Solar Powered Water Heater

[Bad Obsession]

I was thinking about this during down times last night at work.

Wouldn't it be cool if you could build a 5 gallon or 3 gallon water heater that was heated by solar panel. It would be useful for smaller boats driven by outboards or boats without heat exchangers.

If you could design it with a temperature shut off so that it would be similar to a charge regulator. Once the desired temp is obtain the panel is turned off.

If it was insulated like the water tank in my boat, it would hold hot water long after dark. If I run my engine on my Catalina 30 it heats the water and the water stays hot for most of the night and into the next morning.

There are solar water heaters out there, but the design difference that I am thinking of is one where the solar panel is your typical electric panel. It is wired to the water heating element in the water tank. This way it may be smaller. It would be even better if you could run it off of a 20 Watt panel or something similar to that size. The key would be an efficient heating element that would get hot with very little power going into it. If the tank was 3 gallon it would be small enough to heat the water at a good rate, be easily installable in a small area.

Does anyone else think that this would be possible and a money making prospect?

 

[Steve Dion]

The Solar Showers in a bag work great. I doubt that you would be able to get enough juice out of your solar panels to heat your water and charge your batteries. These newer solar showers are better quality than the ones that we used to use 10-15 years ago.

http://www.rei.com/product/850733/s...ferralID=fb238f14-eb26-11e2-9dea-001b2166becc

 

[Gary_H]

My solar shower is some kind of vinyl plastic water bag that is clear on one side and black on the other. lay it on the deck for an hour in the sun and the water is so hot you have to mix it with cool water to use it. hang it up over your head and there is a short hose with a shower head on the bottom. works good actually.

 

[cb32863]

And then there is this little unit.....

http://www.amazon.com/Coleman-Water...60864&sr=8-1&keywords=coleman+water+on+demand

 

[kloudie1]

The physics of this quickly tell ya why it is not done.. in rough, round numbers, A typical water heater in a boat is 1400 watts.. to heat the same water amount to the same temperature with a 20 watt electric panel would take at full output, 70 times as long.. so if it takes the shore power about 30 minutes to heat the water, the panel would take 35 hours at full output, which would require around three real world days.. That would take probably another couple of days once ya crank in heat loss overnight.. That is the problem with solar, not enough "energy density"..

 

[Bad Obsession]

I figured that, Kloudie. It is a shame. It would be nice to have a dedicated solar panel that was small enough to work on a small boat but it would power a small solar water heater. If it was three gallons it isn't too much water to deal with but it would still take a while for the element to heat the water with current specifications.

Who knows, eventually solar may power most things as technology improves.

 

[Ross]

You have a potential of about 24000 btu's per square meter per day in the eastern USA and about 20% more in the western USA during July. Converting that to heat depends on many factors.

 

[kloudie1]

Exactly, Ross.. the bugger is converting it to electricity and then back to heat.. If ya use a collector that looks kinda like a fridge evaporator (laid out flat and with a black anodize finish and inside an insulated frame with a glass cover), and have a little circulating pump to circulate the water between the tank and the collector, you can actually have a pretty good small solar heater in a space about twice the area of a 20 watt panel. Energy conversion is what eats up efficiency.. using a rig like that takes in heat (infra-red) and uses it directly..

 

[Oblivionboyj]

The answer is a solar coil doing this job, not a solar panel.
The only electricity needed is to run the pump that pushes water through the coil.
A refrigerator coil painted black and cased in a box works great.
It's really not a crazy hard project, and pretty cheap.

You could also go with a single commercially made coil and build your system around it.

I'll try and find links.

Edit...
This is a commercially made coil...
http://www.amazon.com/gp/aw/d/B0041VM58E

 

[Doc_holiday]

There was an article in popular mechanics years ago about building one out of an existing tank painted black and installed in a box that opens top and front to expose a foil insulated lined box. When the sun goes down, you close the box keeping the tank warm.

 

[Oblivionboyj]

There was an article in popular mechanics years ago about building one out of an existing tank painted black and installed in a box that opens top and front to expose a foil insulated lined box. When the sun goes down, you close the box keeping the tank warm.

I have a friend who built something similar for his house.

 

[Ross]

if you have ever had a black garden hose left full of water out in the sun. You know how hot the water can get inside the hose. Fifty feet of black garden hose coiled flat in an insulated window box would serve as a good collector.

 

[Ross]

Using 5/8 inch hose it would contain .8 gallons of water. The hose out front gets "hot" in an hour.

 

[Benny17441]

Why re-invent the wheel. Solar shower bags can be found for under $10 and they heat up to 5 gallons of water in a couple of hours and can be rolled up and easily stored when not in use.

 

[Bad Obsession]

My thoughts are that it would be cool to add it to an existing fresh water system and have a pressurized system. It would be like any existing boat system where there is a hot water tank into the fresh water system so you have pressurized hot and cold water.

 

[capta]

There are 12 volt water heater elements that work with overload shunts on wind gens. That would probably be the way to go.
When I circumnavigated, I had a 5 gallon black square chemical container which would get water very hot on a sunny day. It had a spigot on one side near the bottom and we would position it so the spigot was over the open head hatch and we could take hot showers inside the boat. No muss no fuss.

 

[vimocam]

I've been looking at this unit. You hook it up to your existing water heater. They also sell a solar water circulating pump.
http://www.amazon.com/MH-37-Marine-...1373848884&sr=8-1&keywords=mh-37+marine+solar

 

[Ross]

You can wet a couple of dark color towels and place them in plastic bags in the sun. They will get hot and you can wash yourself clean with a quart of water.

 

[Bad Obsession]

The panel is interesting, but how would you circulate the water from the tank without an expensive motor and the power consumption?

 

[vimocam]

The panel is interesting, but how would you circulate the water from the tank without an expensive motor and the power consumption?

They sell a small circulating pump that has it's own built in solar panel. The water only circulates when the sun is out.