Patent ID: 8651734

Claim:
A method for controlling a drywell comprising: measuring a receiver temperature proximate a lower end of a receiver having an upper end opposite the lower end, wherein the lower end is substantially more insulated than the upper end, wherein the receiver has an upper heating element in thermal contact with the receiver proximate the upper end and a lower heating element in thermal contact with the receiver proximate the lower end, and wherein a thermal sensor is in thermal contact with the receiver proximate the upper end; comparing the receiver temperature to a set temperature; based on the comparison, calculating a lower end power value that is substantially effective to drive the receiver temperature to the set temperature; measuring an ambient temperature; determining a heat loss gradient based on the receiver temperature and the ambient temperature; powering the lower heating element according to the lower end power value; and powering the upper heating element according to an upper end power value determined as a function of the heat loss gradient and the lower end power value.