Last summer, at the northern end of Iceland, the Holsvirkjun hydroelectric power station, yet another small-scale hydropower plant went online in an island state dominated by hydroelectric production.

The plant was equipped to the very latest standards of hydropower technology, most of the infrastructure being provided by the internationally active Upper Austrian hydropower specialists at Global Hydro. As well as the 6-nozzle 6.7-MW Pelton turbine, the turnkey provider also supplied the entire control infrastructure for the power plant, the latter being the central technical pillar of the project. Ultimately, the aim was to guarantee a sophisticated regulation approach to balance out the peaks and troughs in demand on the grid serving the small local town of Akureyri, the frequency deviations, and for the plant to be able to guarantee isolated operation.

Iceland is a country with far more to offer than glaciers, volcanos and geysers. It is also a country of hydroelectric power production. No less than three quarters of the island’s energy demands are covered by hydropower plants. Hence, the island in the far north of Europe is one of the continent’s hydropower hotspots. Experienced hydroelectric station managers are increasingly relying on the practical and theoretical expertise offered by businesses from the central alpine regions – businesses like Global Hydro Energy. The innovative Upper Austrian hydro­power specialists have already successfully implemented around 30 hydroelectric projects in Iceland. One of their latest reference projects is the Holsvirkjun hydropower plant in the north of the island – a drive of around 30 minutes from the small town of Akureyri. The order to equip the small-scale hydro­power plant in the north of the island was submitted to the Upper Austrian water power experts by Orkuver, a local Icelandic partner, at the end of January 2019. The comprehensive overall order was for a vertical 6-jet Pelton turbine, a ball inlet valve, hydraulic generator, synchronous generator, and for the plant’s electrical and control infrastructure. The contract was successfully completed over the following 16 months.

Potential for grid optimisation
Preparations for the Holsvirkjun small-scale hydroelectric power plant had been underway since 2011. The goal was to realise a significant improvement to the previously unsatisfactory grid power supply to the small town of Akureyri. Until recently the power supply had been dependent upon several diesel generators; an unacceptable situation for a country with such a climate-conscious population. Following a comprehensive period of preliminary planning, a concept was developed for a plant served by two separate rivers – and was finally ready for implementation in 2018. This required the construction of two transverse structures to produce a certain degree of water volume build-up. Philipp Meindl, Global Hydro’s project manager, outlines the operation of the plant as follows: “The two reservoirs were established in their respective valleys at approximately 315 m above sea level. The penstocks leading down from each reservoir join in a surge tank at around 310 m above sea level, from which the works water is guided down a single pipeline to the machine room at just 60 m above sea level.” The penstock down to the power house consists of about 6000 m of glassfibre-reinforced piping (GRP) and transports a maximum water volume of 3.2 m³/s.

Special turbine housing
The power house was given a compact design that blended well with Iceland’s natural surroundings. A 35-ton indoor crane was installed in order to manoeuvre the heavy machinery and components correctly, and for conducting maintenance tasks. Delivery of the electro-mechanical infrastructure postponed until last March due to construction delays caused by extreme weather at the construction site. The machines were transported from the Global Hydro works in Niederranna to Rotterdam, and from there to Reykjavik by ship. The experience, expertise and technical flexibility of the Upper Austrian turbine manufacturers were also required to find the best way of arranging and installing the turbine to suit local conditions. Philipp Meindl ex­plains: “Part of our job is to adapt solutions to the prevailing conditions on site and to the special requirements expressed by the customer. In this case the customer asked for welding activity at the plant to be kept to a minimum. The response of our construction designers was to produce a solution for the turbine housing that involved just one single screwed joint, although the overall diameter was around 7 metres.” Global Hydro sent two supervisors to Iceland to ensure all challenging assembly procedures ran smoothly – one for mechanical and one for the electrical aspects of installation. Obviously, protective Corona rules and restrictions also had to be strictly adhered to, as did the legally-required quarantine measures, all of which was subject to continuous monitoring.

Compensation of Load Jumps
The main challenge for the Global Hydro team was to guarantee island mode operability; a common requirement in and on Iceland – in this case to compensate power demand changes of up to 600 kW within a maximum frequency deviation of 2 Hz. “Variations of this scale can account for around 10% of the turbine’s intended output. This would require an immense change of momentum which, in view of the weight involved, would negatively affect the working life of the bearing. That’s why we settled for another, more intelligent solution,” Philipp Meindl stated. The sophis­ticated hydraulic regulator meant equipping the Pelton turbine’s six jet cut-outs with a specially devised hydraulic valve, allowing the jet cut-outs to be precisely positioned within 700 to 800 milliseconds, so any power demand ­changes can be detected and compensated for in a fraction of a second. In the engineering phase a CFD simulation of a cut-off device designed especially for the purpose showed that the jet could be cut cleanly without being destroyed, thus avoiding damage to the Pelton wheel. When tested in practice in Iceland, the sophisticated solution was an immediate success. Meindl: “In cooperation with RARIK, the local Icelandic energy corporation, the system was put through a late-night test, and the plant easily coped with power consumption variations of 700 kW and frequency deviation of 1.7 Hz.”

Modern control system
All machines, auxiliary and support generators are also controlled and monitored by the HEROS power plant management system developed by Global Hydro. Specifically, HEROS Connect was the system chosen, and was enhanced by linking up to an intuitive web application. Hooking up to HEROS Connect enables the customer to check the operational status and condition of the turbine, simply and without the installation of software. The broad spectrum of functions offered by the automation solution enables the operators to choose from a variety of operational options, as project manager Philipp Meindl details: “The large dimensions of the 60,000 m³ intake reservoir ensure a customer using the HEROS system has great flexibility in terms of adjusting to grid requirements. Theoretically, the plant could work at full capacity for over five hours without any additional water. There’s also a pre-programmable calendar function to allow the output to be set in advance for any part of a day, on any day. Furthermore, HEROS automatically regulates the turbine when works water is lost over the edge of the overflow.”

Customer confirms success
The heart of the power plant is a 6-jet Pelton turbine that generates 6,686 kW from a head of 235 m and a capacity flow volume of 3.2 m³/s. This drives a synchronous generator directly coupled to the vertical shaft at a speed of 600 rpm. The newly-installed machine group guarantees efficient and, most importantly, reliable operation for the coming years and decades. After being successfully installed at the beginning of June 2020, the system commenced grid-parallel power generation at the start of August.
The new Holsvirkjun power plant is another key building block in Iceland’s strategy of expanding its use of renewable resources. Furthermore, the plant has now taken on the important task of guaranteeing the stability of grid power provision for the town of Akureyri. It is equipped to secure island mode operation and black start capacity. The success of the implementation was convincingly confirmed by the same Icelandic customer, who in the ­meantime awarded a subsequent project to Global Hydro.