Generating electricity using household water pressure

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Earl Smith

I would like to generate 12 volts AC or DC using only household water pressure. What is the smallest this generator can be? Is there a component/device already out there on the shelf?

earlsmith3rd @ aol. com

Thanks!

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Phil Corso, PE

Responding to Earl Smith’s 21-Mar-08 (23:46) query... unless your utility can provide water flow-rates much greater than typical, or you have a way of beating the laws of physics regarding fluid-flow, I suggest a return to Physics 101:

With an available house pressure of 35-psi a flow-rate of 10-gpm will produce about 1/8-Hp (approx 90-W!)

Please note: this calculation ignores efficiency of whatever you intend to use to convert fluid-flow energy to electric energy.

Regards, Phil Corso ([email protected])

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Phil Corso, PE

Earl, I aplogize for neglecting to answer the second part of your query... the term 120cc:

If you mean a flow-rate of 120 cm^3 per sec, then you will generate 30-milliwatt!

Regards, Phil Corso ([email protected])

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Robert Scott

Earl,

Following on to Phil's analysis, you should also include the cost of the water. Typical municpal water rates are 1 cent per gallon (in the US). So a 10 GPM flow is costing you \$6/hour. But the electricity generated (90W) makes the rate for this electricity equal to \$67 per kW-hr, as compared to a reasonable grid rate of \$0.10 per kW-hr. So using household water pressure is a really expensive way to make electricity.

Robert Scott
Real-Time Specialties

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Stevan Lieberman

All you've said below is true, but multiple units turning water flow into electricity that run only when some one is going to use the water any way would more then offset the cost of the water itself plus feeding electricity back in to the grid. Further, the idea is to not try to get big gains, but for thousands of households to install such units obtaining a very small gain from each. Even installing such units in gutters would garner a little bit of electricity. A lot of little steps equal one huge step.

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Robert Scott

Stevan,
Yes, a lot of little steps forward equals one huge step forward. But if all the steps are backward, they make one huge step backward. And here is why they are all backward steps:

Relying once again on Phil Corso's analysis posted earlier, a typical 10 gpm flow would generate 90 watts while it is flowing. It is generating zero watts when water is not flowing. And since you are hypothesizing this generator as something that only runs when you would be using water anyway, we must consider how much of a typical day is spent drawing water at the rate of 10 gpm.

Let's leave farming and golf course watering out of the discussion and focus only on residential homes. They consume water when you draw a bath, do the laundry, or wash dishes. I think it would be generous to say that 10 gpm flows for about 1 hour per day. 90 watts one hour per day is 32.85 kw-hr over a one year period. At \$0.10 per kw-hr, that produces \$3.29 worth of electricity per year. Whatever water turbine/generator you install to capture this power is certainly going to cost you more than \$200. With this kind of investment, and getting \$3.29 back per year, you will recoup your \$200 investment in 61 years. I doubt that any \$200 turbine/generator is going to last 61 years without maintenance. So you will never break even, so it was a step backward.

Another thing that extracting energy from the domestic water suppy does is lower the pressure at the point of use. In fact, to gather 90 watts, you will have to lower the pressure to almost nothing. That is going to be pretty inconvenient for taking a shower, or just about anything else. If there was excess pressure in the water supply, then the proper thing to do would not be to deploy millions of little generators to capture that energy. The proper thing to do would be to lower the municipal water pressure and realize the savings by not having to pump as hard - all without any capital investment at all.

Robert Scott
Real-Time Specialties

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Sean

@ Robert

A few things.

First off, there it typically a pressure gradient in the water system depending on how far the residence is from the reservoir and the elevation difference between the home and the reservoir. So some houses (I believe most houses have one installed) have a pressure regulator installed on the house side of a water meter, so, in essence, a turbine could be just as easily used to lower the pressure from the street as a valve, while recovering some of the energy.

That being said, I doubt there would be a generator/ turbine anywhere near efficient enough to make this plausible or useable.

At least it's forward thinking, even if it results in backwards results.

Alternatively, a home could set up their own water reservoir in their attic, to gain an energy boost from gravity. I envision a large tank (appropriately supported) which has a level switch so that it turns on water from the street as water is used to maintain a constant volume of water in the house. Depending on the amount of water in the tank, a large potential energy store could be created, potentially with a larger pressure gradient than the street pressure. Slap a turbine on the outlet valve for the reservoir and generate electricity there.

Again, I don't feel like doing the fluids and thermodynamics to find out how much height/ volume would give a usable pressure, and I'm sure that there would be a significant danger in thousands of pounds of water in the attic. So it's probably not at all plausible, but it's an interesting problem to think about.

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Stuart Hiley

We know that you can't get something for nothing and that tapping the house water pressure will take away from the pressure at the tap. But if you utilize a water line where the pressure drop is not an inconvienence, like the washing machine, you could realize modest returns.

Modest is the key word. Using the house pressure to run a pump that pumps a low volume of rain water from a cistern up to an attic resevoir would be useful. Use it to flush the toilets. Toilets are big water wasters and do not require potable water. So using the otherwise unused potential of your house's water pressure to save water makes sense. (Not to mention it is enviromentally friendly).

Based on annual rainfall, the area of your collection surface (your roof) and your water bills, you could calculate how long it will take you to break even. In my neck of the woods (South suburbs of Chicago) it will take under three years.

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Mingwah

I would like to offer a better solution or better question to the answer. If you would like to augment the power generation which charges a battery system that is fed by other means of charging then this is a great idea. Other systems meaning solar, or wind. There are off peak times when solar and wind cannot produce the power needed to charge a batter. A simple shower or watering of the grass may provide that extra boost. Have a nice day.

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Lester

What about people that happen to run swimming pools with pump systems that run from 4 to 8 hours per day. Could some advantage be taken of this? It is a closed system that needs to run anyway.

What if we were to tap the main the comes from the water tanks that feed the water systems? Yes a pump is used to fill the tank but the water that comes from these tanks, and feeds the whole community is gravity based why waste this energy resource?

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Robert Scott

About people that happen to run swimming pools with pump systems, there is no advantage that could be taken, unless the pump system was seriously over-powered. If a swimming pool pump system is properly designed, then the pump is just powerful enough to circulate water through the pool. If the pump is more powerful, and water is being circulated faster than needed, then the thing to do is not to try to recapture that excess energy with a turbine. The thing to do would be to replace the pump by a smaller pump and not waste that energy in the first place.

As for tapping the gravity-based outflow of a municipal tank, that too is not the best use of resources. Those tanks are built as high as they are to get the needed pressure to run the system. If there is excess energy in the system, then the tanks should have been built lower in the first place. The only truly excess energy that has been cited in this thread is the energy that gets wasted in the pressure-reducing regulators. And even in that case the economics of the situation is such that the gain from a turbine would never outweigh the capital expense of installing the system.

Robert Scott
Ypsilanti, Michigan

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GasGeezer

I've been interested in all the information on this topic. I have a small stream running right through my property and I'd like to be able to harness the potential of being able to generate enough electricity for our residential needs. Can anyone suggest anything to help me please??

thanks

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curt wuollet

Yes, see if you can conveniently enlarge the stream :^). Seriously though, people need to consider just how much power it takes to run our modern conveniences. It's a lot for anything that heats or is motorized. From a small stream, if you have enough head on your property, you might be able to provide basic LED lighting for example. For an example, look to the once common water driven grain mills. It was a lot of doing to get a few HP, but it's free once it's paid for. Thoughts of "going off the grid" have often occurred to me lately, I have the Rum River flowing through my property and I've pondered a water wheel driving a car alternator to charge batteries. The local power cooperative has been most encouraging in these schemes, not that they would want me to do it, but by the incentive their 10.4 cents per kwh rate provides. The Rum will freeze solid soon, which curbs those thoughts.

Regards

cww

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Walt Boyes

If you can find it, 20-something years ago Smithsonian Magazine did a feature on the use of low-head pelton wheel turbines to power residences with streams available. There is/was a Chinese company that was making an Allis-Chalmers knock-off pelton wheel that was being used with good results.

Unfortunately, Smithsonian's online archives only go back to 2003, and this was sometime in the early 1980s or late 1970s.

Suffice it to say that you can make a small bypass dam in your stream and put a Pelton Wheel style turbine generator in it that requires relatively low head to operate.

Good luck,

Walt Boyes
Editor in Chief
Control and ControlGlobal.com
555 W. Pierce Rd Suite 301
Itasca, IL 60143

wboyes [at] putman.net
www.controlglobal.com
630-467-1300

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M Griffin

You need to calculate the energy available based on physics before you go any further. What is the water flow? What size of head (drop) do you have available? Would you need to build a dam (and would you be able to get planning permission for it)? What is the *minimum* seasonal water flow?

1 W = 1 N*m/s = 9.8 * 1 cubic-metre * 1000 / sec

So, 1 cubic metre per second of water falling a distance of 1 metre would give you 9.8 * 1000 kg * 1 m = 9.8 kw. That's a useful amount of power, even once you subtract efficiency losses.

However, 1 cubic metre per second is also a fair amount of flow for a "small" stream. If you only have 1 litre per second of flow, then you only have 9.8 w (not kw!). That's not enough to light a light bulb, even a small CF bulb. If you have more head (drop), then you can generate more power will less flow. However, unless you have very favourable geography, you probably don't have a lot of head to work with on a small property.

Small 19th century water powered grist, flour, or saw mills typically operated on no more than a couple of kilowatts. That's why most of them were abandoned when electricity became available instead of being converted into power generation plants. Unless your location happens to be very good, generating your own hydro tends to be more of an interesting hobby than anything else.

CSA

This popped up during a related search:

http://www.ashdenawards.org/

I haven't looked at it very closely, but it seems to have some interesting projects of all kinds.

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serb

I would like to make private contact with:
earlsmith3rd [at] aol. com

mine Email:
daliborrmilicevicc [at] gmail.com

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David Nguyen

I agree with the fact that using your utility water to generate electricity is not efficient but how about using the turbine at the water entrance to the house in a close loop? That means the turbine will rotate everytime water is used, the more water is used the more we will save. I saw one like this online a month ago but did not remember the website. I will post the product as soon I find it. In the mean time, please contact me at david.vapc [at]gmail.com if you find any. Best,