Water heater using solar (not the camping bag)

[swampbush]

Originally Posted by a64pilot

All I know is it takes my water heater 1 hr to heat water until it’s 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 don’t 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 don’t need 11 gls, or scalding hot, but still the pool heater is a whole lot more logical.

I actually left room for a heliatos solar hot water panel on my arch, but it turned out easier to use the inverter than spend $800 on the panel, pumps, and solar panel and trying to get the pipes through in a neat way. Might still get around to it but $60 for a new element and ten minutes to change it won over solar direct.

[LoudMusic]

I don't think storing energy as hot water is the most efficient. I wonder about storing it as compressed air though. It could be used to pressurize water, or in dive tanks, or to power tools, or to turn a generator and make electricity.

[newhaul]

Originally Posted by LoudMusic

I don't think storing energy as hot water is the most efficient. I wonder about storing it as compressed air though. It could be used to pressurize water, or in dive tanks, or to power tools, or to turn a generator and make electricity.

where did anyone suggest storing energy in hot water? Just using excess solar to help heat the water for dinner dishes and such .

[Q Xopa]

Originally Posted by LoudMusic

I don't think storing energy as hot water is the most efficient. I wonder about storing it as compressed air though. It could be used to pressurize water, or in dive tanks, or to power tools, or to turn a generator and make electricity.

Sure whatever suits you. I'm not sure how you might best generate compressed air from hot water, but no doubt there are ways.

[Q Xopa]

Originally Posted by newhaul

where did anyone suggest storing energy in hot water? Just using excess solar to help heat the water for dinner dishes and such .

Guilty your Honor.

that would have been my post #18.

I have started a new thread called 'Refrigeration- 50-80% less daily power possible?'

[Captain Bill]

I have been considering the Heliatos system. One 2x2 panel should provide plenty of capacity to heat the water in my 6.5 gallon water heater in the summer in Maine and in the Bahamas in the winter. My biggest issue is figuring out how to insulate the tubing running through the various channels and conduits to get to my water heater. I have 640 watts of PV panels and they are doing quite well here in the Bahamas keeping up with my power needs, at least on sunny days. Using the inverter for running my heating element might be a possibility and would probably be simpler than installing the Heliatos. In the dead of the solar winter (late November through late January) I do not have excess power to spare for this as the SE US seems to have a plethora of cloudy days this time of year, not to mention a very low sun angle and short days. I have a nice spot to put a Heliatos panel and would not have to sacrifice power generation during the winter. I guess it will be a project for next year.

[Q Xopa]

It looks like the solar water heater mentioned by the OP dont require any additional boat real estate. As they are stuck to the underside of existing PV panels.

[Captain Bill]

Originally Posted by Q Xopa

It looks like the solar water heater mentioned by the OP dont require any additional boat real estate. As they are stuck to the underside of existing PV panels.

This is true, but the tradeoff comes in heating up your solar panel. You can only heat water when the temperature of the panel is higher than the temperature of the water. This is not a big problem when the water in the tank is cold but gets worse as the water heats up. Even if you have a thermostat that shuts off the water at a fairly low temperature the collector blocks airflow and proper cooling of the panel thus reducing its output. It may well be that if you have an abundance of solar that the impact is not enough to cause problems, especially if you get to absorption by midday. If you have marginal amounts of solar power it could create a problem.

[Q Xopa]

Yes you may well be correct. I dont know exactly how the water control circuit works. But if it does work as you say it would indeed not be good for PV production. I would think it should be possible to have this arrangement only transferring heat out of the PV panels. Ie liquid cooling of the PV Panels. This is after all a heat transfer system.

[Captain Bill]

Originally Posted by Q Xopa

Yes you may well be correct. I dont know exactly how the water control circuit works. But if it does work as you say it would indeed not be good for PV production. I would think it should be possible to have this arrangement only transferring heat out of the PV panels. Ie liquid cooling of the PV Panels. This is after all a heat transfer system.

Indeed liquid cooling of the panels would be very good, but one would need a very large heat sink to avoid the cooling water from getting too hot. In a home situation a large swimming pool might work well, but on a boat the only plausible heat sink is the ocean. That of course implies dealing with corrosion and all the other problems associated with seawater. If you dumped it into the fresh water tank you wouldn't have any cold water on the boat. A quick calculation indicates that I would raise my 100 gallon water tank about 50 degrees f above ambient with excess heat from my panels ( about 3 sq. meters) in the summer.

[sailorchic34]

The whole idea of using a PV panel as a heat exchanger to heat water is a very bad idea and a non starter. If the water did not circulate or got too warm it would drop the PV output voltage too low to charge the batteries to 100%. It looks good on paper only to those that don't understand the inverse relationship between PV output voltage and PV cell temperature.

Yes one could use water to cool the PV panel but the use of a small pump to circulate the water would cut any energy savings by maybe 50%. And you would get no useable heating from it.

The issue is the surface area of the PV panels is far larger then what is needed to heat the water in a water heater on the typical boat. What happens is the water continues to get hotter under the pv panesl which would cut PV voltage output during mid day, when it's needed most. So yes You can hot water using a PV panel heat exchanger. But the PV output would be drastically effected in a negative way.

BTW, I am an engineer who thought of this very idea 15 years ago. But it reduces PV panel output too much to be practical.

A dedicated 2x2 solar hot water panel would be a far better idea and is the perfect size for a 6 gallon marine water heater. Add some 3/8" pex, a 1 gpm 12v pump and a DeltaT controller and your mostly in business.

[Q Xopa]

Yes agreed.

Seawater cooling would ideal except for the corrosion issues. This sounds a bit like a fridge water cooling condenser thread.

This would all be dependent on the specific temperature numbers involved. But making a few assumptions here I would think that your PV panels and water coming from them are going to be hotter than ambient. Seeing it is meant to be a water heating device that your PV panels are the heat source for. So it should air cool. Indeed you were expressing wanting to insulate your water pipes.

Maybe with a thermostatic controlled bypass. It would all depend on the specific numbers for the temp diff (delta T) between the hot water in the pipes and the the ambient air temp. Also the surface area of that contact.

[Captain Bill]

Originally Posted by Q Xopa

Yes you may well be correct. I dont know exactly how the water control circuit works. But if it does work as you say it would indeed not be good for PV production. I would think it should be possible to have this arrangement only transferring heat out of the PV panels. Ie liquid cooling of the PV Panels. This is after all a heat transfer system.

Indeed liquid cooling of the panels would be very good, but one would need a very large heat sink to avoid the cooling water from getting too hot. In a home situation a large swimming pool might work well, but on a boat the only plausible heat sink is the ocean. That of course implies dealing with corrosion and all the other problems associated with seawater. If you dumped it into the fresh water tank you wouldn't have any cold water on the boat. A quick calculation indicates that I would raise my 100 gallon water tank about 50 degrees f above ambient with excess heat from my panels ( about 3 sq. meters) in the summer.

[Pete7]

Originally Posted by LoudMusic

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.

So having poured scorn on Loud Musics suggestion, actually I wonder if it would be better to ignore the solar panels and put a swimming pool flexible tank on top of the sprayhood. Will it work for say a 22L or 6 US Gal tank?


https://www.amazon.co.uk/dp/B00ITPQ2...a-391853315919

[sailorchic34]

[QUOTE=Pete7;2580106]So having poured scorn on Loud Musics suggestion, actually I wonder if it would be better to ignore the solar panels and put a swimming pool flexible tank on top of the sprayhood. Will it work for say a 22L or 6 US Gal tank?/QUOTE]

From a heat exchage standpoint it would work ok connected to the U loop exchanger in the water heater. The issue is working pressure and the pool heater would most likely have too low a working pressure to even work with the engine loop (13 psig)

But, If you buy a 25 foot pvc hoses, paint it black and put it tightly coiled (ziptied??), that would work just as well and not have the pressure issues of the heat fused pvc. The pvc pool heater listed is really too small for any pool. Most solar pool heaters are larger in the order of 10 feet x 30 feet or more.

But for a solar boat heater a 25 foot length of garden hose with a 12v pump and a small accumulator for thermal expansion would work fairly well. Even better if it's inside a glass (or clear plastic enclosure. You want a fairly low flow pump of less then 1 gpm. https://www.aliexpress.com/item/New-...iABEgJPQPD_BwE