Energy efficiency startup Carbon Lighthouse closed a $32.6 million growth round on Tuesday -- including a $20 million stake from Cox Enterprises, the cable and media giant -- to expand its sensors-and-data-driven approach to reducing buildings’ wasted energy and carbon footprints. 

Tuesday’s investment brings the San Francisco-based startup’s total venture funding to more than $70 million. This figure includes last year’s $27 million round of investment led by GRC SinoGreen, with participation from JCI Ventures, Ulupono Initiative, SV Tech Ventures, and Tesla co-founder and CTO JB Straubel, and a $7.5 million follow-on investment from CEAS Investments. 

The equity investment follows the $65 million project finance fund Carbon Lighthouse secured from Generate Capital Inc. in October, meant to expand the company’s current footprint of about 500 buildings in 16 states by an additional 200 to 300 buildings. 

Carbon Lighthouse, founded in 2009, offers big commercial building owners a simple proposition: a nonintrusive energy efficiency project, without hefty upfront equipment or construction costs, paid for through a flat monthly fee. In return, the startup offers its customers a guarantee of how much money they’ll save per month on their utility bills — and promises to pay the difference if it doesn’t hit the target. 

CEO Brenden Millstein said in an interview last year that customers achieve an average of 20 to 30 percent in utility bill reductions. That’s a relatively typical level of savings for big commercial building efficiency or retrofit projects, as long as they’re tackling the “low-hanging fruit,” such as lighting replacements or HVAC upgrades and tuneups. 

But Carbon Lighthouse tends to achieve its results on top of these more easily achievable savings, and without any expensive upgrades, Millstein said. It does this by installing hundreds of sensors to collect tens of millions of data points, and then analyzing them with its Carbon Lighthouse Unified Engineering System software platform, to optimize the right mix of initial efficiency measures and maintain any upgrades over time.  

Carbon Lighthouse’s data-driven approach to building energy efficiency is not unique in the field. Other companies and startups that have combined sensors and analytics with more traditional building retrofit and continuous commissioning include FirstFuel,  Ecova's Retroficiency, BuildingIQ, and NRG’s Station A spinout, while industrial giants such as Siemens and Schneider Electric have developed big-data analytics for their building energy services offerings. 

But there’s plenty of room for competition in the field of maximizing the efficiency of buildings, which account for roughly 40 percent of U.S. energy consumption, and waste a significant portion of that energy through inefficient equipment, poor heating and cooling insulation, or improper management. But these inefficiencies are being tackled through a combination of new building codes, state and local efficiency mandates, federal mandates and incentives, and utility efficiency programs, to name a few drivers. 

Carbon Lighthouse doesn’t offer its software as a subscription or a service, unlike some other startups in the field, but instead works with a network of contractors to deploy the equipment it monitors on behalf of its clients, Millstein said. Since 2010, it has begun to include rooftop solar as a potential factor in its building energy analysis as well. 

Some of the startup’s premier customers include Hilton Hotels, which has bragged of achieving nearly $1 million in savings with no money invested at one property, and Tesla, which engaged it in a six-year contract that’s helped reduce utility bills by $90,800 per year — or by 106 tons of carbon dioxide annually — across its Palo Alto, Calif. manufacturing, office and R&D facilities. 

Most recently, Carbon Lighthouse landed a contract with Hawaiian Airlines last month to install sensors and optimize the energy use of a 14-story multitenant office building in Honolulu. In April it added a new Los Angeles office to its existing sites in San Francisco, New York and Honolulu. 

Cox Enterprises, which becomes the largest investor in Carbon Lighthouse with its $20 million round, has also invested more than $350 million in sustainable businesses and technologies since 2007, according to Tuesday’s announcement.

Other Cox investments include sustainable agriculture startup BrightFarms, sustainable technology investment firm True North Venture Partners, and the Southeastern Solar Farm Fund, a partnership that operates four solar farms across Georgia and Florida.