Hello everyone! 
I wanted to share a project I recently completed that I’m really proud of. It’s a DIY solar water heater for my spa pool, and I thought I’d walk through the process and share some tips in case anyone else is interested in something similar.
The Goal
My main objective was to reduce my electricity bill while keeping the spa pool temperature as high as possible using the sun’s energy. I’ve always been fascinated by renewable energy projects, and this seemed like a fun and practical way to dip my toes into solar solutions.
The Build
I decided to go with a simple design using mostly scrap materials. Here’s a quick breakdown:
- Base: An 80cm square plywood board.
- Absorber: Black-painted metal sheet (reused from old shelving).
- Insulation: Acrylic roofing sheet for the front.
- Pump: A 12V motorhome whale pump to circulate water.
- Automation: An ESP32 with ESPhome to control the pump and monitor temperatures.
I also used three DS18B20 sensors to track the temperature inside the box, the input water temperature, and the output temperature. The pump runs when the temperature difference between the box and the pool is greater than 7 degrees.
Results
I’ve been running this setup for a few months now, and the results have been impressive! Even on cloudy days, the box temperature often exceeds ambient temperature, and the pump runs more frequently than I initially expected. While it doesn’t heat the pool to the desired temperature on its own, it does a great job maintaining a base level, which should save me money in the long run.
Challenges and Learnings
- Material Efficiency: I realized that while my design worked, using proper materials like solar evacuated tubes would significantly increase efficiency. However, I was happy with how much I could accomplish with scraps!
- Pump Struggles: The initial pond pump I used struggled with the hose length, so switching to a 12V pump was a game-changer.
- Automation Fun: Setting up the ESP32 and automations was a bit of a learning curve, but it added a whole new level of convenience and insight into the system’s performance.
Final Thoughts
This project was a lot of fun and a great way to experiment with solar energy on a small scale. It’s definitely something I’d recommend to anyone looking to reduce their energy consumption while having a bit of DIY fun. If anyone has questions or suggestions, I’d love to hear them!
Cheers, and happy building! 
