If a neighbors tree that is shading a solar power system that was installed many years ago (2009 homes were built in 2004) in CA (tree might have been existing in a shorter form and the trees grow very quickly), what are the legal obligations of the neighbor to trim the tree?
The Act requires that
After the installation of a solar collector, a person owning or in control of another property shall not allow a tree or shrub to be placed or, if placed, to grow on that property so as to cast a shadow greater than 10 percent of the collector absorption area upon that solar collector surface at any one time between the hours of 10 a.m. and 2 p.m., local standard time.
The subsequent paragraph pertains to notice that can be given to property owners, and ultimately the tree would be deemable to be a public nuisance and subject to removal. However (25984):
This chapter does not apply to any of the following:
(a) A tree or shrub planted prior to the installation of a solar collector.
(b) A tree planted, grown, or harvested on timberland as defined in Section 4526 or on land devoted to the production of commercial agricultural crops.
(c) The replacement of a tree or shrub that had been growing prior to the installation of a solar collector and that, subsequent to the installation of the solar collector, dies, or is removed for the protection of public health, safety, or the environment.
(d) A tree or shrub that is subject to a city or county ordinance.
In other words, if you place a collector where an existing plant can eventually cause shade on the collector (it can be a short tree), you have no remedy. This follows the doctrine of coming to the nuisance.