Here’s some questions from Ben, one of our Small & Micro Hydropower Newsletter readers. He asked these questions regarding turbine sizes, efficiency and penstock design.
Sincerely,
Jess
Hydro System Design Questions:
——– Original Message ——–
Subject: turbine size
From: Ben
Date: Thu, June 11, 2009 8:16 am To: jess.blog@smallhydro.com
Jess,
- Was wondering, does a smaller hydro propeller, ( not sure of terminology) add rpm’s thus giving more electric production?? If so, what is a general increase??
- Also, in the formula you sent me about converting to psi, how can you increase the effeciency rating of 72%, in general terms???
- Finally, on the penstock, how much do you typically decrease the intake from the main water line?? In other words, with a 4″ line is the penstock intake 4″ or does it decrease to 3″, and what if you decreased it to 2″ penstock intake?? Will that increase the flow pressure and what impact does it have on spinning the turbine?? I still don’t have specifics but working on it.
Thank you,
Ben
Hi Ben,
Looking at your questions I’ll try and answer them the best I can. Turbine deisgn and choice is complex and efficiency of hydro design is also. Mixing both in one response is a great simplification. With that said here are my Answers.
Jess
Hydro System Design Answers:
- Choosing Smaller or larger propeller or water wheels is not the issue. Fluid flow over the hydro generator propulsion device gives rise to rotational motion. Rotor specific speed is the issue you refer to and different designs have higher or lower specific speeds due to the physics involved with that wheels geometry. That is the rotational speed of a rotor of one design compared to others will be higher or lower depending on the actual design or geometry involved regardless of scale. Specific speed is a comparative “unitless” number much like a Mach number is used for supersonic flow. Specific speed often stated something like this “ηs= η/η0″. Efficiency at a given flow/pressure regime depends on this number a lot. Enough on that topic for now. What a smaller diameter wheel (using a pelton wheel for example) does is imply that for a given water jet velocity they must spin at a faster rate to produce their optimum power output. Max Pelton efficiency is at about 47% of the water jet velocity. This speed maximizes power output for given a pelton impulse design. So with all other factors being fixed the wheels pitch or diameter will increase rotational speed to keep the center line of water impact moving at the same 47% linear speed of the water jet. Power will be about the same, but generator frequency will change with rotational speed which may make a speed reducer/increaser a requirement.
- Increasing hydro system %efficiency is a complex art, starting with intake and Penstock friction, then turbine choice & performance curve optimization, combined with inlet valve and draft tube design if required, then any speed transmission or reducer friction, next will be generator/alternator efficiency, finally the transmission losses including wires, transformer/inverter systems. The 72% efficiency example I give is a very simple average of a model 85% turbine x 85% geneator/transmission output. Mileage for your site and turbine choices will vary. The more accurate you make your hydropower model the better the result will be. You will be modeling power production and loss until the first water flows through the system, then you get your course grade based on how close your “Real/Model” score approaches 100% of actual results.
- The last part of your request has more to do with jet design and penstock friction. Typically the penstock will be much larger diameter than the jet intake. The pipe friction means that there is a large dynamic head loss over long distance flows. The jet or turbine intake design then takes the pressure drop and accelerates water through the intake throat, a much smaller distance. These cross sectional intake areas are much smaller on higher head units like pelton and turgo units vs. lower head pressure ones like Francis, PAT and Kaplan/Popeller ones. That’s part of why the low head turbine prices rise so rapidly with flow rate, there’s a large opening to a much larger volume of machine for the same output power. Generally you should seek to keep penstock intakes and penstocks free of friction loss, then reducers at the turbine may be possible if required. For example a PAT I know of takes a >30inch diameter main and necks it down to 10inches right at the PAT input valve. The overall system efficiency is just a part of the equation, remember those big penstocks cost big bucks so make sure you balance the equation for optimum water power system ROI$.
I hope this helps clarify things,
Sincerely,
Jess
DoradoVista, Inc.
PS. I plan to post this set of question/answers on the Blog OK? Generic name & content only.
Ben replied,
Use the question, so far I am 2 for 2 in getting my questions in the blog. Batting a thousand here.
Thank you for the answers.
Ben
You’re welcome!
Jess
July 3rd, 2009 at 7:59 am
I want to design an undershoot water wheel (Stream wheel or kinetic energy water wheel),kindly send me some help regarding the design or design literature which i can download from websites
Thanks
July 3rd, 2009 at 8:30 am
Dear Jess,
I have just bought a property with a leat supplying a water meadow. At the end of the leat – about 400 metres long, there is about a 2 metre head. Flow rate is about 100 lps. If I insert a pipe along the line of the leat instead of allowing it to be open will I benefit from the additionbal fall along the length of the leat to give me additional head?
In either case would you anticipate that an installation based on the above might be viable and what sort of output might be achieved?
Jon Kelway
July 4th, 2009 at 1:04 pm
Ashin,
Take a look at the SmallHydro.com store, the books section first page has a great book on water wheel design. with the engineering math to back it. It is, “Water Wheels or Hydraulic Motors” by Jacques Antoine Charles Bresse.
I have to agree with one commenter’s statement about the book “I looked all over, and called all kinds of people trying to find real engineering design criteria for paddlewheels. There isn’t much out there. There are a few books, that give rules of thumb, for design and contruction of waterwheels, but this is the only one that is an engineering text, complete with the physics and math of why and how they work. ”
Jess
PS. Water wheels done right can be efficient and cost effective, but if not they can be very expensive.
July 4th, 2009 at 1:51 pm
Greetings Jonathan,
For starters regarding your leat (canal) proposed hydro site, you could generate about 1 kW at that head & flow combo. This estimate assumes about 65% hydro turbine efficiency and 80% generator efficiency.
I’m sending the detailed estimated a worksheet to you by email.
That’s a pretty low head and flow combo, but you may be in good shape for a single home. Power Pal makes a 1 kw – 1.2 kilowatt max Pico Hydro Unit that is optomized for 1.5 ft head and 130 l/s flow. With battery backup that’s in excess of 24 kWh per day. Perfect for everyday usage off grid. Note: A/C load & Ovens would require big inverter/battery storage systems though. Hydro power requires dump loads for speed control, these can be used for hot water and/or air too.
You don’t say how high a head you could get at the other end of the leat (canal.) How much higher is that end?
See this link for more on the Power Pal spec sheet (PDF) – http://www.powerpal.com/lowheadmanual.pdf
Jess
July 6th, 2009 at 2:01 am
I would like to know some details about your products and whether you could provide me with the turbines I’m looking for the following :
1. Turbines of 2 types
2. One is a large turbine that has capacity to take 6000m3/hr of water through the turbine to produce electricity
3. Second is a very small capacity model of a turbine which has 10-20m3/hr of water to produce electricity.
4. I need to know the exit speed and power/energy of the water from the turbine with calculations.
5. Also please suggest which turbine is better to use, whether Francis or Kaplan
I hope to receive your reply at the earliest.
July 12th, 2009 at 6:18 pm
Jess,
I’m glad I found a website where I can ask someone knowledgeable on hydro-power a few questions and see if I am in left field. I have been attempting to design and prepare the preliminary specifications for a hydro-magneto in line electrical hydro pod for use with either H2O or oil to generate electricity in a pressurized flow system.
Example 1: a residence would have a water heater tank installed in attic area (120 gal.) center tapered drain falls 10′ – 14′ would the traditional paddle wheel method work if the system had to stay pressurized so water could flow through and back UP to tank even when H2O wasn’t being released from the contained, pressurized system and replenished by a well or city water inlet?
Example 2: a fluid power system in a larger factory uses pressurized oil so to what ratio do you think you could compromise to if you installed in line magneto turbine electrical mini-power generators considering you create a fall from main supply tank of 25′ – 50′ to power supply and maintain pressure and flow @ 150 psi if liquid passed through magneto hydro turbin then into “actual” fluid pump?
Example 3: a hotel with an indoor pool on the third floor, fall of 30′ to basement level ( 10,000 gal. ) would the creation of energy ( through current paddle wheel method ) be serving a purpose considering you have to use a filter and H2O recirculation system to operate a pool regardless so would any energy produced at least cancel the energy used resulting in a savings of the annual cost of operating the pool?
My thoughts lead me to believe that there is a hydro-propulsion-magneto in line electric producing mini-power plant design just waiting to be the next iPod of billionaire making and I’m getting closer but have hit a few stumbling blocks. Thank you for your time and any advice you may be able to share.
Thanks,
Kirt
July 26th, 2009 at 2:59 pm
Kirt,
My answer to all three example systems is the same. Can you draw a circle around the whole fluid and energy loop in each case? If so, can you identify where mass and energy enter and leave that circle. By conservation of mass and energy you can not destroy or create additional mass or energy without something consuming it elsewhere (hint: your electric load.)
Yes, you can store energy in potential form by pumping up hill (or floors.) No you cannot store infinite quantities of it, 120 gal is pretty small when compared to Micro Hydro (or even Pico <=1 kW) quantities of energy production. Water energy is stored in the pressure difference and/or mass velocity (as kinetic energy). When you drop pressure and/or slow it’s speed you release that energy. To get energy back into the system circle you must supply either of these energy inputs by pumping or some other energy input source.
To see this yourself look at the energy calculation post on this site or simply use flow(cfs) x head(ft)/10 for an approximation of instantaneous power.
Remember to take the stored water volume and divide by your max power flow rate to get max run time for that flow.
For example at 20 feet of head and 1 CFS gives 2 kW for [120 gal/ (7.48 gal/sec) = 16.04 sec] (neglecting head loss in emptying the water tank.) Modern hydro is efficient, but the quantities of water moved still require high enough head or large volumes to produce sufficient power for longer periods of time.
There is also the issue of water pump & hydro turbine loss too. I am not trying to dampen your fervor regarding the potential for new inventions here. Just remember that inventors stand on the shoulders of giants. Many giants have tried working on hydropower energy storage before… You must keep on trying, because in hydropower invention some still succeeded even where others had previously failed…
Jess
July 26th, 2009 at 3:39 pm
MBarham,
My response — to you questions are inserted between each one.
Jess
MBarham says:
I would like to know some details about your products and whether you could provide me with the turbines I’m looking for the following :
1. Turbines of 2 types
2. One is a large turbine that has capacity to take 6000m3/hr of water through the turbine to produce electricity
— What is the head?
3. Second is a very small capacity model of a turbine which has 10-20m3/hr of water to produce electricity.
— What is the head and flow variability for each?
4. I need to know the exit speed and power/energy of the water from the turbine with calculations.
— That requires more information regarding the site altitude, etc.
5. Also please suggest which turbine is better to use, whether Francis or Kaplan
— Again that depends on head and turbine altitude for reaction turbine draft tube design.
I hope to receive your reply at the earliest.
—————————
Send us more info about the head, altitude and variability of flow.
Send data to SmallHydroBlog@smallhydro.com
September 17th, 2009 at 2:01 am
Jess,
I am planning to go into detailed study for the optimal shape and some detailed perfromance analysis of paddle wheel turbine-generator for my dissertation.
Do you have any advice where I can find some literature because there are only few I can find in the internet. Any previous study would be of great help as my starting point.
Thanks..
Jojo
September 24th, 2009 at 9:18 pm
Jojo,
Look in the SmallHydro.com Store at the upper right side of the site. We have asection with several design books on water wheels there is a bit on the use of undershot paddle wheel designs.
The title is: Water Wheels or Hydraulic Motors
By Jacques Antoine Charles Bresse
The book is in our “1.1 Water Wheels and other stuff” section
Jess
September 26th, 2009 at 3:10 pm
Have a pond on my 30 acres and have a 10 inch asbestos pipe about level with my little pond which I use as a road over the pipe to get home, wish to build a small dam to install a plateform and dam to set up a five horse moter with 230 volts in going with three phase coming out one leg hotter than the other two legs. Which will be turned by a water wheel,( I hope ) What is the best way to build a higher dam to measure the h2o flow out the pipe I have now or after a dam is built ? Thanks Jerry
September 28th, 2009 at 1:13 pm
can i use a 10,000gal tank filled from my house roof or filled by a windmill,to produce enough energy to run my house on a hydro generator? where can i go to get info. do i need batteries or can i go straight power?thank you mark any info would be appreciated
October 1st, 2009 at 6:19 pm
Jerry,
I’m not very clear on how your site is set up. If you have a 10 in pipe with full flow through it you can estimate flow by making a few simple measurements of the flow trajectory at the mouth of the pipe.
I’ll write up a blog post with a pipe measure procedure shortly. (See updated blog post for Full Flow Pipe flow rate measurement.) Otherwise it may be easiest to take your spill way and create a weir structure across it to measure flow, another post on that coming soon.
Jess
October 1st, 2009 at 6:30 pm
Mark,
10,000 gallons flowing at a Q of 1,000 gallons a minute from 30 feet up will at most produce about 4kW for less than 10 minutes.
(See the Hydro power calculations post at : Hydropower Calc Example in Metric (SI) & British (US) units )
That’s just about enough time and hydroelectric energy to finish 2 toasters worth (4 slices) of toast. Then you’d have to pump it all back up to the roof with some other source of energy.
Jess
October 11th, 2009 at 2:16 am
Mr. Jess,
hello. I want to know, the cost and water backup required for 5kba capicity submercible turbine.
With Regards
Virk j S.
October 15th, 2009 at 6:49 am
May you kindly send me the type and size of: Turbine,generator, load controller and send me contacts of European and Asian Suppliers.
you may also advise on how to affect payment and the mode of ferrying the complete set of items to Kampala Uganda.
Flow rate 60 liters per second with a gross head of 5m
Thank you for the Information.
MURANGA MACHI
October 21st, 2009 at 3:39 am
Dear Mr Jess
I will appreciate it allot if you can help me with the following…
We’ve got a 1000 meter pipeline with a 30 meter head, size of the pipe is 150mm diameter.
How much power can I generate from the water?
Thank you for all the good information
Kind Regards
Lee Meissenheimer
South Africa
PS: Great Blog!
November 4th, 2009 at 8:38 am
Please could you tell me the rough size and weight (and preferebly supplier and model number) of a francis turbine that would operate under a head of 126.5 m with a flow of 0.89m^3/s.?
Regards,
Richard
November 11th, 2009 at 5:21 am
Please i want to know the procedure of power optimization and plant sizing
if someone have any example of Hydrpower project power optimization
As for design flow we do the optimization by selecting the different flow from FDC so
- how we calculate the Headlosses for different flows?
November 18th, 2009 at 4:30 pm
Azeem,
We are working toward revealing that procedure in a way that allows you to tailor it to your site’s needs.
One thing you should look into is the Penstock design software regarding PipeFlow – Check back through our site linke for great price breaks that they offer our readers from time to time. Using that dynamic flow analysis software you can get a great estimation for Hydropower Pipeline or Penstock Head loss. You should check it for max and min flow regimes.
Yes your FDC curve should be analyzed typically using the 50% point or the 80-20% rule – that will account for the Mid more typical flows. This number will strongly depend on your FDC shape. A broad high FDC may be worth having a larger penstock and turbine because the higher value in the large flows. A sharply dropping max end of the curve is a warning to not plan for large ROI from flows on that end of the FDC.
November 26th, 2009 at 2:45 pm
Hey guys,
I was speaking with a relative and they mentioned hearing about a form of micro hydro that I want to learn more about. I don’t know the specific term or reference, but essentially, it is a 40′ x 8″(diameter) tube that you place in a river. My understanding is that it is a self contained DC unit and several can be placed in the river with no harm to wildlife. Anyone know about this, what it is called, their efficiencies, or who makes them?
Cheers,
G. Gibson