Can you force your neighbor to trim their trees if it shades your PV system? As California moves towards reaching the goals of the California Solar Initiative and beyond, disputes relating to solar access are likely to grow. In California, the Solar Shade Control Act (sections 25980–25986 of the California Public Resources Code) governs solar access. The Act was passed in 1978 and until 2008 stated that trees or shrubs may not cast a shadow over more than ten percent of a solar collector on a neighboring property at any one time during the hours of 10:00 a.m. and 2:00 p.m.

A dispute between two Santa Clara County neighbors[1] was one of the first to raise widespread awareness of this conflict.  Citing the Act, a PV system owner brought criminal charges against a neighbor because the PV system he installed in 2001 was shaded by the neighbor’s trees that were planted six years prior to the installation. The lawsuit lasted from 2001 to 2008 and cost $37,000 in legal fees.  Ultimately, the tree owners were convicted and ordered to cut down a portion of the trees. Six months after this ruling, California amended the Act to account for existing trees.   The amended law “exempts all trees and shrubs planted prior to the time of the installation of a solar collector.In other words, the Act allows trees and shrubs to grow and shade solar panels without penalty as long as they predate the neighboring solar collector.[2]”

Since 2008, lawsuits in California[3] and the rest of the country[4] have continued to surface. In all these lawsuits, both sides argue their environmental benefits. PV system owners cite that the PV system avoids more CO2 emissions over the course of a year, while tree owners argue that trees provide shading which offsets the need for air conditioners to run as much in warm summer months and provides habitat and food for local animals. No matter the merits of either argument, recent rulings have been decided by local laws.

The revised Act has implications for both residential and commercial building owners in California. Before installing PV, the site analysis must take into account not only shading from current trees, but also future impact of nearby trees that will grow over time. Likewise, someone planting a tree must see if any PV systems are installed nearby and either select a different location for the tree or plan to prune it over time.