Analysis Shows Great Potential for Rooftop Solar on City of Austin Buildings
By Mary Michael
With climate change worsening and a new administration widely expected to ignore climate action for the next four years, expanding local clean energy is even more important. Rooftop solar is a rapidly growing source of clean energy, and it is a great way for Texas to do its part to reduce harmful pollution.
Austin is a particularly great city for rooftop solar. The capital city gets plenty of sunshine, with around 300 sunny days yearly. Not only do we have a climate suitable for solar energy, but the city also has a municipally owned utility, Austin Energy, which has several programs encouraging rooftop solar.
Though Austin is in a great position to host a massive amount of rooftop solar, the city’s solar potential is largely untapped. Public Citizen conducted a project to estimate the solar energy potential of City of Austin-owned buildings to demonstrate this untapped potential. We used ArcGIS, a mapping tool, to calculate how much energy these buildings could produce from solar in a year and a separate analysis to find the total capacity (size) of the solar panel systems that could be installed.
Calculations
We used a list of city-owned buildings for the solar production analysis and geocoded them into ArcGIS. These buildings included libraries, city department offices, police department buildings, water treatment plant buildings, and more. Next, we created a digital surface model, converted from LIDAR data, to incorporate the detailed elevation data necessary to run the analysis. We then used the “Raster Solar Radiation Tool” on these buildings to calculate the amount of solar radiation they receive over a year. We used the rooftop area and converted solar radiation to determine the annual power production potential. We calculated using 75% of the roof area to account for HVAC systems and other parts of rooftops unsuitable for solar.
For the capacity analysis, we used the same list of buildings from the ArcGIS analysis but excluded buildings within the downtown utility area because it’s more difficult to deploy rooftop solar on that part of the electric grid. We calculated the system size of each building by finding the building’s usable rooftop area for solar. We did this on Google Earth using the “Measure Area” tool. In addition to HVAC systems, we excluded areas covered by trees or other obstacles. We also excluded areas of the roof where solar installation already exists.
Once we had the usable roof area in square meters, we calculated how many solar panels could be installed by dividing the roof area by the size of one solar panel, which is 2.3 square meters on average. From there, we found the system size by multiplying the number of solar panels by 400 watts, which is the average efficiency of solar panels, divided by 1000 to convert to kilowatts. For our final calculation, we reduced the system size by 10% to account for any errors and avoid overestimating the solar potential.
Results
We found that 96 city-owned buildings could produce over 38,000 megawatt-hours (MWh) of electricity annually. For the system size analysis, we examined 63 buildings that cumulatively have a capacity of 14 megawatts (MW) of rooftop solar.
GIS Analysis Results:
Our interactive GIS map has three pieces of data: The name of the building, the solar radiation it receives, and the annual power production potential in MWh it could produce with rooftop solar. You can click on the purple circles to find the name of the building and click on the yellow, orange, and red polygons to find the power production potential. The solar radiation layer shows which parts of the building are more suitable for solar panels based on the sunlight they receive.
Capacity Analysis Results:
Why it matters
This analysis demonstrates the city’s untapped potential and shows that rooftop solar can generate lots of electricity. The city could produce a lot of energy just from their buildings alone. Installing solar on all city buildings would be good for energy resiliency and sustainability. It would set a good example for residents, businesses, and other municipalities. Austin Energy has a community solar program, and the energy generated from city buildings could be used to expand this program. The community solar program currently has three sites with a capacity of 4.5 MW, but they could potentially add another 14 MW with the buildings studied in our solar analysis. This would also help make progress toward some of the city’s sustainability goals, such as those outlined in the Climate Equity Plan and the Austin Resource Generation Plan.
Regarding Austin’s climate goals, the City Council has agreed to move forward on an environmental investment plan. This plan will involve creating a climate bond package to fund sustainable projects. The climate bond will be put on the ballot no later than 2026, and if it passes, it could provide significant funding for rooftop solar.
Mary Michael recently graduated from the University of Texas at Austin with a B.A. in Sustainability Studies. She is the Fall 2024 Environmental Policy and Advocacy Intern for the Texas Office of Public Citizen in Austin.