Introduction

In a world that is increasingly struggling with climate change and its consequences, solar energy is a significant way to reduce your personal carbon footprint. As students based in Cambridge—a city that prides itself on being a “leader in sustainability”—we found ourselves asking a simple yet important question: how solar-friendly is Cambridge, really? How has the adoption of solar power evolved here, and does it match the ambitions of its residents?

Our project set out to explore these questions by focusing on photovoltaic (PV) systems, the core technology behind solar energy. We examined data on solar panel installations, tracked trends over time, and considered the factors influencing the city’s renewable energy landscape. By combining research with local context, our goal was not only to assess Cambridge’s progress but to understand what influenced citizens to install PV systems.

What is photovoltaics?

Photovoltaic solar panels, or PV for short, are what most people think of when they picture solar panels. A module of this type is made up of an array of cells that convert sunlight into direct current electricity. They are usually installed on the roof of a house and feed their electricity into the household grid, providing renewable energy and reducing electricity bills. Solar hot water systems, on the other hand, are somewhat rarer. Instead of producing electricity, they use the sun’s heat to warm up water, which you can use for things like showers or heating your home. While solar hot water needs direct sunlight to heat up water, PV also generates electricity in cloudy and snowy weather and actually works even better with cold temperatures, making Massachusetts an excellent location for solar systems.

This map indicates which Cambridge households use solar panels: check out the interactive version here!

Fig. 1: Map of households using solar panels in Cambridge

When people started installing solar panels - and why

Fig. 2: Annotated Cambridge Solar Installations by Year and System Type

While the solar installations in Cambridge appear to have had a slow start after their invention in the 1950s, their number has grown exponentially since around 2009, approaching a total of 1,000 installations last fall. So, what changed?

In August 2008, Massachusetts signed the Global Warming Solutions Act (GWSA) into law, setting economy-wide greenhouse gas emission reduction goals for the state. In order to help achieve these goals, the Green Communities Act (GCA) was passed in the same month, which, among other things, promotes renewable energies. The act’s aim was to further develop green energy and make it accessible to more people.

Two years later, in 2010, the Solar Carve-Out Program was launched, providing strong incentives for private households to purchase solar systems by securing an ongoing and stable revenue from the PV system, which would offset installation costs and ensure long-term return on the investment. Another major incentive program was introduced in 2018: SMART (Solar Massachusetts Renewable Target). This is a monthly payment that Massachusetts homeowners can receive for 10 years after the installation of PV systems in addition to income from the electricity production itself.

The climate change bill passed in Massachusetts in 2021 also deals with the promotion of solar energy and prioritizes in particular low-income households and nonprofits. Last year, a recent edition of the law also makes it easier to get PV permission in historic districts and wants to explore further areas for expansion with solar panels, such as parking lot structures. The impact of these changes on the number of solar panels will probably become visible in the next few years.

Increasing costs? No problem!

Fig. 3: Cost of Solar Power Construction by Year

Basic economic law states that as price increases, demand decreases. In terms of solar power, Cambridge seems to act in a different way.  Like most other goods and services in recent years, the cost of construction for solar installation has also increased. Surprisingly, Cambridge citizens have only continued to increase solar panel installations in their homes, office buildings, and more.

Through an analysis of the total cost of construction for solar panel installation and the calculation of the median costs (to get a better sense of pricing outside of outliers), we see that from 2018 to 2023, solar panel construction costs steadily increased. In 2018 (when the data was first gathered by the Cambridge City Government), the median price of solar panel installation construction was $8,656. By the end of 2023, the median cost of solar panel construction was $15,850. The most dramatic price increase occurred recently between 2022 and 2023 when the total cost of construction soared by $2,750, just beating the price increase between 2021 and 2022 of $2,338. As time passed, there was also a rise in outliers who spent an overwhelmingly large amount of money on incorporating sustainability into their buildings. The outliers were typically commercial use building structures, and five of them spent upwards of $200,000 on solar panel installation. The largest outlier, seen in 2024, spent upwards of $500,000 on installing  592 solar panels to their commercial buildings!

Regardless of these price increases, the number of solar power installations has only continued to rise, in part due to federal and state action taken to lessen the burden of the overall cost of construction for the promotion of clean energy. With the introduction of the federal 2022 Inflation Reduction Act, “homeowners are eligible for a 30% tax credit on the total cost to install a solar array” and Massachusetts allows citizens who produce solar power to sell the power for personal profit (Revision Energy). Both of these as well as various other financial incentives continue to promote the growth of solar power installation, and often help tip the scale towards solar panel installation for Cambridge citizens who may have been indecisive.

Conclusion

In the grand scheme, Cambridge citizens continue to increase solar installations each year and spend a generous (and increasing) amount of money on solar panel installations. This shows both that Cambridge citizens have a generally positive attitude towards solar energy, as well as the effects that economic and government incentives have on the actual environmentally conscious behavior of citizens.

A Deepnote file with our raw data, cleaned data, and analysis can be found here.