The set up

The set up
5.46mm jet delivering 0.68 l/s to the pelton which is rotating at 900 rpm and generating 135 watts into the grid.

Friday, 14 November 2014

TIC, DNC, Abstraction and all that stuff.

For the first time, I now have the Powerspout operating at 'design flow', - at least it's the first time I've had any certainty the flow being delivered is the design flow: 3 lps. So for the first time too, I have reliable figures for those two parameters so loved by OFGEM: Total Installed Capacity (TIC) and Declared Net Capacity (DNC). OFGEM is the UK body giving accreditation for an installation to receive payment for the electricity it generates.

Just to set the record straight: DNC is TIC "less any electricity consumed by the generator".  So for a Powerspout the power taken by the inverter (see last post) has to be deducted from TIC to get DNC. Both of these figures need to be specified at the "highest capacity at which the generating station could be operated for a sustained period ... without causing damage to the generating station". I took that to mean at 'design flow'.

I may have taken it to be at design flow but in fact a Smart Drive alternator can put out in excess of 1kW for a sustained period and without being damaged, so there is nothing actually to stop me from delivering a flow in excess of 3 lps, when it's available, and getting more power.  That would've meant giving OFGEM a higher TIC and higher DNC.  So where do you draw a line in the sand ?

I opted to give values for TIC and DNC based on 3 lps because my abstraction licence limits me to that flow.  Which begs the question "why didn't you ask for a higher abstraction volume?" And the answer to that is another line in the sand: it seemed from the flow duration plot for my site to be the optimum peak flow when the pattern of flow over a full year is taken into consideration.

I relate all this to make the point that filling in all the forms to make an installation 'legal' is a headache.  Moreover what you put on one form, the Abstraction application, has a bearing on what you put on your OFGEM form to get accredited for Feed in Tariff payments.

To get back to real figures, below is the actual return I submitted to OFGEM last year for my FIT accreditation...



... and as you can see, I put 0.8 for TIC and 0.75 for DNC. These were, at the time, the best estimates I could come up with.  They were supported, as the extract above requires, by independent confirmation from Michael Lawley, the manufacturer of Powerspouts, who used the calculator tool on the Powerspout website to confirm my expected output.

But the thing is: it's very difficult to get the accuracy of the inputs to that calculator tool to be spot on; now I have real data available, I find the true TIC and DNC aren't what I submitted.  The DNC turns out to be 0.84 and the TIC 0.74.

Do these small differences matter ?: no ! - no one at OFGEM is going to be any the wiser that my submission figures were 5% out.  But the saga does draw attention to the fact that in completing these forms, what you enter on one, the abstraction application, has a bearing on what you should enter on the other: the FIT application. And deciding where 'the lines in the sand are to be drawn', I found to be a hard call.

Finally, if you're wondering what OFGEM's definition of DNC is in full, as hyperlinked in the above extract, this is it:





Confused ? - so was I, - and to a large extent, I still am.  The forms are, truly, a headache.
 

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