Sunday, August 10, 2014

Silicon Solar Cells Transformed

David Ginley, NREL

The limitation of silicon solar is silver for contacts which maxes out at around 5 TWatt.  Single cell efficiency maximizes out at around 29% efficiency. Bell Labs first cells were 6% efficient.  World installed solar is .3 TWatts by 2014.
Chinese dominate the PV market because they are the only ones who built silicon plants when supply reached scarcity.
Panasonic has a 25.6% efficiency HIT cell [mono thin crystalline silicon wafer surrounded by ultra-thin amorphous silicon layers] with contacts on the back .  SunPower has a 25% six inch cell built on their production line (but not in production yet).  Sharp also has a 25% cell.  
Theoretical efficiency of a single junction cell under 1000 sun concentration is around 33%.
25 year warranty but some companies are going to 35 with a possibility of 50 years and it is not the silicon cell with fails but the packaging or contacts.
Fifty cents per watt is the accessible price now.
University of New South Wales is working on thin film silicon, 20 microns rather than the 75 microns now used. 16.8% efficiency.
Tandem cells - silicon paired with other substances including  quantum dots, perovskites, theoretically to 34%
Multiple exciton generation (MEG) in colloidal silicon nanocrystals can theoretically go beyond the existing limits.  Two or three photons per carrier.

Addressing Climate Change through Community Engagement and Behavior Change

David Gershon of the Empowerment Institute
webinar, slides and recording at

70% of atmospheric carbon comes from cities
Second order social change:  empower transform innovate collaborate disseminate
Gershon founded Ecoteam - “unsurpassed in changing behavior” which sustained over time
Everett Rogers' Diffusion of Innovation:  early adopters 15% (tipping point) early majority 35% late majority 35% laggards 15%
15% population makes the tipping point
Laggards never participate and no use trying to engage them [the climate change movement, seemingly, has concentrated on the laggards for the last 20 years]
Neighborhood is the scalable diffusion platform, usually with 25% participation
Adjacent possibilities:  becoming a driver for a green economy, generating social capital, building “high performance” teams, promoting social innovation and collaboration, creating socially engaged citizenry
Philadelphia wanted to use the EcoTeam model to address other social change issues, Livable Neighborhood campaign, 101 block-based teams formed
NYC for disaster resilience after 9/11:  Ready New York’s All Together Now, 153 buildings or blocks, 5,000 participants, 68% recruitment level
Low Carbon Diet Program:  Portland OR, 41% block participation, 25% CO2 reduction, Davis CA first US city to develop carbon neutral plan by 2050
Global warming cafe to get large numbers of people to participate and form smaller teams
[Robin] Dunbar strategy:  150 people at Dunbar limit is a cool block, 1,500 cool neighborhood, 15,000 cool ecodistrict, to cool city - now working in Northern CA on Cool City Challenge
Better lifestyles are infectious
12 hour webinar series 10/9 - 12/18, 2014 at