In an earlier blog post I described how a solar panel can be used to heat water using the sun's radiant energy (not the electricity generated by the solar panel). This year we put the concept of heating water by collecting the sun's radiant energy coming through the back of the solar panel to work during our 35 day cruise. I mounted a custom made heat exchanger to the back of our 150 watt solar panel, added some insulation and a new back panel. Water is circulated from the boat water heater through the heat exchanger and back into the water heater using a small circulation pump that draws less than .4 amp.
Here is what we found during our 35 day cruise in northern Lake Huron:
1. Running the circulation pump for several hours midday on sunny days provided us warm water for showers and dish washing within two hours.
2. Water was heated from 60 degrees F to about 110 degrees F on sunny days.
3. Water was heated faster and to a higher temperature on calm days than on windy days. This is because the wind tends to cool off the front face of the solar panel.
4. We enjoyed warm water from the solar panel water heating system 12 days at anchor. Other days we either had warm water from running the engine to move the boat or the days were cloudy so no heat was collected.
5. The small circulation pump did not draw a significant amount of solar power. Besides, our batteries were topped off by early afternoon so we had plenty of excess power.
6. Having the system tapped into our boat's water system made it very convenient to take advantage of the warm water.
7. The added weight (10 pounds) of the water heating system was no problem for the pole brackets or stern rail.
8. I added a T and a valve in the solar heater tubing to make warm water available in the cockpit for showering or rinsing off after a swim. It worked perfectly.
All in all, the system worked as planned and provided us with warm water conveniently when we needed it. Our next step will be to make a kit available to our customers to retro fit their solar panel systems or to order a water heating system with new installations. We will have kits available for both our larger 150-160 watt panels and our smaller 100-105 panels.
Thomas Trimmer has been cruising with his Ericson 38 sailboat on the Great Lakes for over 20 years. He has pioneered the use of solar energy for wilderness cruising. He is continually designing and building equipment to simplify and enhance the cruising experience.