Photovoltaic water heating control system and process

A photovoltaic water heating control system comprising:

• a photovoltaic power input coupled to a photovoltaic inverter;
• a grid power input;
• at least a first electrical heating element electrically coupled to a first thermostat forming a first heating element circuit, the at least first electrical heating element and first thermostat immersed in a water tank wherein the first thermostat opens the first heating element circuit above a predetermined water temperature threshold and closes the first heating element circuit below the predetermined water temperature threshold, the at least first electrical heating element is disposed towards an upper portion of the water tank;
• at least a second electrical heating element electrically coupled to a second thermostat forming a second heating element circuit, the at least second electrical heating element and second thermostat immersed in the water tank wherein the second thermostat opens the second heating element circuit above a predetermined water temperature threshold and closes the second heating element circuit below the predetermined water temperature threshold, the at least second electrical heating is disposed towards a lower portion of the water tank;
• a photovoltaic controller having control circuitry comprising a processing unit, memory, a means for external communication, and software comprising operating efficiency routines, wherein a set of installation parameters are set in the memory of the control circuitry, the set of installation parameters comprising at least one of the following:
• predetermined water temperature threshold;
• photovoltaic panel peak output power;
• photovoltaic panel tilt angle;
• predicted daytime shading of photovoltaic panel;
• azimuth angle;
• number of heating elements;
• heating element power rating;
• predicted water use periods;
• or
• water tank volume;
• the photovoltaic inverter and the grid power input coupled to the control circuitry wherein the photovoltaic inverter and the grid power input are isolated through a power input switch controlled by the operating efficiency routines;
• the at least first heating element circuit and the at least second heating element circuit are coupled to a current sensor and the control circuitry through a heating element switch isolating the first heating element circuit from the second heating element circuit;
• wherein the control circuitry determines if a water temperature is above or below the predetermined water temperature threshold by polling the current sensor to detect whether the first heating element circuit is open or closed and wherein the control circuitry through the operating efficiency routines determines a position of the heating element switch to power either the first heating element circuit or the second heating element circuit;
• wherein at least the predetermined water temperature threshold is set in the memory of the control circuitry and the processing unit executes the following operating efficiency routine steps:
• determining a current tank water temperature;
• determining a grid electricity rate schedule;
• analyzing installation parameters, predicted water use periods, predicted weather data, and projected energy demand needed to power the at least first heating element or at least second heating element to meet demands of the predicted water use periods;
• preparing an optimal photovoltaic and grid energy use schedule from the installation parameters, the predicted weather data and the grid electricity rate schedule to meet the projected energy demands;
• determining if the current tank water temperature is above or below the predetermined water temperature threshold;
• wherein if the current tank water temperature is above the predetermined water temperature threshold, the steps of determining a current tank water temperature, determining a current grid electricity rate, analyzing predicted water use periods, and preparing an optimal photovoltaic and grid energy use schedule are repeated;
• further wherein if the current tank water temperature is below the predetermined water temperature threshold, the processing unit execute additional operating efficiency routine steps comprising:
• analyzing the optimal photovoltaic and grid energy use schedule to determine if use the current tank water temperature exists in a photovoltaic use period or grid use period of the use schedule;
• wherein if the current tank water temperature exists in a photovoltaic use period the processing unit switches to the photovoltaic power input to provide photovoltaic energy to the at least first heating element or the at least second heating element, thus heating raising the current tank water temperature;
• and
• further wherein if the current tank water temperature exists in a grid electricity use period the processing unit switches to the grid power input to provide grid energy to the at least first heating element of the at least second heating element, thus heating raising the current tank water temperature.