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Author Topic: Stored micro hydro calculations  (Read 3708 times)
Toberwine
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« on: January 12, 2020, 08:34:51 AM »

I note there are a few threads here relating to the use of a pond to regulate the flow / store surplus water for hydro schemes.
I am looking to do something like this on a very small scale. I have a fair idea of how to calculate output based on fall and flow and efficiency of a running stream and I have just installed a v notch weir so that I can start to build up a flow database over time.
The stream is small with a 5m head from the surface of a 200 square metre man made pond to the lowest point on my property which also happens to be nearest to the house, and at the moment (January) I am measuring about 2 litres per second. I know this gives a pretty feeble output of a few tens of watts but I would be OK with that.
What I would like to do is increase the depth of the pond by about 50cm to give me a usable head of 5m, which can be done by simply raising the overflow pipe, then fit an intake about a metre below the surface.
This is where I need some reassurance that my maths is correct: If I can regulate the flow at the intake to say 2 litres / second, and I have 200 cubic metres of water, I calculate it would take 100000 seconds to deplete the top 1m of water, assuming thereís nothing being added to it. This is about 27 hours. Obviously during the winter the pond will be refilling all the time too, although in the summer the source dries up completely.
I suppose what it would be nice to know is how long I would be able to run the hydro at a given output. Once I have a yearís worth of data, I will have a better idea of week to week flows (although I know a single yearís data carries a strong health warning). Has anyone an idea of how I will be able to calculate how long I can sustain 2 litres / second through drier periods using the pond to store the reserved water?
Obviously if I am aiming for 2 litres / second as a minimum, during wetter periods I could use more water than this once the reservoir is full, but I am interested to know for how much of the year I can sustain this minimum.
I already have a 32kW commercial hydro which I had built in Scotland (I live in S England) so I know a lot of the ins and outs but am hoping to build something small and under the radar that I can actually use.
Beyond that, Iím not sure
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pantsmachine
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« Reply #1 on: January 12, 2020, 08:39:04 AM »

Anything living in the pond before you begin? It's an interesting idea.

27.7 hours although you lose 1/5th of your header pressure if pond not refilled.
« Last Edit: January 12, 2020, 08:42:04 AM by pantsmachine » Logged

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billi
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« Reply #2 on: January 12, 2020, 10:33:30 AM »

Hi , i had a scheme like this
 i never drained it completely  for a environmental reason , but i always have   some water in-flowing  and 9 month of the year i did not operate it at all ,
cause  had enough electicity from the PV

my system i calculated to achieve 1000 watt , in the end i received  about 750 watt  , so  i asume i did not do the upfront head (20m) measuring (through brambles and gorse ) too accurate and some other loss factors ...
Anyway , worked  well as a backup generator to charge batteries

In your case  you will hardly find a suitable waterturbine to work with 5 m head and 2 lps , if the flow is increased  to say 5-10 lps and the time of drainage limited than you might find an off the shelf turgo  waterturbine

Do you know of a turbine that could suit your 2lps flow ?

Billi



* mylake.jpg (138.35 KB, 960x441 - viewed 211 times.)
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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
Toberwine
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« Reply #3 on: January 18, 2020, 08:13:29 AM »

Thatís some lake, Billi!
I believe I may have enough flow / head for a Powerspout.
Yesterday after lots of rain my 90 degree v notch weir, which is 13cm high, was overtopped, having sat at a water depth of around 7 cm for a fortnight. So estimating 15cm this equates to around 10l/s. Putting the data into the Powerspout calculator gives around 200W of power.
I guess one problem would be how to cope with such a large variation in flow with the nozzle size; is there any simple way of regulating the flow in the penstock? The only way I know is with a head sensor and controlled variable intake valve but that is less than simple.
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billi
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« Reply #4 on: January 18, 2020, 08:48:12 AM »

well sure there are adjustable nozzles ,  and  regulating flow sensors , etc

In my case i just should have gone for a 200-300 watt waterturbine  instead of a 1.1 kW one,  that needed  more flow ,  so that would have meant in winter , when i had a constant inflow in the lake ,  that i would not have to shut the gate valve , so much and just let the turbine run  24/7   .


I was fiddling  around a solution  to  automate the open and shuting the supply of water to the turbine , according to Battery state of charge , but in the end , i just behaved and let iti run for a few hours after work and closed the gate valve manually befor bed time


Billi


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1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
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