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temperature differential phase change power generation

Generate Energy from the change in ambient temperature during a day
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My idea is basically giant Atmos Clock or Reverse icyball that uses phase changes in a liquid with a low boiling point (butane, r134a, ammonia, methylene chloride) in order to take advantage of the changes in ambient temperature between morning and evening. Basically you have a a giant absorption refrigerator that converts the movement of gas into mechanical energy (via pistons or turbines), then from mechanical energy to electricity (via traditional generator).

Imagine two giant variable volume storage tanks. When the day heats up the liquid in one tank (with the air space lowered via movable baffles) would boil and pass through pipes to a turbine, then to another empty tank (adjusted to maximum volume). During the night the gas would cool back into a liquid. The volume of the tank would be reduced (via movable baffles) and the process would start over the next day in the reverse direction.

There are many devices (sterling engines, peltiers, solar thermal concentrators) that use the sun or geothermal in in order to generate energy by having a hot side and cool side to the device. What I am proposing is a device that only depends on day being hot and night being cool.

(edit two hours later)I just read the thermal hydroelectric idea on here. This gave me the idea... Two tanks like before, but this time fixed volume. One small tank at the bottom of a hill, one large tank at the top. During the heat of the day the liquid in the small tank turns into a gas and goes up hill through a pipe, turbine, then into the top of the large tank on top of the hill. When the gas cools at night into a liquid, it runs through a pipe in the bottom of the large tank, down the hill, through a turbine, and back into the small tank at the bottom of the hill. The night pipe may need a one- way valve in it to prevent the liquid from being pushed up through it during the day gas/pressure phase.

dlapham, Aug 05 2010

Icyball http://en.wikipedia.org/wiki/Icyball
This principal being used for cooling rather than energy generation [dlapham, Aug 05 2010]

Atmos Clock http://en.wikipedia.org/wiki/Atmos_clock
This concept in a very small device. [dlapham, Aug 05 2010]

Very Similar Thermal_20hydroelectric
This idea is quite similar to mine and in fact the two could be combined. [dlapham, Aug 05 2010]

I like to do it in the desert temperature_20difference_20generator
Like this but with less sand [Voice, Aug 08 2010]


       The maximum theoretical efficiency of a thermodynamic engine is 1-TempCold/TempHot.   

       The daytime temperature rarely varies more than 15 C at most, 5-10C is much more likely. Converted to the absolute temperatures required in the formula above, thats a best performance of 1-273/283 (at 0 C night time) 3.5%. This will result in an output of .1 Wh per kg of air or 0.123 Wh per m^3.   

       Note that this does not make the idea impossible, just that a huge system is going to be required to generate any appreciable power, and the cost of a plant in this size is likely to be significantly more than it can generate over any reasonable life-span estimates.
MechE, Aug 05 2010

       Mech E, I realize that this would require a lot of volume. I also realize that you would need a very volatile fluid that has as much expansion as possible when in gas phase, yet cools to liquid during the evening.   

       You would ideally choose a location with a hot and dry climate for this installation in order to take advantage of maximum day and evening temperature swings. You could also use simple solar thermal assistance to the process by painting the tanks an infrared absorbing color.   

       As far as expensive, I disagree. This is where this idea shines. It is very mechanicly simple. Uses very low cost materials, and can easily be scaled to any size. I agree that the efficiency per square foot is much lower than solar or wind. But energy potential over the lifetime of the device per dollar/euro invested in building and maintaining the device and purchasing land, should be much lower than solar and wind.
dlapham, Aug 07 2010

       //You would ideally choose a location with a hot and dry climate...//   

       Yes, that would be ideal, but we did that one already. More than once, actually.
ldischler, Aug 08 2010


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