Large steps in small hydro21 July 2006
The 18th Hidroenergia conference took place in Crieff, Scotland, UK, on 8-9 June. The biennial European event continued its trend for interesting and diverse papers and presentations on the topic of small hydro power, writes Jon Last
Set in the extravagant Crieff Hydro hotel in the beautiful Perthshire region of Scotland, the country that is the main source of the UK’s hydro power (160 sites, 120 of them small hydro), the Hidroenergia 2006 conference was another memorable entry to the series of symposiums that began back in 1989 in Madrid, Spain. Papers presented at the conference – which was organised by the British Hydropower Association (BHA) and the European Small Hydropower Association (esha) – were separated into three categories, and delivered in sessions accordingly: Policy & New Opportunities; Environmental & Planning; and Engineering Solutions. These sessions looked at the key issues affecting small hydro developers today – and the following paragraphs take a look at a paper from each.
Policy and new opportunities
‘Community Hydropower In Somerset and Dorset – Mill Owners Working Together’ by Keith Weaton-Green of South Somerset District Council is the tale of a ‘trail blazing’ mini hydro project in the southwest of England, UK, where owners have worked together to create a small hydro network across the region’s historic mills.
In 2001, Weaton-Green, the environmental projects officer for the council, had the dilemma of trying to appease a community that was keen to embrace renewable energy (required by the council’s renewable energy objectives) but had shown disdain for the ‘obvious’ choice, wind power. As a result, Weaton-Green began investigating the idea of developing small-scale hydro power. He decided the most straightforward way of producing this new energy would be to consult owners of the Somerset region’s several mills, and see if they would develop hydroelectricity at their sites. The general consensus was that they would, provided they were supported both financially and technically.
A first meeting was set up at Gants mill, with mill owners informed about the process of getting abstraction licences from the Environmental Agency; the availability of feasibility studies from consultants Hydrogeneration; and how the council would provide its own administrative support. This satisfied a number of candidates, and 12 mill owners agreed to put £100 (US$184) each towards feasibility studies at their own mills, with the council matching that amount again.
Since then, the organisation dubbed the Somerset Mills Group has flourished. It meets every six weeks at a rotation of mills, has received grants from central government and an electrical supply company has installed turbines at seven of the sites – with the remaining five locations set to be equipped by the end of 2007.
The small-scale nature of the operation means that even with grant funding it has been difficult to achieve a return on the mill owners’ investment of less than eight years. Similarly, in this size project, crossflow turbines have proved to be the best value equipment; a more efficient Kaplan model would doubtless put the sites beyond financial viability. But equipment choices vary across the mills – in fact, at one site, a low cost Vietnamese fixed flow propeller turbine has been used; at another, the mill owner has designed and built his own 10kW double regulated Kaplan turbine and cleared the silt from 200m of clogged, brick lined, underground leat by hand. The complete line-up of turbine types at the seven sites is as follows: Vietnamese propeller (producing 2kW); Valley H crossflow (3.7kW); Ossberger crossflow (3.7kW); plastic Francis + Armfield (1.6kW+); Valley H crossflow (8.2kW); Valley H crossflow (12kW); double regulated Kaplan (10kW).
The scheme in Somerset has been successful and well-publicised, and has left something of a legacy – its mill owner/civil society partnership model has inspired similar groups to form across the UK.
One such group is the Stour and Vale Hydropower Group, based on the Stour catchment in Dorset, a potentially lucrative area geographically adjacent to the south Somerset group. The spirit of openness and communication has transferred to this newer group, and personal contact is made between them, resulting in fast progress being made. The Stour and Vale set has been granted similar support from its own council, the North Dorset District, and has received a healthy £30,000 (US$55,600) in grants to date. Following intense lobbying, the group has attracted the interest of a major electricity supply company, whose board of directors is currently discussing a package for site owners that will give them returns proportionate to their investment – a financial model that promises a productive future. Feasibility studies for most of the viable Stour sites are now complete and detailed design and abstraction licence negotiation is underway for the first tranche of sites for development.
Further small-scale hydro power developments are emerging in the south and west of England, in areas such as Mendip, West Dorset, Wiltshire, Dartmoor, Exmoor, Kent and South London. It seems that the success in Somerset has lead to an endowment of new hydro in the UK – an example of what can happen when people work together.
Environment and planning
This section bought with it a paper titled ‘Rivers Exempt From Damming – Case Study of Lowlands’, by Petras Punys of the Lithuanian Hydropower Association (lha). This piece chronicled a situation that occurred recently in Lithuania when a law was introduced that actively subdued hydro power development in the country, despite the nation’s strong potential, and a subsequent study on two of its largest rivers to investigate the consequences of this dam prohibition.
Lithuania is located in Europe, sandwiched between Poland, Belarus and Latvia. An amendment was made to the country’s national Water Law in 2004, producing a subsequent act that made it illegal to construct a dam on any of its largest rivers, along with a very high number of medium and small watercourses. The new law decided that dams would affect the rivers ‘from an ecological and cultural point of view.’ This naturally decreased Lithuania’s economically feasible potential of small hydro power, and basically eliminated the potential for large hydro (classified as more than 10MW).
This, the paper infers, comes as decidedly odd considering the government’s attitude a mere two years earlier. Lithuanian renewable energy policy is consistent with the EU RES-E relevant policy documents, and fosters the use of hydro power. The National Energy strategy of 2002 emphasised the use of the largest rivers of the country – Nemunas and Neris – for hydro power purposes. Furthermore, the government’s ‘master plan’ for the country’s development is to further modernise the main inland waterway on the lower Nemunas (just downstream of Kaunas, the second largest city in Lithuania), as well as constructing a new waterway on the lower Neris river, between Kaunas and Jonava, including the establishment of a river port. Banning the construction of dams – a list of 169 ‘forbidden rivers’ was compiled – undermines this strategy.
As a reaction, the LHA commissioned a study of those two largest rivers, the Nemunas and Neris.
Nemunas river is the largest river in Lithuania, flowing through Kaunas city and discharging to Curonian bay (the Baltic sea). It has a roughly 100,000m2 catchment with mean flow of 630m3/sec, and currently has only one hydro power plant operating, producing 100MW.
The concern for the LHA study was how to improve the technical conditions of the waterway on the Nemunas. To do this, the lower part of the river was subject to a feasibility study, one of the main aims of which was to determine the cost effective means for providing sufficient depth. All through the investigation, as the consultant involved carried out studies including river bed and valley digital terrain modelling, it became clear that building dams on the river would certainly benefit the waterway and make it more commercially attractive.
A range of possible depths for the navigation fairway were considered: 1.5m (zero option); 2m; 2.5m; and 3m. It was concluded that a more significant depth was required: at least 3m. This level could be assured by building low head dams. In fact, the paper says that many advantages of damming were taken into account: multipurpose utilisation of water resources including power generation, the opportunities to develop recreational activities, improvement of the landscape surrounding the river, the status of which is currently poor, and so on. But, of course, the new Water Act forbids the construction of any such structures.
The second LHA study was of the second largest river in Lithuania – the Neris river’s catchment area and mean flow are 24,942km2 and 179m3/sec respectively. The study of this river was more focused on how to use it to its best potential; its water resources are not being as intensively used for economic or recreational purposes as they could be. The list of advantages of using dams to regulate the river and its depths include: protecting the Neris’ wide fish population; the regulation of depth to allow water tourism (such as navigation by cruise ships) in the three short summer months of the summer tourist season; prospects for allowing recreational fishing; developing drinking water supply through reservoirs; and flood control. But since dams are not permitted on the Neris, these opportunities are going to waste.
All this is before generating hydroelectricity has been mentioned – a factor which, the paper says, could go some way towards justifying any large costs. Naturally, the LHA’s reaction to the 2004 Water Act seems to be one of frustration, and Punys is confident in his paper that if the national environmental legislation is reviewed then it would find that building dams does not necessarily have to hinder the country’s economic and social welfare – in fact it may be found that quite the opposite will be true.
‘Vasocompact – A European Project For the Development of a Commercial Concept for Variable Speed Operation of Submersible Compact Turbines’ is a many-authored paper from the Engineering Solutions section of the event. It is written by Jochen Bard (from the Institute for Solar Energy Supply Technology, Germany); Heikki Pirttiniemi (Waterpumps Oy, Finland); Prof. Dr. Eberhard Goede (Institute of Fluid Mechanics and Hydraulic Machinery, University of Stuttgart, Germany); Albin Mueller (Elmotec Antriebstechnik AG, Switzerland); Dr. Drona Upadhyay (IT Power, UK); and Martin Rothert (SMA Technologie AG, Germany).
The project, developed between 2001-2005, was to design mechanically unregulated submersible turbines operating at a variable speed. It was based on an existing turbine concept, modified using a permanent magnet synchronous generator (PMSG) directly coupled on the runner shaft and a frequency converter (FC) for variable speed operation. After a new runner was designed using computational fluid dynamics (CFD) and tested in the hydraulic test rig, Tirva hydro power plant in Finland played host to a 50kW field test version of the new turbine concept, which was developed manufactured and tested at the facility.
The paper reports that variable speed operation in small hydro power plants has already been tested in a number of projects (some of which can be observed in the ‘Status Report on Variable Speed Operation in SHP’ document, published on the DGTREN website at http://ec.europa.eu/energy/res/sectors/doc/small_hydro/statusreport_vspinshp_colour2.pdf) – but has been more often than not considered unfeasible. But these past tests, usually reliant on using a modified Kaplan turbine design, were not, according to the paper, efficient enough to give a significant cost reduction.
The project presented in the paper offered what its calls an ‘optimised technical concept’ for VSO of compact turbines, and yielded an ‘innovative turbine concept’, based on a submersible unregulated compact turbine concept of the Finnish manufacturer Waterpumps Oy, whose turbine runner and intake, PME-generator and frequency converter are optimised for VSO. The paper also states that speed variation is used for optimising hydraulic performance at different heads and flows; the permanent magnet generator avoids any kind of mechanical speed increaser and is optimised for operation with a frequency converter; and a special frequency converter for the speed control and grid connection eliminates the need for power factor correction and other additional grid connection requirements.
The development goals of the project were as follows:
•Achieve a high system performance over a wide operating range.
•Reduce the overall investment cost for small hydro power.
•Reduce electricity production cost at low head hydro power sites.
•Increase the flexibility and operating range of the compact turbine series in order to maximise the advantages of the concept for a wide range of sites.
Using CFD, three options for runner geometries were investigated: divergent radial, convergent radial and axial, with the latter chosen. The final design specifications for the axial runner were as follows: design net at optimum 3.5m (from demonstration site Tirva); design discharge 1.4m3/sec (required to achieve 50kW); design speed 600rpm; operational speed range ± 25% from design speed; number of blades: four (a better option than five in terms of cost, soiling tendency etc.); and an outer diameter of 0.6m (determined by available draft tube).
The speed–torque characteristics of the runner and the next design phase, the generator, had to match. The following specifications for the generator were agreed for the laboratory test machine:
•Rated speed: 600rpm.
•Rated power: 54kW (56kVA).
•Rated torque: 840Nm.
•Number of poles: 40 (rated frequency 200Hz).
•Rated voltage: 313V (open circuit).
•A sinusoidal voltage shape (at no load).
•Rated current 92.4 A (eff).
•The use of standard plate design for the stator, but improved materials (higher efficiency).
•Runaway speed >300% of rated speed (has been set to 2000rpm).
•IP44, external water cooling.
•Integrated temperature sensors (2 Pt100).
Finally, after the generator design was in place, detailed specifications of the frequency converter (FC) could be made – the generator is directly connected to the FC. A controlled rectifier was selected over an uncontrolled diode rectifier, partly as it represented a cheaper option for a 100 to 200kW energy range. The FC’s functions are to convert the variable generator frequency into 50Hz, to compensate the variable voltage from the generator; to control the speed of the runner by controlling the generator torque through the electric current; and to supervise the generator as well as the grid with respect to frequencies and voltages.
Careful attention was paid to the torque control of the FC, as it and the PMSG were tested intensively in the laboratory. Following the successful field tests, the turbine was set up to operate continuously at the Tirva site – for about 2849 hours between November 2005 to April 2006. About 87MWh, with an average output of 30.6kW, was produced during this test phase, where three different speeds of 450, 600 and 750rpm were trailed at three different heads of 3.37, 3.81 and 4.44m (resulting in nine different operating points). The maximum mean power output in a one hour interval during the test phase was about 45kW.
The project was an encouraging endeavour for those involved; total ‘water to wire’ efficiencies in the range of 80% were found during the tests, and the paper insists that that, as in any new concept, room still remains for optimisation in the future.
Lack of recognition
It was an opportune time to be meeting in the UK to talk about small hydro, since the long-anticipated UK Energy Policy Review has just recently been carried out by the Government’s Department of Trade and Industry. Along with predictable talk of nuclear development, the review encourages the acquisition of power through renewable means, with an obligation to push this towards 20%, which would mark a 5x increase, in order to reduce carbon emissions.
However, any mention of hydro power in the official press report is conspicuous by its absence; wave and tidal is the closest reference. This lack of recognition is a sometimes frustratingly common theme where hydro is concerned; it was pointed out in the opening address of Hidroenergia 06 that hydroelectricity is often overlooked as a power source, even when talking about renewables. The reasoning is not certain – suggested factors include that it may not be new enough – but, as we have seen at times in the featured papers above, often when initial ignorance or apprehension are tackled, the dam and hydro power route can prove to be a truly worthwhile option.