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All About USB Solar Battery Chargers for Mobile Phones and Tablets

usb-solar-battery-chargers-for-mobile-phones-and-tabletsThere are different types of solar chargers for your iPhone, Android or other smartphone. There are big chargers, small chargers, all-in-one chargers, folding solar panel chargers and solar backpacks.

We’ll look at the advantages and disadvantages of each type, as well as explain at a high level, how they work.

Solar chargers are suitable for long duration (weeks or months) off-grid or emergency use, providing electrical power when you have no access to conventional mains power.

They will not reduce your carbon footprint or save on your utility bills (your bills will go down, but not enough to offset the cost of your solar equipment). Numerous studies have shown that it takes decades for solar panels to earn back the energy used to make them, and the money used to buy them, if ever. And this is for fixed installations that are exposed to the sky 24x7x365, not a portable system that is used a few hours a week.

For a short camping trip or emergency (days, not weeks), you might be better off with a few spare power bank chargers (lithium-ion external phone batteries with a USB output). Even if you do go the solar route, it’s always good to have a backup – stock up on power banks anyway.

Solar chargers might be useful for people who are always on the move and can’t reliably find a power outlet – in an airport, cafe or library. However you’ll need to find a seat by the window to have a chance to use a solar charger – indoor lighting is too weak. Even if you do manage to get some window light, your solar charger might be too small to work without direct sunlight – you’ll need a large solar panel.

Why so Complicated? How Solar Power Systems Work.

A complete solar system consists mainly of a solar panel and a “solar battery” (a normal rechargeable battery, we’ll call it a solar battery to avoid confusion with your phone’s battery). You’ll also need connecting cables.

Electrical power from the solar panel is weak and varies depending on how much sunlight the panel gets (depending on the time of day and the cloud cover). The solar battery stores or concentrates the electricity from the solar panel over the course of the day, so that it can push out the stored energy at high power when you need to power your devices.

Sun —> Solar Panel —> Solar Battery —> Mobile Phone

The problem with this approach is that it is inefficient, wasting some energy in charging up the solar battery. It’s possible to skip the solar battery and power your devices directly from the solar panel, if the solar panel is powerful (big) enough.

Sun —> Solar Panel —> Mobile Phone

But unless you are using your equipment the whole day and you have a cloudless sky, it’s more reliable and convenient to get a small solar panel and use that to charge up a solar battery.

Apple products have a reputation for being especially finicky with their power supply. If a cloud passes over the sun, your iPhone will stop charging even when the sun appears again. You’ll need to unplug your device and plug it back in.

To fix this problem, some solar chargers have an auto reset or auto retry feature, to enable charging to continue without you having to unplug. If you want to use a solar charger without a solar battery, you’ll need this feature.

Another useful feature is reverse flow protection. When the solar panel is in the shade, it generates a lower voltage, possibly lower than the phone’s voltage and draining power from the phone (depending on the type of phone). Reverse flow protection allows electricity to flow from the solar panel to the phone, but not the other way round. This is not an issue for power banks because they have a dedicated input port which should not be able to discharge their battery.

Solar Charger Voltage

Today’s mobile phones and tablets can be charged from a 5 volt USB port. A solar power system should allow you to plug in your phone into their USB port, just like any other charger. You can use your existing charging cable.

Solar Panel —> Solar Battery –USB–> Mobile Phone

The solar panel itself should also have a USB output socket, allowing you to use a standard mobile phone USB power bank (using lithium-ion batteries) as the solar battery.

Solar Panel –USB–> Solar Battery –USB–> Mobile Phone

You can also use something like the Goal Zero 10, which is a USB-powered AA battery charger, that also has a USB output port. This makes it similar to a power bank, only with removable AA batteries.

USB and Solar Panel Power Output

Most power banks can supply 5 to 10 watts of power to charge a phone:

  • USB 5 volts, 500 milliamps = 2.5 watts, most PC USB Ports
  • USB 5 volts, 1000 milliamps (1 amp) = 5 watts, most power banks and wall chargers, not powerful enough to charge tablets
  • USB 5 volts, 2000 milliamps (2 amps) = 10 watts, some power banks and wall chargers, needed to charge tablets

You’ll need a 2 amp (10 watt) USB output on the power bank to charge a tablet.

Solar phone chargers vary in power from 1 to 16 watts. That’s the rated power under ideal sunlight conditions. Actual power will be lower. If you’re familiar with how slow it is to charge your phone from a computer USB port (2.5 watts) you’ll be prepared for how slow a small solar charger (1 watt or less) will be. This is why smaller solar chargers use a solar battery to store the power.

The smallest solar panels (1 watt) are the size of a mobile phone. Larger solar panels reach the size of 2 to 4 A4 or Letter sheets of paper and consist of a few panels that can be folded for easy storage.

All solar panels work best outdoors, in direct sunlight. If your panels are big, they will even work on cloudy days and indoors next to a window. However they will not generate enough power from indoor lights. If you expect to sit indoors and charge your notebook computer from the power of the fluorescent lights in the ceiling, well, forget it.

All-in-one Solar Phone Chargers

all-in-one-solar-phone-chargersThese are small solar chargers, about the size of a phone. They generate 1 watt of power. They are integrated with a power bank as the solar battery, making them easy to deploy and use – they look like a power bank with a solar panel glued to the top.

They cost from $20 to $50 above, depending on the capacity of the power bank. Their capacity is similar to normal power banks, ranging from 1,500 milliamphours to 10,000 milliamphours. You’ll need 2500 milliamphours to fully recharge a phone, 10,000 milliamphours to fully recharge a tablet.

A 5,000 milliamphour device can take 3 to 6 days of full sunlight to fully charge. Some units can’t even charge the power bank to 100% and can only reach 50% when charging by solar. They need to be plugged into a USB port to charge to 100%.

Their small size and power means that they only work in direct sunlight.

Advantages

  • Compact size.
  • Easy to set up – no cables or folding panels.
  • Often waterproof or splashproof.

Disadvantages

  • Limited power – 1 watt. Many users report insufficient power to charge the battery.
  • Difficult or impossible to change the battery when it gives out after a few years.
  • Power bank is directly below the solar panel, and can be overheated by sunlight.

Useful features

  • Charging via USB to top up the power bank. This should be the common micro USB port. Some still use the older and less common mini USB.
  • Attachment hole to hang on a backpack.

Standalone Folding Panel Solar Chargers

standalone-folding-panel-solar-chargersThese are typically the size of a DVD cover or a sheet of paper when folded. They contain 2 to 4 panels that fold out to cover a larger area. There is no built-in solar battery.

Prices range from $50 to $100 and up, not including a power bank. They are often paired with the manufacturer’s own power bank but as along as they have a standard USB port, you can use any USB power bank.

Rated power ranges from 4 to 16 watts, meaning that they an charge up a 5,000 milliamphour power bank in a few hours or a day. They might even charge when used indoors next to a window or in the shade of a tree. The smaller ones (1 to 2 panels) can be clipped to a backpack, allowing you to charge the power bank when on the move.

Most will only output 5 or 10 watts maximum, throught the USB port. For higher power, you’ll need to use the 12 volt port, designed for charging lead-acid car batteries. The reason to get a panel larger than 5 watts is for power generation even cloudy days – you might get 4 watts with a 16 watt panel, compared to 1 watt with a 4 watt panel.

This is the most popular type solar charger, with many reputable brands in the market – Goal Zero, Brunton, Powerfilm, Powermonkey, Instapark, Voltaic, Joos, Anker, StrongVolt, SolarAid, and Battery Tender.

Advantages

  • Higher power, up to 16 watts and more, making them more reliable sources of power.
  • Flexible. You can charge your phone directly, plug in your own power bank or even use a USB AA battery charger. When the power bank dies, you can replace it.
  • Power bank can be protected from the sun.

Disadvantages

  • Messy, with dangling cables to connect to an external power bank. Some have a built-in pouch to store the cables and power bank.
  • Large, not practical in some situations.
  • Large and floppy – hard to orientate to point directly at the sun. Most of the time you’ll lay it flat on the ground or on a table.

Useful features

  • Works with some panels folded. You should be able to fold up some panels when space is limited and still be able to charge. (The panels should be electrically linked in parallel, not in series.)
  • Daisy-chaining – connecting two or more units together for more power, while still charging the same power bank.
  • Splash-proof. Many are rain-resistant, but you’ll still need to keep your power bank or phone covered.
  • Attachment holes to hang on a backpack or tent.

Tips

  • Place cloth between the panels when folding them, to stop the plastic coverings from scratching each other.
  • Use a PC screen protector to protect the panel coverings from scratches.

Backpack Solar Chargers

backpack-solar-chargersSome solar chargers are built into a backpack. They combine the convenience of an all-in-one charger with the power of a standalone solar panel. Rated power varies from 2 to 4 watts.

This is a niche market, with few big brands. Quality and reliability vary a lot. Be careful when ordering online. Some solar backpacks are quite small.

Advantages

  • No need to set up. Solar panel is always deployed.
  • More powerful than all-in-one chargers.

Disadvantages

  • Less powerful than folding panel solar chargers.
  • Inflexible. You can’t mix-and-match with a different bag with the solar panel, unless the panel is detachable.
  • Looks geeky.

Useful features

  • Plug-in USB power bank allows you to replace the supplied power bank. Those that don’t have a replaceable USB power bank should be avoided.
  • Detachable solar panels allow you to use the solar panels without the bag. This is especially useful if the bag is damaged beyond repair.

The Best Solar Phone Charger

Solar chargers are all about power. You should get the largest solar panel that you can comfortably carry around. The smaller the panel, the higher the chances that it won’t be powerful enough to charge your battery quickly, or even charge at all. A larger solar panel means that you can get a charge even under non-ideal conditions.

The larger solar chargers can be used to power a tablet, but laptop computers will need higher voltages and power. Don’t expect a phone charger or power bank to charge your laptop. You’ll need different, larger equipment, including a 12 volt solar battery.

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