Harnessing Energy from Water: Is it Possible?

[DaveC426913]

The issue here is that PSI is NOT the basic unit of force that will power your device. i.e. PSI is IRRELEVENT.

A 50PSI garden hose is 50PSI whether the hole is 1 square inch in area or 0.01 square inch in area. (Do the math). No matter how large or small a hole you put it through, it will still only do the wsame amount of work. And THAT is what is going to power your turbine.

Look at it this way. Say, your turbine has blades that are 1 inch in area. We apply 50 pounds of pressure to it to get it to move. If we apply that 50 pounds across the WHOLE blade (i.e. with the garden hose wide open) or if we apply it to the blade in a tiny area (i.e. fast moving stream that could give you a nasty blister), it will still push your turbine just as fast.

 

[uart]

I'd like to get back to the original question.

How much energy can you get from water? For example can you use a water mains safely to turn into energy? i.e. harness the energy somehow from the water in a pipe? Is it possible? Would you get much energy out of it?

If you are prepared to suffer some loss of pressure then yes you could extract some energy from your home water supply. Let's work out how much.

Typical domestic water mains pressure is 50 to 75 psi, so let's assume you are willing to suffer a 25 psi drop in delivery pressure. The theoretical work that can be done with that is equal to the pressure drop times the total volume of water passing (using SI units).

For the sake of a "ball park" calculation let's assume that your daily water consumption is 700L (0.7 m^3) then the available energy at 25 psi (approx 170 kPa) is 0.7 * 170k which is approx 120 kJ (kilo Joules). I don't know the overall efficiency of conversion (turbine plus generator) but I doubt it would be more than about 30%, so for the sake of having a numerical solution let me take a conversion efficiency of 1/3 (btw if this figure is way off target then hopefully someone can pitch in with better info). So in this example you could expect to extract maybe 40kJ of energy per day.

To put that into perspective divide by 3600 to get about 11 Watt-hours per day, that is a 24hr average of just under half a Watt continuous (0.46 Watts). Now your energy company probably sells you power at about 20 cents a kW-Hr but if you produce surplus energy and sell it back to them they'll probably pay you about 5 cents a kW hour. At this rate you would make a whole 5 cents every 3 months of generation. Hardly very impressive, especially if you consider that the turbine and associated plumbing would probably have a high upfront cost and the adverse effect on your water pressure making your bath tub fill slower and your hose spray weaker etc etc.

BTW. A cheap 10cm x 10cm solar panel would produce more energy per day in most geographical locations and it would probably cost between 10 and 100 times less to implement.