Solar Map Helps San Francisco Residents Plan Solar Power Installations

Solar maps let citizens investigate their home's solar potential and learn about local installations.

by / January 7, 2009

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.

Information that's publicly available is posted for each solar installation, but Partin said about 1 in 500 owners chose not to participate in the Solar Map.

The second feature of the Solar Map is for people who are interested in installing solar panels. "They enter their address, and that address hits a database that contains their building-specific characteristics. That information is then rendered on the page and includes the PV potential and computations based on that PV potential, such as the amount of CO2 [carbon dioxide] that would be reduced, the [power] output, the estimates of cost, etc.," Miller said.

If users want a more detailed price, they may click on "get cost estimates" and the information is tied into Clean Power Research's Clean Power Estimator. According to Jeff Ressler, product line manager of Clean Power Research, the company was approached by CH2M HILL and San Francisco, who asked that solar economics analysis be added to the map. The information provided by the Solar Map is shared with the estimator.

"The Clean Power Estimator Web services can produce a total energy output, and that energy output can dictate what incentives are paid out and thus the overall cost of the system," Ressler said.


Environmental Investment

Hermann said the Solar Map's accuracy is dependent on the data because cities can choose between a low-resolution or a high-resolution map. The map's assessments have been compared with those made by a solar installer who does the measurements in-person. The installer tells CH2M HILL the information meets their needs and the technology can be used in place of physical assessments, though the installer didn't reveal the exact results.

According to Hermann, the high-resolution version of the Solar Map costs about $4,000 per square mile, which is a one-time fee and covers approximately 2,500 buildings in an urban area. The low-resolution version costs about $25,000 for a 50-square-mile city or county. "The low-res version is really a great marketing tool and is a great one-stop shop for all your solar information as a city or county," he said.

Miller added that there's a cost-accuracy tradeoff depending on how detailed the client wants the data to be. The less detailed, the less expensive the map will be.

San Francisco first launched the site in low resolution for it to display quickly and then updated the portal with high-resolution information. The site was expected to be updated to high resolution by November 2008.

It takes about 45 days to launch a low-resolution solar map, as long as there isn't a backlog, Miller said.


Made-to-Order Maps

Clients can add unique details to their solar map. CH2M HILL has cities that are interested in allowing users to draw solar panels on their rooftop in the Solar Map; for example, if users add three solar panels, the map will determine the details and then they can see what the difference would be compared to two solar panels.

According to Hermann, Los Angeles County is customizing its solar map with high-resolution imagery for county buildings, and each city within the county can decide whether to fund the high-resolution imagery.

The Solar Map site can also match the colors and structure of a government's overall Web page style. "The goal is to have the Solar Map feel like a part of their existing city presentation," Miller said.

San Francisco hasn't yet received feedback from citizens that the Solar Map led directly to solar installation, Partin said, but the Department of Environment has heard that potential customers use information garnered from the site when speaking with solar installers. She suspected city grants for residents who install solar power is the main driver of solar installations.

The Web site receives about 200 page hits per month, according to Partin. However, the number increases after a big announcement is made about solar.

In the future, San Francisco will add measurements of solar water heating potential to the map and eventually make it a wind power resource. Hermann said estimating wind power depends on if cities can measure the wind microclimate - the climate of a specific place in contrast to the climate of an entire area - but San Francisco has some capability to do that.


Video: Sacramento, Calif., nuclear facility used as solar farm.

Elaine Rundle Staff Writer