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Board raises solar-access concerns after UDC shadow studies; planners did not model PV performance
Summary
Advisory board members asked whether new taller buildings in revised zoning could shade existing residential photovoltaic (PV) systems. City planners have produced shadow studies but did not model PV energy losses; staff offered to investigate site-specific cases.
Questions from board members flagged potential impacts of taller buildings on existing rooftop solar.
Board member Kolani asked whether the city's shadow studies had considered effects on photovoltaic arrays "throughout the year" and whether that analysis was integrated into the UDC work. Tom Rogers replied, "We have not considered and looked at what partial or complete shade will do to an existing array," noting there are many variables (array height, building height, separation and orientation) that complicate a generalized model.
Rogers explained the city had produced illustrative shadow studies for a 37-foot building at solstices to show what shadows would look like on neighboring lots; those materials are posted on the Engage Bozeman site. He said the city's current minimum building setback standard requires five feet from a lot line on each side, producing a minimum 10-foot separation between adjacent structures. Rogers invited the board to provide specific addresses or cases for staff to perform site inspections and data analysis: "If you know something, I'd love to learn from that experience," he said.
Board members and public commenters said there have been instances where new apartment buildings partly covered residential PV arrays, reducing residents' ability to use or recoup the investment in rooftop solar. Rogers and staff committed to reviewing concrete cases and incorporating findings into recommendations if warranted.
