The Original 2 Questions –
Subject: Hydro turbine questions
From: Peter
Date: Wed, July 01, 2009 4:58 amTo: smallhydroblog@smallhydro.com
I have a few questions that I need answers to. I have a seasonal water fall with 38 feet of head. The flow rate varies with the weather.
Q: My first question is why isn’t there a turbine that works on variable speed? As flow increases, the output should increase.
Q: My second question is in your opinion would it be worth investing a small turbine knowing that I may only get 180 days of power.
I hope to build on this site and will be off the grid. I know I will need a hybrid system with solar/possible wind or water. I want the best, but yet the cheapest way to go.Thanks for your time!Pete
My Answers –
Peter,
That’s a great pair of questions about Variable Flow & Speed. There are hydro turbines to solve the variable flow problem, but that is not the same situation as variable speed. The two parameters are related, since an increase in water turbine shaft speed due to pressure changes will cause a proportinate increase in turbine water flow rate for a fixed load. The problem is that variations in turbine RPM will cause generator output frequency to vary too.
For AC generators, transformers and AC motors variable frequency is a very bad thing, it will cause heating and damage insulation, solder and machines. Frequency variation will cause transmission and synchronization problems, leading to brownouts and other problems too.
This varible speed turbine control ability is an area of recent hydroelectric system research. DC alternator designs can tolerate this Hydro turbine generator RPM variation because the final AC power output frequency is defined by the inverter design not the alternator speed (output power will vary though.)
So, let’s look back at the possibility of site flow variation solutions and not hydro generator speed variation;
A: Several variable flow Small & Micro Hydro turbine options exist for you –
A few variable flow Hydro Turbine configurations that come to mind are:
- Multi jet Turgo or Pelton wheels may work but may not be as efficient as they are when that type of turbine is used for higher head >100ft 30m sites. Low head sites favor reaction turbine types.
- A better turbine choice would be crossflow with multiple inlet gates.
- Typical multi gate crossflow uses 2 -3 sections on turbine inlet for 1/3, 2/3, 3/3 or 1/4, 1/2/, 3/4 and 4/4 flow curves respectively.
- You can use other low head variable flow options, Francis with wicket gate, Kaplan with wicket gate >$, etc.
- Propeller and simple PAT (unregulated Francis type) systems operate in a narrow efficiency band or curve, yet if you can put 2 or more of these in parallel you can sequence their inlet valves much like the crossflow. Say that you have a 5 kW and a 10 kW pair of units, now you get a 5, 10, 15 kW range efficiently over a broader range of flows – if the turbine curves overlap effectively.
A: Some things to consider about Site Stream Flow Variability and Availability –
The site with flow variation and some months with zero flow may or may not be economic to set up for hydropower, depending on your Flow Duration Curve or FDC and the overall ROI for your hydropower equipment costs. An FDC is a pareto chart or ordered histogram of a stream’s frequency of flows at a given Q or water flow rate. We’ll cover FDC’s and their creation later in the 12 step Small & Micro Hydropower evaluation process.
Here’s some Additional Questions for you to Answer about your Potential Hydroelectric Site…
1. How much peak, avg vs low flow do you have? (Start with a guess, get an FDC later)
2. You said that you have 38 ft head, is there any storage or just natural falls?
3. Do you have flow data showing avg daily flow for greater than 10-12 years?
FYI – Climate change tends to follow 11 yr sunspot cycles more than anything.
4. Do you have water rights or can you get them?
180 days of 100% flow at your sweet spot may work fine energy wise, if you can punch out enough power. Hybrid solar may help. If you can grid tie, then Hybrid with net metering may work well for you $ ROI wise. If enough power then you can become an Independent Power Producer…
Sincerely,
Jess
DoradoVista, Inc.
PS. Let us know how we can help with your turbine selection. I wanted to let you know that we have some great turbine and water to wire hydropower system sources too depending on what units you are looking for.
July 17th, 2009 at 8:42 pm
If you only have water 1/2 the season, you would want your installation to be as inexpensive as possible.
One way to save some costs is to make your own crossflow Banki turbine. QUESTION: Do you have any design documents so that we can construct a unit in a machine shop with all the appropriate diameters, sizes, angles, etc. for the proper head pressure and water volume? I would want the optimal design considerations for maximum efficiency (which would be calculated with mathematical formulas).
I have looked around the web, but have only found a couple of documents that come close to what is needed.
July 26th, 2009 at 2:14 pm
Dwain,
I agree with you regarding low to medium flow sites. Good Cross-flow or banki mitchel turbines make a great low cost solution. Although if variable flow is involved the methods to solve that situation can add some to the cost and water to wire hydro system complexity.
We have some files and links for Banki designs as well as the ability to supply water to wire crossflow turbine systems too. We’ll put together a post for everyone to look at when we get to turbine and generator choices. Thanks for the request!
Sincerely,
Jess
August 7th, 2009 at 9:51 am
There are other generator technologies taken from the Wind Power market that can be applied to Hydropower. In specific, I am speaking of Permanent Magnet AC generators in combination with an AC output Inverter.
The overall goal should be maximizing system efficiency regardless of power out. With this approach, 60Hz (or 50Hz for that matter) is an output requirement, but has no connection with turbine speed and therefore efficiency.
Being constrained by synchronous generator speeds sub-optimizes the overall system performance.
How much efficiency can be gained with variable speed output of the turbine? If the generator outputs 110Hz in high flows and 45Hz in low flows, the AC inverter outputs a constant 60Hz to the grid.
PM Generators are significantly more efficient than synchronous machines across their load curve. A PM machine at 1/4 load can operate at efficiency levels in the mid 90% range, whereas a synchronous machine at 1/4 load may be in the 60’s.
To be fair, there are electrical losses in the conversion (Generator AC to DC) and inversion (inverter DC to grid AC) steps. In both cases, the conversion efficiencies are in the high 90% (well above 96% at 500Kw or larger).
This trade-off is well worth it for the pick-up in turbine efficiency and overall generator efficiency.
August 19th, 2009 at 6:20 am
if we know the head,stream flow rate,demand of power,can we which turbine is suitable
August 19th, 2009 at 6:32 am
dear sir
i want to construct five mega watt hydel power plant at my place under some mp government scheme on bot system at mp in india. so what will be the tentetive cost for instaling a 5 mva power plant
August 21st, 2009 at 8:05 am
I have clients with wildly fluctuating water flows and their dams reflect flows that range from under 300 gps to over 7,000 gps….Heavy rains and spring runoff .
One dam has 11 gates and no spillway.
In another the forebay—a good way to store water and moderate flow variations, has two penstocks. During low flow periods, one is gated shut enabling the other to run at optimal capacity.
So, instead of trying to find a turbine/generator combination to accommodate a fluctuating flow; you should design your system with an impound and forebay to run two turbines and then store enough water to match the lowest flow period.
September 16th, 2009 at 1:03 am
i am from india.i have a 250kw mini hydel scheme,which is a canal based project with gross head of 5.5 meter and desinge discharge of average 6 cumecs.i would like a cost effective turbine with minimal civil cost.the lenth where head is avialable is 300 meters.the water is discharge is for 300 days.
i was going through a company called waterpumps from finland.i think there mechinerey may be suitable for this type of project.please advic me on this.
regards
chetan
September 24th, 2009 at 8:59 pm
Dear Chetan,
If the company you are referring to is “Water pumps WP OY” it looks like their low head compact turbine are low head tube turbine are in the right range for your project. Both of them look like a semi-Kaplan designs which would be applicable for this lower head high flow site.
One of the features that they report is that their turbine designs are fairly compact and can be installed at pretty much any angle without much interference with your infrastructure since they are using a bulb turbine inside the tube.
This compactness, can lead to a more eco-friendly site since the unit can be placed below ground in a vault. Although their turbine is not the only bulb design on the market it is pretty small. A small S type Kaplan unit may be a viable option as well.
Your head pressure is right, but the flow is about half what you need if you were to use a VA Tech – Eco-bulb type turbine. So that is out.
Send me an email if you have more info to go over about your site and turbine choice.
Sincererly,
Jess
January 2nd, 2010 at 10:34 am
Is there any turbine vendor interested in BOT basis supply of a suitable turbine(s) for a small dam (about 250 feet head) in Pakistan? We are in contact with the authorities and have good chance of acquiring the contract.
March 29th, 2010 at 12:13 am
HI guys I have 25 mtrs of head at 30 liters per second what type of mini hydro system is the best for efficency and reliability.
Thanks
Brendan