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Old 24-08-2016, 17:11   #16
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Re: Solar hot water

Good stuff for this thread too!
Handy stuff for pocket cruisers, et al.
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Old 24-08-2016, 18:18   #17
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Re: Solar hot water

In Winter months I usually "cheated" by heating up a kettle on the stove, & then adding the water to my garden sprayer. But regardless of the month, for $20 it was a darned good shower.
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Old 25-08-2016, 07:04   #18
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Re: Solar hot water

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Originally Posted by Franziska View Post
Len,

if you have a small photovoltaic powered pump it should stop/reduce the flow at night or cloudy days.
Otherwise add a bypass valve.

By the way in colder climates add a drain to prevent damage from freezing.
Might be a thought to loop an antifreeze liquid and have it transfer the heat with a coil in the boiler.
Most marine boilers have this loop already as boats with inboard engines would connect their cooling water outlet to it.

Interesting project for those who like to shower inside and without restriction on waterflow.
The other solutions work too, but some people prefer a truly fixed solution.

Have fun,

Franziska

www.ladyrover.com
Ive thought about a similar project to heat the heat exchanger on the hot water heater. Essentially the same concept as commercial solar hot water heaters. PV switched circulation pump would avoid circulating cold water.

Have also considered a DC powered heating element driven by the AUX output of the solar controller (which only turns on when there is excess solar...almost every day during our cruising season). The upside to this is a much cleaner simpler install than plumbing an external solar collector to the hot water tank.

With good sun we only need to start engines to heat water...very inefficient...either solution would totally eliminate that need.

Here in the tropics, hot water is not a necessity, but it is sometimes handy for washing dishes or to reduce the initial shock of a cold shower sometimes.
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Old 25-08-2016, 08:06   #19
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Re: Solar hot water

Here in the "frozen" north,solar hot water in homes is not uncommon.
Usually consists of circulating antifreeze protected water thru solar water panels & a boiler equipped with a heat exchanger coil.
There are many variations of these systems & lots of info on Google(solar hot water).

As to dumping excess solar electric via a resistance heater,just connect the excess to the existing heating coil. Existing coil (120/240 VAC) will accept 12/24 VDC just fine. Watts are watts.DC current will be limited to solar panel's max current output. Do not connect batteries in this manner though.
It makes sense that any boat with excess solar electric dump into their water heater in this manner.
It would mean a couple of solenoid valves & relays to eliminate shore/genny AC power "mixing" with DC solar power & engine coolant "mixing" with solar panel coolant to automate a system-or some manual ball valves/switches if you have a good memory.

Fun project. / Len
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Old 25-08-2016, 09:39   #20
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Re: Solar hot water

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Originally Posted by deblen View Post
Edit: I meant Polyethylene pipe-not PVC-though I,m sure flat black painted PVC would work as well.
Attachment 130070
And copper would work much better. But if you have a working system that's what counts. for anyone else interested google plastic as a heat insulator and what came up for me was it is very poor at conducting Heat. This may work fine for pools where you're changing the temperature a very small amount and you have plenty of space but on a boat metal tubing makes more sense to me. And for maximum efficiency put it in an insulated box with a glass front or use vacuum tubes. PS if you do decide to use PEX make sure you paint it because it's not UV resistant.
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Old 25-08-2016, 09:55   #21
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Re: Solar hot water

I've been using the "Sunshowers" for years. Current one is a 6 gallon that I bought over 10 years ago. I added an extra long length of PVC tubing and leave the "bag" on deck and run the hose and sprayer end into the head. Plenty of flow and you have privacy which the wife likes.
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Old 25-08-2016, 15:53   #22
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Re: Solar hot water

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I came across this video yesterday while considering methods of providing hot water on my Grampian 26 for a shower.. http://youtu.be/dG2HK9JsAjw
Its a solar and pressurized hot water heater designed for campers to put on the top of their vehicle.. Its a DIY project based on a commercially sold product, which this guy details clearly in his video for a very moderate expense in parts (well under $100) His design provides about 6 gallons of hot water.
I contemplated on installing this contraption on the cabin top..
A guy built a small barge (a cabin on a pontoon boat base) and anchored it down the river from my marina. He installed a 55 gallon drum, painted black on top of the cabin for solar hot water. He used to motor up to our marina and steal water.

A storm came up and the barge capsized.

I suggest factoring in the weight of that much water on top of your boat before you go ahead with your plan. That much weight should be as low in the boat as practical.
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Old 25-08-2016, 16:11   #23
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Re: Solar hot water

Yep. There is a couple of ways. You can actually use solar electricity to power a small electric water heater. Also from caravan shops.

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Old 25-08-2016, 16:22   #24
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Re: Solar hot water

I once pondered those coils of copper tubing they sell at Home Depot for radiant heating in floors... just lay it on the deck, leave it coiled, pretty easy to stow and you'd have scalding water in an hour or so...doubt you'd need to paint it black... mix it with a batch of ambient temp water and voila.. lots of shower water. Haven't tried it though.
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Old 25-08-2016, 17:40   #25
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Re: Solar hot water

well I know there's a way to cut and paste I just don't know how to do it. but this is an interesting YouTube video called why solar electric water heater is best option. By Steve Robertson. now this might not be feasible on a small boat but I already use an induction cook top to heat water for my pressure sprayer when I have excess solar electric and I plan on expanding. The problem with solar Direct is it's hard to have water at the proper temperature, in 4 minutes on my induction cooktop I can have a gallon and half of water at the perfect temperature.
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Old 28-08-2016, 15:15   #26
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Re: Solar hot water

I don't know why this hasn't dawned on me before but after discussing how much better metal is at conducting Heat than plastic a metal container for solar shower makes so much sense. The handles won't tear and it won't grow algae. It comes in green but an easy thing to spray paint it with flat black . Adding a spigot shouldn't be too hard either.https://www.amazon.com/gp/aw/d/B01KZ...gallon+gas+can
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Old 28-08-2016, 16:09   #27
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Re: Solar hot water

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Originally Posted by sparrowhawk1 View Post
I don't know why this hasn't dawned on me before but after discussing how much better metal is at conducting Heat than plastic a metal container for solar shower makes so much sense. The handles won't tear and it won't grow algae. It comes in green but an easy thing to spray paint it with flat black . Adding a spigot shouldn't be too hard either.https://www.amazon.com/gp/aw/d/B01KZ...gallon+gas+can
Green is probably dark enough to get pretty hot, but that can did not look waterproof. How about:
https://www.amazon.com/dp/B005B53I26?psc=1
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Old 28-08-2016, 16:34   #28
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Re: Solar hot water

There is a company called heliatos ( Heliatos Solar ) that makes 2 ft square solar water heaters that can plug directly into your engine/waterheater glycol loop. They come with a solar panel to run the circulation pump which is included in the kit for a little over $400. The solar panel only runs the pump when the sun is shining so there is no need for any kind of solar controller. The PVC or copper coil will work within limits, but if the thing is not covered with an infrared blocking glazing it will start loosing heat to the environment as soon as the water starts getting hot. This is also a problem with a metal container. It conducts heat so well that the side facing away from the sun looses heat almost as fast as as the sunny side absorbs it. I could not connect to the article on solar electric, but if they were suggesting that solar electric was efficient, they don't know what they are talking about. Resistance heaters are almost 100% efficient at converting electricity into heat, but the best solar panels today are only about 22% efficient and most are in the mid teens. Flat plate solar thermal on the other hand can be up to 80% efficient. You'll get a lot more hot water from a solar thermal system than by heating your water with the output of a photovoltaic panel.

The only problem I've had with the sun showers is that they cool off very quickly after the sun gets low in the sky and you don't always have hot water when you want it. The garden sprayer lasts a bit longer because the plastic is thicker and hold the heat in longer. Oddly enough the most efficient way to set up the garden sprayer is to put the black paint on the inside as that puts the heat absorbing layer in contact with the water. It probably doesn't matter that much since I have noted that simply leaving a 5 gallon blue plastic paint bucket full of water on the back deck gets it plenty hot enough for a shower by the end of the day.

There is a company in Turkey that makes hybrid solar panels. They have photo voltaic cells mounted on a flat plate solar collector and achieve very high efficiencies. They are oriented towards building heating and not appropriate for mobile applications.

I have thought about the possibility of taking some of those aluminum radiant heating plates and mounting them on the back of a photovoltaic panel. They get quite hot and normally radiate this excess heat through the back of the panel. In theory one could remove the excess heat by conduction and capture it. I'm sure it would blow the warranty, but I am planning to replace my old 75 watt panels with modern efficient panels and it might be worth experimenting with one of them.

Good luck with what ever you decide to do.
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Old 28-08-2016, 16:57   #29
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Re: Solar hot water

What about using those solar water vacuum tubes. The advantage of the vacuum is that it cuts heat loss.

https://www.google.co.uk/search?q=so...CBwQ_AUIvAEoAQ

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Old 28-08-2016, 18:17   #30
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Re: Solar hot water

All good points Captain Bill. but you really should try and watch the video. His point was solar water heaters on the market are expensive and if he took the same amount of money and put it into solar panels he could have solar hot water in two hours and put the "excess" electricity to use, where if your heating up the hot water "directly" when the hot water is hot that's it. I totally agree with you about efficiency from an energy in energy out standpoint but there's also the most bang for the buck efficiency. And the efficiency of Versatility. I'm also not saying this is the way to go or not, just that it's very interesting.
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