"Shadow state" discovery could dramatically boost solar power efficiency

Researchers at the University of Texas say it is possible to hike the energy yield of solar cells by exploiting what they call a photon's "shadow state", doubling the number of electrons that may be harvested in the process. They claim the discovery could up the theoretical maximum efficiency of silicon solar cells from 31 to 44 percent.

Prior research led by chemist Xiaoyang Zhu demonstrated that a theoretical increase in efficiency to as high as 66 percent would be possible if solar cells could be made to additionally harvest so-called "hot electrons", residual heat energy that is lost within about a picosecond after a cell absorbs a photon. Zhu then found that this was possible, but only when harvesting photons from "highly focused" sunlight, impractical in real-world applications.

But the team's latest findings point to an alternative means of boosting efficiency. The organic plastic semiconductor pentacene, when absorbing a photon, creates an exciton (an electron paired with an electron hole) which is quantum mechanically coupled to a dark "shadow state" multiexciton from which an additional electron can be harvested. This way, a photon provides double the electrons. Zhu says that the process could see solar cell efficiency increase to 44 percent without the need for a focused solar beam.

"Plastic semiconductor solar cell production has great advantages, one of which is low cost," said Zhu. "Combined with the vast capabilities for molecular design and synthesis, our discovery opens the door to an exciting new approach for solar energy conversion, leading to much higher efficiencies."

The latest University of Texas findings were published on December 16 inScience.

mPowerPad - all-in-one portable solar charger, radio, reading light, torch, and ultrasonic insect repellent

With recent advances in photovoltaic panels and rechargeable batteries, it's only natural that there should now be an influx of solar-powered electronic devices. Just last week we profiled the Sunbox solar power system, that uses energy from the Sun to power three kinds of lights, recharge AA batteries, and juice up mobile phones. Now, it's time to take a look at a similar product, Third Wave Power's mPowerPad. It can charge mobile devices through its two USB ports, along with serving as a radio, flashlight, reading lamp, and even an ultrasonic insect-repelling device. As you might have noted in the photo, however, it has no external controls ... so how are you supposed to use the thing?

Third Wave describes the mPowerPad as the "world's first All-in-One portable solar charger with gesture-based technology." This doesn't mean that you gesture to it, but rather gesture with it - the pad contains an accelerometer, that allows users to change settings and functions by tilting or turning the device. That feature isn't just a quirky gimmick. Combined with its water-, dust- and shock-resistant qualities, the pad's lack of the traditional protruding knobs and switches makes it a fairly rugged little unit.

One does have to wonder if unintentional switches could be activated when simply moving the device around, although presumably this has been thought of.

In order to reach its full 2500mAh battery capacity, the mPowerPad's 4-watt solar panel must bask in the Sun for a little under six hours - it can likewise be charged from mains power or a car adapter in just one hour. A full charge is said to provide up to 20 hours of 8 watt bulb-equivalent illumination, radio listening, or bug-bothering. That figures goes down to 4-5 hours if it's simultaneously charging another device. The pad can also completely recharge an iPhone, reportedly in the same amount of time it would take using a traditional AC outlet.

The mPowerPad was unveiled in Singapore this month, and should start shipping in January. It is priced at US$80.

LuminAID solar-powered inflatable lantern - simply a good idea

Although it can be considered as a basic human need alongside food, water and shelter, 1.6 billion people all over the world have no access to stable and safe source of light. It's a situation that two bright young Architecture graduates are aiming to combat with the LuminAID solar-powered lantern. Like the Solar Pebble initiative, the LuminAID lantern is designed to address dependence on kerosene lamps in the developing world and its extremely lightweight and easy to transport inflatable design is also targeted at use in disaster relief situations ... plus it makes a very handy addition to your camping kit.

At first glance the LuminAID resembles a simple plastic bag, but its coating is made of flexible, semi-transparent waterproof material with a printed dot matrix to diffuse light and it incorporates a very thin solar panel, bright LEDs that provide the light source and a reinforced handle for easy carrying.

LuminAID is fully charged after 4-6 hours in sunlight makes and is reportedly good for up to four hours of lighting at 35 lumens, or up to six hours at 20 lumens. The battery can be recharged 800 times.

Founded by Anna Stork and Andrea Sreshta, both graduates from the Columbia Graduate School of Architecture, Planning & Preservation in New York LuminAID Lab is currently field testing the inflatable lamp is in Rajasthan, India, where fifty percent of households lack electricity. It's being distributed to rural schools, homes and small-business owners.

LuminAID Lab says 100 percent of funds will go to producing and distributing the LuminAID lights to you and to our community projects.

It's possible to back LuminAID project by purchasing the lamp via onIndieGoGo. A pledge of US$25 results in purchasing two units - someone in need will obtain one lamp for free, while you'll get your own too.