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Old 15-02-2018, 07:08   #16
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Re: Water heater using solar (not the camping bag)

I wonder how effective these swimming pool solar heaters would work for shower water. It'd probably take several of them and a little pump to circulate it to a tank, but seems you could soak up a lot of solar heat with that.

Unfortunately the reviews I skimmed through quickly said these thing spring a leak, and I didn't find much better options.
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Old 15-02-2018, 07:15   #17
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Re: Water heater using solar (not the camping bag)

How much!!!!

Most folk just use the solar shower types.

https://www.amazon.co.uk/SWT-Heating...s=solar+shower
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Old 15-02-2018, 10:55   #18
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Re: Water heater using solar (not the camping bag)

Hmmm interesting.
OK I know a lot on here will say the ideas and concepts I mention here are ĎScience projectsí at best probably more likely Ďfantasy landí akin to the other side of Electric propulsion reality or Lithium viabilityí.
Water heating is Energy storage. It can be used for the obvious hot showers, but also maybe in supplement to battery capacity or perhaps even thermal cooling. (oops said it now, I can hear the cries of that crazy/ illogical etc, and eyes glazing over as I write this).
For those few skeptics, still humoring me, I hear the chorus of please explain.
I saw the comment of better to have air flow cooling the back of our solar panels. Couldnít agree more. Cooler PV panels are more efficient than hot ones. Unless perhaps, if in the process of heating water we were also sucking heat out of our panels at the same time. Water cooled panels. Iím not saying this is the case here as it would depend on the temperatures involved and where in the system those temps are.
Hot water as an additional energy store to add to battery capacity. OK sure this energy can only be used practically on a boat in a few possible ways. Whether this was worth it would depend on the cost and benefit comparison.
Just to through some other fuel (propane maybe?) on the fire. Propane is another bottle we have to go into town and pay to keep feeding. Safety, donít know, but I suppose there has to be a greater risk than not having it.
Letís say $500 for a 5 gal, $700 for a 10 gal water heater doing a quick look on the Defender page. The Water heater silicone to the back of our PV panel kit listed by the OP is $400. So we are talking $900- $1,100 for starters. If we donít already have a water heater.
If we have a water heater that we heat using Solar PV after our batteries were topped off that would otherwise not be utilized. Or by suck the heat out of the back of our PV panels.
So the questions could be how much battery power could we get for $900 or $1100. Not much Lithium. And how much energy can our 5 or 10 gals of hot water
OK if this is worth it, cost wise, perhaps we should have a bigger water heater. There are valves at around $90 that can increase the Ďeffectiveí size of your water heater. They do this by increasing the thermostat setting of your water heater but using a mixing valve to mix in cold water to bring the output water temp back down. So less/ hotter water is used.
So using some of our PV panel out put to heat our water tank after our batts are topped up. If we had our DC element connected via a bi stable VSR above our float voltage (14.8V or as applic to your partic batts).
Then if we used an Upper water tank heater thermostat unit (has extra set of contacts) we could also wire it to sequence on the next load down our priority list when the water heater was up to temp and we still have some solar/ engine alternator power coming in. When we have to motor for other reasons etc. We are capturing more energy that would just otherwise be wasted. Might be cheaper, or more practical for space reasons than having more batt capacity. Iím sure we will all do our own sums here.
What else can we use that stored energy for. Cooling maybe. Refrigeration is mostly a large slice of our power budget for most of us. Letís not even mention air conditioning, oops I said it.
Thermal cooling. It sounds crazy (maybe it is, and me) and counter intuitive. I assume I will get a lot donít be so stupid or more politely please explain.
The short version, most relevant to this thread. A fridge compressor increases pressure of our refrigerant gas, which also increases the temperature before going into the condenser. The condenser then sucks some of that heat out to turn it back into a liquid.
What would be the result if we just heated our refrigerant before it went into the compressor. If the refrigerant was heated first to increase itís pressure? Is this the same result as what the compressor does mechanically. Ie a higher pressure and temperature. Some people say this decreases the load (unloads) on the compressor, which decreases the amps required to spin it.
I hear people saying why would we want to put heat into a system we are trying to by its very nature trying to remove heat from. And wont that place more heat for the condenser to remove. Some out there believe hotter refrigerant going into the condenser may increase the delta T through the condenser thereby increasing itís efficiency. I am not trying to convince anyone here, you guys decide.
Wouldnít it be good if the hotter our environment was the better our fridge, (or maybe even air cond) worked
If any of our Fridge guys on here want to get this going on their systems to get the lowest amp system around putting them way ahead of the rest. I would of course be completely morally supportive and behind them. I know you guys already provide great products and Iím sure are way too busy for this sort of shenanigans.
Nah this is not the way itís always done, cant be any good. There might even be some crazy fringe dwelling types already doing stuff like this.
Anyway, Iíve gone on too much already. Iíve obviously got too much time to think. Hopefully it is some entertainment story or comic value to some of you.
Cheers all.
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Old 15-02-2018, 11:20   #19
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Re: Water heater using solar (not the camping bag)

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Originally Posted by zboss View Post
THat second system looks appealing... its purpose built instead of using the back of a PV panel. You could make your own.
I did that very thing back in the '90's on our previous boat.
I integrated a 2'x4' (approx) panel into our solar arch.
It recirculated the hot water tank contents with a magnetic drive March pump which was controlled with a differential controller.
We always had hot water on tap.

Of course, we were in Mexico at the time, but it was great having hot water for dishes and taking midnite showers.
I had to occasionally "burp" the hot water panel with a small valve on the arch.
People had a WTF ?? look when they saw that !

With our current boat, I just use the inverter for 15 or 20 minutes. Ah, Lithium !!
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Old 15-02-2018, 21:49   #20
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Re: Water heater using solar (not the camping bag)

Somebody please check my math here but it should just take about 750 watts to raise five gallons of 60 degree water to 120 degrees.

>BTU needed to raise 1 gallon of water by 1 degree = 8.33 BTU

>8.33 BTU = 2.4412820131 watts

>Raise that 1 gallon of water from 60 F to 120 F = 2.4412820131 watts * 60 degrees = 147 watts per gallon

> 5 Gallons * 147 watts per gallon = 735 watts plus losses.

So why not just run the water heater through an inverter, say a 1500 watt element for an hour, to get hot water? You would need a sunny day and two 250 watt solar panels to put that power back into efficient batteries, like lithium.
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Old 15-02-2018, 22:52   #21
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Re: Water heater using solar (not the camping bag)

Quote:
Originally Posted by zboss View Post
Somebody please check my math here but it should just take about 750 watts to raise five gallons of 60 degree water to 120 degrees.

>BTU needed to raise 1 gallon of water by 1 degree = 8.33 BTU

>8.33 BTU = 2.4412820131 watts

>Raise that 1 gallon of water from 60 F to 120 F = 2.4412820131 watts * 60 degrees = 147 watts per gallon

> 5 Gallons * 147 watts per gallon = 735 watts plus losses.
You have it right. Though you have to factor in heat losses from tank, while heating and inverter efficiency at 90% so it would probably be more around 950 watts give or take a bit.
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Old 16-02-2018, 00:17   #22
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Re: Water heater using solar (not the camping bag)

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You have it right. Though you have to factor in heat losses from tank, while heating and inverter efficiency at 90% so it would probably be more around 950 watts give or take a bit.
The calculation requires time as well. It is watts times time that is required. At 750 watts it takes about one hour to heat the water in your example. Half the power takes twice as long. I used to heat my 6 gallon tank in 15 minutes at 1500 watts. This was hot enough for a shower, not full temp. I changed element power by using 240v elements powered by 110v. Power drops to 1/4. Hit water now takes an hour to heat, but the solar can keep up easily. See this calculator to check. https://bloglocation.com/art/water-h...e-energy-power
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Old 16-02-2018, 00:27   #23
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Re: Water heater using solar (not the camping bag)

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Originally Posted by sailorchic34 View Post
You have it right. Though you have to factor in heat losses from tank, while heating and inverter efficiency at 90% so it would probably be more around 950 watts give or take a bit.
It needs a time in the calculation. 1hour at 750 watts is about right https://bloglocation.com/art/water-h...e-energy-power
I dropped power to 375 watts and can still heat hot water just takes 4 times as long but easier on the inverter.
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Old 16-02-2018, 14:05   #24
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Re: Water heater using solar (not the camping bag)

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Originally Posted by swampbush View Post
It needs a time in the calculation. 1hour at 750 watts is about right https://bloglocation.com/art/water-h...e-energy-power
I dropped power to 375 watts and can still heat hot water just takes 4 times as long but easier on the inverter.
Swampbush,

What's your house bank specification, type and sixe please.

Thanks
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Old 16-02-2018, 15:22   #25
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Re: Water heater using solar (not the camping bag)

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Swampbush,

What's your house bank specification, type and sixe please.

Thanks
I have 900ah of trojan t105 flooded lead acid batteries and 1200 watts of solar. If I had lithium i would have left the power at 1500 watts but my batteries pulled down too much unless I heated water at full solar power at midday. You can buy different power hot water elements down 600 watts for most tanks.
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Old 16-02-2018, 15:35   #26
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Re: Water heater using solar (not the camping bag)

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I have 900ah of trojan t105 flooded lead acid batteries and 1200 watts of solar. If I had lithium i would have left the power at 1500 watts but my batteries pulled down too much unless I heated water at full solar power at midday. You can buy different power hot water elements down 600 watts for most tanks.
Thanks, I thought that the voltage sag would be significant with fla batteries but you seem to have mitigated it quit well with a lower wattage element.
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Old 16-02-2018, 16:01   #27
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Re: Water heater using solar (not the camping bag)

If you are going to use solar and batteries why not use a 12v element as a diversion load for when batteries are full.
Here is an example element
https://www.ebay.com/p/Dernord-12v-6...d=122866074764
(There are many available from 300 watts and up)
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Old 16-02-2018, 16:06   #28
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Re: Water heater using solar (not the camping bag)

Don't forget that 600 watts divided by 12 volts is 50 amps.
Use big wire if you use the one on the link newhaul provided.
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Old 16-02-2018, 16:21   #29
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Re: Water heater using solar (not the camping bag)

All I know is it takes my water heater 1 hr to heat water until itís cut off point.
It draws 1200 Watts I think, so that is 1.2 KWH.
Folks, that is a whole lot of electricity, roughly a 100 amp draw on my bank, or 100 AH if you look at it that way, and that is assuming 100% inverter efficiency, cause I donít want to do the math.

Much, much better to heat water directly with Solar radiation.

Course at the end of one hour, I have 11 gls of scalding hot water, maybe you donít need 11 gls, or scalding hot, but still the pool heater is a whole lot more logical.
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Old 16-02-2018, 19:18   #30
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Re: Water heater using solar (not the camping bag)

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Originally Posted by newhaul View Post
If you are going to use solar and batteries why not use a 12v element as a diversion load for when batteries are full.
Here is an example element
https://www.ebay.com/p/Dernord-12v-6...d=122866074764
(There are many available from 300 watts and up)
I did read somewhere that the thermostat doesn't like to work with dc.
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