In the process of designing and select our solar panels, we researched many options. Many of the “marine” solar panels were quite expensive. What I came to find out was that a part of the “marinization’ boiled down to the fact that the junction box had been sealed with ‘potting compound’.
So long story short, we bought two 160 watt Grape Solar panels from Home Depot along with two controllers. I put each panel on it’s own controller for redundancy. The only thing I did was to purchase several tubes of potting compound, opened the junction boxes and filled them with the compound to seal all the connections. After two years of constant use our system has easily handled all of our charging needs with the exception of the seven days down the US west coast when we had no sun. Other than that, we have never even had to plug into shore power.
In the course of sourcing panels I wondered if there was a way to utilize solar water heating. I found that Custom Marine Products offered a Solar Water Heating kit. https://www.custommarineproducts.com/solar-water-heating-system.html
I purchased the system which I installed with the circulation panel glued to the back of our starboard solar panel with thermally conductive silicone. The install is very simple requiring only a couple of isolation valves and tees off of the boat’s water heater circuit. The small circulation pump is controlled by a simple heat sensor on the panel that is set to come on at 104F and turn off at 100F.
The system worked great! It provided daily hot water up to 120F on any day with sunshine (99% of the days in Mexico). All was great for six months UNTIL it began to leak out of the circulation panel. After checking all the obvious things like hose connections, we determined that the leak was from the panel itself. Really a bummer given that there was no way to remove it from the panel without destroying either the circulation panel or damaging the solar panel.
After much discussion with Tom Trimmer at Custom Marine Products, he agreed to send me a new panel. It finally arrived in Puerto Vallarta. The dilemma was whether to glue it to the back of the port solar panel or just ‘layer’ it onto the leaking one. I opted to layer it using thickened epoxy. Not the ideal, but I reasoned that if I ended up damaging a solar panel, I didn’t want to have to replace both.
The new circulation panel worked well in spite of not being directly attached to the solar panel. Most sunny days show a panel temperature of up to 140F, providing very hot water. Again really wonderful to have hot water for showers without needing to run the engine…until ANOTHER LEAK! Once again, no way to identify where the panel was leaking given the attachment with epoxy. After MUCH discussion with Tom at Custom Marine, he agreed to send me another panel, this time while we were visiting family in the US. I agreed to fabricate a completely separate, stand alone panel that could be taken apart if it failed again. I made a simple frame of aluminum channel with polycarbonate “Twinwall” sandwiching the circulation panel and a layer of foil faced bubble wrap. Once again, six months later, it leaked. Super frustrating but all part of R&D I guess. When I took the panel apart I found that the two sheets of thin gauge aluminum tha make up the panel had split at the point where the inlet and outlet tubes are attached. Whether from copper next to aluminum corrosion, or the metal being too thin the fact is that they failed with small hairline cracks. I tried several times to repair the cracks with no success. In the course of conversation with Custom Marine, Tom contends that I am the only one that has experienced failures. I don’t know where the other users are so it could be the intense Mexican sun. At one point Tom thought the system water pressure might be too high so I installed an adjustable pressure relief valve on the pressure side of the loop. It still failed.
The final soluion was to purchase 30 feet of 1/4” copper tubing, form it into a coil of sorts and glue it to the now defunct panel with epoxy. It’s not pretty but I have no doubt that this will not fail.
So for anyone considering a solar water heater, my recommendation would be to either build a stand-alone panel with copper tubing glued to a panel of aluminum or to form the coils and glue them directly to the back of a solar panel, then cover it with a layer of insulation.
In spitemof all the failures, it remains one of the coolest things on the boat. Hot water without running the engine or generator.
I will try to post a drawing of the stand alone.