Sunlight to Electricity: Navigating the Field An Energy Technology Distillate of the Andlinger Center for Energy and the Environment Princeton University Contributors Barry P. Rand, Forrest Meggers, William C. Witt, Manali Gokhale, Samantha Walter, Robert Socolow August 2017 Table of Contents Acknowledgements .............................................................................................................................. page 2 Article 1: Overview ............................................................................................................................... page 3 Article 2: Key Concepts and Vocabulary ............................................................................................. page 6 Article 3: From the Sun to the Solar Project ....................................................................................... page 9 A. The Sun and the Earth ............................................................................................................. page 9 B. The scale of current solar power ...........................................................................................page 11 C. Solar energy projects .............................................................................................................page 14 D. Distributed generation ...........................................................................................................page 15 E. Balance of system .................................................................................................................. page 16 F. Building-integrated photovoltaics ..........................................................................................page 18 Article 4: Solar Cell Technology .........................................................................................................page 20 A. The solar cell ..........................................................................................................................page 20 B. Today’s technologies ..............................................................................................................page 23 C. The photovoltaic frontier ........................................................................................................ page 27 D. Energy and greenhouse gas performance indices, materials scarcity, toxicity, end of useful life.. ......................................................................page 29 Article 5: Grid Integration and Policy ................................................................................................ page 31 A. Grid integration and supply variability .................................................................................. page 31 B. Enabling policy .......................................................................................................................page 35 Appendix 1: The Princeton University Solar Project .........................................................................page 40 1 Acknowledgements Ted Borer was a valuable guide to the Princeton University case study. William Hackett, Anne Hoskins, Benjamin Scott Hunter, Ralph Izzo, Tom Kreutz, Tom Leyden, Andrew Mills, and Michael Winka provided insights into enabling policy and commercialization. We benefited from the summer research of three Princeton undergraduates: Angelo Campus, Lindsey Conlan, and Isabella Douglas. An intermediate version of this report was critiqued by the eight graduate students in a Policy Workshop at Princeton University on community solar power taught by Anne Hoskins and Jeanne Fox. Stephen Lassiter, one of these students, judiciously combined his comments with the others – from Vivian Chang, Cara Goldenberg, Jack Hoskins, Zhongshu Li, Eri Nakatani, Sheree Oluwafemi, and Hannah Safford. We also benefited from comments on early drafts from Emily Carter, Philip Chew, Phillip Hannam, David Kanter, Elena Krieger, Eric Larson, Nicolas Lefevre, and Sigurd Wagner. A late draft was helpfully reviewed by Joe Berry, Michael McGehee, Cliff Rechtschaffen, Lenny Tinker, and Jessika Trancik. The production of this report was guided diligently and creatively by Nari Baughman, Darcy Cotten, Joel Oullette, and Jennifer Poacelli. At every stage, our revisions were propelled by Lynn Loo’s commitment to clear and effective communication. The Andlinger Center for Energy and the Environment is grateful to the High Meadows Foundation, the Nicholas Family, and an anonymous donor whose gifts are helping to advance public understanding of critical issues related to energy and the environment through this Energy Technology Distillate. 2 Article 1: Overview The goal of this Distillate is to enable the reader to understand the state of solar energy today and to develop his or her own views of some of the key issues that loom over solar power’s future. Today, for the first time in human history, a commercially 2. How much can balance-of-system costs be significant quantity of solar energy is being turned reduced? The principal challenge of past decades directly into electricity. Global capacity to produce solar was reducing the cost of the solar cell and electricity was about 50 times greater in 2016 than 10 the solar panel that houses the cell. Now, years earlier. Solar power has grown rapidly in Europe, “balance-of-system” costs are emerging as Asia, and North America. the principal cost concerns. The balance of system, here, is all of a solar power project except No one knows how long future solar growth will for the solar panels: the land, the structure that resemble the past. It is conceivable but far from certain holds the panel, any tracking hardware, the that solar power will dominate the global electricity inverters that change the direct current (DC) system by mid-century. There is still a long way to go. In produced by the cell into the alternating current 2016 only about 1.5 percent of total global electricity (AC) required by the user, installation at the site, came from solar power. In the U.S. the percentage was interconnection to the grid, and business costs nearly the same, even though one million U.S. homes such as financing, permitting, and insurance. have solar panels on their roofs and several of the world’s largest solar installations are in the deserts of 3. Will crystalline silicon remain the workhorse the southwestern U.S. of solar power? Today, crystalline silicon has 90 percent of the solar cell market. Can any of This Distillate explores five open questions related to the new thin-film technologies challenge silicon’s solar power’s future: dominance, now that the silicon cell industry has developed so much infrastructure and 1. Will distributed and centralized deployment experience? The crystalline silicon solar cell has both flourish? Solar cell technology is the limitation (thus far) of being available only as spectacularly modular: a solar cell will convert a rigid structure, which limits potential sunlight into electricity whether on a rooftop or in applications. Its competitors are thin films, a multi-thousand-acre field, and assemblages of whose versatility assures that there will be at these cells are housed in panels that are least niche markets for some of them, even if they essentially the same wherever they are used. do not become significant producers of solar Due to this modularity, the plummeting costs electricity. To enter the market, a thin film will of solar cell technology have had a dramatic, need to convert sunlight to electricity at positive impact on the growth of solar power substantially higher efficiency than the at all scales. Future deployment could tilt toward crystalline solar cell, demonstrate stability very large projects because of economies and ease of manufacture, and avoid scarce of scale: large projects have substantially lower or toxic materials. construction costs than small projects, for the same amount of electricity generated. 4. Will solar power subsidies disappear? However, distributed electricity generation, Government policies favorable to solar electricity especially if accompanied by distributed electricity are called “incentives” by their proponents and storage, may enable innovative grids that are “subsidies” by their detractors. Subsidies more flexible and resilient than the centralized have enabled solar energy to mature, and now grids of the past. If deep penetration of they are shrinking, both for centralized and distributed solar generation into electricity distributed generation, as solar power becomes markets is achieved, political support for pro-solar increasingly competitive. The system costs of policy will strengthen, to the likely benefit of incentives for distributed generation were small centralized solar power as well. The path forward when they were paid only to “early adopters,” may well feature parallel development at large but as the fraction of beneficiaries in an eligible and small scale – with much geographical group grows, the non-adopters bear more variation in the mix of the two scales. noticeable costs and push back. 3 On the other side of the argument, those who favor incentives stress their direct Roadmap environmental benefits, including cleaner air and less rapid climate change. Specific to We have endeavored to treat technology and policy distributed generation, they also note that with equal seriousness. We have written for the reader producing electricity closer to the point of use, who has little technical background but an appetite especially in combination with