The effects of reduced flow rates on the performance and effectiveness of domestic unglazed, uninsulated pool solar collector heaters are investigated. The study shows electrical energy savings in excess of 80% are achievable for typical solar collectors operating at flow rates reduced by up to 75% while collector efficiency is only reduced by approximately 10-15%. The reduction of electrical energy required for pumping and the increased COP of reduced flow through typical pool solar thermal collectors is shown to far outweigh the small loss of collector performance attributable to the change in flow rates. The ratio of thermal energy delivered to the electrical energy supplied was improved in the order of 400% for the collector tested. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.