There are a bazillion solar-powered portable batteries on the market. But they have this little problem: they need the sun in order to work. Inventors and engineers, seeing the need for portable power generation that doesn't require daylight, have been hard at work coming up with some creative ideas for alternative energy sources. Let's call them the Earth element batteries (or just call them awesome). Now you can get a portable battery powered by wind, water, fire, and even mud. Here's the science behind how these mini-generators work.
The FlameStower is a portable device that uses temperature variations to generate electricity. It's based on a simple principle called the thermoelectric effect. To put it in the most simplified way possible: all you need is to put two materials that are effective at moving electricity next to each other and add an electricity-capturing device on one end. Then you heat one side and cool the other. Electrons move from the hot side to the cool side (because they like to be where energy is lower and heat has a higher level of energy, a concept you probably know as diffusion). As they travel into the cool side they release heat energy and voila! You have a battery. Yay physics! This method of power generation is regularly used to power devices in space, where it's easy to generate heat naturally with a decaying radioactive material while subjecting it to the extreme cold temperatures of the vacuum outside.
The FlameStower generator works over any flame or heat source (a cook stove, a campfire, or even the stove in your kitchen). You simply put one end of it over the heat, pour some water into the cold side to keep the temperature there low, and plug in any USB device. They even have a version that can charge your gadgets using a candle. Depending on how powerful your flame is, the FlameStower can produce about 3w of power, which its makers calculate out to about two to four minutes of talk time on your phone for every one minute of charging. You can get one for $70 on their website and their candle charger, which will cost $99, is expected to be available soon.
This neat device is less portable battery and more science experiment. The MudWatt is a DIY kit that allows you to take mud from anywhere, build a small battery that sticks into the mud, and generate enough electricity to power a series of small electronics like an LED light, a clock, or a buzzer. Its purpose is to teach kids how power generation works, but it's also a fun way to experiment with different types of soils and ingredients to see which generate the most electricity.
It works by harnessing the power of microorganisms. Bacteria called shewanella and geobacter live in nearly every type of soil or sediment on earth. They eat sugars they find in the mud and release electrons as waste. The mudwatt battery's anode, which comes into contact with the mud, captures those electrons from the soil and transfers them up through a wire to a cathode, which uses oxygen and protons to react with the electrons and form water, which closes the circuit. It's basically a way-better potato battery. The overall amount of energy generated depends on the health of the bacteria colony in the mud--so theoretically a MudWatt battery could last an eternity as long as the bacteria continue to live and eat.
One of the device's creators, Keegan Cooke, came up with the idea when he worked as a microbiologist developing new fuel cells from bacteria he collected in the deep ocean. He and his partner Kevin Rand have also designed an app that allows you to track the health of your battery, measure its output, and connect with other battery builders around the world. The classic MudWatt is available at its website for $40 -- with less complex (cheaper) and more complex versions coming soon.
Portable Hydropower Plant
A hydropower plant has two main parts. The first is a turbine that spins when water passes over it, generating kinetic energy and essentially transferring the energy of the water movement into mechanical energy of the spinning turbine. The second part is a generator, which captures the mechanical energy of the turbine and converts it into electrical energy that can be used to power anything that needs electricity.
The Blue Freedom mini-plant works the same way, just on a much, much smaller scale. It uses a 12 cm by 6 cm turbine that spins when you plop it into any type of moving water (even shallow water). The turbine turns a rotor that powers a generator located inside the O-shaped main housing. It generate 5 watts of energy, which means that it can fully charge its 5,000 mAh battery in about three to four hours (if the water is flowing about 3 mph). The device also comes with a high-speed USB charging port and integrated LED lamps to create light if you happen to be in the dark when your gadgets go dead. The company recently completed a Kickstarter campaign and is currently in the manufacturing stages.
Portable Wind Turbine
Wind turbines work a lot like hydropower plants -- except instead of water spinning the turbine, which turns a rotor, which creates energy inside a generator, the turbine is spun by the wind. There are a few companies out there making small, portable wind turbines. One of the latest is called the Trinity. This turbine comes in a small 2 lb size and a larger 6 lb version. Each one folds up into a small tube that makes it easy to transport. The smaller size turbine has a 15w generator (and a built-in hand crank if the wind doesn't happen to be blowing when you need power). It has 2 5v USB power outputs and an internal 15,000 mAh battery.
The unique design of this particular turbine is in its blades. The three blades are flat, long, and curved -- and they sit vertically on the round stand. That way they can capture the wind, but still fold up into a neat little tube for travelling. The devices creators believe that the vertical axis is better for capturing wind coming from any direction, something that's not the case in the traditional horizontal blade design. The team just completed a Kickstarter campaign and is hoping to start shipping their turbine by the end of the year.