Simplifying solar thermal systems offers a number of potential benefits, including lower initial investment, lower maintenance costs, and reduced likelihood of operating faults. Reduced capital cost leads to increased competitiveness in the energy market. With appropriate care, a simplified solar thermal system design can maintain competitive energy performance with more complicated designs. We propose to simplify small-scale thermal storage systems by the use of a spiral-jacketed storage tank that combines the function of both the heat exchanger and storage tank. The new storage tank is designed and manufactured to maintain performance comparable to a conventional system, and its functional performance validated by retrofitting an existing system and operating it under real conditions over a multiple month period. The system retrofitted with a spiral-jacketed storage tank showed performance competitive with the previous system that utilized a typical storage tank and heat exchanger during a day with a good solar radiation but experienced somewhat diminished performance during a month that included cloudy days.