In autumn of last year, Austrian KELAG-Kärntner Elektrizitäts-Aktiengesellschaft commissioned a new small hydropower plant in north-west Montenegro.
The energy service provider carried out the project over a period of three years with its Slovenia-based subsidiary Interenergo d.o.o. Kelag did not just pay special attention to the technical design of the 6 MW power plant, it mainly paid attention to winning over the Montenegrin population. Numerous discussions were held in the run-up to the project, local residents were included in the plans and the benefits of the project as well as the unavoidable impact on surrounding nature were communicated in a clear and transparent way. The operators used modern Coanda systems from Wild Metal GmbH, the South Tyrolean hydraulic steelwork specialist, in order to operate the power plant with as little maintenance as possible.
Montenegro is seen, quite rightly, as a hydropower country. The hydropower plants in this small Balkan state produce around 5.4 billion kWh per year (Source: Laenderdate.info). This means that hydropower provides the lion's share of around 69 % of the country's total electricity generation. One of its hydropower plants stands out from the rest and is known beyond the county's local borders: It is the Piva power plant which has a total installed capacity of 360 MW. This is a megaproject dating from the Yugoslavian era which was realized in the first half of the 1970s. Mratinje dam's specially built 220 m high concrete arch dam was one of the highest in the whole of Europe for a long time. The damming led to the formation of the Piva Lake, which is Montenegro's second large lake covering 12.5 km2. The small town of Plužine, which was lost in the process, was rebuilt on the shores of the dam. All that was preserved was the famous Piva Kloster, which was previously removed piece by piece and later reconstructed at its new location from the original pieces.
A new single-stage power plant concept
Plans were simultaneously pored over during the implementation of the project, such as how to get the best possible use out of the body of water in the upper reaches. Taking the Vrbnica River as an example, engineers from Titos had envisaged a three-stage project with a small dam wall. However nothing was to come of it, as Sebastjan Rozman, engineer at Interenergo and proven expert in all questions relating to hydropower in the Balkans, confirms: “Such a project would come nowhere close to being approved today". It was therefore obvious to us that we required a completely new concept at this site. The question that we'd been asking ourselves for a long time was: Should we build two stages, or will it work with one?" Interenergo subsequently carried out preliminary investigations at the site and developed the first project designs with the Kelag planning team in 2015. It became apparent that the optimal solution would be a single-stage high pressure power plant with a 6-jet pelton turbine. This would also determine the winner of the 2017 internal concession tender. Mountains scatter the region close to the border with Bosnia-Herzegovina, reaching 2,000 m above sea level, along with woodland. An area where questions of accessibility were raised, and energy transport do not play an insignificant role.
Uphill struggle for backing
However, the challenges of the technical realization caused the team fewer headaches than the social aspect of the project. "You can have approval by the State in Montenegro, but if you don't have the support of the Montenegrin population and each of the affected municipalities and residents, you don't build. This causes so many projects to fail”, explains project manager Sebastjan Rozman, adding: “It was therefore part of our strategy to involve the local population and all those affected as much as possible in the project. That was very time-consuming and roughly took a year but was ultimately the reason for the project's success. Some of things that we endeavoured to do was to create a synergy effect so that the municipalities, the local residents and the population also benefited. Evidence of this was the construction of a penstock whose route followed a country road where a drinking water pipeline had been built covering long stretches of land. The old drinking water supply network had already reached the end of its technical service life, therefore a decision was made to replace it when laying the new pipes. Another example was a small tunnel through which the mountain road leads: "The rockfall gallery had to be urgently restored. Therefore we came to a compromise with the community in which we would restore the tunnel from top to bottom. In return we were allowed to lay the pressure pipeline here," says Rozman. A win-win situation for both parties.
The small power plant is a high-pressure system that uses water from the Vrbnica. A Tyrolean weir with an installed Coanda system was built at 980 m above sea level for this purpose, downstream from a small desanding structure. The operators opted for the Grizzly Protec Vibro Bars 2500 System by Southtyrol-based Wild Metal, a company well-known in the industry. This type of rake is a further development of the well-known Grizzly Protec. Like its classic predecessor, it consists of a coarse screen and an underlying fine screen. The special placement of the protection bars prevents material i.e. bed load or floating debris from settling or causing jams. This reduces the already minimal maintenance costs and increases the operating reliability even in winter.
Constraints of space when installing pipes
The work water is then fed from the desanding structure into a penstock which was built using GRP pipes manufactured by Superlit. The route extends over around 3000 m from the water catchment to the power house and overcomes a natural gradient of around 263 m. Most of the pipeline was laid in the existing country road. The plastic pipes, reinforced with glass fibre, proved not only to be the most economical solution for the penstock, but also a very practical one. Last but not least, the low weight eases handling and installation. In specific terms, the pipes that were used had a pressure class of PN16 to PN32 with a diameter of DN1400. Rozman mentions the confined space as the main constructural challenge: "Since the drinking water pipe had been laid in the road over a large distance, the space for the pressure pipes was quite narrow in many areas of the narrow mountain road, since around 2.5 m was required along with bedding."
Elaborate construction: Construction of the high-voltage line
The power house, where the mechanical heart of the system is located, was built at around 718 m above sea level: a 6-jet, vertical-axis Pelton turbine, designed for an expected 30 to 40 days full load. The turbine has a power rating of 6.4 MW, with a suction capacity of 3 m3/s. It drives a brushless, directly coupled synchronous generator at 600 rpm. A powerful, robust machine that guarantees a reliable power supply for centuries. The new Vrbnica power plant will generate around 18.5 GWh of clean electricity in a normal year, which meets the needs of around 8,000 households. The energy is transported via an 8 km long 35 kV line, which had to be specially built for this purpose. "The energy transmission from the dam was quite clearly one of the key challenges of the project. The terrain through which it leads is rugged, steep in areas, densely wooded and difficult to access. It therefore took around a year to erect the high-voltage line, including a substation", remembers Rozman. The high-voltage equipment, the substations and the transformers were realized by Siemers, as well as the entire control and pneumatical machinery of the power plant.
Flooding and Corona pull the brakes
The course of the construction work in the remote mountainous region of north-west Montenegro would ultimately prove to be very challenging, as civil engineer Rozman confirms: "We were confronted with several smaller and larger challenges". This concerned securing an unstable slope, or also reinforcing one or the other bridges on the access routes. This also presented logistical questions: For instance, the trucks were not allowed to exceed a certain height or weight." Yet it was the torrential nature of the Vrbnica that caused the largest number of headaches, causing some minor floods and two severe floods. "Thankfully, there were no injuries, however a few structures and sheet pile walls were torn away, which led to small delays".
Another difficulty which by far caused the greatest loss of time was Corona. The pandemic slowly began to hamper the progress of the work. "Unfortunately not all work can be done via "remote-control." You often need to have specialists on site. We ran into certain obstacles as travelling in particular, but also opportunities for subcontractors, were limited. Great flexibility was needed to progress the audit in the difficult phase. We likely lost half a year due to Corona" said the project manager.
Investor with responsibility
The final milestone was finally reached in November last year: The Vrbnica power plant fed electricity to the public grid for the first time. Since then the plant is in the first few months of operation and has already proven its operative worth. Nowadays it not only makes an important contribution to the region's supply, but also serves to stabilize a distribution network that is not always entirely secure, as Rozman confirms: "There always used to be power failures in this area during the winter. The new power plant is now helping to reduce these power failures to a minimum." With almost 19 GWh of standard operational capacity, it is a small hydropower plant, yet one of the largest in the country. "Strictly speaking it is actually the third largest hydropower plant in Montenegro", according to Rozman. He does see significant potential for further expansion, but a strong headwind for new projects. "NGOs voiced their disapproval for a new power plant. The main reason for this is that it is not only serious investors who tender. We can only distance ourselves from that. After all, we see ourselves a long-term owner who has responsibility towards nature, the environment and the local population; we are not short-term speculators. We decommission a power plant if, for example, too little water flows. Unfortunately, this does not apply to all investors in the Balkans. Rozman: There must be more positive examples like that of KW Vrbnica so that new power plants in the Balkans are not categorically refused. This would be twice as regrettable especially in the case of Montenegro, but at the same time the country does have the highest hydropower potential per inhabitant in the whole of Europe.