Solar Heat Controller

    Automating the process of collecting solar heat is the job of the solar heat controller, more commonly known as the differential controller. This should not be confused with the Charge Controller. Because of the diffuse, intermittent nature of sunlight a differential controller is used to harvest a net heat gain from sunlight. It's designed activate a pump when heat is available and turn off when heat is not available. All a person has to do is choose the right controller for a solar heat collecting system. To do this know if the system is open loop or closed loop and if the pump requires AC or DC power. The power demands of the pump and the method of monitoring temperature are other important considerations.


The AC/DC Differential Controller  responds to the difference in temperature between collector and storage and turns an AC or DC pump on and off to maximize the heat harvest from a solar hot water or solar heating system.  Temperature monitors are used to display the actual temperatures inside the collector and inside the heat storage tank, but the controller will function without them.  

This AC/DC controller consumes less than 1 watt of power per hour yet it is capable of regulating 300 Watt pumps.  It's a rugged, dependable, analog controller that may be mounted on a wall. The temperature probes and power connections are attached to the terminals on the bottom of the controller to facilitate wiring.

     AC/DC Differential Controller ........$150

This PV Differential Controller has been designed to work in harmony with a photovoltaic power supply and a closed loop solar hot water system without a battery back up. The differential on adjustment has been integrated with the differential off adjustment to simplify the optimum setting between heat gain and energy conservation. 

A counterclockwise adjustment maximizes heat gain and a counterclockwise adjustment maximizes power conservation.

The green LED comes on when the pump is activated and the red LED brightness increases as the heat available for collection increases. As long as the DC power requirements are less than 30 Watts the PV controller is all that's needed to optimize the heat gain of a closed loop system.


PV Differential Controller    USA    $85

The Enclosed Basic AC/DC Differential Controller may look similar to the PV controller but it's different because this basic controller uses a mechanical relay that can handle up to 300 Watts of power and it may be used to regulate either AC or DC pumps. Unfortunately a battery backup must be used with a PV power supply to moderate voltage swings. The differential adjustment potentiometer is just below the hole in the center of the face plate. The red LED comes on when the pump is active and the green LED brightness indicates that heat is available.



   AC/DC Enclosed Differential Controller  $99

This OPEN BASIC DIFFERENTIAL CONTROLLER is identical to the  Enclosed Differential Controller above except that the relay and other components are exposed.



     Basic Differential Controller Kit  + probes    FREE   SHIPPING    $65

    Basic Differential Controller assembled + probes...FREE SHIPPING    $85

The Thermostatic Differential Controller  is like other differential controllers that use thermistors to sense temperature, but these controllers use a bar graph indicator to display either collector temperature or storage temperature with an accuracy of +/-5*F.

When the toggle switch is up the bar graph indicates collector temperature. When the bar graph is down storage temperature is indicated. The bars light up in approximately 5*F increments between 90*F and 140*F

One differential potentiometer is used to adjust the pump on and pump off settings. If we set the differential too high we´┐Żll collect less heat. if we set the differential too low we may collect more heat but we may be using too much power.

AC only B differential controller has the DC power adapter built into the controller. This basic controller mounts inside a single AC outlet The AC connections as well as the probe extension wires are hidden behind the walls. 
A differential adjustment is made with one toggle button. 
A red LED comes on when the pump is activated.
A built in fuse protects against overload situations


AC only M differential controller has a monitor. It's mounted inside a double outlet box and has more features than the basic AC controller above. 

The TEMPERATURE MONITORING STATION  and the Sky Eye have nothing to do with with controlling a pump and harvesting heat. They are tools used by experimenters to determine the effectiveness of a solar application. The six position temperature monitoring station is used to display up to six temperature readings from six remote locations with a rotary dial.

The Sky Eye is a solar flux monitor  or kind of low cost pyrometer used to measure the intensity of sunlight. It is used in conjunction with the six position monitoring station to measure the percentage of sunlight available.


     Basic Differential Controller Kit  + probes    FREE SHIPPING                                            $65


    Basic Differential Controller assembled + probes...FREE SHIPPING                                $85

    Differential Thermostat with bar graph + probes                                                                $125

     Differential Thermostat with one monitor + probes                                                           $125

     Differential Thermostat with two monitors + probes                                                        $150

    Temperature Monitoring Station                                                                                             $75

    Fahrenheit Temperature Probes                                                                                             $10

    Thermistor Temperature Probes                                                                                            $10

    DC 9 Volt Wall Adapter                                                                                                             $10


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