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Solar Hot Water with Motor Oil
By arcandspark, Section Remote Living Posted on Mon Feb 14, 2005 at 02:41:07 AM MST
Solar Hot Water

I am planning on installing a solar hot water system. I want to use oil or some other liquid to runthrough the collector on the roof and then run it through a heat exchager to heat the water. I have seen systems with antifreeze, mineral oil, peanut oil, and some very expensive commercial chemicals that absorb and store heat extremely well but cost over $700 per gallon, (Doupont). What I am looking for is a liquid that will have a long life before it has to be removed and replace. Motor oil and cooking oil will only last about one year before it starts to break down. Antifreeze, about six months. Does anyone know of something that last longer and may also be environmentally friendly? Also anyone with a good heat exchanger design I would be very interested.
Thx, arcandspark

Solar Hot Water with Motor Oil | 13 comments (13 topical)

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#1)
by pyrocasto on Sun Feb 13, 2005 at 08:32:35 PM MST

Cant say that I do. I know alot of people use antifreeze, because it wont freeze(duh) and because it's thinner and easier to pump. Seriously though, I would use antifreeze, because with a few feet of extra tubing you could very easily drain the old system, and fill again. That would also cost you alot less than other chemicals.

As for design, it depends on what you're looking for. If you dont want to use a tracker, some pipes through a box(almost that simple) would be what you need. If you dont care, then maybe a trough, or a parabolic dish setup would be better.

I'm sure others will have better imput than me.

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#3)
by arcandspark on Sun Feb 13, 2005 at 09:15:56 PM MST

I am thinking about using Mobile One Synthetic motor oil instead of the antifreeze. It has a wide temp operating range. I feel it will not break down for a long time because of the lower operating temperature compared to the higher temps seen in an engine and there will be no blow by carbon contamination to get the oil dirty. It will cost a lot more but I am looking for as much maintenance free operation as I can put into the system. I can not find Stainless Steel water heater tanks, they had them years ago, my father was a plumber and he said they would last up to thirty years before showing signs of any leaks, usually caused by poor welded joint or seams. I am going to find the specific gravity of the Moble One oil and then do some calculations and testing to find a DC pump that can handle it. I only need about one gallon per minute for each solar collector panel. I plan on using a heat exchange solar system to heat water with panels on roof running synthetic oil as transfer media. Experiments have shown temperatures of up to 180 degrees with no problem. Solar pumps seem to handle the oil with just a little loss in flow rate, as long as the oil is moving thats all I care about. We used a synthetic oil as a heat transfer media in a number of high temperature machines at one place where I use to work back in the 1970's. That is when I start learning about solar systems and became interested in alternative power and energy efficient homes. I did a lot of experimenting back then. Florida University students came up with a solar stove using a large parabolic reflector and they would heat peanut oil up to over 400 degrees with the tracking reflector collector, pump it into what they called a phase exchange storage tank. It was a steel take filled with thing like, once they used wax, another time lead. The tank would store the heat the collector got during the daytime. At night they could then pump through second copper tubing coil inside the tank more oil that was used to heat water in a storage tank for washing with. They also had a coil of stainless steel tubing that was formed to look like a heating element on a stove. They would pump peanut oil from the secondary coil in the storage tank, and run it through this coil on the stove and actually boil water and fry eggs and hamburger using the heat stored in the phase exchange tank. They were going to wrap a coil around the outside of an oven chamber and try to bake with it. They called it a phase exchange tank because the wax or lead which ever you used, would be hard when at low temperature and would melt to a liquid when heated. There were all kinds of problems and issues that had to be resolved like expansion and oil break down, but these could be taken care of. Well the oil crisis of the early 70's ended and with it went the University's experiments with alternative energy. I started to build a phase exchange tank back in the 70's using solder as a media, of which I had a few thousand pounds of sitting around back then. I remember the 400 degrees and that is why I like the synthetic oil. Moble One stays liquid from like well below 0 degrees to well above 300 degrees. So it will not freeze in the collector during winter, and with a flat plate collector I will never see temps over 300 degrees in the summer so its perfect, it should last for at least five years or more, I am hoping for ten years. What makes oil break down and become acidic is all the blow by and extreme temperatures seen in an automobile engine. If you do not expose the oil to temperatures over say 240 degrees and don't add gasoline and burned hydrocarbons from the explosions above the pistons, the oil does not decompose and breakdown. It should last for years. I have to look up the specific gravity and see how close it is to water. The solar pumps are designed for water but an experiment has shown they will push the oil only at a slightly lower flow rate and not quite as much head or height. So where I would normally use say a 3-gallon per minute pump, I will now use a 6-gallon per minute. I will experiment with different ones to make sure I get the oil up to the roof collector. As long as the oil "is flowing" I will be happy. Sorry for rambling on. We also experimented with solar steam generators but its a hard animal to control and make it go where you want it to go, and safely.

arcandspark

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#2)
by bkrahmer on Sun Feb 13, 2005 at 09:14:15 PM MST

You want a liquid with a long life and environmentally friendly? Water. Its thermal conductivity is superior to any other common liquid. Glycol has about 50% of the conductivity that water does. I can't find any data showing the conductiviy of oils. If you are in an area where you are worried about freezing, I would suggest using a water/glycol mixture with just enough glycol to give you the freeze protection you need.

I'm planning on building a hot water storage tank with simple copper coil heat exchangers in the tank, powered by a woodstove, for my house. The idea is to heat the house, get domestic hot water, and heat the hot-tub, all from wood. I think a storage tank is also a good idea for solar hot water systems. Both solar and wood are victims of the same characteristic: they generate heat which is useful, but not necessarily needed at the moment it is created.

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#4)
by arcandspark on Sun Feb 13, 2005 at 09:18:38 PM MST

Water has to be changed out to often, rust, corrosion, agie, many other problems. I want a maintenance free system. Mobile one will last for ten years or more before showing signs of problems. Water would have to be changed each month in the hot months.

arcandspark

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#5)
by jimovonz on Mon Feb 14, 2005 at 12:47:30 AM MST

Because of the temperate climate I live in, I do not have these same considerations (freezing is not an issue), however I can say that I have seen many many solar systems that use a propylene (not ethylene!) glycol solution (40-50%) for heat transfer from the panel. I have never heard of a panel using 'Mobile One'. I might consider using Mobile One in my car, but it would cost a similar amount to the fuel I use...
My heat exchanger is simply coiled soft copper pipe.

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#6)
by PaulJ on Mon Feb 14, 2005 at 04:57:35 AM MST

I was quoted an expected lifespan of 90 years (!) for the propylene glycol/water mix in my solar HWS. The manufacturer says to change it every 5 years, probably just to cover themselves, but even that is not much of an issue given the small amount of liquid in the panels.

Paul.

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#7)
by ghurd on Mon Feb 14, 2005 at 06:05:02 AM MST

Wow. 90 years. I was just going to say I know it is more than 6 months for darn sure. I would bet regular antifreeze / water mix will last over 10 years (not being run through a cast iron block, etc). The stuff in at least 1 of my cars is getting close to 10 years and still tests fine, (a little cloudy but not too bad), and didn't freeze at -15'F last couple week.

The roof water seperator from Oz a few posts up may help seperate solid junk?

G-
Ghurd.info
[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#9)
by arcandspark on Wed Feb 16, 2005 at 11:01:37 AM MST

A little cloundy means it breaking down, if you took a close look at the walls of the cooling system you would see a build up of crude and goo that is impeding the ability of the cooling system to work. That is why the manufactures of antifreeze tell you to change it each year. The Mobile One at temperatures of my flat plate collectors will never see over 190 degrees and therefor never really start to break down. Thus the ability of the oil to transfer the heat energy will remain above 90% for many many years. People, you need to try to think outside of the box.

arcandspark

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#8)
by arcandspark on Wed Feb 16, 2005 at 10:56:54 AM MST

Great ideas come from thinking outside of the box. Mobile One stays liquid from -40 to 300 degrees and a typical DC water pump and move it just like water. The specific gravity is less than water, that is why it floats on water. (Remeber to think outside of the box)...

arcandspark

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#10)
by jimovonz on Wed Feb 16, 2005 at 12:11:32 PM MST

Yes synthetic motor oil does have some desireable properties. After a bit of Googling I have found that your typical syntheic motor oil has a thermal conductivity of around 0.2 - 0.25w/mK in the temperature range concerned. Water has a conductivity of 0.58w/mK and glycol/water is 0.45w/mK. This would indicate that for equivalent sized heat exchangers (both in the panel and in water tank), the glycol solution would be twice as efficient at transfering the heat. So while your oil may last a long time, it will be harder to pump and require heat exchangers twice the size (thats twice as many risers on your typical flat plate collector) to perform the same as a glycol solution.

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#11)
by arcandspark on Fri Feb 18, 2005 at 10:30:50 PM MST

There is always a trade off. If the owner wants a maintenance free system than he will just have to have twice as many flat plate collectors. Great information on the thermal conductivity. That was going to me the next item I was trying to find out about. Dupont made a thermal condutive liquid that was super at transfering heat, we used it in manufacturing back in 1980's, but it cost about $750 per gallon. Now that is just alittle to high priced for my needs.

arcandspark

[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#12)
by ghurd on Sun Feb 27, 2005 at 01:21:08 PM MST

Lets see... You need a compound specifically designed to transfer heat, be of a low viscosity, non-corrosive, long lasting, and reasonably priced?

Hmmm... How about antifreeze? Even if it is too inside the box.

G-
Ghurd.info
[ Parent ]

Re: Solar Hot Water with Motor Oil (3.00 / 0) (#13)
by arcandspark on Fri Mar 04, 2005 at 10:18:14 AM MST

If you would have read all the posting you would have seen several other water and anti-freeze lovers had already suggested anti-freeze. I guess some people just dont get it. Anti-freeze breaks down and becomes corrosive over time and has to be replaced, also causing corrosive damage to the system components. I have seen other fluids in use in industrial enviornments that ran for years and were not corrosive, but yes were expensive. In my situation this person has nine oil wells on his property and money is not a problem. He wants something that will be almost totally maintenance free. So please no more WATER or ANTI-FREEZE suggestions. I am looking for people that have open minds and think outside of the typical uncreative box.

arcandspark

[ Parent ]

Solar Hot Water with Motor Oil | 13 comments (13 topical)

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