603 Solar

603 Solar has grown into one of New Hampshire's most consistently recognized residential solar specialists since co-founders Zachary Haithcock and Sean Carlson launched the company in 2018. Headquartered at 24 Charter Street in Exeter, the firm has helped more than 1,200 home and business owners install systems that have collectively produced over 20 million kilowatt-hours of clean energy, and its service territory now reaches across New Hampshire, southern Maine, and northern Massachusetts from a single in-state base of operations.

What stood out to our research team is how the company stacks credentials against the market it serves. 603 Solar holds NABCEP certification, has been BBB-accredited with an A-plus rating since 2019, and is a member of Clean Energy NH, the Northeast Sustainable Energy Association, and Sustainable Seacoast. The company is an EnergySage-approved supplier and has won first place in the 'Best of the 603' Magazine awards in 2023, 2024, and 2025, alongside repeated wins in the Best of the Seacoast Community Choice Awards. That kind of sustained local recognition is difficult to manufacture and reflects a track record that customers in Rochester, Portsmouth, Manchester, Concord, Dover, and Exeter have validated repeatedly.

The numbers behind 603 Solar's customer satisfaction are unusually strong for a company at this scale. The Birdeye platform aggregates 177 reviews at a perfect 5-star average, the Google profile shows a 5.0 rating across 160 reviews, and SolarReviews customers describe the team as 'extremely knowledgeable, transparent, and prompt.' Founders Haithcock and Carlson each bring nearly a decade of solar industry experience predating 603 Solar's founding, and the company performs site evaluation, system design, permitting coordination, and installation in-house rather than relying on subcontractors. They also work with multiple inverter brands, which gives homeowners flexibility on equipment.

As a New Hampshire-rooted installer that has built its reputation entirely within the state and its immediate border markets, 603 Solar brings firsthand familiarity with Eversource and Unitil interconnection workflows, New Hampshire's net-metering rules, and the specific permitting expectations of Rockingham, Strafford, and Hillsborough County jurisdictions.

With a composite score of 82.1 out of 100, 603 Solar stands as our top-ranked solar company in New Hampshire for 2026.