Archive for March, 2008

New solar technologies

Monday, March 24th, 2008

A recent article (subscription needed) in Science lists new technologies that may decrease costs or/and increase efficiency.

In the past few years, [chemist David] Ginger [of the University of Washington, Seattle] and others point out, solar researchers have hit upon several potential breakthrough technologies but have been stymied at turning that potential into solar cells able to beat out silicon. “The next couple of years will be important to see if we can overcome those hurdles,” Ginger says. Although most of these novel cells are not yet close to commercialization, even one or two successes could dramatically change the landscape of worldwide energy production.

Light hitting today’s photovoltaic cell creates current if there is enough energy to excite the electrons. Efficiency is about 15 – 20% in commercial cells. The rest of light hitting the PV cell becomes waste heat. The theoretical limit of this kind of technology is 31%.

Increasing efficiency
Colors vary with size of quantum dots
Colors vary with size of quantum dots

The quantum world is different. Varying the size of quantum dots (crystals of a few hundred or thousand atoms) changes the colors absorbed or emitted. Theoretical efficiency may be as high as 44%, or even more with concentrated sunlight, but the details are difficult: efficiency today is only 2.5%, up from 1.6%.

To learn more:
Nozik and Hanna,
Los Alamos,
or just search on quantum dot.

Cheaper technologies
Organic molecules, such as plastics, are cheaper to manufacture, but they respond to a smaller part of the spectrum, and waste most of the light. Add some metal nanoparticles, and there is surface plasmon resonance: light causes the nanoparticle to act like an antenna, capturing and channeling more of the light.

The good news is that the use of silver nanoparticles increases efficiency 40%; the bad news is that it is still less than 1%. Still, Ginger calls such a large increase “very promising.”

Another approach to organic solar cells is to increase the surface areas between the layers by shifting from one layer on top of another to layers that interpenetrate: bulk heterojunction. Alan Heeger of the University of California feels they may be ready for the market by 2010.

Other research strategies are being pursued.

For now, there appears to be no shortage of ideas about creating new high-efficiency, low-cost cells. But whether any of these ideas will have what it takes to beat silicon and revolutionize the solar business remains the field’s biggest unknown. “There are a lot of ways to beat the Shockley limit [31% efficiency limit] on paper, but it’s difficult to realize in the real world,” Nozik says. So far, it’s not for want of trying.

Subsidizing today’s technology
Severin Borenstein, director of University of California Energy Institute, has recently analyzed The Market Value and Cost of Solar Photovoltaic Electricity Production (go here for his talk and to download the analysis).

Borenstein looks at the cost of PV, including considerations re time of day and location. In the near term, the cost/ton greenhouse reductions people (legislators and others) are willing to pay will be less than $20, and it will be a while before they are go above $100/ton, in part because most renewables become good choices at less than that cost. The real cost of today’s technology, no matter what reasonable assumptions are made about the real cost of money or the yearly increase in electricity rates, exceeds $100/ton. Research into better PV looks like a much better use of the yearly $300 million California subsidy of installing solar cells.

It’s easy to reduce greenhouse gas emissions!

Tuesday, March 18th, 2008

Someone asked me to look at his piece on how to tackle climate change without nuclear power, using only 8 wedges. Solving climate change is relatively easy–an underlying assumption of anyone who believes it can be done with only a portion of today’s technology. Policy reports, on the other hand, emphasize the need for applying today’s technology today and increasing energy research by a factor of 3-4 times so that we can apply new technologies tomorrow.

image credit

I’ve seen this optimism often, from the Sierra Club and other environmental groups.

I updated my own calculation for how many wedges are needed. I used a more realistic rate of increase than do Pacala and Socolow, and reduced carbon dioxide emissions 80% by 2058 rather than keeping them the same. These assumptions lead to a need for 18 wedges. If you are good at math, please check! Reductions for all greenhouse gases, not just carbon dioxide, require even more wedges.

How easy will this be? I went to Intergovernmental Panel on Climate Change Working Group 3, and the reference case from the World Energy Outlook 2004 (International Energy Association). These do not use the term wedge, nor do they look at 50 year chunks of time. How do these reports reduce greenhouse gases enough to keep the world below the 2 C temperature increase many climatologists see as too much?

glum face
image credit

They don’t.

IPCC WG3 summarizes 177 analyses. Of those I’ve seen, most give a small number of examples, say a reference and mitigation scenario. Of these 177 mitigation scenarios, 118 reduce GHG emissions enough to keep temperature increase to 3.2-4 C. Only 6 try to find ways to keep the increase at 2 – 2.4 C. None look at even lower caps.

Business as usual (BAU) GHG assumptions are worse than when the studies were done, the world has not acted enough for even more years, so one would expect to find plans for adequate mitigation even more difficult to create today.

There may be post-IPCC analysis on how to keep total GHG emissions low enough to keep temperature increase below 2 C, but I have not seen it.

BAU assumptions assume expanded use of nuclear power, with increases in Asia and elsewhere. I doubt that any of the reports IPCC based its work on produced a mitigation scenario that did not depend on even more nuclear power. Yet none of these reports found sufficient reductions.

Those who communicate that we can do it without nuclear power do more than oppose the largest source of low-GHG electricity that can be added most rapidly today. They tell their listeners that addressing climate change is easy.

If we could agree on the solutions from the policy community, we could move on to the even harder task of cutting GHG emissions even more rapidly and radically. We need to find ways to do more, not argue that we can get by with less.

Small Houses in Sonora

Tuesday, March 4th, 2008

I took Greyhound to Tempe in late December, then friends and I visited south of the Arizona border, the state of Sonora and various people, for several days, including the new year. It was good to see the desert, good to meet new and interesting people. We joined a large family party including a dinner at midnight to greet the new year; it was wonderful and I hope to help with a similar new year’s greeting in 10 months.

I open my eyes more when traveling, attending to details I might ignore at home. In Mexico, I was struck not just by the rickety conditions of many of the houses, but by the size–many of the houses are smaller than my kitchen/dining area.

Image from another area of Mexico
Image from another area of Mexico

Interestingly, Sonora is one of the more affluent areas in Mexico.

Habitat for Humanity
Habitat for Humanity
The Spanish language Habitat for Humanity has more information.

The new Habitat houses are 42 – 49 m2 (450 – 525 ft2) in rural areas, 60 m2 (645 sq ft) in cities. The cost to the family is $74/month for 7 years.

From Lighting the Way, from the InterAcademy Council:

Meeting the basic energy needs of the poorest people on this planet is a moral and social imperative that can and must be pursued in concert with sustainability objectives.…Place priority on achieving much greater access of the world’s poor to clean, affordable, high-quality fuels and electricity. The challenge of expanding access to modern forms of energy revolves primarily around issues of social equity and distribution—the fundamental problem is not one of inadequate global resources, unacceptable environmental damage, or unavailable technologies. Addressing the basic energy needs of the world’s poor is clearly central to the larger goal of sustainable development and must be a top priority for the international community if some dent is to be made in reducing current inequities.

Solar panels and dust
Solar Mexico
Solar Mexico subsidizes photovoltaic panels in Mexico, but some Mexicans in rural areas are buying PVs themselves.

These are needed to pump water and are a more reliable source of electricity than the city utility. Yet dust can reduce the effectiveness, as this NASA picture shows of the Mars Rover:
dusty panels
Rover’s dusty panels improve when the wind blows them clean. In parts of Mexico, the wind makes PVs dustier, and users might benefit from placing PV’s where they can be cleaned.