Grease ...the story !

End of the month again and not a bad month generation-wise: 437 kWh clocked up which, for a month with only 28 days in it, isn't too bad. It makes the capacity factor for the month 87% whereas the corresponding month last year saw 100%.  Ah well, you can't have a bonanza February every year !

End of the month is greasing time and this morning, just after 8am, I gave the Powerspout its usual 2 squeezes of the grease gun which delivers a meagre 0.7 mls ( 0.4g) of grease.

In its first life, the shaft and bearing housing of a Powerspout did service in a Whirlpool washing machine.  In such an application, the bearings didn't get the same 24/7 operational use so there was no need to re-grease them. When they failed, that was the signal for the washing machine to go to the scrap heap. But, if it was a lucky washing machine, its bearing housing, shaft and motor might get salvaged for a second life in a Powerspout.

In this second life, re-greasing becomes essential, not only because of the continuous use but because of the damp environment the bearings find themselves in.  So a greasing point has been added to the bearing housing which connects with a grease nipple on the turbine casing.

The point of relating all this is that when grease is pumped in, it has to envelop the rotating shaft and to travel left and right along the shaft to reach the bearings at each end.  New grease contributes significant drag on the shaft which can be seen as a reduction in power output immediately after greasing. After a few hours, the effect disappears. 

Here is the record of power out to the grid immediately after my greasing at 8am this morning, showing a drop of about 5 w.

Another point arising from this arrangement of delivering grease centrally between the two bearings is that significant hydraulic pressure can be produced by a grease gun especially if it is operated forcefully.  The dust shields, whether metal or rubber, are not designed to have grease forced against them and could conceivably be deformed by the pressure achieved.  (This paragraph was amended 14/4/2016)

To prevent this, I operate the grease gun very slowly. Also, I have removed the inner dust shields of the two bearings so they are more open to let grease enter the ball race, pass through it and out the other side.  It is quite easy to remove the shield by gently bending inward the tabs of the shield where it locates in a groove in the outer race.

So that's Grease...the story !  I don't think it's likely to be shown in a cinema near you anytime soon !

The usefulness of a head level sensor

Over the past ten days we've had a fair amount of rain and I've been gradually "upping" the nozzles to make the most of the increasing flow as it becomes available.

This morning at nine o'clock, I "upped" from a nozzle combination which delivered 2.47 lps to one delivering 2.78 lps, - but it was too big a step to take.  By midday, the header tank had stopped overflowing, the 'spare' flow falling over the quarry face below my catchment site had reduced to a trickle: 

...the online trace of live power showed a falling level of output as the water level in the tank fell:

...and the level sensor sited in the connection pillar by the turbine registered that the tank was 150mm below being full:

I relate all this to illustrate two things:

1. How much more useful it is having a head sensor at the top of the penstock compared with just having a pressure gauge at the bottom. Powerspout provide such a gauge in the kit of parts which comes with each turbine and it does have its uses.  But the pressure gauge for my site was calibrated to a full scale reading of 750 kPa, which is about 76 metres head of water.  There is no way it could have conveyed the relatively miniscule drop in pressure described in the above situation.

The head sensor is very simple: it's powered by three 9v batteries, which need replacing at yearly intervals.  It's connected to a pressure transducer at the top of the penstock, by a 3 core, 1.5 mm², SWA* cable running alongside the penstock. The pressure transducer sits in a vertical pipe, where the water is still and not flowing, with its reference mark exactly 1000 mm below the water level when the tank is full.

This vertical pipe also acts, incidentally, as a vent to let air out of the pipeline when filling it, and air into the pipeline when emptying it.

The sensor was provided by SCS Ltd, a company making turbine control and grid connection equipment for micro-hydros bigger than Powerspout size.  It's a manually operated version of the sensor they use to regulate the flow to a turbine by servo control of its inlet valve.

2. How handy it is to have a good amount of water storage: despite 3 hours operation during which flow out from the tank has exceeded flow in, the tank water level has dropped only 150mm and the turbine is happily still putting 714 W into the grid.  

From the power trace above, it looks as if the water level may have stopped dropping: the trace from 11.30 onwards seems to have levelled out, meaning inflow and outflow may have come into equilibrium.

All this being so, I am not going to rush to reverse the nozzle change I made this morning.  The weather forecast is for more rain, albeit not very much, and my hope is that the yield will pick up sufficiently for me to keep operating with the present nozzle combination.

Perhaps this account will convey something more than I initially intended, which was just to say something about the level sensor.  It will, doubtless, also convey that a micro hydro needs supervision, at least on days like today !

* steel wire armoured

NRW Inspection visit

This week, Natural Resources Wales (NRW), the organisation responsible for regulating water abstraction, paid me a visit to check that I was keeping to the terms of the licence they issued.

 For an organisation which has been deaf to the protestations of the UK Microhydro Association and the British Hydro Power Association that its licensing procedure is inappropriate for hydro installations, I was pleasantly surprised that the two NRW people who came were willing to listen to the arguments I wanted to put forward.

I had prepared for them coming.  I wanted to get across three things:
1. calculating abstraction volumes using the efficiency of the system at maximum power is wrong headed.
2. stipulating an annual maximum volume of abstraction is meaningless if the licence specifies the maximum instantaneous flow which can be taken.
3. the wording of their licence is internally inconsistent by stipulating in one section the maximum volumes to be extracted, yet in another section giving these same volumes as being minimum volumes.

To make the point about efficiency I gave them this graph which shows how efficiency falls off toward the upper end of power output.  It is the same plot as I've posted before but in a different format and with additional data points added:

To make the point about having to adhere to an annual maximum volume, I pointed out that with the volume I've abstracted up to the end of January being 39,727 m³ and with two months still to go before the end of their "abstraction year" on March 31st, I was almost certainly going to breach the annual limit set at 49,982 m³, despite having kept within the limit of instantaneous flow set at 3 litres per sec.

Will anything come of it all ? - I'm not holding my breath, but on the day of the visit at least, it was nice to be reminded that there are, working within this bureaucratic quango, intelligent, approachable, rational, human beings.

Jet propulsion, - for the mathematically (and musically) minded.

When the turbine was off its plinth last summer for its annual overhaul, I took the opportunity to photograph one of the jets in operation, - something which wouldn't be possible in most Powerspout installations and something you don't normally get to see.  Here's what it looked like:

The distance the jet travelled was 15 metres.

Quite early after emerging from the orifice the jet can be seen to begin breaking up, probably due to a tiny irregularity in the plastic of the nozzle at the orifice.  Better transfer of power to the pelton runner would be achieved if the jet remained more compact. Tidy orifices are important.

The net head recorded on the test gauge is 53.3 metres, and with the orifice diameter being 7.46 mm, the calculated flow should be 1.28 litres per second. 

The formula for calculating this is: Q (m³/s) = CD x Anoz(m²) x √ (2g x Hn),  where CD is 0.91

Also by calculation, the velocity of the water at the orifice is 31.6 metres per second, which is 70.6 miles per hour !  The formula is vjet = Cv x √(2g x Hn), where Cv is 0.98

To get optimum energy transfer to the pelton wheel, the cups of the wheel should be moving away from the jet at a velocity just a little bit less than half (0.46 to be exact) of the velocity of the jet.  This wheel velocity needs to be measured at the circumference of an imaginary circle defined by where the jets strike the runner, - a circle which has a diameter, in the case of a Powerspout pelton, of 220 mm, - what is often referred to as the pcd or "pitch circle diameter".  Putting all this together, it can be calculated that the optimum speed at which my runner should turn is 1260 rpm, or 21 revs per second.

This speed of revolution is relevant because it defines the frequency of the sound emanating from a turbine, at least from the hydraulic side but not the SmartDrive side, which tends to have a higher pitched sound. 

The frequency of the sound can be calculated knowing there are 20 cups on a Powerspout runner: each jet will therefore 'see' 20 x 21 cups passing it each second. The resulting sound should have a frequency of 20 x 21 ie 420 Hz, - not far off Standard Concert pitch A, 440 Hz, the note used for tuning musical instruments to in an orchestra.  See what you think from the video clip below; I think it's turning more slowly than 1260 rpm; you can 'tune in' your ear here.

I have found it really interesting getting to grips with the maths which underpins the operation of a micro hydro.  Jeremy Thake's book on the subject is easy to read. I recommend it.

Upkeep

How demanding is it having a Powerspout and keeping it operational to maximum advantage ? - that's what I'm setting out to answer in this post. Every site is different though, and others may have very different levels of upkeep: I'd be interested to hear.

1. Trash clearing is seasonal: every day when leaves are falling, but once per day is always enough.  In times of strong winds, clearance is also needed daily because of the large fall of twigs and branches that rain down onto my abstraction site. For the rest of the time, weekly clearing is enough, although I often find myself up there for other reasons and brush off the screen anyway:

As my scheme has a good head but low flow, the nozzles have small orifices: diameters of between 3.64 and 8.90 mm.  Being so small, it would be easy for them to get blocked so having a screen taking out all the trash before the water drops into the header tank is crucial. The screen is of perforated stainless steel with 3mm holes at 5mm centres, and its value has been proved in that I have only ever had one nozzle blockage from trash.

Whilst only having had one blockage from trash, I used to have a more frequent problem with blockage from another cause: toads finding their way into the tank and thence down the penstock. The old galvanised sheets now covering the tank have put an end to that, which is probably of equal relief to both me and the toads.

2. Greasing is every ~500 hours, which is about every three weeks.  I have opted to retain the manual method using a grease gun, rather than going for the self-dispensing GreaseMax canisters recommended by EcoInnovation because I fear too much grease can be as bad as too little.  The canisters contain 125 mls grease which is dispensed over 12 months.  My turbine only runs for 9 months each year and the greasing schedule I work to only delivers 20 mls in that time.

3. Nozzle changes have been necessary 16 times between Nov 5th 2014, when generation started for this year, and today, 7th Feb 2015. They are necessary in order to keep the flow delivered to the turbine matched to the flow available from the spring source.
  
Each change takes about 10 mins and rather than being a chore, is something I enjoy.  In this second "water year", the shortest time between changes has been 1 day and the longest 23 days.  Last year I had a spell at full flow which lasted 75 days which is the record so far.  It all depends on what the rainfall is.  Designing your installation for good access does make this job very much easier if it's something you're likely to have to do as often as I do.

4. General oversight is something which goes on all the time: a water turbine is NOT a generating source like pv panels which can be said to be "fit and forget".  Having said that,  there has not been one instance of malfunction from my turbine apart from some initial teething problems after commissioning over a year ago: it just keeps on going.  In the 3+ months which have been completed in this second 'water year' of its operation,  it has not ceased generating once, other than for nozzle changes.

Occasionally I notice from the continuous record of power output to the grid that the inverter has disconnected from the grid on account of a transient grid failure or voltage fluctuation. When this happens, the Powerspout copes with it seamlessly by diverting output to its inboard dump element until the inverter has satisfied itself that the grid parameters are back to being OK again.

Oversight is helped in my situation by the turbine being sited close to the track to our house.  Every time we come and go, it is easy to glance at it to check that all is well.  If the season is a time when water availability is changing, whilst passing a check can also be made on the fullness of the header tank using the display housed in the pillar by the turbine. More about that in a future post.

If we go away for a few days, I now have enough confidence in everything to leave it running.  Sometimes this will mean putting in smaller nozzles before going away to be sure the system will not drain down while I'm away.  The 'on-line visibility' of its power output also means I can give myself peace of mind by checking on its wellbeing when I'm away.

In summary, for someone who needs to be around their property most of the time, a Powerspout is very little extra work.  In truth, I keep a closer eye on mine than is needful: I walk with the dog down to the turbine last thing every night, - mostly because it is so nice to hear it humming away to itself !

Small fish: big pond.

I read something interesting today:  

"The UK has topped 3GW of renewable capacity under the feed-in tariffs scheme, according to Ofgem. The scheme started in 2010 and there have to date been 568,612 accredited projects, almost double the amount forecast by DECC*. The figure breaks down as 561,185 for solar PV, 6,256 for wind, 546 for hydro, 490 for microchip and 135 for anaerobic digestion."

So, I'm one of the 546 FIT accredited hydro sites ... and I bet I'm the smallest.  

With January ended, I've clocked up the most productive month ever: 524 kWh.  This represents a capacity factor of 94%, meaning the very most I could have generated would have been 558 kWh.

A tiny drop in the ocean of renewables generation to be sure, but still worthwhile.

* Department of Energy and Climate Change