# solar water heater



## budgetprepp-n (Apr 7, 2013)

I was looking at some of the solar water heaters people have made and
I have a question. Why not use automobile radiators? I would think if they 
were painted black they would be great at heat transfer.

I mean that's what there were made to do. They use the ambient air to cool
the hot water that circulates in your car engine. Wouldn't they work the other way?
Suck up the heat from the sun and transfer it to the water?
If you really look close at a radiator it looks like it would be ideal 
I would think


----------



## Auntie (Oct 4, 2014)

Interesting, I am looking forward to the responses. Would you need to be worried about the sediment and chemicals that can be found in a radiator?


----------



## budgetprepp-n (Apr 7, 2013)

Auntie said:


> Interesting, I am looking forward to the responses. Would you need to be worried about the sediment and chemicals that can be found in a radiator?


I'm sure they could be flushed out ,, Or even get a new one or two 
I have a radiator out in the shed I think it is aluminum and plastic 
Might make a cool experiment when I have time


----------



## Auntie (Oct 4, 2014)

I agree, anything that can be re-purposed is a good thing.


----------



## darsk20 (Jun 1, 2015)

Radiators work via air flow. Without air flow they don't work very well. This is why if you lose your fan in your car it will over heat unless moving.

Not to say it wouldn't work briefly, but as soon as you start to flow water through it the cooler water would chill the radiator. 

Still, don't keep from trying it out. There might be some way to us it.


----------



## Snocam (May 29, 2015)

I have seen a DIY solar water heater work with a grid of copper pipes running through a 4x8 foot shallow box, inside painted black, and plexiglas on the outside. It works well for the owners during the day. You may be able to accomplish a similar setup with a few radiators, but by the time you acquire the radiators it may be just as easy, and cost the same, to use copper pipes. The system seemed to work by pre-heating water before it entered the water heater. During the day, if there is not a tremendous draw for hot water, the water in the pipes has plenty of time to heat up. A hose connection on the end of the collector could be used to get the hot water too.


----------



## darsk20 (Jun 1, 2015)

Given a little more thought, if you could make it recirculate from a reservoir through the radiator (or even better Snocam's described set up) you might be able heat water. You would want only recirculation during the day. Reservoir would need to be insulated. You would need a separate loop for use.

More thinking and it grows to using a solar oven to heat air that is then moved across the radiator by convection. 

So many possibilities - just depends on how elaborate a set up you want. Also depends on your location.


----------



## Slippy (Nov 14, 2013)

I would think that hooking a conventional water heater up to an off grid solar power system would be as cost effecient as trying to setup an ambient heating system with radiators. But hell of an idea Budget! Your ideas are great and they way you think is awesome!


----------



## Chipper (Dec 22, 2012)

The surface area exposed to the sun would be to small. The inner cores of the radiator will do you no good as only the first ones will actually be in the sun. You need a large surface area to absorb the suns energy. As already stated radiators use air flow to cool water, not heat the water for solar use. A lite breeze or wind will set you back. A large black plastic container, barrel or tank will give you a much better surface area to absorb the suns heat.

This is just my ideas on the subject. Try it and prove me wrong as I've never actually tried it.


----------



## 8301 (Nov 29, 2014)

A radiator just sitting in open air with water in it will warm up. A radiator in a sealed box with a black interior and Plexiglas cover will get much hotter. 

The problem with a radiator is that it can be difficult to fully drain to protect from freezing on cold nights. That's why solar water heaters are either simple straight tubes in a box that drain easily (called a drainback system) or run a antifreeze mixture that then is pumped through a "heat exchanger" allowing the sun heated antifreeze solution to heat up the water which stays protected from freezing.

It is generally agreed that if you want to invest in solar energy the best bang for your buck is installing a solar water heater. Financially they will pay for themselves faster than a bunch of solar panels.


----------



## Arklatex (May 24, 2014)

We have a solar-powered water heater. It's a 100 foot long black garden hose. That water is scalding hot after its been in the sun for awhile.


----------



## budgetprepp-n (Apr 7, 2013)

I was sort of thinking of after TSHTF using what you could get your hands on


----------



## Kauboy (May 12, 2014)

A radiator does what it's name implies. It radiates... heat.
It is designed to be a heatsink. The surface area of the fins allows for large amounts of heat to be pulled from the internal coil, and dispersed. Having air moving through the fins increases this effect.
You will be fighting an uphill battle to try to reverse the function and use the design counter to its intended purpose.
Restricting airflow would help, but it won't overcome the heatsink design of the fins. It would take a serious amount of heat to counteract the heat dispersal.
If you smashed all the fins down, and made them all contact one another, that might help to decrease the efficiency of the heatsink, and would increase your exposed surface area pointing toward the sun.

You'd be better just using a copper tubing turned back and forth inside a black painted Plexiglass box.


----------



## Kauboy (May 12, 2014)

Slippy said:


> I would think that hooking a conventional water heater up to an off grid solar power system would be as cost effecient as trying to setup an ambient heating system with radiators. But hell of an idea Budget! Your ideas are great and they way you think is awesome!


I'm not sure this would work very well, Slip.
This would require turning solar energy into electricity, storing it into a battery array, and then converting that electricity back into heat at the WH coil. Water absorbs a tremendous amount of energy to raise its temp, and heating up an entire tank on just solar generated power will likely deplete your battery bank and leave you with lukewarm water.
Anyone with an electric water heater can attest to the cost of keeping piping hot water available at all times.

Fire would be the optimal choice, but direct solar heat is a closer second than battery power.


----------



## budgetprepp-n (Apr 7, 2013)

darsk20 said:


> Radiators work via air flow. Without air flow they don't work very well. This is why if you lose your fan in your car it will over heat unless moving.
> 
> Not to say it wouldn't work briefly, but as soon as you start to flow water through it the cooler water would chill the radiator.
> 
> Still, don't keep from trying it out. There might be some way to us it.


OK yes it needs air flow to cool,,,, But with no air flow and if it was under a glass with sides 
(like a car with the window rolled up) But to heat no air flow would be better I would think


----------



## budgetprepp-n (Apr 7, 2013)

Kauboy said:


> A radiator does what it's name implies. It radiates... heat.
> It is designed to be a heatsink. The surface area of the fins allows for large amounts of heat to be pulled from the internal coil, and dispersed. Having air moving through the fins increases this effect.
> You will be fighting an uphill battle to try to reverse the function and use the design counter to its intended purpose.
> Restricting airflow would help, but it won't overcome the heatsink design of the fins. It would take a serious amount of heat to counteract the heat dispersal.
> ...


If it was in a box with a glass lid the heat sink would work in reverse. (think about it) you would want all the 
surface you could get (via heat sink) The heat sink would heat up and in turn heat up the water.

A radiators job is to transfer heat that's why it has all the fins ( heat sink ) I would think 
the fins would work to gather heat and transfer it to the water. With no air flow that heat
is going to go right into the fins and on to the water

that's why when you use copper pipe you put as much as you can the space you
have to work with -- more surface to gather heat


----------



## Mad Trapper (Feb 12, 2014)

100 ft of black 3/4 " hose in the sun. You can lather up in warmth, then hose down the same, soaping in between. Takes about 5-gal.

Winter is a bitch, but I don't stink that much. Then there is a 10-gal stainless on the wood stove.


----------



## darsk20 (Jun 1, 2015)

Best efficiency will be by convection heating - hence the reason for all the fins and why it works to cool the coolant in a car in motion but not when the car is stationary and without a fan. 

Leaving the air stagnant is utilizing radiant heating, losing all the efficiencies you gained from the fins.


----------



## budgetprepp-n (Apr 7, 2013)

darsk20 said:


> Best efficiency will be by convection heating - hence the reason for all the fins and why it works to cool the coolant in a car in motion but not when the car is stationary and without a fan.
> 
> Leaving the air stagnant is utilizing radiant heating, losing all the efficiencies you gained from the fins.


Yes if you were trying to cool the water down. But think of how it would work in reverse
The hot stationary air would transfer the heat to the fins and on to the water


----------



## darsk20 (Jun 1, 2015)

Not with any efficiency, but like I said in my original reply, try it and see how it works. 

I'm only going off of intuition.


----------



## Kauboy (May 12, 2014)

Wait... are we talking about heating the radiator with direct solar energy, or heating the radiator with heated air? There's a difference...


----------



## budgetprepp-n (Apr 7, 2013)

Kauboy said:


> Wait... are we talking about heating the radiator with direct solar energy, or heating the radiator with heated air? There's a difference...


Ok well,,,,,, I didn't think about it.
I thinking of mounting a radiator 1 or more on plywood 2x4 sides and a clear (glass or plastic) cover 
all painted black same affect as a car with the windows rolled up on a hot day


----------



## Kauboy (May 12, 2014)

This isn't an example of a radiator, but it is an example of direct solar energy versus air.

Yesterday, I was standing outside for 5 minutes in dark slacks.
While standing, I didn't notice the sun's heat on my legs. Once I started walking after those 5 minutes, I realized just how hot my pants had gotten. It felt like my skin was burning as my legs made contact with the inside of the material.
Granted, this was not a "closed system", but it still reveals the large difference between direct heating, and air pocket heating(convection) from the sun.
You can achieve the same goal, but one will take considerably longer.


----------



## 8301 (Nov 29, 2014)

instead of dealing with a radiator in that box why don't you just use some PVC pipe (painted black) or a roll of black plastic tubing. See this video for black tubing.
https://video.search.yahoo.com/vide...65767000&fr2=p:s,v:v&fr=chr-greentree_ie&tt=b


----------



## darsk20 (Jun 1, 2015)

Kauboy said:


> This isn't an example of a radiator, but it is an example of direct solar energy versus air.
> 
> Yesterday, I was standing outside for 5 minutes in dark slacks.
> While standing, I didn't notice the sun's heat on my legs. Once I started walking after those 5 minutes, I realized just how hot my pants had gotten. It felt like my skin was burning as my legs made contact with the inside of the material.
> ...


Thanks for simplifying it. I've been trying all day to come up with this type of example . . . which is exactly why I will never be a good trainer, teacher or coach.


----------



## Ralph Rotten (Jun 25, 2014)

One of my favorite water heaters is also the simplest. 55 gallon drums on the roof. In AZ they get up to 100 degrees, and make for a nice shower in the evening. The only difficulty is getting the water up there, but that's what hand pumps are for.


I saw a show where they used aluminum cans by cutting them with a special saw and using the bodies to form aluminum tubing. Painted black, and placed inside of a box of mirrors (looks like a solar oven actually). Run water through the aluminum tubes, which soak up solar energy better than any other metal, and pump water thru the assembly. I wanna build one for a pool, I have the pump but am still pricing the tubing for the radiator. Mirrors are cheap. 

I dunno about using a used radiator from a car, that's be toxic. New radiators are mostly plastic these days.


----------



## Ralph Rotten (Jun 25, 2014)

I wish there was a way that I could take the heat being extracted via the condensers on my home A/C system, and use that to heat my pool. Like put the condensers in the jacuzzi and use the pool as a heat-sink. Hot pool, cool house. It would be kinda cool to maximize the two.


----------



## PaulS (Mar 11, 2013)

There was a post close to the beginning of this thread that commented about surface area. It was dead on! A radiator only has - say 4 square feet for the sun to heat. The suns heat is measured in watts per square meter and the more area you have the warmer your water will get. Take a 4x8 foot piece of 3/4" plywood, add as much 3/4" black ABS tube as you can coil into that space. Even in the open air the water will get to over 120F. 
If you want an efficient water heater put a couple of inches of rigid foam insulation between the plywood and the coiled tube, enclose the sides with 2x4s and more foam and place a sheet of plexiglass or lexan (more shatter proof) over the top. Have the inlet hose at the bottom and the outlet hose at the top and lean it to face the sun at noon - the correct angle for your location - and plumb the bottom hose into the bottom of a water heater and the top hose into the top of the water heater. Since the water heater should be inside you will want to insulate the hoses going to and from it with as much insulation as you can. The flow is due to gravity and the water tank will hold up to 50 gallons as the water in the hose gets hot it will flow into the top of the water heater and as it cools it will go out the bottom. The flow will be very slow so the water will get very hot. With good insulation it will work even when there is snow on the ground and temperatures are very cold. The one drawback to this system is that If temperatures drop below freezing at night it will freeze and destroy the heater - but the same thing will happen to any single media heater. To overcome this you have to build the coil and plumb it into a second coil that is aluminum or copper (copper is better) and immerse that into a hot water tank that is well insulated. Fill the coil with an antifreeze mixture and the secondary coil will transfer the heat to the water. It takes a bit of fabrication and raises the losses a bit but it is a year-round solution to heating water with the sun. You might even mount two or three of the heating coils on your roof (angled properly of course) and run the plumbing through an exterior wall yo your tank.


----------



## IprepUprep (Jan 2, 2015)

darsk20 said:


> Radiators work via air flow. Without air flow they don't work very well. This is why if you lose your fan in your car it will over heat unless moving.


Um... the water pump has to circulate to help keep the flow of coolant moving as well... If your fan belt breaks... you very well likely do not have your water pump circulating ---- On a side note... Once upon a time... I had a bad clutch fan in my little truck... I lived in the desert. I knew I could get home with "just the water pump circulating" and without the fan... I simply waited for the truck to cool down... and loosened the radiator cap --- NO PRESSURE --- Its not good for an engine for driving LONG distances, but, you can drive your vehicle "nicely" to the nearest repair shop (say 3 or so miles? in HOT HOT weather?) to get replacement parts, or to simply get home, or to a safe place...
You can loosen the cap - but, DO NOT REMOVE it the whole way --- you will lose all your coolant... (anti freeze / coolant --- which ever you want to call it) circulation is the key... so ---
If I were to utilize a radiator, I would make use of some type of pump to help the liquid move along... 
Curiously - has anyone had any luck heating water with said radiator(s)?


----------

