We've had solar hot water collectors on our house for a long time. We noticed they were great when they worked right, but the over-the-counter controllers were ...less than optimal...
So when we updated our hot water heating system my wife and I designed and built a controller that would handle both the solar hot water for washing and the boiler hot water for heating. That was back in 2007 and it's been working without fail since. We made it so it had options and wound up selling some to a power company that was promoting solar hot water.
Here's a picture of the controller, the box is water tight mainly to give us one with a clear lid. To continue the water tightness we used water tight push buttons on the left side of the box.
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