Solar Map FAQ

This page includes frequently asked questions regarding the Solar Map Tool and installing solar in Cambridge.

For More Information

For more information, contact Meghan Shaw at the Cambridge Energy Alliance, 617/349-5323 or mshaw@cambridgema.gov.

Is Cambridge the first city to adopt a solar map? If not, what makes this one different?

No. Other cities have developed similar tools. The difference between the Cambridge solar map and those of other cities is the technical approach and precision developed by the MIT Sustainable Design Lab. The Cambridge solar map takes into account the shape of the building including roof pitch, shading from nearby structures and trees, changes in solar radiation through a typical year, and the effect of rooftop temperatures on the performance of solar panels. The MIT team used this model to estimate the amount of solar radiation that falls on each square meter of virtually all rooftops in Cambridge and verified the results of the model.

The sizing of solar photovoltaic systems is more challenging since it is difficult to see obstructions on roofs given the resolution of the imagery and data available to the researchers. So some assumptions are made to estimate the size of a system that could fit on a roof. Modern Development Studio developed the viewer, which makes the MIT data accessible, and the financial analysis module. The financial analysis takes into account most incentives and allows the user to compare the investment in a solar PV system to alternative investments in the stock market, gold, and Treasury bonds.

For more information about the development of the tool, visit the Sustainable Design Lab and read the “assumptions” tab on the map tool.

How easy would it be to expand the map to other cities?

Modern Development Studio is working to make the map tool available to other cities. Interested persons can contact MoDe Studio for more information.

Are there any other solar mapping tools for towns or cities outside of Cambridge?

Residents of Boston can visit the City’s solar map. Other cities with solar maps include New York, San Francisco, and Los Angeles. The National Renewable Energy Lab has a site-specific solar PV calculator.

Has the solar map data been compared to installed systems? Do people really install to their full potential?

The map has been compared to existing systems. The size of existing systems tends to vary from the potential estimated by the solar map in either direction. The City encourages users to utilize the solar map to understand how much solar radiation falls on his/her roof and the potential. However, the solar map is not intended to substitute for a site visit by a solar installer. It is designed to start the thinking process.

Most property owners are probably going to size a solar PV system to fit their needs rather than to maximize the amount of electricity that is generated. However, excess electricity can be sold into the regional electric grid and there are some systems in the city that are bigger than needed by the owner.

How can Cambridge make the permitting process more “user friendly” for home/business owners?

The City recognizes that the permitting system for solar PV can be complicated. Fortunately for property owners, most installers include handling of permits in their services.

To find ways to make the permitting system easier and thereby reduce some of the “soft” costs of installing a solar PV system, the City is participating in a project with the Massachusetts Department of Energy Resources and other communities called “Mass Solar: Making it EZ” which is funded by the U.S. Department of Energy under their Sunshot Solar Rooftop Challenge initiative. The project involves finding ways to make permitting easier, exploring models for community shared solar systems, and working with financial institutions to facilitate paying for systems.

What other options are there for greening my rooftop?

In addition to solar PV, a property owner could consider the following options:

  • Solar hot water 
  • White/high reflectance roofs 
  • Green/vegetated roofs

There is a new incentive program for solar hot water systems available through the Massachusetts Clean Energy Center.

White/high reflectance roofs tend to be more suitable for buildings with flat roofs. A white roof can be installed on new construction or at the time of replacing a roof. White roof coatings are also available. There are also roof shingles that are designed to reflect infrared light. For more information, visit the Cool Roof Rating Council and theLawrence Berkeley Laboratory Urban Heat Island Group.

Green roofs are suitable for flat and low-sloped roofs. There are various options ranging from tray systems to systems with deep soils. For more information, visit Green Roofs for Healthy Cities

Isn’t solar really expensive?

Solar PV systems have become affordable in the past couple of years. The prices for PV panels have dropped from about $10/watt just a few years ago to the $3 to $4 per watt range recently. In addition, a strong set of financial incentives are provided from the federal and state governments in the form of grants, the sale of solar renewable energy certificates (SRECs), and tax credits and deductions. The federal tax credit is currently 30%. As a result, solar PV systems can pay off typically in 7 or 8 years. The systems tend to last more than 20 years. The solar map will also show users that an investment in a solar PV system is often better than investments in the stock market, gold, or Treasury bonds.

Is the City planning on doing a buying club or cooperative for PV and/or DHW?

The City has been considering the Solarize Mass model of joint purchasing of PV systems. It is our understanding that the Home Energy Efficiency Team (HEET), a Cambridge community organization, is planning to organize a Solarize program in the spring of 2013. The City is also working with the state Department of Energy Resources to assess business models for community shared solar systems that would enable property owners who have unsuitable roofs and renters to participate in a group-owned system.

For solar hot water, offered a grant to supplement the Massachusetts Clean Energy Center grant. The City grant program ended in November 2012. But the MassCEC grant program continues.

Are there different solar incentives for businesses?

Yes. Businesses can take advantage of many of the same incentives as residents, including solar renewable energy certificates. Commercial properties can also take advantage of corporate depreciation deductions. For a comprehensive list of federal and state solar incentives, visit the Database for State Incentives for Renewables and Efficiency.