Solar Photovoltaic Water Heating System

Abstract

A solar photovoltaic water heating system is disclosed having a photovoltaic solar panel array, a storage tank containing water to be heated, a resistance heating element in the water to be heated. The water heating system matches the load resistance of the resistance heating element to the power that is available from the photovoltaic solar panel array in order to maximum energy transferred to the water in the storage tank.

We claim: 
     
         1 . A solar photovoltaic water heating system comprising:
 a. a solar photovoltaic panel for producing direct current power;   b. a water storage tank including:
 i. a cold water inlet; 
 ii. a hot-water outlet; and 
 iii. a variable resistance heating element having an electrical resistance; and 
   c. a control system connected between the solar photovoltaic panel and the variable resistance heating element and configured to vary the resistance of the variable resistance heating element to match the direct current power supplied by the solar photovoltaic panel.   
     
     
         2 . The water heating system of  claim 1 , wherein the variable resistance heating element comprises an array of individual fixed resistance heating rods and the control system is configured to switch the array of individual fixed resistance heating rods into a plurality of single and parallel connections in order to vary the resistance of the variable resistance heating element. 
     
     
         3 . The water heating system of  claim 2 , wherein the water heating system further includes a switching network connected to the individual fixed resistance heating rods and controlled by the control system to switch the array of individual fixed resistance heating rods into a plurality of single and parallel connections in order to vary the resistance of the variable resistance heating element. 
     
     
         4 . The water heating system of  claim 1 , wherein the water heating system further comprises a alternating current power source for producing alternating current power connected to the control system, and wherein the control system is configured to alternatively connect the direct current power from the solar photovoltaic panel or the alternating current power from the alternating current power source to the variable resistance heating element. 
     
     
         5 . The water heating system of  claim 1 , wherein the water heating system further includes a mixing valve having a first hot water inlet connected to the hot water outlet, a second cold water inlet connected to the cold water inlet via a cold water shunt, and a mixing valve outlet for delivering a mixture of hot and cold water to a consumer water system and wherein the control system controls the mixing valve and therefore the mixture of hot and cold water to the consumer water system.