Solar access of residential rooftops in four California cities

TitleSolar access of residential rooftops in four California cities
Publication TypeJournal Article
Year of Publication2009
AuthorsLevinson, Ronnen M., Hashem Akbari, Melvin Pomerantz, and Smita Gupta
JournalSolar Energy
Volume83
Start Page2120
Issue12
Pagination2120-2135
Date Published12/2009
Keywordscalifornia, photovoltaics, Residential rooftops, shading, Solar access, Trees
Abstract

Shadows cast by trees and buildings can limit the solar access of rooftop solar-energy systems, including photovoltaic panels and thermal collectors. This study characterizes residential rooftop shading in Sacramento, San Jose, Los Angeles and San Diego, CA. Our analysis can be used to better estimate power production and/or thermal collection by rooftop solar-energy equipment. It can also be considered when designing programs to plant shade trees.

High-resolution orthophotos and LiDAR (Light Detection And Ranging) measurements of surface height were used to create a digital elevation model of all trees and buildings in a well-treed 2.5-4 km2 residential neighborhood. On-hour shading of roofing planes (the flat elements of roofs) was computed geometrically from the digital elevation model. Values in future years were determined by repeating these calculations after simulating tree growth. Parcel boundaries were used to determine the extent to which roofing planes were shaded by trees and buildings in neighboring parcels.

For the subset of S + SW + W-facing planes on which solar equipment is commonly installed for maximum solar access, absolute light loss in spring, summer and fall peaked about 2 to 4 h after sunrise and about 2 to 4 h before sunset. The fraction of annual insolation lost to shading increased from 0.07-0.08 in the year of surface-height measurement to 0.11-0.14 after 30 years of tree growth. Only about 10% of this loss resulted from shading by trees and buildings in neighboring parcels.

URLhttp://www.sciencedirect.com/science/article/pii/S0038092X0900173X
DOI10.1016/j.solener.2009.07.016