DIY Thermal Differential Controller (Solar Hot Water Pump Controller)

Photo: BotheredByBees

I’ve been looking into solar hot water systems for home heating and domestic hot water purposes for a while now.  I simply love the idea that I could have free, clean heat and hot water.  I’m also a big fan of Gary’s work over on BuildItSolar.com. Reading his site, I noticed that many people are interested in his $1000 solar hot water system. Its a great experimental setup. However, the cost of the thermal differential controller eats up a lot of that budget.

So, what the heck is a thermal differential controller anyway? A thermal differential controller is what is used to control the pump between the solar panel and hot water tank. It senses when the solar panel is hotter than the tank and starts up the pump so that the water can get warmed up. When the panel cools off, the controller turns the pump off so it doesn’t cool down the tank.

It sounds pretty simple doesn’t it? A brain box to turn the pump on and off. If you look at the price of a commercial controller you’d think that there is a lot more to it. These controllers start at $130 and go up from there. $130 is a bit high for a glorified switch in my book.  That price also does not include the sensors that are needed to run the controller.  Each sensor is an additional $13, and you need two.  So, that brings the minimum price for a controller up to $156.

So, I’ve decided to develop my own thermal differential controller. There aren’t many parts, and the parts are fairly inexpensive. The goal here is to make DIY instructions on how to make your own thermal differential controller for less than half of what a commercial controller costs.

For more info on the controller, visit the forum thread here. I’d love some suggestions.