The authors would like to thank the following individuals for their contributions. Editing and other research support was provided by Claire Bolyard, Michael Deneen, Madeline Geocaris, and Mike Meshek. Helpful review and comments were provided by Sam Baldwin, Jaquelin Cochran, Chris Namovicz, Keith Parks, Gian Porro, and Paul Spitsen.

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office, U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office, U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Water Power Technologies Office and U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Office of Strategic Analysis. The views expressed herein do not necessarily represent the views of the DOE or the U.S. Government. This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. U.S. Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.