Pico Hydro

Hello all, and tia for any input.  I am not a technical or mechanical person, but I do have ideas from time to time and would like to know if they are something that could be developed or if I am just spinning my wheels.  I am soon to set up a water catchment system.   In the downspouts I would like to install mini turbines to generate electricity when it is raining to replace the solar that I will not be getting.  It might be possible to also do this in the pipes coming into the houses here, but that is a retrofit.   Is this possible?  Would it generate enough energy to be worth it?  It rains a lot here at times.  I read an article about Portland retrofitting their sewer system with a larger version of this.  Is this something for which there is an economy of scale and my setup would be too small?  I am trying to build a diverse system that will provide me with power no matter what the weather is doing.

I am no expert on water catchment or micro hydro, I have however done a lot of research into both.

I have never heard of anyone doing this idea. So either it is likely not doable, or it is a genius idea that no one has yet implemented.

Sadly I suspect it is just not doable. Micro hydro you need a certain amount of head. A volume of water going a distance and falling in elevation a certain amount. And I suspect the average down spout just doesn't deliver this. That any sort of energy generation you could mount inside a downspout would cost way more than the energy it could ever return to you making it a loosing proposition.

That said, I am not an expert and could be wrong. So please do some more research or others who know more comment and show it can be done if it can be. I think it would be awesome if we could have micro hydro water catchment systems.

I have considered such a system myself.
There were commercial systems that used city water to generate useful amounts of electricity,but the water pressure is higher in such a circumstance, and the water is wasted.
To try this I would use a washing machine pump. Forcing water through the pump should turn the attached shaft, and said shaft could power a generator.
Perhaps a better choice would capturing the mechanical energy to pump a smaller amount of water up to the header tank.
Not something fo nothing ,but Mireille regenerative breaking, recovering some of the energy used.

Devin and William,

Thank you both for your replies.

William,

Are you thinking of using the water after it is captured from the storage tank?  Feeding it through the washer and going into another holding tank? I had not considered that.  I had also thought about using some of the roofs that I will not be catching water from to channel water with force onto a small pelton wheel or something of the sort.  I have several sheds and roofs that have overhanging trees so would not be as good to harvest water from.  The catchment system will be attached to a 24 x 32 greenouse that will hold a "polyponics" system.

I am hoping that others will weigh in with ideas and a workable system that can be easily and cheaply duplicated will come from this.

the possible energy generated is very low because your flow rate and pressure are both relatively low. I've worked it out before and its less than 100w, without friction. The equation for watts is pressure in Pa multiplied by flowrate in m^3/s

Andrew,

Could this be overcome by having multiple downspouts with turbines?  If each one only generates a small amount but you have 50 to 100 generating at one time then would that make it work?  I have 5 roofs and the greenhouse to work with.

Calculate the energy released by a typical rainstorm.

Let's say your roof area is 200 square meters, and the drop from roof to ground is 5m. If a heavy rainstorm brings you 0.05m of rain then then maximum available energy is:

mgh

(200 X 0.05 X 1000) X 5 X 9.8
10000 X 49
490,000Joules

Or 490KJ. Let's say you were able to harvest 50% of this which is highly unlikely, you would end up with about 240KJ.

A typical kettle is rated for 3kW. Your rain storm would provide enough energy to run the kettle for 3 minutes. This is about the time needed to make a cup of tea.

I would suggest that there is simply not enough energy available to be worth while. The cost of the equipment would greatly exceed the value of the energy produced.

The shaft on the washer pump normally spins and pushes the water.
I would remove it from the washer and force water through it, thus turning the shaft. Then,rather than accepting the losses that converting mechanical energy to electrical energy incurs,I would use that spinning to do work directly-like power a pump that moves stored water into  a raised header tank.

Most rainwater harvesting set ups would be best if the the water went directly to a header tank,located higher than the point of use.
But water is heavy and bulky so unless you build with that in mind or you live in perfect circumstances, you will probably end up storing water below the point of use and pumping it to a header tank,pressure tank or directly to the fixtures.
I am aiming to use a header tank , so any free source of energy could be used for pumping, thus storing said energy with minimal loss.

Michael,

I have most of the stuff I would need to do this so cost is not really an issue.  Would there be some way to increase the force of the water and thereby increase the energy output?  And if those calculations were for 1 stream of water and I had multiple streams, would that not also increase the output?  If the calculations you gave were for 1 stream and I had 20 streams then that might generate enough to run something or top a battery off.  

William,

That sounds like it might be more feasible than what I had in mind.  If it produced enough to run a pump or 2 in the greenhouse then that would be worth the time investment to build it.   The greenhouse is going up next month so I need to figure this out before the fall rains start...actually we are having a lot of summer rain this year so the sooner I get it going the better.

Cl Robinson wrote:Michael,

I have most of the stuff I would need to do this so cost is not really an issue.  Would there be some way to increase the force of the water and thereby increase the energy output?  And if those calculations were for 1 stream of water and I had multiple streams, would that not also increase the output?  If the calculations you gave were for 1 stream and I had 20 streams then that might generate enough to run something or top a battery off.  

It doesn't matter how many streams you have, or tricks you employ to try and increase efficiency - that is the maximum amount of energy you an extract from the system. You could, obviously, use a pump to move the water higher, but then you are just extracting energy that you just expended to move it.

Personally I think it would be more appropriate to use you resources and time to ensure that the water is used properly to irrigate your garden.

Michael Cox wrote:You could, obviously, use a pump to move the water higher, but then you are just extracting energy that you just expended to move it.

Personally I think it would be more appropriate to use you resources and time to ensure that the water is used properly to irrigate your garden.

The energy would be extracted from the down spouts. The water would be pumped to a header tank. So we are capturing the energy of water falling from the sky and using it to put it where we want it.
Obviously water going directly to the header tank would be better,but is not always possible for reasons already mentioned.

Overall,I think you are right,it's not worth expending resources with the idea of getting any return.
It does,however,seem like a fun way to play with water and energy.

Yes,

I think it would be fun to play with the water even if it did not produce anything.  As far as putting the water to use in my garden....there is no garden outside of the greenhouse.  There is a cotton field right behind and across the road in front of my lil' acre, so anything I grow outside will be more toxic than any conventional produce I could buy.   Thank y'all for taking the time to answer my questions and if anyone figures out a way to make anything similar work, please let me know!

I thought this video about the subject was interesting.  There are a couple videos on Bootube.

https://youtu.be/0ieFZI4-6K8

Micro-Hydro is about head and flow. Head means from which height your water flows (in a tube) anf low how much water/time, mostly l/s.

The key equation to remember is the following:

Head x Flow x Gravity = Power

So you need at least either much head or much flow. I could only think of if you have enough head. Say you have a storage tank near the roof and a piping to the micro-hydro including the generator that is as much as possible deeper. Say 40 meters or so.

40m x 3l x 9.81 m/s² = 1117 W

Presuming you have 50% efficiency meaning you get about 588 W out. Nice though a 5000l tank will be empty in about 27 minutes,. ;-( Making you gain just about 0,25 kWh.

Now if you had a creek supplying 6l/s (one should not take more then 50%) with those 40 m head that would make a great hydro-power system, generating about 14 kWh daily, usually 365 days.