Passive Electrical Generator

[Nitack]

Ah, but with my end goal, it matters very little how much power I can remove from such a system, only that I can actually remove some power at a relatively constant pace (however minor that may be).

I am interested in this design because it is pretty passive. Once it is set up it will start up on it's own every day, wind down ever day as the sun/temperatures go down every day, and produce electricity (however small the amount). There is another question, will it actually produce anything though. If the current does not create enough friction to turn the water pump it may produce nothing, which i was hoping some one with more experience could address.

The end goal is to feed that electricity back into my house (and possibly the grid if I can produce more than I need at any given time). I know that this will require a complex setup of diodes, fuses and an inverter, but I am not at that planning stage yet. Gotta figure out how to create the electricity before you can figure out how to use it. This is already done with solar panels for most grid tie systems. As I do not have $20k to invest in a PV system, I have been thinking about this poor mans solar electric system design. Don't worry, i have a lot of steps I have to get through first before I tried connecting this thing to my house

[Overdog]

The bigger problem is the design depends on the water sinking/flowing downhill, sunlight isn't going to make that water flow back up-hill (unless it boils it into steam).

EDIT:

You should be able to build a cheap prototype and test the idea (at least with respect to getting the sunlight to power the water flow) without spending too much money...

[Nitack]

Originally Posted by Overdog

The bigger problem is the design depends on the water sinking/flowing downhill, sunlight isn't going to make that water flow back up-hill (unless it boils it into steam).

EDIT:

You should be able to build a cheap prototype and test the idea (at least with respect to getting the sunlight to power the water flow) without spending too much money...

But it is not "flowing" up hill. It is simply flowing to a higher position as it is displaced by denser (lower temp) water. In that sense, i don't think we are actually fighting gravity at all, but i may be wrong.

[Overdog]

Originally Posted by Nitack

But it is not "flowing" up hill. It is simply flowing to a higher position as it is displaced by denser (lower temp) water. In that sense, i don't think we are actually fighting gravity at all, but i may be wrong.

Ah, I see what you are saying. So the question is whether the flow would sufficient to turn a turbine to produce electricity?

[Overdog]

I think what you are describing would be a type of Heat Engine.

Heat engine - Wikipedia, the free encyclopedia

This one actually sounds very similar to what you are thinking about...

ORC TurbinexxGenerator xx System - Solar Thermal Energy Version
The FREEPOWER system has been developed as a cheap reliable alternative to photovoltaic systems. It consists of a micro turbine generator that is driven by a closed loop of working fluid. The working fluid is pumped by a small electrical pump through a solar array, where it is heated and vaporised. The vapor drives a micro turbine generator, and then condenses back to a liquid and the whole cycle recommences. A small ancillary circuit of the same vapor provides cooling for the alternator.

Heat Engine Projects

[freeztar]

The biggest problem I see is that the temperature in the water will reach equilibrium quicker than the water can migrate based on density. Now, if you brought a fresnel lens into the equation...

[Overdog]

Originally Posted by freeztar

The biggest problem I see is that the temperature in the water will reach equilibrium quicker than the water can migrate based on density. Now, if you brought a fresnel lens into the equation...

Yes, the water would have to cool off at least as fast as it heats up or it would reach equilibrium.

I remember reading somewhere that water really doesn't work well for heat engines unless you actually heat it to steam, but I can't find that anywhere now. I recall the ideal substance is something which goes from a liquid to a gas and back during the process...

[modest]

The difference in density between 20 and 30 C water is .0025 g/cm^3. That's 2.5 kilograms at one cubic meter which is a reasonable amount to circulate in a day. The amount of energy you can generate by circulating a cubic meter of water is then equal to dropping a five pound weight the height of the cold water tank... unless I'm missing something.

~modest

[Overdog]

Hmmm, this one looks interesting...claims to be the simplest design. It uses air instead of water...

Rotary Stirling Rotary Overview

Edit: So maybe you could use a fresnel lens for the heat source for something like that?

[HydrogenBond]

This is a slightly different design that might solve the passive pumping problem. This is an affect called osmotic pressure. You have a two compartment system, one compartment with salt water and one with fresh water, separated by an osmotic membrane. The fresh water will diffuse into the salt water side and that height will rise. If we start with equal heights of salt and fresh water, the final result will be two different heights due to the chemical potential in the salt water.

The salty side that rises higher is going to be your water cascade that will spill over and run the pump. This semi-salty water is recycled and run through a solar heater to separate pure water and make the water saltier for recycle, into the osmotic chamber.