Castillo Engineering Launches, the First Company to Fully Automate Solar Letters in All 50 U.S. States

Company’s advanced automation enables 99% accuracy, minimizes projects risks & drastically reduces residential solar project soft costs

MAITLAND, Fla., Oct. 3, 2023 /PRNewswire/ — Castillo Engineering announced today that it has launched, the first company to fully automate structural letters, professional engineer (PE) stamps, and post-installation letters for residential solar installation companies in all 50 U.S. states as well as overseas design firms. The company’s advanced automation, which includes a range of Application Programming Interface (API) integrations, enables a high 99 percent accuracy rate. Backed by over 25 years of structural design and engineering experience in residential solar, Solar Letters will also be incorporating artificial intelligence to further reduce the time and costs associated with solar letters and PE stamps. Solar Letters’ experience combined with its advanced technology has enabled it the capacity to generate over 100,000 solar letters per month, allowing residential solar installers to complete more projects in less time.

“The Solar Letters platform is a game-changer for LGCY,” said Ben Ogden, Manager, Design and Engineering, LGCY Power. “It has simplified the structural and electrical engineering process and increased our turn times on stamped projects.”

There are currently many costly inefficiencies within the solar letter and PE stamp process in the residential solar industry, with most firms still performing calculations manually or using Word or Excel documents. All of these methods have been tested and proven to be highly error prone, particularly with non-degreed engineers manually completing forty to fifty letters per day. As a result of investing in advanced automation and its database of over 40,000 authorities having jurisdiction (AHJs), and associated codes that have been continuously updated since 1998, Solar Letters has been able to guarantee its 99 percent AHJ approval rate.

“We are very excited to launch in response to the high demand for residential solar letters and PE stamps we are seeing globally,” said Christopher Castillo, CEO of Solar Letters. “We look forward to providing the same elite customer service experience for clients as we do through Castillo Engineering. Helping solar installers drastically cut soft costs and mitigate project risks are necessary to ultimately enable solar energy to proliferate across the globe.”

Solar Letters now provides the fastest turnaround time in the industry – guaranteed or a full credit will be issued, as well as the lowest price, which includes price matching. The company also offers volume discounts through its Permit Partner Program, in addition to a full credit if a letter receives an AHJ rejection.

The company is currently preparing for a round of investments to both further improve its automation and AI integration to provide additional quality control through its platform. Solar Letters is expected to incorporate AI into its platform this year as well as throughout next year.

From pre-installation structural letters and stamps to post-installation letters, Solar Letters provides the most accurate, fast and cost effective residential PE stamps and solar letters across the nation. Learn more about Solar Letters at and follow the company on LinkedIn.

About Solar Letters
Leveraging Castillo Engineering’s over 25 years of experience, Solar Letters provides the quickest, most cost effective structural letters, PE stamps and post-installation letters for residential solar installation companies and overseas design firms. Solar Letters is backed by Castillo Engineering and its capacity to create over 100,000 solar letters per month. By providing the fastest, lowest cost and most accurate letters, Solar Letters enables residential installation companies to minimize time spent on the permitting process and maximize profits through the completion of more solar projects. Solar Letters is based in Maitland, Florida, and is licensed in 50 U.S. states, District of Columbia and Puerto Rico. Learn more at

Solar Letters Media Contact:
Lisa DeMarco


SOURCE Solar Letters