The Tekmar 155 Differential Setpoint Solar Control is a microprocessor based difference setpoint control intended for solar and wood stove or other intermittent heat source applications. The Tekmar 155 Setpoint Solar Control is a microprocessor based control that allows the transfer of heat from a solar panel to a storage tank used for domestic hot water or space heating applications whenever the temperature difference between the two is greater than the selected DT setpoint. Additional setpoints are also included in the Tekmar 155 to help prevent the storage tank from overheating or the solar panels from freezing. Both solar drainback and draindown systems can be used with the Tekmar 155 control. The control can display the Maximum and Minimum temperatures measured by both the Storage and Solar Source sensors as well as the total heat transferred from the Solar panels to the storage. Some Solar Panel & Storage Tanks have small wells and may require the purchase of Tekmar 079 Sensors.