Government Technology

Solar Map Helps San Francisco Residents Plan Solar Power Installations

January 7, 2009 By

Cities wanting to remove the guesswork from solar power installations are turning to friendlier technology for citizens. Since typing a street address into a Web site is all it takes to determine how much solar power can be obtained from a rooftop installation, who wouldn't take a look?

An exemplar is the San Francisco Solar Map that lets residents view buildings that are equipped with solar power. Users also can type their address into the Solar Map site to get an analysis of how much solar power their roof could harness.

"We wanted something that would help people, that would break down some myths about installing solar in San Francisco, and then offer a tool to people who were interested in solar but didn't really know how to take the first step," said Johanna Partin, renewable energy program manager of the San Francisco Department of the Environment.

San Francisco has set a lofty goal: 10,000 roofs equipped with solar power by 2012. As of press time, 871 of the city's roofs had solar panels installed. The Solar Map's goal is to offer residents a simple tool to learn about solar installation. The department envisioned a platform similar to Google Earth, so residents could zoom into the view of their building, according to Partin.

In spring 2007, San Francisco presented the idea to CH2M HILL - an engineering, consulting and construction company. "Mayor [Gavin] Newsom was very interested in promoting solar, and they said, 'Can we quickly come up with a solution that allowed business owners and residents of San Francisco to make an assessment of the solar potential of their building?'" said Dave Hermann, client solutions director of CH2M HILL. "And that was really the genesis of the idea of the Solar Map."

Solar Solutions

The Solar Map combines aerial photography, GIS software and data supplied by the client. "It's a combination of parcel data ... and the tax assessor's database, which then gets the size of each building and the number of floors which we used to come up with an algorithm that estimates the photovoltaic potential for a rooftop," said Ryan Miller, lead technologist for solar mapping initiatives for CH2M HILL.

When someone types a street address into the Web site, the technology identifies objects on the roof that cast shadows, such as HVAC units, skylights, perimeter walls or an adjacent building that's taller. "It takes out the unusable space," Partin said. "It takes out the north-facing side of the roof if it's a pitch roof. It takes out the shaded areas; it takes out roof obstructions and those kinds of things."

CH2M HILL uses "stereo-pair aerial imagery" - taking side-by-side photographs to view three-dimensional features - to build models of the buildings, which are run through a computer rendering that determines where the sun is throughout the year in relationship to the building. This determines the ideal location for solar panels.

San Francisco chose Google Maps as the platform, but Hermann said Microsoft Virtual Earth can be used, and the company is working on implementations using ESRI solutions.

According to Miller, there are two features to the Solar Map. First is the mapping of existing solar installations, which required city-provided data for geocoding - the process of determining geographic coordinates. These data points are mapped through the Solar Map Web portal and incorporate characteristics of each installation, such as system size, the amount of electricity it generates, the installer, a link to the installer's Web site, and photos and comments posted by the home or business owner. This information is displayed after users click on a dot on the map that represents each location where photovoltaic (PV) systems are installed.

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