When clean technology incubator Greentown Labs moved from South Boston, Massachusetts, to the neighboring city of Somerville in 2013, the sprawling new facility was a little daunting, said chief executive Emily Reichert. With 18 member companies – all small startups – the organization filled less than half the 33,000 square feet in the building.

“At that time, it seemed like an incredibly big space,” she said.

Less than two years later, Greentown Labs has expanded into every corner of the former envelope factory. With 44 member companies employing 285 people, Greentown Labs has become the largest clean tech incubator in the US, Reichert said. Member startups are working on everything from data-collecting sailboats to floating wind turbines.

“It’s become a cultural center of forward thinking entrepreneurial activity,” said Gabe Blanchet, co-founder of Grove Labs, a Greentown tenant that is developing residential-scale aquaponic systems that allow tenants to grow vegetables indoors.

The Boston area has long been known as a hub of innovation and entrepreneurial activity, from the computer technology corridor that boomed along Route 128 in the 1980s to today’s flourishing biosciences sector. Greentown Labs aims to join this tradition, giving innovative sustainability-focused startups the traction they need to turn their bold ideas into game-changing realities. But until one of its growing startups makes it big – something that has not happened yet – its model of collaboration and resource sharing remains unproven.

The Greentown Labs demo bay. Photograph: Greentown

Greentown Labs began in late 2010, when four clean energy startups, all with ties to the Massachusetts Institute of Technology, came together to split the rent on a rundown warehouse space in East Cambridge. There, they could tinker, tweak, and try out their intended products. When the warehouse was demolished in 2011, the four companies moved to a space in South Boston, expanding and bringing in more young enterprises. After just two years, the incubator had outgrown its new space and decided to move again.

When Somerville mayor Joseph Curtatone heard Greentown was looking for a new home, he decided to woo the group to his city, offering $300,000 in tax incentives.

“They bring us everything we hope for in the type of companies we need to build our locally-sustainable economy,” said Curtatone, who also ordered one of Grove Labs’ first home aquaponics system.

Framed by lime green and teal blue walls, Greentown’s Somerville office is a tightly-packed collection of desks where employees study product designs, cluster together around laptops, and share ideas and advice over cups of coffee. Workshop space runs along the back and side of the building, where 3D printers whirr, plants grow under LED lights, and prototypes are assembled and honed.

Neither traditional incubators nor shared work spaces are new ideas. Greentown Labs, however, is carving out a distinctive space for itself somewhere between the two models.

Unlike most incubators, Greentown does not take equity in member companies, nor seats on their boards. Accepted companies pay $425 per month for each desk they need and $3.20 per month for each square foot of lab space.

Greentown Labs in Somerville. Photograph: Greentown

Greentown does, however, shape the workplace environment with a careful member selection process. Successful applicants intend to produce manufactured products rather than software or services, and generally have existing investments from outside sources, Reichert said. To nurture collaboration, Greentown Labs will not accept any companies that are direct competitors with existing members.

Perhaps most importantly, all members must have an interest in cleantech and in building businesses that solve global problems, Reichert said. The result of these policies is a group of companies that easily and eagerly trade expertise and advice, according to those involved.

“Whenever we have a question or a problem, the first thing we do is throw it out to the Greentown email list,” said Ben Glass, CEO of high altitude wind turbine producer Altaeros Energies, another Greentown founder. Someone is almost always able to help immediately, he said.

Greentown also forms partnerships with corporate sponsors, including Shell, Chevron, American Airlines and Microsoft. These sponsorships, which provide about 20% of Greentown’s revenue, according to Reichert, also connect member startups with major companies that in search of new technology. In addition, the incubator hosts networking events and job fairs to help member companies make business connections and find new employees and interns.

Greentown is also hiring a manager who will help the young businesses contact and communicate with manufacturing partners. Often, Reichert said, new entrepreneurs have big ideas, but little practical knowledge about how to make the leap from prototype to production. She hopes the new manager will help bridge that gap.

The lab space inside Greentown Labs. Photograph: Greentown

With the current facility at 100% occupancy, Greentown’s directors are considering what comes next. They are looking at ways to expand within Somerville and exploring partnerships elsewhere in Massachusetts, Reichert said. The group has already started consulting with organizations looking to build their own technology incubators.

Jeff Anthony, director of the Energy Innovation Center at the Mid-West Energy Research Consortium in Milwaukee, Wisconsin, said Greentown’s advice has been crucial in developing plans for an innovation center. He point specifically to the idea of “maximizing collisions”: creating a space that generates encounters between occupants and their ideas.

“They’ve been a proven success and we’re hoping to learn even more from them,” Anthony said.

Meanwhile, many will continue watching Greentown to see if a physical space that increases collisions will ultimately end up sparking big wins – or not.

This series on bold bets is funded by The B Team. All content is editorially independent except for pieces labelled “brought to you by”. Find out more here.