While many traditional fossil fuel technologies show slow growth in efficiency and design, solar power has instead yielded steady and rapid advances. While many question why a "killer app" solar product has not yet reached the market after years of hype, it is hard to deny the fact that solar costs both subsidized and unsubsidized have been dropping dramatically, being halved every 10 years.
With current costs ranging from 15 to 20 cents per kWh, and wholesale coal power costs between 1.5 and 2.5 cents per kWh (and nuclear in a similar range -- 1.7 cents per kWh by estimates from the Nuclear Energy Institute), solar still has a ways to go and likely a few decades before being ready for full deployment. Still, few technologies show the rapid growth in efficiency solar has and few utilize such a common resource as silicon, so the value of ongoing solar research is apparent.
UNSW's ARC Photovoltaic Centre of Excellence reported a significant milestone this week, with the announcement of the world's first 25 percent efficient unconcentrated solar silicon cells. They had previously held the 24.7 percent efficient silicon cell record, but were denied the 25 percent milestone due to gaps in the understanding of sunlight and its effect on silicon.
New research has led to revisions in how incident light efficiency is calculated. As a result, their record-holding design has reached the 25 percent mark, a "magic" number according to many industry experts. The cell, designed by Professors Martin Green and Stuart Wenham has a wide lead over competitive offerings, according to the Centre. UNSW holds six solar world records now.
Centre Executive Research Director, Scientia Professor Martin Green described how the new research improved the understanding of the efficiency. He states, "Since the weights of the colours in sunlight change during the day, solar cells are measured under a standard colour spectrum defined under typical operational meteorological conditions. Improvements in understanding atmospheric effects upon the colour content of sunlight led to a revision of the standard spectrum in April. The new spectrum has a higher energy content both down the blue end of the spectrum and at the opposite red end with, dare I say it, relatively less green."
While suggesting less green of anything may seem like heresy in the alternative energy industry, it’s good news for the Centre as it means their cells are operating more efficiently than expected. The Centre's cell posted larger gains than its competitors following the revision. It is now 6 percent more efficient than the next most efficient competitor, according to Professor Green.
The Centre's cell is approaching the important 29 percent efficiency threshold -- the maximum theoretical efficiency for a first generation silicon photovoltaic solar cell. Dr Anita Ho-Baillie, who heads the Centre's high efficiency cell research effort, says the new research is a big boost "because our cells push the boundaries of response into the extremities of the spectrum."
She states, "Blue light is absorbed strongly, very close to the cell surface where we go to great pains to make sure it is not wasted. Just the opposite, the red light is only weakly absorbed and we have to use special design features to trap it into the cell."
Professor Green states, "These light-trapping features make our cells act as if they were much thicker than they are. This already has had an important spin-off in allowing us to work with CSG Solar to develop commercial 'thin-film' silicon-on-glass solar cells that are over 100 times thinner than conventional silicon cells."
The biggest goal of UNSW is now to adapt the ultra-high efficiency cells for mass production which should lead to more cost reductions. ARC Centre Director, Professor Stuart Wenham, adds,"Our main efforts now are focused on getting these efficiency improvements into commercial production. Production compatible versions of our high efficiency technology are being introduced into production as we speak."
The center has a close relationship with the world's biggest solar manufacturers, thanks in part to Dr Jianhua Zhao and Dr Aihua Wang, who fabricated the record-setting cell and have since left the Centre to establish China Sunergy, one of the world's largest photovoltaic manufacturers. Professor Green describes, "China was the largest manufacturer of solar cells internationally in 2007 with 70 per cent of the output from companies with our former UNSW students either Chief Executive Officers or Chief Technical Officers."