Homebrewed Electricity > Hydro
Fish-way using low head hydro turbine
Natreely:
Hi all,
Thanks to all who give time and knowledge to help here, as have found much practical information here in the past.
Now on topic:
Being a keen recreational fisherman and liking to think of myself as a conservationist (aren't we all?), I've done a lot of research into fish passes / ways / ladders and low head hydro. While a well designed Archimedes screw generating power, can safely pass fish in the downstream direction, a functional fish-way is still needed for upstream traffic. Then my attention was drawn to a system developed in Austria, patented 2009 so relatively new for hydro technology, which the owner calls a Gravitation Water Vortex Power Plant or GWVPP, and claims to safely enable fish passage in either direction. On his website there is a fish monitoring study summarised, which successfully recorded fish passage in both directions. The major problem we have (that is "Down Under" in A&NZ), is that none of the indigenous or endemic fish are fast & strong swimmers, so they wouldn't be able to cope with the 110 Watts per cubic metre in the Austrian designed GWVPP, so not surprised to note that the fish that passed upstream through the GWVPP are all Salmonids, which are all fast and strong. That means they not only have burst speed but also stamina. So could the Austrian design be adapted for less W/m^?. The patent owner said yes, if you use at least a 6m diameter rotation tank. Well that is nowhere near enough "inflammation" to be able to compare costing with a Vertical Slot Fish Way or VSFW, which basically costs upwards of AU$150,000.00 per vertical metre. Next: more research and more research, finding that enough data is out in public now as some scientists have been working diligently!
Please be patient with me and I'll post some details of what we now know as fact, and not just speculation. Then a question...
Natreely:
The following six points are a summary of known facts copied from [3] which is really from [2] and other research combined.
1. The water surface profile of the vortex can be modeled mathematically and predicted accurately.
2. Optimum vortex strength occurs within the range of orifice diameter to tank diameter ratios (d/D) of 14% - 18% for low and high head sites respectively.
3. The vortex height varies linearly with discharge.
4. Linear correlations for H v Q can be scaled accurately to prototype size using
the Froudian Model to be used as a design chart.
5. Maximum ideal theoretical power output = ρgQHv (Hv = Height of Vortex).
6. Maximum hydraulic efficiency should arise when the impellor velocity is half
that of the fluid velocity.
[1] Power, MacNabola & Coughlan 2015, Trinity College Dublin
“A Parametric Experimental Investigation of the Operating Conditions of Gravitational Vortex Hydropower (GVHP)â€
[2] Mulligan, S. & Casserly, J. 2010 Final Year Civil Engineering Project, Institute of Technology Sligo
“The Hydraulic Design and Optimisation of a Free Water Vortex for the Purpose of Power Extractionâ€
[3] Mulligan, S. & Hull, P Masters in process Civil Engineering Project, Institute of Technology Sligo
“Design and Optimisation of a Water Vortex Hydropower Plantâ€
Paper [1] provides some limited help in blade design, but little else as they completely overlooked the 2010 paper [2].
… So how do we accurately calculate the dimensions of the rotation tank and its' orifice, to allow fish through in an upstream or downstream direction? There are more than 12 working GWVPPs that we can reference output figures and efficiency charts. So added to the research paper findings we have enough data to put together, to add up to something useful…
Having never used an MS Excel spreadsheet before, this was a trial of patience, to group all the facts computing something roughly accurate.
The result seems credible. Can the Excel attempt be posted for suggestions, constructive criticism, or maybe something glaringly obvious that I've overlooked? Any Excel gurus on forum?
My motive is altruistic (now being a full time volunteer), having a couple of sites that would work, but need to be reasonably sure of the design before presenting it as a viable option to the local environmental experts.
Hoping this attracts some expert interest.
Nat.
Natreely:
We are really designing from the perspective of fish passage in both directions, so here are some research results that will influence design in Australia and New Zealand. This really demonstrates how important is the orifice size under the turbine.
Eel Migration in New Zealand
From “Non-fishing Mortality of Fresh Water Eels (Anguilla spp)†in the New Zealand Fisheries Assessment Report, June, 2005
Migrant female longfins range from 800mm to over 1500mm in length and males from 500 to 700mm. Migrant female shortfins range from 500 to 1000mm and males 350 to 550mm (Todd 1980). In comparison to most other freshwater eel species around the world, adults of the two main freshwater eels present in New Zealand are large. The potential for injury or mortality while passing over barriers and through turbines is therefore greater in New Zealand than elsewhere.
Size, Velocity and turbulence
From “Sea To Hume Dam Final Report†of the Murray Darling Basin Commission April 2008
At the remaining 14 low weirs, the MDBC determined a need to pass a wide size range of fish including about half of the sh between 20 and 70 mm long (or all those over 40 mm long) and all between 90 and 600 mm long, with a maximum size criterion of 1000 mm for Murray cod (Maccullochella peelii peelii; Barrett and Mallen-Cooper 2006). A vertical-slot fishway design was selected, as it operated over a wide range of river levels, with a low gradient (1:32), low water velocities (maximum 1.4 m/s) and large pools with low turbulence (40 W/m3; Barrett and Mallen-Cooper 2006).
We will summarise some design conclusions from this in the next post.
Rgds, Nat
Natreely:
Design Conclusion:
The minimum orifice diameter would need to be 1m with the turbine having 4 blades or less to pass Murray Cod of 1m length (as they are deep in girth size) or large eels in NZ (as they are slow). Prescribing a minimum orifice diameter will also make sure that the velocity will be less than 1.4 m/s. Also this will give a wider tank diameter because of the efficiency ratio, thus contributing to less than 40 W/m3. Of course, the higher the efficiency of the turbine, the less W/m3 remains. The turbine rotation will be between 10 RPM and 30 RPM, but as yet we do not have adequate data to link the RPM to the flow rate & head height, but hopefully this can be added to the spreadsheet later.
NB. The W/m3 figure results from Hydraulic power (100%) minus the mechanical power %. Like the Betz limit with wind turbines, hydro turbines have the same issue of getting the water that has spent its' energy out of the way. This efficiency generally follows a bell shaped curve, some turbines having a flatter curve than others. Then to arrive at a prediction of electrical output, we must multiply the figure by the percentage that results from other inefficiencies like gearing / bearing friction loss, generator loss and line loss. Given that outputs now being recorded, range from 50% to 65% total efficiency, considering they are designed for power output with fast swimming fish traffic, then it is not unreasonable to expect that the highest total efficiency will be 55% but in the near future more likely to be 45% - 50% when designed for slow swimming fish. Still, this is not a bad output for 0.5m to 1.5m head height.
Still working on this spreadsheet:
Do you think I need an introduction to Mr Bernoulli and Mr Reynolds for the input of their numbers or, does someone have a simple formula we could use to mesh RPMs into the spreadsheet? As in, at x head height with y flow rate = z RPM?
Rgds, Nat
Natreely:
Firstly, sorry, we need to make a correction to the first post above:
Patents on this technology were granted in Austria 2003, 2010, 2012 and Switzerland 2007 and Germany 2010
Yes, we can still say, a relatively recent addition to the micro hydro list of options.
I'll have to leave Mr. Bernoulli and Mr. Reynolds to the tender mercy of professional mathematicians. For now, we can take a simple route of approximation, being aware that this will render the results more coarsely rough, rather than just roughly accurate! Still it will give an idea of the ratio of gearing required, so to be able to combine with an appropriate generator…
RPM reasoning:
Within the core of a full air-core vortex, the rotational surface velocity can be much faster than the vertical velocity through the orifice. Then, (a) in this case it is not a full air-core vortex as the tail water level is above the orifice, with above that a suspended turbine. Then, (b) we are not just concerned with surface velocity but the average velocity having effect on the surface area of the submerged blades, both with push force and suction drag… Then I take it upon myself (gulp) to put a theory forward: The tip speed of the turbine shall be no faster than the maximum possible velocity through the orifice at the supplied volume, where the turbine diameter is no less than 1.3(Orifice diameter).
We'll get this spreadsheet finished and posted yet!
Rgds, Nat
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