End of 2014 reckoning

Here's something to think about:

Take two sites: one a hydro site, one a solar photo-voltaic;  both are domestic scale installations: the hydro is 0.75 kW peak, the solar 4.0 kW peak; both are located in the same part of the UK, 50 km apart; both have been monitored throughout 2014 using Wattson technology which made it possible to extract the same data from each installation.

Question: which did better in 2014?

Answer: it depends how you look at it:

1. In terms of kWh yield: the solar installation generated 4,441 kWh against the hydro's 3,649* kWh, the patterns of yield for the two sites being as follows:

2. In terms of how much of the generated energy was used on site - hydro: 2,920 kWh, solar: 2,014 kWh. These figures as proportions of total energy generated are as follows:

3. In terms of revenue from FIT and export tariff, assuming the following:

• solar export deemed at 50% of total generated, hydro at 75% 
• using the RPI uprated solar tariffs effective from 1 April 2014 and giving figures for two 'eligibility dates' for solar: 
• eligible in FIT year 1/2 (2010/11): FIT rate 48.07 p/kWh; Export rate 3.39 p/kWh
• eligible in FIT year 4 (2013/14): FIT rate 15.3 p/kWh; Export rate 4.77 p/kWh
• using RPI uprated hydro tariffs effective 1 April 2014 for an installation with an 'eligibility date' in July 2013: FIT rate 22.23 p/kWh; Export rate 4.77 p/kWh

- the solar was worth £2,210 (FIT year 1/2) or £785 (FIT year 4)
- the hydro was worth £942*

4. In terms of the saving on expenditure arising from energy not purchased from the grid because renewable energy was used 'in house', with the following assumption: 

• price per unit, inc VAT @ 5%, 15.13 p / kWh (SWALEC direct debit and paperless billing)

- the solar was worth £305
- the hydro was worth £442*

Putting all this together, the solar appears to pay better if you had installed it in 2010/11 at the beneficial FIT rates then available: £2,515 against the hydro's worth of £1,384.

But if you missed the generous early FIT rates and installed your solar in 2013, then the income in 2014 was £1,090, against the same £1,384 for the hydro.

This analysis would not be complete without mentioning the capital expenditure involved for the different schemes which, in the case of solar, depended on when it was done. The cost of installing a 4kWp solar in FIT year 1 (2010) was about twice what it was in FIT year 4 (2013).  Since my hydro was installed in 2013 and cost about the same as a 4 kWp solar installed in the same year (see previous post), the fairest comparison is between the revenue figures for a 2013 installation date: hydro £1,384, solar £1,090.

So the answer to the question posed involves a lot of variables and many complexities, but the bottom line is that my 0.75 kWp hydro compares favourably with a 4 kWp solar PV.

Hydros might be more noisy and they might be less "fit and forget" than solar, but finances aside, to me at least, they're much more fun.

*regular readers may notice these figures are different to figures given elsewhere in this blog (3,649 kWh vs 3,672 kWh, £942 vs £996, and £442 vs £430).  The explanation is twofold: 'the year' under consideration is different: the 2013/14 'water year' vs the 2014 calendar year;  and the utility tariff I have used is different: standard unit rate vs Economy 7 rate.

Cost and return

When it comes to renewable energy schemes, I find people are usually coy about the costs and rosy about the returns.  So in this post I have tried to set out as accurately as I can the bare facts relating to my set up.

Of course, this turns out to be not as simple as it seems: having the time and inclination to do the drawings for the planning application saved on paying someone else to do it; having a tracked excavator saved hiring one for digging the pit below the turbine; materials were sourced at auctions at less than true cost where possible, ... and so on.  So even with the firm intention of disclosing everything, circumstances particular to me will mean my costs will not necessarily be indicative for someone else.

Stating what the financial returns have been is a simpler matter than dealing with the costs, so we'll start with those: - overall it has worked out that instead of me paying Swalec, our electric utility company, £1,022,  which was the all inclusive bill for 2013 (daily standing charge and tax included), in 2014, with about the same total energy consumption and the same tariff charges, I paid them £592.  So that was a saving of £430.

 On top of that saving, they paid me £996 in Feed in Tariff and Export tariff for the energy I generated.  

So, to give two different ways of looking at these figures: 

• I had all my electricity for 2014 free and additionally I'm £404 in credit.  
• the worth of the turbine in 2014 was the sum of the saving from grid energy not purchased (£430) plus the revenue from tariffs (£996), ie £1,426.

But 2014 was a wet year and therefore may prove to have been more productive than the norm. Only time will tell.

Turning now to costs: below is a record of the expenditure incurred as the project was implemented during 2012 and 2013.  From the outset, I had wanted to see exactly how much the whole project ended up costing and with that intention, I kept a pathologically meticulous record of everything spent.

A word about VAT:  I had hoped that VAT would be chargeable at 5% and part of the reason for keeping such a meticulous record was to aid reclaiming the difference from the point-of-sale rate of 20%.  However, after a tedious correspondence, HMRC¹ eventually ruled that: ...since micro-hydros no longer came under the Micro Certification Scheme (MCS), under which they had qualified for a 5% rate, and were moved from that scheme to the ROOFIT² scheme in Dec 2012, - a move which opened up the way for people (like myself) who were not MCS accredited to do the installation, ... the 5% rate could only apply if an accredited installer did the installation.  Does that make sense ? - not to me, but what can one do ?

The costs given below therefore include VAT at 20%, where it was payable, and they also include the cost of carriage to bring everything on site.  In the case of the Powerspout turbine and spares, the cost also includes UK import duty.

Two grand totals are given at the bottom:

• 'All in' cost for installation as completed, with spares:          £10,387.96
• 'All in' cost excluding:  
• non-essentials (tank water level sensor, and spares) 
• re-saleable penstock construction equipment:              £7,125.97

¹ HMRC Her Majesties Revenue and Customs

² ROOFIT scheme : Renewables Obligation Order Feed in Tariff scheme

It's a J shaped curve.

The aim of this post is to say a bit more about the efficiency of my installation: in particular how the efficiency changes depending upon the flow delivered to the pelton.

In two earlier posts, mention has already been made that overall efficiency turned out to be 50% when water delivered to the pelton was 2.7 lps, and the efficiency dropped from this figure when flow was less than 2.7 lps, mostly due to inefficiencies attributable to the inverter.

Here, I want to show the relationship between efficiency and flow over the full range of flows I have used on my turbine, from under 1lps to the design flow of 3 lps.

Instead of using a numerical value for efficiency, eg 0.5 or 50%, as is usual, I have used instead a unit which is a direct indicator of overall efficiency: the volume of water required to generate one kWh.  This has the unit m³/kWh and is a measurement which I record anyway for the paper return I have to make yearly to Natural Resources Wales (NRW) to tell them how much water I've abstracted.  It's what they call the 'hydro abstraction factor' (HAF) and permits calculation of the volume abstracted simply by multiplying it by the number of kWh's generated.

It is a factor which is easily measured with a fair degree of accuracy: 

• flow rate from the sizes of the nozzles and the net head
• kWh's from the Elster generation meter (reads to 0.1 kWh)
• time from a digital, radio controlled clock with readings taken over a minimum of 24 hrs.

So here is the graph showing the relationship between flow and m³/kWh:

As can be seen, it turns out to be a J shaped curve with optimum efficiency occurring when flow delivered is just under 2.5 lps.

Why should the curve be shaped like this ?  The explanation for the fall in efficiency at flows below 2.5 lps, to the left side of the curve, has already been alluded to in earlier posts: factors intrinsic to the inverter and, at the lowest flows where system voltage rises towards 380 v dc, the onset of power dumping to the heater element within the turbine, which is triggered at that voltage.

As for the fall in efficiency on the right side of the curve with flows higher than the optimal 2.5 lps, the most likely explanation is the 'drag' imposed on the pelton runner from the spray created in the turbine casing by the extra water, - something the text books call 'windage'.

Does any of this have any practical application ? - well yes, it does:  NRW instruct that in working out one's abstraction return, the 'hydro abstraction factor' at Pmax must be used, ie at maximum power output.  For my installation, as can be seen from the plot, this would be 14.5 m³/kWh.  But the optimum point, which is the point on the graph where the installation will be operating for most of each 'water year', the HAF is nearer to 13.5 m³/kWh.

... and that is the figure I'll be using, rounded down to 13 m³/kWh, so as to be sure of keeping my abstraction return for the year as low as possible and within the limit imposed by my licence (49,982 m³).

49,982 m³  ! - it does make you wonder if the people who issue these licences stating such ridiculously specific volumes understand the limitations of the means which will be used to measure said volume.

Testing the system.

I've always wanted to know what would happen to the turbine and its electrical output if the header tank were to drain down to empty. A few days ago I had the opportunity to find out.

After the wetness of mid November, things have turned dry again, so I was in the situation of still having the largest nozzles in the turbine, delivering the design flow of 3 lps, with a supply of water which was slowly diminishing.

Inevitably, a time came when water inflow to the tank fell below outflow down the penstock to the turbine, and instead of overflowing, as is the normal operating condition, the tank gradually began to empty.

The dimensions of the tank are 2.74 x 1.52 x 1.37 metres but since the bottom 83mm cannot be accessed, the useable volume is 5.3 m³.  With this generous volume of reserve, and only a small difference between inflow and outflow rates, it actually takes several hours, more than 12 on this occasion, for the tank to drain down. Somewhat inconveniently this meant all the action was set to happen after dark.

Here is an aerial picture (actually taken from up a tree) of the header tank and the arrangement for gathering water into it:

And here is the record of power output from the inverter into the grid over the period when the tank was emptying.  The record was captured using Wattson power monitoring and the data downloaded to my computer using the Holmes software that Energeno provide free for this purpose:

What did I learn from it all ?  The most useful lesson was that the system is resilient to such an event: nothing occurred which could foreseeably damage the key components of the system, namely: turbine, pma alternator and inverter.

If anything, the system 'fails safely' because the dc voltage falls to a lower operating level than normal (in this event it was 265 v dc at its lowest) because with the lower 'head' created in the penstock, turbine rpm will have decreased marginally.  Against this effect, there will have been a counter tendency to raise voltage created by the inverter lowering the load it places on the pma.  That the overall result was a drop was interesting.  It was not obvious by observation and listening that the turbine rpm was very different from usual.

So, all in all, an exercise which was worth doing even if it did give me a sleepless night !

More paper work !

At the end of each month I need to remember to keep my records up-to-date.  

This November has been a bonanza month for generation, especially considering it was only from Nov 5th that there was sufficient flow to generate anything at all.  By the end of the month, 393.7 kWh will have been clocked up, and the capacity factor for the month will be a very presentable 0.73.

I need to remember because a return stating the volume of water I've abstracted has to be sent to Natural Resources Wales (NRW).  NRW like the year to be broken down into individual months, and you have to give the volume abstracted in each month. The return has to be sent in within 28 days after 31st March but fortunately they post the form to you as a reminder.

For my scheme, to generate each kWh requires 13 m³ of water;  this is a figure the NRW call the Hydro Abstraction Factor and they tell you how to calculate it for your scheme.  The inputs to the calculation, which will vary from site to site, are the 'water-to-wire' efficiency and the head of the scheme.

Here is the spreadsheet I keep of monthly abstraction so everything is to hand at the end of March to complete the annual return:

So that was one bit of paperwork I had to remember to do.  The other was applying for payment for the kWh's generated in the past 3 months.  Since the turbine doesn't operate for most of that quarter, for lack of water, a November claim is the lowest of the year: just £71 on this occasion.

Claiming feed-in-tariff is a much more straightforward business. I opted for a contract with Scottish and Southern Electricity (SSE) simply because they're the company we purchase power from and it seemed to make sense to stick with them.  Submitting a generation-meter reading on-line is simplicity itself at the SSE webpage. You immediately get email confirmation of your claim being processed and payment comes through direct to your bank account, - somewhat unusually on this occasion, within 48 hrs.

Co-incidently, I had a letter from SSE today telling me they're in the process of updating their FIT payment system.  When completed, I'll be assigned a new date in each quarter on which to submit my FIT claim and more detail will be provided about how it is calculated.  Additionally, their man who comes to read the meter will, in future, read both consumption and generation meters at the same visit.

So the take-home message is: in the UK at least, there is a fair amount of bureaucracy involved in operating even a small hydro installation, but like a tax return, so long as you keep on top of all the figures and the deadlines, it isn't burdensome. 

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 0.92kW and the TIC 1.1 kW.*

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.

* figures amended April 2020 with knowledge gained over the 6 years since original post was written.
 

It's just Hinkley B and me now !

What an exceptional week: from scarcely enough flow to more than enough to meet peak generation.  So with all the energy I'm exporting, it's now just me and the nuclear boys keeping the grid from collapsing !

Going through four step-ups in generation in so short a time has minded me to take the four photos below of the meters monitoring the dc output of the SmartDrive, to emphasise two points made in an earlier post:

1.  the pv inverter (PVI) is not very efficient, especially at lower power levels but gets better as power increases
2. the dc system voltage falls as power output increases, and eventually it comes down to within the range  (100 ~ 320v dc) at which the MPPT function of the inverter can operate.

Just nice to see it so clearly illustrated.

Going with the flow

Today has been a good day: the increasing flow available, now up to about 1.75 lps, has meant I've needed to put a bigger nozzle in.  I kept the same one on the bottom and only changed the top one from ∅ 3.64 mm to ∅ 4.96 mm.  An early rule I learnt was only to change one nozzle at a time, - more drastic action usually led to the header tank emptying.

Doing this lifted flow delivered to the pelton from 1.48 to 1.74 lps, and power into the grid from 343 to 421 W.

Small hands are essential and good access to the front of the turbine is helpful.

Off with the glazing

The nozzle to be put in

Nozzle retainer spanner

It's a tight fit getting to the top nozzle

Note the cloth to stop anything dropping into the tailrace

There is space only in the bottom corners to remove a nozzle

The "whole arm in" technique to screw on the nozzle retainer

I use 9 different nozzles to give me flows from 1.18 to 3.43 lps

...and best of all: 421 W generated, thus exceeding usage by 8W

Happiness is...

... the start of a new generating year !  11 am yesterday saw all systems go, and so far everything is performing exactly as it should, right down to the in-house monitoring and on-line visibility of live-power (see link to right).

Now, all that remains is to get the capacity factor for the 2014 / 15 "water year" above the 59% recorded for last year.