Project Description

A home built solar hot water collection system.

This do it yourself solar collector was built at a fraction of the cost of an equivalent commercially installed system. Any adept do-it-yourselfer could build this system. Most of the materials are available locally at the big box hardware stores, and your mom and pop hardware stores. He got the idea for this at Gary Reysa’s website, probably the best DIY Solar website on the net. It is based on Gary’s $1000 solar hot water heater, which he documents in great detail at his site. This is a drain-back system, which means when the pump turns off, all water will drain out of the collector and pipes, thus providing freeze and overheat protection. Since there is no risk of freezing, normal water can be used as the heat transfer fluid. This style of system has a successful track record in the do-it-yourself solar community.

Some features:

  • Self supporting 4’x8′ copper tube, aluminum fin collector with twin-wall polycarbonate glazing
  • A well insulated 150 gallon non-pressurized thermal storage vessel
  • Custom made PEX coil heat exchanger for preheat of domestic hot water before it enters electric water heater.
  • A versatile, yet inexpensive Open Source differential controller that can control solar collection, radiant heating and mor


The Differduino is available as a single circuit board!
The Differduino PCB is an arduino clone circuit designed with thermal control, or differential control in mind. The resistor needed for Dallas DS18B20 1-wire thermometers is on-board, and there is a “1-wire” screw terminal position. These solid state sensors are accurate, and easy to use and work well in thermal control systems. There is also an on board relay circuit with high voltage rated screw terminals and a mechanical relay. This can be used for switching on/off pumps etc. This PCB is ready made to use the Wiznet 812MJ ethernet module. This is like the ‘ethernet shield’ that stacks directly on a commercial Arduino, but in a more compact form factor. It uses the same wiz5100 chipset, and the standard Arduino ethernet libraries.
He also included an lcd header to simplify the connection of an lcd display.

-based on established duino clone circuits
-designed to use the 812MJ Wiznet ethernet module
-on board relay circuitry

-lcd header for simple connection of an lcd display
-voltage divider circuit for sensing power supply voltage, or a seperate DC voltage
-through holes for 3mm screw terminals, and .1″ headers
-small 6×6 .1″ prototyping area with ground and 5v buss.
-versatile board that can be used for all sorts of arduino projects, not just solar hot water.

The cost is $10 plus shipping. 


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