Size for 10gal RV hot water heater

jwzumwalt

I plan to build my own solar hot water heater for a RV. What solar square footage would be appropriate for a 10gal tank?

Iceni John

My approach is very simple  -  as big as you can!   With the limited space in and on most RVs, why would you have anything less than the biggest possible?   Most RV roofs have so much else up there anyway that it may be difficult to build large panels, but if you're making your own you could make them whatever shape fits best.   On my bus roof I also have space for two water heating panels, each about 20 sq.ft., but they'll probably not be simple rectangle shapes!

When have you ever heard any RV owner complaining about having too much or to large of anything?

John

BB.

In general, the rough rule of thumb is 0.5 to 1.0 sqft of collector for every 1 gallon of hot water used per day...

Obviously, where the RV is located, what season(s) it is used, and how it is mounted (flat to roof, tilted, side of RV).

-Bill

jwzumwalt

It will be for one person. I was planning on a 10gal tank so I cold have a nice shower once in a while. It's free energy so why not start with hot water for coffee or hot chocolate so the microwave will not have to work so hard.
My solar panels are 2x4ft and it looks like making the collector 8sqft to match the panels will work just right.
Thanks for the help :-)

Dave Angelini

If you drink your solar coffee in the early morning, it will not be very hot....
You also have to be careful as most domestic solar hot water is for 50+ gallon tanks. Make sure the pressure relief is done right or you could blow up the whole hot water system in the RV.  This one area that the cost of propane might be worth it! Make sure you have a way to shut down the pump at 140F or you will damage the tank.
The 5 gallon solar hot water showers that lay out in the sun might be the way to go also.

Blackda3

As a lover of everything solar and coffee, I would like to offer a few comments.  First, I’ve never found any product that doesn’t impart an awful taste to the water when trying to heat it up using solar.  Stick with a kettle.   Better yet would be to use kettle and mount it in front of parabolic mirror.

Aside from using PV to power my iceboxes while camping, I also enjoy using solar to heat water.  I’ve built several solar water heaters using copper tubing, spray painted black, and the last one was housed inside a home-made solar collector box.  I’ve also experiment with both Nemo - Helio Pressure Shower and Seattle Sports PVC Sun Shower.  Both are great products, provided you understand their limitations.  Even using reflective panels to insulate the water from wind and gather more heat/light, they will only get warm (maybe around 105-110).  The “open surface” method seems to lose a lot of heat to air and wind which is very good at robbing the water of heat.

None of the above mentioned techniques have come close to the results of a real “black box” solar hot water collector.  While looking for small solar hot water panels, I came across the following manufacturer.  I used two Heliatos 2’ by 2’ panels for about two years.  The kit uses a separate 15 watt panel to power the pump which acts like a cloud/shadow detector (i.e. pauses the water pump until the sun comes back).  The hot water is piped via 3/8” PEX (insulated by foam tubing) and stored in an 8 gallon 12v portable shower (made by Big Kahuna).  The system worked so well, I often had to add cold water to lower the temperature.  It could easily reach 140F by 2 or 3 pm on a sunny day.  According to the kit manufacturer, the water pump has a high temp auto shutdown but I don’t think I’ve ever reached that shut-off point.  I recently removed one panel which seems to work pretty well to just take the chill off the water to rinse down after surfing (and under certain conditions) it does get 8 gallons fairly warm.  Obviously, the system will also run hotter, given the same amount of solar heating, if you reduce the amount of water being heated.  Notwithstanding that I live in sunny Southern California, I really like the system I’ve configured.

After this picture was taken, I later used marine grade thru-hulls to route the hoses/wires through the vent to keep out water/rain.

I would also recommend checking with your local library to see if they can find you a copy of a book called A Golden Thread:  2500 Years of Solar Architecture and Technology by Ken Butti and John Perlin.  Simply put, solar has an amazing history and it’s really interesting to see what ideas have been tried around the world.

jwzumwalt

Thanks for sharing your experience with the various products and techniques.