Unintended Outcome? Required Solar Panels on New Houses Limits Future Urban Forest

At today’s meeting of the California Energy Commission, an update to the California Building Energy Efficiency Standards was passed that would require solar panels on the roof of all new residential construction.  In the abstract, I am a strong supporter of distributed solar generation, especially as a means to reduce impacts to wildlands from extensive solar arrays and distribution systems.  The update was passed through on a Negative Declaration, with no adverse impacts to the environment anticipated.

Required solar photovoltaic panels on all new construction, however, will dramatically impact the ability of developers of and neighbors to new housing to plant and maintain trees for shade and their other benefits.  California has a solar shade law, the Solar Shade Control Act, which prohibits planting of trees and shrubs that would shade more than 10% of an active or passive solar collector between 10 a.m. and 2 p.m.

The net result of these two regulations is that the number, type, and location of trees that can be planted in new housing developments will be dramatically constrained, and those living next to new construction will be constrained from planting trees for beneficial shade if they might eventually shade the solar panels next door. I don’t think the Energy Commission thought about this, or at least they didn’t include it in their environmental review. The conflict between urban forest benefits and the solar shade law has implications for stormwater management because trees reduce peak flows and help to improve stormwater quality.

Obviously there is a tradeoff between access to the sun for solar power and the benefits of a healthy urban forest.  The ability to have both an urban forest and distributed solar generation depends on planners, urban designers, and regulators working out the tradeoffs ahead of time — figuring out the lost benefits from shade trees (to biodiversity, local temperature and cooling costs, stormwater quality and quality) relative to the energy savings from solar panels not being shaded.

Let me know what you think. Have I missed something?

Travis Longcore, Ph.D.
May 9, 2018