Possible solar water electric?

Solar Expert Posts: 201 ✭✭✭✭✭
Had a brain flash yesterday. I don't know if this will work, or if it would even be worth the effort, but it occurs to me that if water will climb a pipe when heated, and supposedly you gain more energy from heating water directly with sunlight, perhaps this might be useful for generating electricity.

How would it work to use the sun to heat water, to make it move upward, then use that raised water to drive a water turbine? The idea would involve building a tower about 25 ft high, with a, say, 50 gallon capacity to start with. Next to a lake would be the ideal site.

Next, along the south tower wall, put up a flat wall that reaches from the waterline to the top of the tower, perhaps extending a few feet to either side. Paint the wall black, and put sides on the wall.

Attach copper lines, 1/2 inch in diameter, about 2 inches apart that extend the length of the wall. There would be a trough along the top of the wall that the pipes would empty into, and the trough would route the water to the holding bucket. Once the copper lines are installed, paint them black and put a glass wall over them to help hold the heat in.

The bottoms of the pipes would be inside of a long metal tray with a screen wall along one side, and the tray would be submerged. The top of the tray would be just above water level, with a glass top. The inside of the tray would be painted black and extend 6-8 inches below the water level.

The 50 gallon holding bucket would have a 3 inch diameter pipe coming out the bottom, and this pipe would go to a water turbine at the bottom.

The idea here would be to use the sun to heat water, and make the water rise up the pipes to the trough. I don't figure that the sun would get enough energy in to use a large diameter pipe because the water's weight has to be overcome, but a whole lot of small diameter pipes might be able to do it. Might also be possible to do this with several shorter runs of pipe into several buckets, kind of a step up action.

Comments? Any possibility something like this might work? I only see it working in a lake, since thermosiphoning would require a drastic temp difference in the source water vs the output water, so you'd not only want to use a large body like a lake, you'd also want to drain the water turbine to a point several yards away from the water source. I have no plans to build anything like this, this is more of a mental exercise.

• Solar Expert Posts: 9,363 ✭✭✭✭✭
Re: Possible solar water electric?

Water won't "climb a pipe".

A thermosiphon could work, but you need a MUCH larger scale, with several hundred feet, and 6" pipe to create enough flow to pay for the pipe. And then the " pink water flea " will die off, because the lake is too warm, you evil capitalist pig, destroying the environment to power your TV.

The same concept has been tried in the tropics, with 30F water 2,000' down, and 75F water at the surface.
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• Solar Expert Posts: 5,433 ✭✭✭✭
Re: Possible solar water electric?

Thermosiphon will take water up some distance, but I would guess that given the laws of physics that you couldn't possibly get enough energy with the water coming down. Remember, for the water to go up, it needs to be a closed loop. (I suppose you could come up with a way to "pump" relatively small quantities of water up out of a closed loop, but I bet you couldn't get much volume or much head,,,certainly not both.

The energy required to raise it HAS to be greater than that it creates on the way down, even if you could have 100% efficiency. I also think there must be a maximum distance that you could push a head of water up.

Perpetual motion anyone?

Icarus
• Solar Expert Posts: 201 ✭✭✭✭✭
Re: Possible solar water electric?

Well, this wouldn't be perpetual motion. A lot of devices can appear to be perpetual motion, but in actuality aren't. In this case, energy would be imparted by the sun into the water to pull the water up, then gravity would pull the water back down to produce electricity.

But, I was unaware that for the water to move that it has to be a closed loop. Makes sense though, since heated water would find it much easier to go up as evaporation than to climb a pipe as a hot liquid.

So. In order for this to work, you'd need many small lines to get the water heated quickly, a very large reservoir on top with a means to quickly cool the water back down, with a single larger pipe to run the water through a water turbine. I wonder how high the sun could pump water in a closed system, up a 3/4 inch diameter pipe?

New design, large tank at the bottom, sealed system. This also means it could work anywhere, not just near a body of water. I'm assuming that you need the same diameter of pipe going up as you do going down, otherwise you start having a vacuum/pressure issue and you would want to have a more or less equal pressure system, perhaps a vacuum going down and pressure going up, but overall equal pressure. A 6 inch diameter pipe has a 28.2744 square inch cross section, a 3/4 inch pipe has a .4417875 inch cross section, so you'd need 64 3/4 inch pipes on the upside to match. Seems like a lot there but that's how the math works out. The 64 pipes would feed a top reservoir, with the water. The top reservoir would then drain to the single 6 inch line. Might want to go 70 pipes to keep a net gain on the top tank, and if you sized it right the top tank would be full at the end of the day, which would drain back after the sun went down for that last little bit. Might have to have 2-3 steps on the upside to get the water high enough, but if this would work then it would reliably produce electricity as long as the sun heated the water. No idea how efficient this would be or if it would be more or less efficient to do this than to use a solar cell (would certainly be more complicated to build and tune). But, it could conceivably produce power all day every day, even on an overcast day.
Re: Possible solar water electric?

As was stated before, hot water won't "climb" a pipe. You might get some to sputter out the top of a pipe, if you boiled it and had pockets of steam pushing it up the pipe like a coffee perk. Or you might blow it up the pipe with steam pressure, but that's it.
What happens with a thermo-siphon is that as the water is heated, it expands, so is lighter than cold water, therefore in a closed loop the heated water moves very gently up the pipe as it's replaced at the bottom by cold water. There is no pressure to push the water up the pipe without the closed loop, and without the closed loop, the water will find it's own level, regardless of the temp and it will not move.
Perpetual motion was mentioned before, because, whether or not you yet see it, this project is along those lines of thinking. You're hoping to get HUGE returns on what, for all intents and purposes, will be zero input.
As was said already, hot water will not move up a pipe on it's own, it must be pushed up by a pump, or steam pressure, that kind of thing, or "sucked" up by a reduced pressure over the end of the open pipe, which by the way, is limited to a max of more or less 28 feet, depending on existing conditions.
Cheers
Wayne
• Solar Expert Posts: 5,433 ✭✭✭✭
Re: Possible solar water electric?

Look at the numbers (Cfm, head pressure etc.) to see the minimum wamount of water needed to create even a small hydro system. I think that physics wins.

Icarus
Re: Possible solar water electric?

You will not be able collect energy via thermo-siphon effect.

One alternative method is to use a working fluid that can boil/condense at relatively low pressures.

Take a look at this Sea Power Inc. project to tap the ocean's differential temperatures (by the way, I don't know anything about SPinc. As they share a fax number with another company and are claiming that facility as their own--I would not invest any money in them without much more research).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 201 ✭✭✭✭✭
Re: Possible solar water electric?

K, I see where the failure on this is now. The only way thermosiphon works is if the water downflow is the same speed and mass of the upflow, which isn't going to be fast enough to get usable power from. Nope, this won't work. Thanks for the clarification.

Probably wouldn't be able to heat enough water to a high enough temp to drive a steam turbine to a usable level either, at least not at the individual level.

Oh well, back to the 'ol drawing board...