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Solar ponds for electricity?
By Texas Al, Section Solar Posted on Tue May 10, 2005 at 04:45:55 PM MST
Anybody have any links/info on them?

I've searched both on this forum and on Google, and so far haven't found any concrete instructions on how to the heat stored at the bottom of a solar pond is used to actually generate electricity. Mostly everyone is talking about using it for cooking/manufacture/home-heating... but only passing mention of electrical generation.
I wonder if they use Stirlings, or is there some simpler way to turn it into electricity?

Solar ponds for electricity? | 23 comments (23 topical)

Re: Solar ponds for electricity? (3.00 / 0) (#1)
by fishfarm on Tue May 10, 2005 at 11:08:55 AM MST

Wally Minto's Wonder Wheel could be hooked up to a generator.

http://www.i4at.org/lib2/rotate.htm

Re: Solar ponds for electricity? (3.00 / 0) (#2)
by Texas Al on Tue May 10, 2005 at 11:20:30 AM MST

w00t! That's so cool. Thank you, it really looks like it could work, and it might not even have to be freon... maybe I could get away with methanol if the temperature gradient is high enough... and the wheel could be in a submerged watertight container inside the solar pond (you don't want it mixing up the water layers).

Help us write a manual on how to reboot a crashed civilization!
[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#4)
by kitno455 on Tue May 10, 2005 at 12:11:37 PM MST

actually, you can effectively change the boiling point of any liquid to be near the temperature of the units heat source. water will boil at room temperature, if you just evacuate the air above it out of the container. much safer and easier to use water and vacuum than methanol and air :)

it should even be possible to use the power source itself to run a small pump/blowoff contraption to keep the pressure over the water set so that it runs at exactly the right temperature for the current conditions, and keep the thing running even in the dead of winter.

allan

[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#11)
by Kwazai on Wed May 11, 2005 at 07:44:32 AM MST

mother earth news built one of the propane ones-on a small scaleand it was fairly expensive and 'scary' pressure wise with freon. I have been 'playing' with an aqueous ammonia one-(that I don't have working yet)-trying to get the 'low' pressure side lower (at lower) working temps-- because its actually the % pressure difference(high side to low side) that affects the performance-not the max pressure.
Unfortunately at 20F temp diff-water only is good for about 3"h2o head pressure. nh4oh quicks it up to about 12"h2o at 20F deltaT (real slow though and takes a lot more heat input to vaporize the ammonia).most of my delay has been in verifying particular cheap materials- current version is nylon tubing and flexible (good up to about 60psi total) and has yet to provide any noticeable turning for various reasons. actual performance should be somewhere around 1rev/min or less.it would make an excellent pump (though expensive if bought new) for hydro power generation.
I suggest you check out the mother earth news archives.
just my .02$.
Mike

[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#12)
by ghurd on Wed May 11, 2005 at 08:39:02 AM MST

The one in Mother Earth News had the problems of, I believe in wind term they would be called "not enough poles" and those very long tanks caused "cancelation".
But maybe not.

Minto's wheels had smaller tanks.

G-
Ghurd.info
[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#14)
by nothing to lose on Wed May 11, 2005 at 09:23:10 PM MST

My thoughts too when I looked at one they built. Also I think they used pretty thin lines on what looked to be fairly large tanks, not good for rapid flow of large volume I think.
With all other things considered, it is still ONLY the differnce in weight between the bottom and top that works the wheel! Nothing else matters except that the top and right hand side is heavier than the bottom and left hand side. That is if you want clockwise rotation. The other thing important is where that wieght is located. On the bottom you have the liquid in the bottom of the tank at the outer rim of the wheel. At the top the liquid will still be in the bottom of the tank, but the tank is upside down now so the bottom is not on the outer rim of the wheel, it is inside the rim however long your tank is! 12" tank gives the bottom 12" more leverage to fight the top tank, sort of like running the wheel mounted 12" off center hanging low I think.
Mother earth used what I thought was goofey sideways tanks as I recall, so the liquid is at the outer rim at the top, but it is not at the top at all because the top tank is still off to the side trying to raise to the top. Well I would think that kills that right there. Pretty sure that was the Mother Earths design I am thinking of, I have seen others also.

Now something I am thinking to solve both such problems maybe? Use some type of weighted pistons basically. Use the pressure of the tanks to raise and lower a metal wieght. Top tank is cooler and less pressure, bottom tanks is hotter and more pressure, so the wieght is moved to the top outer rim more and away from the bottoms outer rim and more to the center. This will make the top and right hand side heavier without the movent of the liquid which slops to the side or sits below the top outer rim.

It does not take much weight to create movement. Watch an out of balance blade turn in reverse some time, not that much out of ballance. So by moving a weight up from the bottom a little bit we now have a heavier top, as that wheel rotates then we have a heavier side.

If we balance a 6' wheel, place 12 evenly spaced tanks of propane (maybe those throw away small ones) how much pressure do we need create to move a 1lb weight 1' high at the bottom. If the top is cooling at the same time and setup to create a vacume type effect to pull the weight upwards also that should help. Using a pressure to move the weight back and forth a short distance instead of transfering a liquid a long distance I think would work far better. This of course is not a Minto wheel by design then either, It is a "Nothing To Lose" wheel and I reserve all itellectaul property rights to it :-
You can build all you want free of charge for non comercail private use by non-money grubing greedy corporations! Oil/power companies beware I will SUE!!

So if we take a propane tank, run a hose to a empty cylinder on the outer rim, sealed piston to push upwards, when we heat the propane and presure is created in the tank and below the piston the piston shall rise. The more the piston rises the lighter the bottom becomes. You could have a rod connected to the piston at the other end to also push it to the outer rim at the top. Or it can be made to sit at the outer area by default, vacume of cooling gas sucks it back out, light spring pushes it back out etc.. combination of both? As long as the weight at the top is at the outer rim and the weight at the botton is not, this make the wheel top heavy, and untill things equal out as it turns and temps equal out it will be side heavy also. It could be rotated either direction.

The trick here again though is to not have so much liquid as to equal out the wieght as it flows to the lower end/side of the tank always. Using a moving wieght should mean using less liquid, and the pressure is what moves the weight which in turn moves the wheel.

I think the basic idea of a Minto wheel is somewhat correct, but using a liquid in that manner is not.

Another thought is using simple water and springs to move the piston/weights. Filling and sealing the water tanks so the water does not slop around shifting weight, but does expand when heated and moves the piston. Then use a couple well defined solar collecters to quickly heat the lower tanks. Aluminum tanks could be used for faster heating and cooling cycles. I have a nice portable oxygen tank here I got at a scrap yard, the medical type. Something like this made somewhat into a blader tank should work well, but you need quite a few. Water would not have to steam to a high pressure, only expand enough to move a weight. Other pressurized gas could still be used, but water itself should work provided it is heated and cooled quick enough to expand and contract.

Yet another thought on this, you normally have a friction of the tanks flowing through water in a Minto type design which also is slowing the moving wheel as it works. Using solar collectors to focas the sun under and through the wheel will not cause any fricton forces to fight the wheel rotation. You will not have the extra heat around the wheel like wheel using water tanks. The only heat will basically be where the tanks are in the sun being heated, when the tanks are not there then the sun passes through not hitting any mass and no heat is created. This in turn helps in cooling the tanks when they should be in cooling cycle since no heat is rising from standing water heating the surrounding area. But then it only works on sunny days.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.
[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#15)
by ghurd on Thu May 12, 2005 at 02:24:39 PM MST

With those real long tanks, I figure they were getting weight up to the top before it was even near TDC.
Ghurd.info
[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#13)
by fishfarm on Wed May 11, 2005 at 08:39:59 AM MST

Here's a site that has considerable detail on construction and calculations. They recommend methylene chloride for the heat transfer fluid (it's near the bottom).

http://www.keelynet.com/minto/minto2.htm

Here's the Mother Earth News article. The site author believes the construction was flawed.

"Why did this 20 foot Minto wheel fail to turn as fast as expected? Have you ever tried to fill a very large container with a small garden hose? It takes a long time for enough liquid to flow though such a small pipe. The pipes on this Minto wheel were much too small if they wanted it to turn at one RPM. They had so much pressure that they changed to a lower pressure freon. But they restricted the flow with small pipes.

I believe if a Minto wheel is properly designed, it would function just as Wally Minto said it would."

http://my.voyager.net/~jrrandall/MintoWheel.html

(Hmm...this link doesn't want to work in preview. Do a google search on jrrandall and it should be the first hit).

[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#16)
by Kwazai on Thu May 12, 2005 at 03:07:43 PM MST

the Methylene chloride is carcinogenic if I remember right.

possibly adjusting the high side and low side pressures with freon (and I'm no expert) would be a lot safer-though not as low buck.

the water/air version would need to be small enough to function much like the rota-sola cola engine at www.rotarystirlingengines.com. it used about 18cc of water (thermodunamic calcs showed about 14 to 15-turned out 18 due to wetted surface area). (approx. 3inH2O head pressure at 20F deltaT(12inH2O at 100F deltaT))
the gravity shift is what you're after so pumping left to right rather than up and down would make it less pressure/less volatile fluid/ etc..
.. much like an old water wheel--MAYBE this could be done with the Minto's wheel style with just a solar lens pointed at the end of one of the tanks (55 gallon drums???).
my .02$
L8r
Mike

[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#17)
by fishfarm on Fri May 13, 2005 at 06:37:16 AM MST

Good point, OSHA considers methylene chloride to be a potential occupational carcinogen.

"the gravity shift is what you're after so pumping left to right rather than up and down would make it less pressure/less volatile fluid/ etc.."

My daydreaming about this concept led me to a thought of using solenoid or mechanically operated valves in the connecting pipes to control the fluid/weight transfer, essentially allowing you to "time" the engine for optimum performance. Of course, this makes it more complicated, more expensive, etc. for something that may not work, or not work well enough to justify itself. But it's fun to think about.

[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#18)
by Kwazai on Fri May 13, 2005 at 07:10:06 AM MST

what about a tire innertube on a lever arm on a wheel- such that the expanding(heated tire tube at the top) tube pushes the lever arm past center (again whats the costs involved) and makes the wheel rotate-- like a wheel that moves about 15deg. then pauses while the tube/arm at the top heats up and pushes the lever arm/wheel out of balance another 15deg (not solar ponded, but gravity wheel anyway).

The ammonia wheel I've been messing with from time to time -I plan on using a nichrome heater and small pv cell with reed switches. right side up reed switch open, down-closed. nichrome wire (model rocket igniter without pyruvate) and yard light pv cell. the reed switches and nichrome would ideally 'flash boil' the ammonia. I haven't figured a good way to mount the nichrome for heating fluid-not gas-without melting stuff. The reason for the ammonia rather than water /air is because standard household ammonia will about double in volume from a 17% by volume solution at low enough temps/pressures I can use plastics.
haven't really figured how to quickly cool it either. anyway
L8r
Mike

[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#20)
by fishfarm on Fri May 13, 2005 at 08:29:46 AM MST

I do have ponds that stay at a constant 70 degree F (at the bottom). I was thinking of using this water for the cooling half-cycle and solar heated water for the heating half-cycle. I say half-cycle because, if you can control the timing of the fluid transfer, you can maximize the temperature differential by heating the heavy side continuously from the time it receives the fluid to the point of transfer; the light side is similarly cooled throughout the time it is empty. If the fluid is transferred at say 45 degrees from vertical, you could spray hot water from 45 to 135 degrees; cold water the opposite. Again, more complicated but potentially much more efficient.

[ Parent ]

a few minor points about the Montos wundar veel (3.00 / 0) (#3)
by wdyasq on Tue May 10, 2005 at 12:09:11 PM MST

Before one builds one of Wally's devices, they should do a little work on heat transfer analysis, pressure gradiants, flow and a few other 'minor' things that are involved. I built one in the late 1970's with a 40' diameter and learned calculations might be a lot cheaper than the ton of propane, pipe, tanks, the vacuum pumps to evacuate and charge the thing and electricity to weld it.

Your mileage may vary, but I doubt it.

Ron
Adventure is just bad planning." -- Roald Amundsen
[ Parent ]

Re: a few minor points about the Montos wundar vee (3.00 / 0) (#5)
by Texas Al on Tue May 10, 2005 at 04:14:52 PM MST

I need a more obvious clue, here, I'm feeling a bit slow today.

Are you politely hinting that it can't be done efficiently enough to be useful? (an example of something that can't be done efficiently enough to be useful would be elevated water storage for people who don't have a hill and a body of water handy)?

Or is your statement at face value and you're saying it can be useful, but that I need to do my homework ahead of time (an example of something that can be useful but requires homework would be a typical wing genny)?

By "useful" I mean "put out a kWh for about the cost of a wind genny of comparable cost". I don't mean "exactly as cost-effective as a genny", just somewhere near the same ballpark.

Help us write a manual on how to reboot a crashed civilization!
[ Parent ]

stick the F_ word in where necessary (3.00 / 0) (#6)
by wdyasq on Tue May 10, 2005 at 06:51:36 PM MST

Try this Alex - it didn't work. I won't go into how much 'head' - pressure wise it takes to push a liquid 45 or so feet vertical... even if it is just propane. In the real world - SOME THINGS JUST DON'T WORK -

Ron
Adventure is just bad planning." -- Roald Amundsen
[ Parent ]

Re: stick the F_ word in where necessary (3.00 / 0) (#7)
by Texas Al on Tue May 10, 2005 at 07:25:53 PM MST

Got it. Thanks for saving me from the aggravation.

Help us write a manual on how to reboot a crashed civilization!
[ Parent ]

Re: stick the F_ word in where necessary (3.00 / 0) (#8)
by nanotech on Tue May 10, 2005 at 07:42:00 PM MST

How about making them in ganged pairs? Kind of like making a V-twin motorcycle engine to increase displacement past the feasible single cylinder mark?

What I mean is make two or three (maybe four) that share a common shaft.

They wouldn't spin any faster, but the output torque (I would think) would be a multiple of the number of "cylinders".

Or am I way off the mark here?
__________________________________________
My ship finally came in, but it was the Kobayashi Maru!
[ Parent ]

Re: a few minor points about the Montos wundar vee (3.00 / 0) (#19)
by Kwazai on Fri May 13, 2005 at 07:16:00 AM MST

the Minto wheel- like Einsteins refrigeration (butane-ammonia) has no moving parts in contact with the working fluid. My guess would be like a lot of the solar that when gas in the US hits about 6$/gallon it will get real attractive. One of the things curiously memntioned about the Minto wheel was that it would break a 4x4.....
wouldn't want to get in its way...
L8r
Mike

[ Parent ]

Re: a few minor points about the Montos wundar vee (3.00 / 0) (#21)
by Nando on Wed Dec 06, 2006 at 03:55:16 PM MST

He is trying to say, without really saying it, that the did not do the proper mathematical calculations to define the necessary energy to be able to move the "load" form a lower tank to the upper tank.

The basic reason why the "Minto" wheel does not work well is that the efficiency is low -- low --- low -- low -- and lower.

The Minto Wheel for such large diameter, DEMANDS a lot of energy, and many times will require cooling of the tank up in the wheel.

Nando

[ Parent ]

Re: a few minor points about the Montos wundar vee (3.00 / 0) (#22)
by offgridman on Wed Sep 16, 2009 at 09:47:45 AM MST

I was wondering what size interconnecting pipes/tubes you used between pairs when you built your wheel?
I think I will construct a small one to test the idea one day.
I generate all of our electrical energy we need for the island household with solar now.
I cannot get air conditioning from solar I don't have that much money to buy the panels with.If I can create a Minto wheel powered airconditoner of any size that will run a small AC unit I would be ecstatic.

I know this post is OLD but hey, I just read it.

We have 4.5 hours of sun here a day so using a mirror dish to heat water in bulk to run the thing through the night periods should be pretty easy. I have enough excess electrical power to pump heated water to the trough and back to storage for reuse.

I can build most of the wheel from scrap I have already.

Offgridman
Solar energy can supply all of your needs and most of your wants!
[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#9)
by nothing to lose on Wed May 11, 2005 at 02:49:15 AM MST

Sometimes I think the problems can be caused by over sizing things also. A small one works well so lets build a gaint one that works super good, but then it don't work at all :)
Not meaning the Minto wheel in particular, just everything is general. We still sometimes have that bigger is better type thinking.

Kinda like building a working 4' blade for a 8" gennie, hey that worked so lets stick a 16' blade on the same gennie and really get it working. Well we all know that's not gonna do so well don't we :)

Now what if we increased everything by 4X? 16' blades, 32" gennie? Probably still not gonna work right.

Some where though is a near perfact combination. But where? I think that will hold true for Sterlings, Mintos, wind, water etc... Someplace things will come together and work well, but not everywhere.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.

Re: Solar ponds for electricity? (3.00 / 0) (#10)
by Texas Al on Wed May 11, 2005 at 05:43:01 AM MST

Well put.

I still wonder, though, what the government experimental sites who keep talking about "solar ponds can blah blah blah ...and make electricity" are actually using to make this electricity.

As far as ganging up the wheels, why not make a cylinder made of pipes attached in parallel and joined at interval by spokes going to the opposite pipes? It couldn't be too long because then it would start losing power due to variability in temperature from one spot to the next, but maybe it would still work.

Help us write a manual on how to reboot a crashed civilization!
[ Parent ]

Re: Solar ponds for electricity? (3.00 / 0) (#23)
by spinningmagnets on Wed Sep 16, 2009 at 08:10:26 PM MST

The pack-Rat workshop had some interesting ideas about using low-grade heat, but the lower the temp differential, it takes a big machine to make a small amount of generation. But might be fun to ponder some of his stuff...

http://www.packratworkshop.com/alteng.htm

Solar ponds for electricity? | 23 comments (23 topical)

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