The set up

The set up

Friday, 9 September 2016

Rotor packing - the sequel

Early September and I'm well into the driest time of year.  In actual fact, there has been quite a bit of rain but at this time of year it does little to augment the spring flow which is the source for my Powerspout; I'm presently running on my second to smallest nozzle and generating 136 w into the grid; I've needed to install the reduced core (i.e. 18 pole) stator to manage this output, something which I was hoping rotor packing with the 42 pole stator would avoid.

Dropping down through my nozzle sizes in the past months has given plenty of scope to experiment with rotor packing at each flow level and collect data about its effects. I have written before of how it increases rpm and thereby keeps the pelton operating at nearer its 'sweet spot' speed; I thought this would make for better power output but reviewing all the data has cast doubt in my mind about such an assumption.

Below is the plot of watts output to grid vs dc operating voltage.  Remember I am using a WindyBoy inverter which does not use MPP tracking; it simply draws a current from the turbine which is determined by the dc operating voltage; the magnitude of that dc current is reflected in the ac watts output to grid (LH vertical axis); the dc operating voltage reflects the flow delivered to the pelton (horizontal axis);  the plot, unsurprisingly, shows a polynomial curve on which all the data points sit with remarkably little spread; what did surprise me was how tidy it all looked.

My surprise at its tidiness was because the data points were the result of very different operating states for the turbine; some were with rotor packing and some were not.

For each of the data points on the graph above, I also measured rpm; and for the data points arising from the lower flows, I used rotor packing to keep rpm up to above 900.
With rpm data superimposed on the above graph, using the RH vertical axis for rpm, this is the picture:

As can be seen, for those data points where rpm was kept above 900 by rotor packing, there seems to have been no obvious improvement in ac watts over the trend established by there being no packing. 

But perhaps I'm being unduly negative; perhaps without the rotor packing the polynomial curve would have been a straight line relationship between dc volts and ac watts, making for less output than I actually got at the low end of the plot.

What counts for me is that to the eye and the ear the turbine undoubtedly appears happier with rotor packing.  I will continue with it.

Thursday, 1 September 2016

Sun and water

The end of August sees the completion of the first full year of having both hydro and solar generation being harvested here where I live. In this brief post, I want to present the data.

The synergy of solar with hydro is well recognised: of benefiting from hydro in winter and solar in summer; so the pattern of yield for the two as seen in the graphs below comes as no surprise.

In the UK, the total amount of generation that can be contributed to the grid at one meter point is restricted and although my Powerspout could never generate at its maximum at a time of the year when the solar panels were also generating at their maximum, the sizing of the solar array was limited to keep the sum of the peak outputs of the two within the permitted total.

For this reason the array is less than the maximum normally allowed; it is a 3.42 kWp installation and its yield is reduced by being in a location which is not ideal, facing as it does east-south-east (S60degE), on a roof pitch which is rather flat (30deg).

Nevertheless it does the job nicely of keeping the energy generated each month in summer up to the winter peaks the Powerspout reaches.  Over a full year the hydro generates more, which considering its design rating is just 0.75 kW says much for how good very small hydros can be.

A finishing thought: energy from the sun is the source of both solar and hydro generation; were it not for the sun taking water as vapour from sea level up to the sky so it can drop on the hilltops as rain, not a hydro installation in the world could work.

A post script to my last blog post: I have had much interaction with NRW since writing about my 'grievances', all of it good and positive.  Having been decidedly critical in that post, I just want to put on record my thanks and appreciation to all those, from the member of the board downwards, who tolerated with good grace what I wrote and are looking into some of the points I raised. Diolch yn fawr.

Monday, 8 August 2016

Grievances with NRW.

In the past couple of weeks I've been having a dialogue with a very nice lady at NRW. NRW stands for Natural Resources Wales.  It is the body in Wales responsible for issuing and regulating licences for water abstraction.

In the UK, we call such a body a "quango", - an acronym for quasi autonomous non-governmental organisation.  A quango has power to set and enforce legislation. The disconcerting thing about the power possessed by a quango is that where such legislation is later shown to contain glaring anomalies amounting to abuses which arouse protest, yet can the quango close its ears and say that such abuses are in the nature of things so must be accepted without demur.

Ordinary people like myself, coming into contact with NRW for the purpose of getting an abstraction licence, may perceive these wrongs; may perceive that an injustice is being imposed; and this creates a feeling of resentment at being unfairly treated.  Yet the deafness of the organisation makes it impossible to get even a hearing, let alone redress.

The particular matter which has been the subject of my dialogue concerns the imposition of a charge for the water I abstract.  Water abstracted for the generation of electricity does not attract a charge. Neither does water abstracted for domestic use, so long as the volume is less than 20 m³ per day. Yet if these two abstractions come from the same place, the way NRW has written the rules makes it compulsory to 'aggregate' the two volumes and aggregating inevitably brings the total daily volume to greater than 20 m³. Such a volume now triggers a charge; in effect: two abstractions, each on its own free yet together being made not to be free !

There have been other injustices in NRW's self written rule book which I have drawn attention to before. Let me mention two again:

1. - in this third year of operating my Powerspout I am going to generate over 4000 kWh of energy.  The volume of water I have abstracted to generate this is calculated by applying a 'hydro-abstraction factor' (HAF). For my site this is 13  per kWh; To have generated 4000 kWh I will thus have abstracted in excess of 52,000 m³. This is more than the limit set by my licence (49,982 m³) and yet I have generated this number of kWh's, an exceptional number for me, only because it has been an exceptionally wet year;  the instantaneous flow abstracted and the daily volume abstracted, figures for both of which are also stipulated on the licence, have not been exceeded.  

The injustice here is that it is inconsistent for a licence to set both a daily limit and an annual limit; there is no knowing when one applies for a licence how many wet days there will be in future years, so making prediction of an annual limit impossible. All that should matter to NRW with its concern for harm to the watercourse is that the daily limit is not exceeded. It ought to matter not at all to them if a year happens to be so wet that water is plentiful enough to allow people like myself to generate an exceptional number of kWh's.

A subsidiary point to be made about the yearly volume, if indeed there has to be one, is that it is mathematically amateurish to stipulate a figure which purports to be more precise than the accuracy possible from the method used to calculate it.  My licence, instead of saying 49,982 m³ would better have said 50,000 m³, and better still from a mathematical standpoint, should have added an error allowance of, say, 10%, acknowledging the calculation method can sustain no greater accuracy than this. By allowing some measure of flexibility then at least licence holders would be saved the anxiety of overstepping their limit in occasional years.

2. - in describing the way to calculate one's HAF, NRW say that the component efficiencies of the different parts of the installation 
at maximum power
must be used.  To say this is unscientific and subtly over calculates the HAF by the effect of two linked factors: 

  • 'run of river' hydros in Wales will never operate at maximum power throughout a year
  • efficiency, at least for a pelton, is not very good at maximum power
It would be better to calculate the hydro abstraction factor either from the efficiency at the flow which predominates through a year (the mode flow value) or, and this would be being generous to the licence holder, at the flow where the installation is most efficient.

These points of grievance are highly specific.  They refer to arcane detail which is not for everyone. There is however another matter of grievance, which requires no knowledge of obscure detail, is relevant to all hydro owners and reaches to the deepest level. It has been the subject of a long running argument between NRW and the two organisations in the UK which represent owners of small hydro installations, the British Hydropower Association and the Micro-hydro Association. 

It is the argument about how abstraction for electricity generation should be treated; the proposition that abstraction for the generation of electricity should not be treated as abstraction for other purposes because the one permanently removes water from a watercourse whilst the other does not; that the principles, right and proper principles as they are which guide NRW in wanting to restrict and have control of the removal of water from Wales' water courses, need to be modified when applied to abstraction for electricity.

Unfortunately for hydro owners, the response of NRW so far has been characteristic: the organisation has been unwilling to engage on the issue.  In like manner I have had no real engagement on the particular grievances I have put forward. Such is the typical quango stance.

Who in an organisation like NRW are those responsible for the conduct of the organisation ?
Certainly it is not those like the lady I have been corresponding with or the two NRW field workers who paid me a visit two years ago, all of them open and approachable people but people who are necessarily constrained to work within the legislation that NRW has itself devised. What needs changing is the legislation itself.

The people at the top who sit on the board are the ones who carry the responsibility for the image the organisation conveys.  As it happens, I am familiar with a few of them ! One is a micro-hydro owner who lives near to me and whose installation I have visited. With two others I share the experience of having been a senior employee of the Welsh Health Service. 

Come on you board members ! - ensure NRW puts in place mechanisms for real consultation on matters of grievance concerning your legislation.

Why not have a board member who acts as an internal 'ombudsman', to whom grievances about your legislation can be addressed ? Your complaints procedure specifically excludes using the complaints route for legislative change.