Hydrogen. Lithium. Solar. Flywheels. Ethanol. Now add compressed air to the list of possible energy sources that will propel future vehicles. French automaker PSA Peugeotannounced this month it will build a hybrid gasoline vehicle that can store energy as compressed air. The air-hybrid car, the AFP reports, should achieve 81 miles per gallon, while emitting just a fraction of the carbon dioxide per mile of conventional vehicles. "This breakthrough technology…represents a key step towards the two-liter-per-hundred-kilometer car by 2020," said Chief Executive Philippe Varin at a press conference.

The "breakthrough," however, has been a long time coming. Like many auto technologies, the first versions were tested in the mid-1800s without ever gaining much traction. Although materials and engineering are better now, today’s engines work in a similar way. Fresh air is pumped into a chamber under high pressure, and then released into "combustion" chambers where the air forces down pistons and turns the wheels.

It would seem that compressed air has plenty going for it: It’s compact, emissions-free (except for the energy to compress the air) and dirt cheap compared to the typical $11,000 lithium battery pack. But that has not inspired many carmakers to jump on the technology.

It turns out it’s hard to match the efficiency or the energy density of rival batteries or liquid fuels: "Air compressors are one of the least-efficient machines to convert electricity to work," said Harold Kung, professor of chemical and biological engineering at Northwestern University, to the AP. "Why not use the electricity directly, as in electric cars? From an energy utilization point of view, the compressed (air) car does not make sense." And Indian carmaker Tata has reported they’ve struggled to get enough compressed air energy into their Airpod (although the buglike three-seater should go on sale soon).

Despite their drawbacks, compressed-air cars (you can see a line developed by the firm MDI) are cheap, straightforward to design, and demand little in the way of exotic technology or infrastructure. That, at least, has been enough to convince Peugeot that an affordable compressed-air car offers another alternative to today’s hybrids.

It may be full of potential, but wind power is still a young industry with many design challenges that prevent it from scaling up. From an environmental perspective, how can designers and entrepreneurs lower the technology’s impact on local ecosystems? Bird populations in particular, can be harmed by the swiftly spinning turbines. And how can wind power be brought to a wider variety of landscapes, including urban ones, as opposed to the rural, mountainous, or desert areas where you typically find fields of hulking turbines?

A new manufacturer thinks its figured out the answers to these two questions with a new turbine design called the Windstrument. They’re hailing the product as "a truly affordable wind energy system,” that’s "quiet and powerful, bird safe, and scalable."

This last attribute is particularly compelling. The technology is compact and unobtrusive enough to be installed in an urban area for smaller-scale use. For homes or businesses who don’t require much power, a pole with a single, four-foot turbine would suffice, and a rooftop mounting option is available. But for the power needs of a whole neighborhood or an industrial complex, for example, many turbines can be added to a single pole, a configuration the company calls a “Windorchard.”

The shape of the turbine’s blades are called conical helicoids, inspired by the design of racing sails and capable of sustaining their functionality even in fierce winds. And unlike other turbines, the Windstrument’s design disperses the air in such a way that birds don’t get sucked in. In nearly two years of trials in a wetland heavily populated by birds, not a single one was harmed.

So far it seems the biggest problem for the company is scaling up their own production. Right now, they’re just able to produce "several thousand turbines a month. Our goal is to quadruple that, at a minimum, over the next year," according to their website. Unified Energies International, the Michigan-based firm behind the Windstrument, just announced this summer that they had patented the design and were working with a plastics company to bring the product to market.

It’s no science-fiction fantasy. With wearable gadgets like Google’s Project Glass on the horizon, all that’s missing is an ultraportable power source that never needs recharging--like, say, your own body heat. A startup in Corvallis, Oregon, has developed a small chip that can turn body heat into electric energy, using the same technology found in solar panels. “We absorb the heat from your body, and that heat is funneled through a thermoelectric generator that converts it into electric power,” says Perpetua Power Vice President Jerry Wiant. The result: a single, square-inch TEGwear chip generates enough power (up to 3
watts volts) to power anything from the accelerometer in your pedometer to the wireless headset for your smartphone.

The physics behind TEGwear is basic: Your body is always generating heat, even when you are asleep. And heat, regardless of the source, excites electrons. The flow of electrons, in turn, generates electricity. The tricky part is harnessing enough electricity to power a small device. Wiant says TEGwear will do just that, as long as the chip is either touching your skin or separated from it by only a thin layer of clothing.

Originally developed using technology licensed from the Pacific Northwest National Laboratory (a Department of Energy research lab in Richland, Washington), TEGwear-powered devices are still in development and won’t hit the market until 2014. But this ultimate clean tech has a whole host of potential applications, from mobile health to national security. The company will demo the device on a new Swatch Touch watch at the annual Consumer Electronics Show in Las Vegas this month. In addition, it has a grant from the National Science Foundation to develop a prototype wristband to track the whereabouts of people with Alzheimer’s as well as funding from Department of Homeland Security’s Science and Technology Division to power wearable devices used for surveillance operations. It’s also partnered with several private companies to develop body-powered smartphone accessories (like headsets), health-monitoring devices (such as wearable heart-rate monitors), and military applications (like monitoring a soldier’s vital signs and location while on a combat mission).

The added bonus of using body-powered devices? They eliminate the toxic waste generated by the heavy metals used in the billions of batteries we currently use--and toss--each year. In other words, your body heat is good, clean energy.