Group items tagged

In a paper published in Nature Photonics, University of Toronto researchers report the first efficient two-layer solar cell based on colloidal quantum dots (CQD) to capture both visible and near-infrared rays. CQDs are nanoscale materials that can be tuned to respond to specific wavelengths of the visible and invisible spectrum. By capturing such a broad range of light waves - wider than normal solar cells - tandem CQD solar cells can in principle reach up to 42 per cent efficiencies. The best single-junction solar cells are constrained to a maximum of 31 per cent efficiency. (In reality, solar cells that are on the roofs of houses and in consumer products have 14 to 18 per cent efficiency.) The researchers expect that in five years, solar cells using the graded recombination layer paper will be integrated into building materials and mobile devices.

It's a sports car few people will be able to get their hands on. In production since last December, only 500 Lexus LFAs will be produced and they were already sold out in early June 2010 (see photo below). But it's not just its top speed of 325 kilometres per hour that's attracting buyers. The car is being used as a test bed for newly-designed parts made from carbon fibre and plastic. Compared to steel or aluminium, it makes the car stronger and lighter but producing these components is much more time-consuming: only one car is currently being assembled per day. One of the key technologies being used is a high-tech circular loom, guided by lasers, that can weave 3D objects (see video above). The machine's futuristic design attracted lots of media attention two years ago, but the video was pulled for fear it would expose company secrets. Now Lexus is revealing how the loom is being used to create complex 3D parts with varying thicknesses and curved shapes. For example, it can create roof rails by weaving fibres around a core, two layers at time, until twelve layers later a hollow roof rail is produced. The piece can then be moulded and injected with resin to create the finished part. The machine was also used to create the car's chassis and front pillars as well as the steering wheel.

Duke University engineer Nico Hotz has proposed a hybrid solar system in which sunlight heats a combination of water and methanol in a maze of tubes on a rooftop to produce hydrogen. The device is a series of copper tubes coated with a thin layer of aluminum and aluminum oxide and partly filled with catalytic nanoparticles. A combination of water and methanol flows through the tubes, which are sealed in a vacuum. Once the evaporated liquid achieves higher temperatures, tiny amounts of a catalyst are added, which produces hydrogen. This combination of high temperature and added catalysts produces hydrogen very efficiently, Hotz said. The resulting hydrogen can then be immediately directed to a fuel cell to provide electricity to a building during the day, or compressed and stored in a tank to provide power later. After two catalytic reactions, the system produced hydrogen much more efficiently than current technology without significant impurities, Hotz said. The resulting hydrogen can be stored and used on demand in fuel cells. "This set-up allows up to 95 percent of the sunlight to be absorbed with very little being lost as heat to the surroundings," he said. "This is crucial because it permits us to achieve temperatures of well over 200 degrees Celsius within the tubes. By comparison, a standard solar collector can only heat water between 60 and 70 degrees Celsius." Holtz performed a cost analysis, comparing a standard photovoltaic cell, a photocatalytic system, and the hybrid solar-methanol system.  He found that the hybrid system is the least expensive solution, with a total installation cost of $7,900 if designed to fulfill the requirements in summer. The paper describing the results of Hotz's analysis was named the top paper during the ASME Energy Sustainability Fuel Cell 2011 conference in Washington, D.C. Topics: Energy | Nanotech/Materials Science