Well.. here you go then if you want solar hot water. Size it for your needs. I have done the same before with coiled black garden hoses... maybe not as efficient, but same results with just more hose.
https://youtu.be/nC_Ql5qVs4QSeriously though and to get more on original topic, unless you just want to live off grid fulltime, I'd keep it simple with an RV hot water heater capable of gas or electric heating. I was plugged into shore power all this weekend camping, so why use propane when I already paid for the power and it seems to work the same? Ditto for when you have excess solar electric power.
If I was to have just propane for the energy source, I'd probably get the " on demand" tankless type. Probably the best use of propane in this case.
20 years ago you pretty much used propane for refrigerators, hotwater, stove and heat with a small 12vdc system for fans and lights on most all RVs and had to run the generator to use the blender for a smoothie. Still a good approach.. but the cost to establish a photovoltaic energy source then offset by cheaper, more abundant in variety, and more efficient electric appliances (mainly fridge that must run 24/7) is changing the paradigm.
That is where the industry is going especially at the higher end where now all sorts of regular household appliances are demanded and desired (Smart TVs, Cell Boosters, PCs and laptops, microwaves, blenders.. etc.).
Given all that, I think a hybrid (gas/electric) system is ideal for cost effectiveness and redundancy of energy sources for an off grid CTC that also will be used on grid with shore power from time to time and still maintain modern functionality compatible for on grid folks. I am very happy with the way it works and is so adaptable.
Just food for thought.
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