Hydro calculations

[noah]

I`m having a dispute with Ofgem about reclassifying output
I have two hydro generators, 10.5 & 5.5 kw. These obviously sum to 16kw which is just over the 15kw FITs step.
However as the two share a common feed pipe and when both are running the crossflow (10.5) has the effect of reducing the head on the waterwheel (see the attached pdf-never tried to attach anything before, hope it works) so that the max output is 4.5kw.
I`ve offered the proof to Ofgem with a realtime video showing that pond level is at max (so cannot get any more water through pipes), WW & T are fully open and generated kw on control panels is <15kw, or an independent witness statement to the same effect.
It seems that they may not accept this and are insisting on `calculations made by a suitably qualified person`.
My response is that any calculations made are likely to be no better than +-10%: consider
(1) Get incoming flow rate. Measuring the flow in an open leat you`d be lucky to get more than 90% accuracy.
(2) Turbulence and friction in pipes: we know the pipe sizes but dont know the exact point and angle of join and the amount of rust and other crud inside.
(3) Efficiency of WW and T. I have an efficiency curve for the turbine but the WW is homemade and its eff can only be guessed at.
(4) The suction effect of the turbine. All hydro models that I know of assume a single turbine or a small array but all at the same level.
All of these things combine and in my opinion getting an output prediction any better than +-10% is highly unlikely.
As a 10% swing either way is greater than the difference that I am claiming (eg if the `predicted` output is 15.5kw +-10% then we could easily be on either side of the fence) it seems to me that in this instance this is an ill posed problem and there is no calculation that can be reasonably made that will give a reliable enough result.
Therefore IMHO Ofgem should take a pragmatic approach and be happy with conclusions drawn from actual data.
Anyone have any thoughts to add?

[Heinz]

Keep it simple, give them what they want. It's a bit like a business plan, you know it's boll*cks, they know it's boll*cks but you've given then an answer. It may be a load of bull but if it gets you what you want.... 

H

[noah]

They won`t accept calculations from me, has to be from an outside `expert`. So I`d have to pay someone probably a couple of c`s to come round and, if they were really an expert, agree that this is not really a calculable situation. They would then just make something up based on empirical evidence or decline to get involved.
I`ve always tried to stick with Proverbs 26:4 ` Answer not a fool according to his folly lest thou be like unto him`
Problem is the Ofgem people are civil servants: they have no engineering expertise themselves and no in-house experts to call on. They are not of course fools, just out of their element.

[Heinz]

That's what I meant by give them what they want. Easier to pay a friendly engineer a couple of hundred quid for a probably worthless bit of paper, than to argue common sense and get nowhere....

H

[Ted]

I would've thought that an initial enquiry to the Computational Fluid Dynamics Dept at Swansea University College of Engineering might be worthwhile. At least get an opinion from them if they thought it was capable of being modeled.  They might even have a PhD student they could hand it to.

http://www.swansea.ac.uk/engineering/civil/research/computationalfluiddynamics/

[knighty]

15kw = 62.5amps....

if you're never going to make that much... can't you just put it all behind a 60amp fuse and tell them that's your limit ?


even it's it's a D rated mcb so you have a bit of wiggle room with the generating

[noah]

Ted, I think that, given smooth clean pipes of known diameter etc the problem might be computable. But considering the unknowns (uncertain diameters,rusty,angle of join, exact length of each size of pipe, efficiency of WW) all of which could easily be 5/10% out I think even Deep Blue could only get it within wideish error bars. As the contested power range is only 6.6% any calculation with probability of error >6.6% is pointless. However I will give Swansea a try. At least if they agree that it is non-computable Ofgem will find that difficult to argue with.

Knighty. Ofgem will not accept anything as simple as that (I`ve tried). They insist that any changes have to be `robust` ie not easily circumvented as a change in MCB or output software would be.
Of course this is nonsensical as all FITs installs (and all electric meters) are easily fiddleable and the real disincentive is the threat of surprise inspection. So anything that you cant immediately change when they come knocking on the door should be acceptable.
However the truth is that Ofgem just doesnt have many (any?) inspectors to police FITs installations.

[brackwell]

Noah,

I have to say it looks like you brought this problem on yourself.  If the form for hydro is like the one for Pv  Then it is the MAX generator capacity that can be fed into the grid that matters.  For this you should have put the lower figure (or indeed any figure you like below the limit).  Nobodies interested in how big your plant could deliver only the max it can deliver to the grid.

My advice - scrap this application and make out a new one correctly completed.

Ken

[noah]

Hey thanks for the vote of confidence Brackwell!
Actually: I had already installed and accredited the 5.5kw unit when I decided to add the 10.5. At that time the (expected) FITs step for hydro was 10kw. I asked Ofgem if these two would be treated as seperate installs or if they would be amalgamated. I have their reply (by email) which clearly states that they would be classed as two seperate installs requiring two seperate accreditations. I then went ahead with the 10.5 (by which time they had increased step to 15kw) At this time (dec 09) the ruling was that installs after 1/4/10 would have to be MCS accredited- which, as any fule kno, was impossible for microhydro, so I was under a bit of time pressure.
I commissioned the 10.5kw unit and applied for accreditation in Feb `10. I heard nothing from Ofgem for approx 18 months and was then told that the two were in fact going to be treated as one! I pointed out the guidance they had given and so far the only relevant reply I`ve had is that `Ofgem does not have a remit to give advice`. No need to explore the Kafkaesque ramifications of that: this is now going through the treacly process of Ofgem official complaints.
So I was stuck with a system just 6% above the FITs step (which means a 10% reduction in FIT).
As it happens, the actual output of the total system is only 15kw because when both units are on the bigger one starves the smaller one a bit.
So I asked Ofgem to derate the entire system to 15kw. They agree that this is OK but demand `calculations` (while I think not understanding the idea of error margins being greater than the figure you are trying to prove).
And here we are.
My last email to Ofgem was to tell them that I considered the problem to be noncomputable within the necessary margins of error.
Let`s see what they say next.

[Iain]

Hi Noah

From your first post you have shown that in practice your output is limited but need it quantifying to a level that OFGEM will accept.

Then from Ted

I would've thought that an initial enquiry to the Computational Fluid Dynamics Dept at Swansea University College of Engineering might be worthwhile. At least get an opinion from them if they thought it was capable of being modeled.  They might even have a PhD student they could hand it to.

If it is too difficult to calculate could you use Ted's idea and ask the University to do a practical experiment on site covering all the variable parameters and having all the data logged to show that the system can only produce a maximum under all the variable parameters. If all this was logged as a practical trial by the university and they produced a report/conclusion I am sure it would carry more weight and I am sure the university would be able to gain a lot from it as well.

Iain

[noah]

Iain
Sledgehammer to a nut.
The idea of having to bring in a whole bunch of graduate students in order to satisfy a bit of bureacratic whinnying gifts far to much credence to said beareaucrats.

[Iain]

Hi Noah
It might just be what the University are looking for, a "real world" practical experience. Putting all that theory into practice!
Iain

[noah]

Iain
We`ll see. I`ve sent them an email.

[smegal]

I'd de-rate one of your generators!

My company could (not sure if we would but could, I don't know how it works) do you a letter but it would cost. Something to consider if you're really stuck.

[noah]

Smegal,
one of the conditions of derating is that it has to be `robust` ie not something that could be easily reversed by me. without actually rewinding a generator I don`t see how it would be possible. Even so I could replace the 5.5kw generator with a 4.5  and change the output fuse and reprogram the software in about an hour. They would not see this as a `robust` alternative.
Of course the stupid thing is that the whole process is unnecessary: the actual output is already limited to <15kw and cant be increased beyond this without major engineering.
The problem is that Ofgem seem to have a ruling that empirical evidence is not adequate and all claims must be backed up with measurement and calculations. Anyone who knows anything about waterpower will be familiar with the difficulties of estimating exact outputs when dealing with turbulent flows in less than pristine environments.
Its quite likely that in the end I or someone else will have to just fudge the figures to make it work. I don`t necessarily consider myself a paragon of honesty but I don`t like that sort of thing.