Solar water heating on a sailboat

[la7qz]

Hi Doug

Well, I agree with you that she will probably adjust, but I don't think it would be realistic to expect her to adjust to me saying she can't have hot water because I don't want to run the engine when we already have a well functioning hot water tank running off the engine coolant. I don't think modifying the system to run off solar is too much to ask. I don't at this point have the choice between hot water or not hot water, just a choice of how to heat the water in the already existing system.

I also like the challenge of getting these systems working. In many cases, her arrival is making me get started with things I had always planned to do "sometime". It took a little push to get the PV and wind chargers upgraded to where we don't have to worry too much about electricity consumption, but there is no way I would go back to where I have to watch every milliamp. I resisted having a fridge on my boat for 16 years, but then I found the Coleman Stirling Cooler which draws 5-600 mA and I like having cold beers in the fridge too much to go back to living without it now.

I have to admit I enjoy the challenge of getting these systems going. Getting it all working on the boat will help me later when we start looking for somewhere on land. Having seen the systems working on the boat will prove to her that it is realistic and economical to live totally off renewable energy without having to go back to 19th century technology.

Owen

[la7qz]

Hi

Thanks for that link.

I see the smallest size they do is 4 x 8 feet.

So, I'm thinking why don't I build the whole box from this type of sheet, top and bottom and just paint the inside of the bottom sheet black? This would give me a very light-weight collector which would work well in my chosen location. One 4 x 8 sheet would still give me enough for one more collector for someone else.

Or....? If someone here is interested in sharing??? I'd take half of a 4x8 sheet if someone buys it, cuts it in half and ships the second half to my employer's shipping agent in Miami.

One thing I noticed... It blocks UV light. Is there any heat energy in UV?

Owen

[la7qz]

Hi

A couple of issues occur to me if I were to circulate the water in the hot water storage tank rather than coolant through the coil. The most obvious is that the system would have to be drained (and therefore not functional) if the boat ever goes to a cold climate. Well, I don't know how much hot water it would produce in a cold climate anyway, so that may not be a problem.

If I were to stay long term in a cold climate again, I would install an oil furnace with a water heater coil and also some heat radiators around the boat. I didn't have a heat coil in the furnace on my old boat, but I helped install a couple of systems like that back in Norway. In that case, the hot coolant flowing through the engine block was very welcome to keep the raw water side of the engine from freezing.

As for the oil coolers. They look a bit small to me. I would probably need four and then we're over $200 by the time I have them on the island. I did think of using two car coolant radiators in the box, but don't know how much it would matter that the fins are not at 90 degrees to the sun. (If I use the double greenhouse glass, the collector itself isn't really visible, so the "not pretty" factor of two old car radiators would probably not be an issue.)

It would be very rare that the sun shines through the collector fins, but even so, I wonder whether it would collect less than a normal collector. I mean, the energy gets into the box and hits the black metal, the box is insulated so most of the heat energy stays in the box. Does it matter which angle the rays hit the metal at as long as the box itself is at a good angle to the sun??

Owen

[la7qz]

Hi again

Another possible issue that I forgot to mention in the previous message. If the water in the storage tank circulates through the collector, I would have to find some way of preventing it from circulating at night when the hot water in the tank would flow up to the collector, continually cooling the water. I suppose this would depend on the design of the pump.

Owen

[dnix71]

Since you have diesel, why not just use that to heat water on demand.

http://www.doctordiesel.com/index_files/page0004.htm

It needs about 100 watts when running. (120VAC, >1 amp) and burns about 1 gallon an hour.

[Ungrounded Lightning Rod]

The pressure cap keeps the coolant from running down - when it's on.  Coolant can only get out if the pressure is higher than the cap pressure.  Coolant goes back in when its contraction produces a vacuum.

You could hook the collector straight into the cooling system if you add valves to cut it off before you take off the pressure cap.  (But forgetting to close them could cause a slug of coolant to come at you when the air hits one of the tubes to the collector.)  And you'd need a bleed valve on the collector to clear the air.

A simpler approach is to put the pressure cap fitting at the high end of the collector and hook up your reservoir there.  You'll need to run the plumbing so any air bubbles in the engine's cooling system goes up to the pressure cap fitting or through the collector to it.  But that will solve both the overflow and air-lock problems.

[Ungrounded Lightning Rod]

The pressure cap keeps the coolant from running down - when it's on.  IF it doesn't leak!

[la7qz]

Hi

This one misses out on a few requirements.

First of all, diesel fuel is not renewable energy.

Also, it's a complicated device that combines fuel. electronics and water. This is not a good combination at sea. I like simple stuff on the boat because simple means reliable.

Another factor is that the thing also has an exhaust, and it looks like a balanced flue design where it gets the combustion air from the same skin fitting. I would have to find a dry place to install it where the exhaust would not be at risk of getting dowsed with seawater AND where there would be no risk of a draft into the accomodation AND where there would be no nasty smells to bother us when it was running while someone was out in the cockpit. Those who have spent time at sea in rough weather on a small boat will know how unrealistic it would be to meet those requirements.

Owen

[tbird]

hi owen,

i stumbled across this thread and it appears to me you are missing the easiest and most logical solution.  12 volt heater elements are available for $60 or less and simply screw into a fitting on the tank.  since you mainly use the heated water once a day (and only 4 gallons at that), a simple switch and led (light to tell when it's on) would get you started.  if worried about forgetting to turn it off, a termostat could be installed too.

this will be a small increase in the daily consumption.  if your batteries don't recover with the days' charging, then maybe you have to add one more solar panel (RE).  if your input is above your current usage, you probably won't notice a thing.

like you, i've lived on my boat for quite awhile.  i also made changes to get along with my girlfriend.  she liked using a hair dryer, so i put in a 7.5kw gen and as long as i had the power, why not a water maker and as long as i had a w.m., why not a washing machine (& dryer), and etc.....  i'm sure you understand.

i had the system you have been talking about. i took it out.  too much extra weight and too many parts to maintain.  just my feelings at the time.  as you can tell from above, i more than made up for it.

tom

ps i'm in curacao as we speak.

[tbird]

BTW,

if you do decide to build a collector, you can get thin copper in widths up to about 4" from your local raditor shop (they use it for making new fins).  it comes on a roll that looks like it could be a mile long.  the raditor shops are usally pretty reasonable in pricing when it comes to home projects like that.  they might even have some scraps for free if you talk nice to them.

also, car air conditioner condensers are usually thinner than raditors if you decide to go that way.

one last thought.  if you know someone changing their cold plate frig system over to something else, you might consider the old holding plates.  they are usually stainless steel and as long as they don't leak externally, they would be perfect for your use (if you build a collector).  some home built plates just used 2 ss cooking sheets welded together with tubing inside.  for your use, the tubes wouldn't be needed, just an in and out fitting.

tom