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Old 26-04-2014, 10:50   #1
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Spare Solar Power Used to Heat Hot Water

Hello all,

I've been really impressed with the 300watts solar on our new yacht (Hanse385). She must be pretty energy efficient as the solar tops the batteries off by 10-11am, even on semi cloudy days.

In short I love the solar setup, but I'm left wondering if the extra energy the panels must be able to create can't somehow be used.

The only time I really now need to connect to shore or run the engine is for hot water. After researching I can't find much on this. Just like a fridge once it's cold the solar is quite able to keep it cold, can't the same be done with the hot water somehow?

Regards,
Simon
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Old 26-04-2014, 10:57   #2
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Re: Spare solar power used to heat hot water

We did that.
Reinsulated the tank with Aerogel, and now we turn on the inverter about 20 minutes a day.
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Old 26-04-2014, 11:00   #3
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Re: Spare solar power used to heat hot water

Quote:
Originally Posted by simonpickard View Post
Hello all,

I've been really impressed with the 300watts solar on our new yacht (Hanse385). She must be pretty energy efficient as the solar tops the batteries off by 10-11am, even on semi cloudy days.

In short I love the solar setup, but I'm left wondering if the extra energy the panels must be able to create can't somehow be used.

The only time I really now need to connect to shore or run the engine is for hot water. After researching I can't find much on this. Just like a fridge once it's cold the solar is quite able to keep it cold, can't the same be done with the hot water somehow?

Regards,
Simon

300 watts of electric heat would be almost but not quite trivial. You might warm your toes with it. Even it you let the juice accumulate, it would'nt warm too much more than your feet (for a shorter time). Could knock off the chill maybe. Would depend on the chill. I think one could put water based solar panels on a boat though - and get either cabin heat or a warm shower from it. Anyone have experience with such a thing?
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Old 26-04-2014, 11:16   #4
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Re: Spare solar power used to heat hot water

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Originally Posted by senormechanico View Post
We did that.
Reinsulated the tank with Aerogel, and now we turn on the inverter about 20 minutes a day.
Great to hear! We also have an inverter on board, but it isn't linked to the Emerson heater. How did you go about this? Also how much does that 20mins take out of then batteries, and how big is the inverter you have? I think ours is pretty small around 350watts or something.

Regards,
Simon
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Old 26-04-2014, 11:30   #5
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Re: Spare Solar Power Used to Heat Hot Water

300W will raise the temperature of 6 gallons of water 40C in about 4 hours. So the math says your solar panels can make some hot water off the inverter. It amounts to approximately 400AH at 12VDC. The size of your battery bank needs to be considered though.
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Old 26-04-2014, 11:40   #6
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Re: Spare Solar Power Used to Heat Hot Water

Don't know where you call home or do your cruising but if you have sunshine a simple 50 foot black garden hose coil makes a perfect solar water heater. Use the 'extra' power from your panels to run a circulator pump. Even in cooler climates black can get quite warm.
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Old 26-04-2014, 12:14   #7
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Re: Spare Solar Power Used to Heat Hot Water

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300W will raise the temperature of 6 gallons of water 40C in about 4 hours. So the math says your solar panels can make some hot water off the inverter. It amounts to approximately 400AH at 12VDC. The size of your battery bank needs to be considered though.

Your math is a bit off somewhere. 400AH at 12V is 4800 watts, NOT 300 watts.
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Old 26-04-2014, 12:15   #8
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Spare Solar Power Used to Heat Hot Water

You are right.
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Old 26-04-2014, 12:19   #9
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Re: Spare Solar Power Used to Heat Hot Water

Oops I see what you are saying. 1200 WH is 4 hours at 300W. But typical AC heater is 1200 W. So 1 hour would be 100AH not 400AH. Sorry for the confusion.
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Old 26-04-2014, 14:16   #10
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Re: Spare solar power used to heat hot water

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Originally Posted by simonpickard View Post
Great to hear! We also have an inverter on board, but it isn't linked to the Emerson heater. How did you go about this? Also how much does that 20mins take out of then batteries, and how big is the inverter you have? I think ours is pretty small around 350watts or something.

Regards,
Simon
320 watts of solar,
Mppt BlueSky
200 aH LiFePo4 cell bank (12 volt)
1500 watt sine wave inverter
17 liter hot water tank with 120 volt 1kw element
There's always enough water for doing dishes and a short shower.
With the Aerogel insulation in both the fridge and hot water tank, there's always enough solar to keep us happy.
We don't live aboard, so we're only sailing when the weather is halfway decent.
We never need to run the engine for electricity or hot water, and I HATE to motor anyway.
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Old 26-04-2014, 14:48   #11
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Re: Spare Solar Power Used to Heat Hot Water

maybe something like this would work, find it at s/v hotwire

works with wind ..why not solar also..

John



Water Heater Load Diverter


For those of you planning to spend the vast majority of your time at anchor, a better option is a 12V/24V water heating element which replaces your 120V element in your hot water tank. (The threads are identical on most heaters.)
If you are providing power with your wind generator, the hot water heat exchanger from the engine will not be making hot water, and your 120V heater element won’t be working for you. So the advantage to the 12V heater element is that you can use any excess power to make hot water.
Winter is generally the time when the winds blow hardest, when your wind generator is producing at its peak, and when you’ll most appreciate the hot water!
The best option is Hotwire’s 12V/120V combo element so that you can use a single heater element for both anchoring out AND for shore power!! One loop is 12V at 300W; the other loop is 120V at 500W.
Let us know what brand of hot water tank you have and we can match the heater element to your tank. So far, we can fit any brand except Isotemp. BUY NOW
Prices

Each divert option is $95.00 and can be used with any of our diversion-capable charge controllers.
Frequently
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Old 26-04-2014, 16:40   #12
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Re: Spare Solar Power Used to Heat Hot Water

A 12v element for your waterheater and diversion regulator are all you need. Alternatively a diversion regulator hooked to turn on an inverter hooked up to your 110v water heater. I had thought a watermaker turned on after the bats are topped off would be a better way to store excess power. Or an icemaker etc...... I use very little hot water around florida. That is heated on the stove,
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Old 26-04-2014, 18:54   #13
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Re: Spare Solar Power Used to Heat Hot Water

IMHO, you guys are making this a lot harder than it has to be. How about just putting a solar shower bag in the sun? Or, failing that, how about painting a pump-up pressurized garden sprayer black on the outside, and use it?

Is this really a problem you want to throw a lot of money at?

If so, have at it. I've had my say.

Ann
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Old 26-04-2014, 19:12   #14
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Re: Spare Solar Power Used to Heat Hot Water

I think extra power will be like extra money, somehow or another you find a way to spend it, and after it's spent, you wonder where it went.
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Old 26-04-2014, 19:16   #15
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Re: Spare Solar Power Used to Heat Hot Water

I agree with you Ann T Cate. Why make stuff so complicated. I thought my suggetion of black garden hose was a simple solution even if you just use the dribble out of end of the hose to shower with. Lin & Larry use a pressureized bug sprayer for their shower. Works great.
In the South Pacific where the water is 85 degrees ... just jump in the water.

Electric this and that, microwave ovens, where does it end ... go back to living in a house.
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