Small Hydropower & Micro Hydropower

Hi there,

I have only subscribed yesterday to the Small & Micro Hydropower Newsletter and I really need your help,we are based in South Africa and we started refurbishing a Francis turbine and will commission it early may 2009.  Our hydropower company is in Africa.

Q: Currently we are busy proposing for a new site with a 80m head and would like to install a Pelton turbine I need some info regarding the hydropower foundation setup.
Please can you give me some guidelines I will be very thankful.

Hope to hear from you soon

Mark

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Dear Mark,

We’re glad to have you join us!

A: May I suggest the first thing you need to establish for Pelton wheel hydropower design infrastructure is the same as your need for good turbine and penstock choice. Basically you need to know your static head pressure (80m) AND flow rate (m^3/s) The penstock and turbine are chosen to gain the best fit for efficiency of the available flow regime, but there is a dynamic force caveat.

Penstock length and diameter and geometry (turns & angles of turns) will determine the maximum dynamic flow forces at your thrust blocks or pipe anchor points. Every change in angle and every flow rate change will generate thrust forces, From Newton’s first law of motion. Your infrastructure & power-house design must exceed these forces by a wide margin or there will be BIG problems.

One more non-linear issue is that you must keep the linear flow rate below 5ft/s or 1.5m/s to avoid the effect of catastrophic water hammer. Remember, you are moving a freight train’s weight of water in the penstock there’s a lot of energy stored in the water’s momentum (Momentum=M x V.) The kinetic energy is (E = 1/2 m x v^2.)

If the jet(s) of a Pelton turbine gets plugged by debris the flow can stop abruptly causing a huge energy or pressure pulse to form(a.k.a. water hammer.)  This in turn will lead to huge forces on the thrust blocks and penstock walls (including the turbine mount & thrust structure) but every bit of the penstock structure will be exposed to huge pressure waves traveling back and forth at the speed of sound in water (pressure reflections).

It is not unusual for steel pipe to rupture or collapse depending on the magnitude and sign of this pressure/vacuum wave. All of these design issues are pretty much the same as large scale water conveyance pipelines in any system. For example eg. sewer or domestic supply.

So, start with your flow needs and penstock design to determine each thrust block’s forces and the terminal powerhouse (turbine foundation) forces. Make sure you consider maximum flow & catastrophic pulse generation. Then engineer each concrete and steel anchor to exceed these by a good margin. A good pipeline designer should be able to do these calculations and design this aspect of your system.

Note: All DoradoVista Small& Micro Hydropower site recommendations are not meant to replace a good design or design engineer, they are for informational and technical seeding of ideas only. You must get a locally qualified engineer to evaluate all aspects of your hydro system design including all of our recommendations for your project. Hydro system safety and economics design issues are both involved here even at 80 m of head.

That discussion on good penstock and turbine foundation design is just for starters –

Here’s a link to some more Hydropower books from Amazon.com that we’re collecting on various Hydro topics. It’s from our Small & Micro Hydro Reader’s corner.

The inexpensive CD’s on that web page (from the DOE on hydro) may likely give more detail on your topic question.

Sincerely,
Jess
DoradoVista, Inc.

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Tim,

Thanks for the words of encouragement about our “Small & Micro Hydropower Newsletter” work at DoradoVista, Inc. and now with our SmallHydro Blog and Small & Micro Hydro site at SmallHydro.com !

If there’s one thing I’ve learned in 30 years of engineering and management experience. There are no stupid questions. I am amazed how often the experts and novices alike assume a given field of knowledge is obvious.

One of the reasons we started the “Small & Micro Hydropower Newsletter” was the realization that people who are considering Renewable Energy Hydropower need a certain introductory level of Energy & Systems knowledge to get started. This is so individuals are comfortable asking what they need to ask about each unique project. This helps get the Hydropower projects evaluated accurately and allows them to make good decisions for project success.

Our plan is that part of this sequence of newsletters will become the basis for an on-line introductory to Small & Micro Hydro-power systems class. There are a few decent sites that start the ball rolling, but they often are talking only to experienced engineers in the hydro field. The two ESHA PDF links on the http://www.DoradoVista.com/DV_Hydro_Power.html pages have just such a course. Great stuff, but we’ll need to assist you in understanding what it means.

When we get to the various options and procedures, you should have enough knowledge to understand what to do, How to do it, who can help, and when. It’s a big goal, but worth doing. Once this base of understanding is established then we can begin the real fun with some Hydro-Pro-Amateur Blog-comments-forum type interactions to help one another.

By the way, feel free to ask questions. We’ll try to get you answers either via the newsletter or email.

Sincerely,
Jess

DoradoVista, Inc.
PS. Do you mind if we reprint your name (Tim), your question and this answer in a future newsletter update? It helps others to feel comfortable with the same issues you ask about. (You are not alone!)

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Q: Say you want to convert Psi & GPM to kW water power?

A: Good question – unfortunately there are a myriad of Unit conversions, like furlongs per fortnight.

Follow my round about conversions, I like to focus on the most common formula to start my thinking.
(unfortunately in English Units)

So I stick with the following formula and convert units to fit it. Metric converts too…
I usually think in CFS & Ft head:

I usually start with this formula –>  kW ideal = (CFS flow x Ft head)/11.8

But you have GPM & Psi for units

1 ft head = 0.433 Psi –> (1 ft/.433 psi) x Z Psi = ft head

There are 60 seconds to a minute –> 1 min = 60 sec

There are 7.48 Gal per Cubic Feet volume –> (1 CF /7.48 Gal) x (Gal /sec) = CFS

So say we have 78 Psi -> 78 psi /.433 psi/ft = 180.14 ft head

And now we’re given 1000 GPM = 1000 GPM x 1 Min/ 60 sec = 16.67 GPS

Now convert to CFS -> 16.67 gal/sec /7.48 Gal/CF = 2.23 CFS

Therefore our kW ideal is = (2.23 CFS x 180.14 ft)/11.8 = 34.02 kW Ideal –> Efficiency % not included

To factor efficiency in Multiply x ~72% for water to wire typical. (must use chosen Gen % x Turbine %).

So we get something like 34.02 kW x 72% = 24.49 kW Typical power as a more realistic measure of output potential.

I sure hope this helps,

Jess

DoradoVista, Inc.
PS:  Mileage will vary, there are a lot of issues not modeled here. It is a start though.

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