Tag Archives: solar energy

Solar toilet turns sewage into power

One Per Cent: Solar toilet turns sewage into power.

Combine sunlight and sewage and what do you get? Sanitation, of course.

Michael Hoffmann at the California Institute of Technology has been experimenting with solar-powered water treatment on a small scale. Now he plans to incorporate this technology into a portable toilet.

Sunlight powers an electrochemical reaction with human waste in water that generates microbe-killing oxidants and releases hydrogen gas. The researchers plan to collect the hydrogen in a fuel cell to power a light or possibly even a self-cleaning mechanism.

Solar.jpg(Image: Brian Lee)

He received a grant this week from the Bill and Melinda Gates Foundation to build a prototype. He says he can build one toilet for $2000 and hopes to reduce the cost through design refinement and mass production.

This grant is part of the Gates Foundation’s latest global public health initiative to improve sanitation.

Several other awarded projects propose to build toilets that generate energy for the community, either processing solid waste into biological charcoal or vaporising it into plasma that generates hydrogen and carbon monoxide to run a fuel cell.

According to World Health Organization estimates, 2.6 billion people – about 40 per cent of the world’s population – do not have access to sanitation.

New solar cell: Engineers crack full-spectrum solar challenge

New solar cell: Engineers crack full-spectrum solar challenge.

ScienceDaily (June 26, 2011) — In a paper published in Nature Photonics, U of T Engineering researchers report a new solar cell that may pave the way to inexpensive coatings that efficiently convert the sun’s rays to electricity.

The U of T researchers, led by Professor Ted Sargent, report the first efficient tandem solar cell based on colloidal quantum dots (CQD). “The U of T device is a stack of two light-absorbing layers — one tuned to capture the sun’s visible rays, the other engineered to harvest the half of the sun’s power that lies in the infrared,” said lead author Dr. Xihua Wang.

“We needed a breakthrough in architecting the interface between the visible and infrared junction,” said Sargent, a Professor of Electrical and Computer Engineering at the University of Toronto, who is also the Canada Research Chair in Nanotechnology. “The team engineered a cascade — really a waterfall — of nanometers-thick materials to shuttle electrons between the visible and infrared layers.”

According to doctoral student Ghada Koleilat, “We needed a new strategy — which we call the Graded Recombination Layer — so that our visible and infrared light-harvesters could be linked together efficiently, without any compromise to either layer.”

The team pioneered solar cells made using CQD, nanoscale materials that can readily 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 work expands the Toronto team’s world-leading 5.6 per cent efficient colloidal quantum dot solar cells.

“Building efficient, cost-effective solar cells is a grand global challenge. The University of Toronto is extremely proud of its world-class leadership in the field,” said Professor Farid Najm, Chair of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering.

Sargent is hopeful that in five years solar cells using the graded recombination layer published in the Nature Photonics paper will be integrated into building materials, mobile devices, and automobile parts.

“The solar community — and the world — needs a solar cell that is over 10% efficient, and that dramatically improves on today’s photovoltaic module price points,” said Sargent. “This advance lights up a practical path to engineering high-efficiency solar cells that make the best use of the diverse photons making up the sun’s broad palette.”

The publication was based in part on work supported by an award made by the King Abdullah University of Science and Technology (KAUST), by the Ontario Research Fund Research Excellence Program, and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. Equipment from Angstrom Engineering and Innovative Technology enabled the research.