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									                                                             Mayor’s Training Program Case Study

                                 San Francisco Solar Map

                    Location: San Francisco, California (USA)

Abstract: The San Francisco Solar Map is an Internet-based solar energy calculator and tracker for
use by city residents, businesses and the solar industry for making quick and easy assessments of
rooftop solar energy potential. Cities can use the Solar Map to educate the public about
opportunities for installing solar energy technologies on their roofs, link consumers with solar
vendors, provide cost and benefit data to interested residents and business, and track local progress
in deploying solar technologies. In 2008 the Interstate Renewable Energy Council gave the City of
San Francisco its Innovation Award for the site.

• Promotes local solar energy technology deployment using Internet-based mapping technology
• Solar PV cost-calculator quickly estimates cost of installing technology on any building rooftop in the
• Vendors can link to the site promoting local energy business development
• Government can use the site to highlight relevant policies and incentive programs
• Projected cost: $20,000 - $250,000 (depending on the map resolution, size of city, and degree of site
   maintenance required)

The Concept: On a daily basis, the earth receives far more solar energy than the total amount of
energy used in homes, businesses, and industry. If harnessed, solar power has the potential to
dramatically reduce the total amount of greenhouse gas emissions released into the environment
by replacing electricity produced from fossil fuel-based sources. In cities, a large amount of
unused land – in the form of building rooftops – can be put to productive use by covering them
with solar photovoltaic (solar PV) systems that convert sunlight into electricity. Most homeowners
and businesses are unaware, however, of the total amount of solar power potential that exists on
their building rooftop, where other PV systems have been installed in their area, and how cost
effective these systems can be. Readily available geographic information system (GIS) mapping
software exists, however, that can be tailored to provide this information to the public in a
relatively inexpensive, easy-to-use manner, supporting public or private solar PV marketing

GIS mapping technology is a powerful tool that merges computerized database information on
building size and category (e.g., residence, business, etc.) with maps or photographs of a city or
region. The user can then manipulate the map so it shows all buildings in an area that share
certain characteristics, such as all buildings that have installed solar PV systems. The software
can also be manipulated to estimate how much solar power ‘potential’ exists on buildings currently
lacking a solar PV installation, and how much it would cost to install these systems by drawing on
database information detailing the measurements (or ‘footprint’) of the building.

There are many different types of GIS programs available on the market, most of which can be
configured so they may be accessed via the Internet, thereby allowing authorized users (or the

                                                        Mayor’s Training Program Case Study

general public) to look at information about their building or other buildings in the area. These
programs can be supplemented with other features to help the user obtain information on where
to buy solar PV technology, or whether financial assistance is available to help them pay for a

Goals & objectives that can be achieved by pursuing this policy/project:
• Promote more widespread use of renewable energy (solar power) to generate electricity for
  homes and businesses
• Provide an easy-to-use tool for home and business owners to estimate how much power can
  potentially be generated on their rooftop, what such systems might cost, and learn who can
  install the systems
• Provide a visually attractive and easy-to-use tool to show the public that renewable energy
  projects are feasible in their community and to demonstrate the success of renewable energy
  technology marketing efforts

What Mayors can do: Mayors can partner with GIS experts at a private company, a university,
or within local government to develop this type of system for their city. To ensure widespread
access to this information, local government can host these systems or link these systems to their
own local government website. Mayor’s can also direct local government agencies to provide
information relevant to the database(s) at the heart of the GIS system, and allow private solar PV
installation companies to link their own marketing websites to the system to help promote local
economic development. Finally, local government can develop education campaigns promoting
solar power that refer the public and local businesses to this website.

Key stakeholders involved in carrying out this type of policy/project:
Municipal government officials: May be involved in collecting and providing information necessary
to develop or support the on-going functioning of the mapping system.

Building owners: The beneficiary of information about solar PV potential on their building

Solar PV system installers: Private companies meeting minimum electrical system knowledge
requirements will generally be responsible for the installation of these systems.

GIS software firms and consultants: May be responsible for the development or on-going support
of the computerized mapping system.

                                                          Mayor’s Training Program Case Study

                      Detailed Case Study: San Francisco Solar Map

The City of San Francisco has long been recognized for its innovative local energy and
environmental practices. To support its goal of installing 10,000 solar PV systems on local
rooftops and reduce the City’s overall carbon footprint, the City’s Department of the Environment
contracted with CH2M Hill, an environmental and technology consulting firm, to develop the San
Francisco Solar Map. The map informs local residents and businesses about the solar power
potential of their buildings, the cost of installing a solar system, the names of local solar PV
system installers, and information about subsidies and tax breaks available from the City of San
Francisco and State of California.

Residents and businesses can enter their building address into the map search box and the
system responds by providing solar data specific to their building. The Solar Map bases its
calculations on the estimated size of the roof and the amount of solar radiation striking the rooftop
over the course of a year. Importantly, it also takes into account such factors as whether the roof
is flat or slanted, and nearby obstructions that would impede solar power production, such as
shading cast by nearby trees and tall buildings.

Relying on information provided by City government agencies, building owners and local solar
system installers, the map also highlights where solar PV systems have already been installed
around the City. By clicking on each dot on the map, which indicates where solar PV systems
have been installed, it is possible to get detailed information about the size of the system, the
company that installed it, the cost of the installation, and how much money the building saves on
electricity costs each year by relying on “free” power provided by the sun. The amount of
information provided about each solar PV installation is up to the discretion of the building owner.
To guarantee privacy, building owners can opt out of the map system to ensure information about

                                                          Mayor’s Training Program Case Study

their PV system is not made public.

The San Francisco Solar Map supports the City’s overall campaign to expand the use of solar PV
locally by summarizing how many systems have been installed citywide, how much energy is
produced by these systems, how much local customers have saved on electricity purchases, and
how much the city’s overall carbon footprint has declined as a result of the increased use of solar

CH2M Hill, a private consulting firm, developed the solar map system for the City using a series of
aerial photographs, proprietary GIS synching software, a Google™ web mapping visualization
platform and data provided by different government agencies. The San Francisco Department of
Building Inspection (DBI) provided information on existing solar installations, while the San
Francisco Public Utilities Commission provided insolation data collected by solar monitors located
throughout the city. A link to the Solar Map can be found on the City of San Francisco’s main
website at: http://sf.solarmap.org/. The City expects to eventually expand the map to include
other renewable technologies such as small wind turbines and solar hot water systems.

Benefit/Cost information: The initial version of the solar map was developed in-house by the
San Francisco Department of the Environment using data provided by City agencies and the help
of community volunteers familiar with GIS software. At the time, the City did not have the financial
resources to hire a firm to develop a new piece of software, but it was able to recruit the help of
local residents with GIS expertise. Using very general assumptions regarding rooftop dimensions
and orientation, this map first became operational in June of 2006. The following year, after
receiving a $5.5 million grant from the U.S. Department of Energy’s Solar America Cities program
to help 25 U.S. cities develop solar mapping systems, CH2M Hill developed an enhanced and
more precise version of the Solar Map using advanced 3-D imaging. To date the work performed
by CH2M Hill has cost the City of San Francisco approximately $250,000, although much of this
cost was covered by the U.S. Department of Energy grant. These costs cover CH2M Hill’s
development and maintenance of the website, production of digital three-dimensional aerial
photographs of the city, generating the rooftop solar energy estimates, and the hosting of the site
as well as quarterly updates for a period of two years. This cost does not include City government
staff time and resources.

CH2M Hill estimates that a low-resolution solar map for a smaller city might cost about $20,000;
while a high resolution map for a larger city would cost closer to $200,000. CH2M Hill estimates it
costs them approximately $5,000 per urban square mile to develop a solar map. However,
whenever possible, CH2M Hill tries to rely on existing computerized datasets or aerial
photographs to reduce costs.

Timeline: From conception to launch of the initial website in June 2006, the Solar Map took
approximately 1.5 years to complete. As noted above, City government staff and community
volunteers with GIS experience developed the first site, as it was difficult to find a private sector
partner capable of performing the tasks required by the project. Once CH2M Hill started work on
the project, the enhanced website was completed in approximately three months. CH2M Hill
claims that it can map a city’s rooftops in a matter of weeks, but the exact time required will
depend on the size of the city and the degree of resolution desired.

Results & Evaluation: The SF Solar Map was developed as an education tool, and anecdotal

                                                           Mayor’s Training Program Case Study

evidence suggests that it has proven very effective at improving local awareness and knowledge
about solar power issues. Solar installers and customers alike use it to make initial
determinations of the feasibility of installing solar systems on roofs in San Francisco. Since the
final version was launched in late 2007, the site has received more than 32,000 visits by more
than 27,000 people. During this time, the number of rooftop solar systems installed around San
Francisco has nearly doubled from 585 systems (representing approximately 3.25 MW of power
generation capacity) to 1,030 systems (about 7.25 MW of capacity) as of February 1, 2009.
Despite the positive feedback, however, the growth in the number of PV systems deployed
around the city cannot be attributed to this website alone. Both the State of California and the
City of San Francisco offer attractive financial incentives to customers installing solar PV systems,
making it difficult to isolate the impact of the Solar Map. In 2008, the San Francisco Solar Map
received the Innovation Award from the Interstate Renewable Energy Council (IREC).

Lessons learned: The City of San Francisco experienced several challenges in developing the
Solar Map. The first was identifying a suitable partner and securing funding to develop and
maintain the website. Originally, City staff and local volunteers initiated the project, but the City
eventually decided additional expertise would provide for a more sophisticated and useful
website, so it hired CH2M Hill to upgrade and maintain the site. Second, City staff found it
challenging to locate data on existing solar installations in the city. Initially, staff utilized solar
permitting records. Since then, the staff has worked with local solar vendors and installers to
voluntarily provide updates; it also draws on a database that tracks projects receiving financial
incentives from the City. Another challenge involved the synching together of different databases
that identify the same building using different methods (e.g., “parcel” numbers versus street
addresses). There still remain some inconsistencies, but to date, the Solar Map covers over 90%
of the buildings in the city. If City staff could start the project all over again, they would use the
more accurate solar estimation software provided by CH2M Hill from the beginning instead of the
time-consuming manual digitization process initially used. Finally, due to concerns about the
potential liability associated with promoting a given solar technology or installer, San Francisco
does not use the site to promote or highlight specific companies. Instead, it relies on a list
developed by the State of California that is searchable by address and allows customers to find
solar companies providing service in their area.

Is This Policy/Project Right for Your City? In order to determine if a solar mapping system is
appropriate for your city, several factors are important. First, the city must have a range of
information available in a format that can be used by GIS software programs. If a city already
uses GIS technology for land use planning or other purposes, some building data and a mapping
system may already be available for use and can defray some of the project costs.

The data required includes:

•   Aerial photographs of the city, preferably those allowing for three-dimensional analysis;
•   Building size, rooftop dimensions and other important information such as rooftop shading
•   Solar availability (insolation) data. In some cities, it may be important to develop this
    information for different parts of the city to account for localized climatic conditions (such as
    neighborhoods that are particularly foggy, reducing the amount of available sunlight); and
•   Solar PV system and electricity cost data to allow for basic benefit-cost calculations, including
    total system cost, electricity cost savings, and system payback period.

                                                         Mayor’s Training Program Case Study

Second, local government and the public must both be comfortable making building-specific
information available via the Internet. Privacy concerns may make this concept unacceptable to
some local decision makers.

Finally, this project may require the allocation of additional budget resources to implement and
manage on an on-going basis. The size of this budget may vary depending on whether local
government already has staff capable of carrying out this project.

Johanna Gregory Partin
Renewable Energy Program Manager
Department of the Environment
City and County of San Francisco
E-mail: Johanna.Partin@sfgov.org

Nigel Nugent, Vice President
CH2M HILL (consultant responsible for the development of the system)
Enterprise Management Solutions
E-mail: Nigel.Nugent@ch2m.com

Dianna Herbst, Marketing Director
CH2M Hill
Telephone: (720) 286-3008
E-mail: Dianna.Herbst@ch2m.com

 Case study prepared by:
 Michael A. Hyams, Columbia University
 February 2009


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