar panel, 10,000mAh battery and 40cm USB cable into its stylish design.
This is one of the lightest bags in our round-up, weighing in at just 708g, and handily the USB battery has two ports, so you can charge two devices simultaneously.
The battery also has built-in surge protection to ensure the electricity output remains consistent, so your phone won't get fried if the sun suddenly comes out.
Oh, just make it yourself
And finally… if you can't find the solar-powered bag that's right for you (or you find one but can't afford it), why not simply build one for yourself? Instructables has detailed instructions on how you can take almost any bag, and install the necessary hardware to enable it to soak up the sun's rays.
It's easy, as long as you're a dab-hand with a soldering iron – but we'd suggestion you have your explanation ready if you're taking your creation through airport security.