for storage of heat from the solar panel for use during the absence of solar rays is the oil itself thus if solar panel 19 can provide sufficient heat and storage tank 17 is sufficiently large and well insulated no other heat source or heating device will be necessary during periods when solar heat is available the oil in flow line 15 is heated beyond that required for demulsification this correspondingly raises the temperature of tank 17 beyond the temperature required for demulsification during nights or other periods when the solar heating is unavailable the heat stored in tank 17 heats the unheated incoming oil to allow demulsification to continue as long as the temperature of the tank does not drop to low demulsification can continue in order to prevent the loss of heat or the passage of oil through the tank without heating the inlet on tank 17 should be located away from the outlet for oil 31 and the outlet for water 33 in this manner a thorough mixing of the oil entering tank 17 is achieved as indicated above the placement of the heat source outside the tank can be an advantage this advantage is derived from the relationship between temperature and the process of demulsification demulsification becomes increasingly difficult as the size of the entrained droplets decrease temperature increases improve demulsification by creating a lower viscosity which in turn allows accumulation of larger droplets these larger droplets are then able to settle faster due to differences in specific gravity the placement of the heater outside the tank is important due to the cyclical nature of the solar heating processes if the heater is placed inside the tank zones of oil.