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a Senior Electrical Engineer, Entura, Level 25, 500 Collins Street, Melbourne Victoria 3000, Australia. b Director of Renewable Energy Development Division, ...

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ScienceDirect Energy Procedia 103 (2016) 207 – 212

Applied Energy Symposium and Forum, REM2016: Renewable Energy Integration with Mini/Microgrid, 19-21 April 2016, Maldives

Cook Islands: 100% renewable energy in different guises Dusan Nikolica, Tangi Tereapiib, Woo Yul Leec*, Chris Blanksbyd b

a Senior Electrical Engineer, Entura, Level 25, 500 Collins Street, Melbourne Victoria 3000, Australia. Director of Renewable Energy Development Division, Office of the Prime Minister, Avarua, Rarotonga, Cook Islands. c Energy Specialist, Asian Development Bank, 6 ADB Avenue, Mandaluyong City, 1550 Metro Manila, Philippines. a Senior Renewable Energy Engineer, Entura, Level 25, 500 Collins Street, Melbourne Victoria 3000, Australia.

Abstract In its approach to delivering a 100% renewable energy target across 12 islands by 2020, the Cook Islands presents a rare insight into how planning requirements of high penetration renewable island systems vary with scale. To support this ambitious plan the Asian Development Bank and the European Union fund the Cook Islands Renewable Energy Sector Project, which will construct up to six solar photovoltaic (PV) power plants with a total installed capacity of about 3 megawatts-peak coupled with battery to store electricity from solar energy. The first three islands have small, standardized, centralized solutions (solar PV coupled with battery with existing diesel backup). An order of magnitude larger, Aitutaki will be implemented as a centralized solution in two stages, allowing detailed data collection and capacity building. An order of magnitude larger again, Rarotonga requires progressive planning and implementation including distributed generation, advanced control and integration, and sophisticated commercial structures. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( © 2016 The Authors. Published by Elsevier Ltd. Peer-review under responsibility the scientific committee the Applied Energy Symposium and Forum, Selection and/or peer-reviewofunder responsibility of of REM2016 REM2016: Renewable Energy Integration with Mini/Microgrid. Keywords: high-penetration; Cook Islands; micro-grid

1. Introduction Micro-grids are a well-established research area in power engineering. The last two decades has produced a vast amount of knowledge on integration and control of renewable energy (RE), with the emphasis on isolated power systems, especially on island systems. Real projects implemented on island

* Corresponding author. Tel.: (632) 683 1803; fax: (632) 636 2444. E-mail address: mailto:[email protected]

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license ( Peer-review under responsibility of the scientific committee of the Applied Energy Symposium and Forum, REM2016: Renewable Energy Integration with Mini/Microgrid. doi:10.1016/j.egypro.2016.11.274


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systems across the globe have reached 100% RE penetration. Successful completion and operation of these systems delivered practical knowledge that could be replicated on other islands. This paper focuses on common technical hurdles in integration of renewable energy sources in island systems and describes this through the example of the Cook Islands’ 100% renewable energy journey. 2. The Cook Islands Located in the South Pacific Ocean, the Cook Islands has 15 islands, of which 12 are inhabited. Most of the Cook Islands 13,000 permanent residents live on Rarotonga, in the south. Aitutaki has a population of approximately 1,800, and remaining islands are sparsely populated.

Fig 1. Cook Islands Map depicts Northern and Southern Island groupations. All Islands from the Northern group are smaller and have limited requirements for electrical energy. Most of the Cook Islands people live in the Southern Islands. Two largest Islands are Rarotonga (main island) and Aitutaki

Average Island Load (kW)

The Government of the Cook Islands has a long standing policy commitment of 100% renewable electricity by 2020. Its island power systems can be grouped in three categories – small (under 100kW; 10 islands), medium (under 1MW; Aitutaki), and large (over 1MW; Rarotonoga), as shown in Fig 2. Thus it is an ideal candidate for understanding high penetration renewable energy in island grids. 3,500 3,000 2,500 2,000 1,500 1,000 500 0


415 51 44 31 29 21 11 10 7



Fig 2. Average load (kW) in the Cook Islands, showing three scales: Rarotonga, Aitutaki, and the other 10 inhabited islands. [Ministry of Finance and Economic Management (MFEM)].


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The Cook Islands Electricity Sector

All inhabited islands of the Cook Islands currently have centralised power supplies that have historically been powered by diesel generators. Since around 2011, increasing solar PV generation on Rarotonga has changed this situation. And in 2014-15, installation of 95-100% renewable solar hybrid systems on the Northern Group Islands further altered the mix. The focus is now on the Southern Group Islands, with characteristics shown in Table 1. Table 1. Southern Group Islands; population and electric energy demand [MFEM] Island


Average load (kW)

Peak Load (kW)

Atiu, Mangaia, Mauke, Mitiaro












System Type Small Medium Large

3. Technical opportunities, scale and renewable energy contribution 2.2.

Small scale Island Projects (less than 100kW average load)

Reaching 100% renewable energy penetration in small systems is relatively straightforward due to: ƒ Off-the-shelf technologies which easily integrate and control solar PV and battery storage, ƒ Very low maintenance costs and almost no imports over the life of the plant, ƒ Short maintenance periods requirement, and only essential skills are needed – an approach well suited for remote islands. It is important to note here that new systems (solar, battery) require less technical knowledge from power station operations crew than diesel generator systems. ƒ Remote monitoring capabilities. ƒ Limited reliability requirements. Fig 3. presents a schematic for a small system. Small systems have four main components, renewable energy generators (sized to cover almost all energy needs of the community throughout the year), battery energy storage (sized to cover almost all shortages in renewable energy resource), backup diesel generator (sized to provide power for the entire system and charge the batteries, if necessary), and connection and control (a part which controls how energy is delivered into the distribution system).

Fig 3. – (left) Typical small system schematic, with four main components: renewable energy source, energy storage, backup generation and connection/control system. (right) as installed on Cook Islands (Rakahanga)

Small systems are usually based on fully integrated technology that uses power electronics to manage all the functions of a grid (such as spinning reserve, frequency and voltage control, inertia and reactive power), albeit without necessarily having the same reliability standard as a larger grid would require. Fully integrated power management systems offer a straight-forward, though relatively expensive approach to achieving renewable energy penetration above 90%. In small systems, periods of time with absolutely no diesel generation could span for up to a month or two. Finally, systems with no enabling technologies have very simple control systems, and need only limited technical control and maintenance.


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Medium Scale Island Projects (between 100kW and 1MW average load)

Medium scale island power systems, with larger populations and commercial enterprises can typically justify higher reliability and power quality standards, and this requires additional, customised design. As well as offering better reliability and power quality, at this scale it can be more cost effective to employ dedicated equipment (enablers) such as flywheels and dynamic load banks to provide the grid functions that were fully integrated at a small scale. A more complex system also requires more skilled and trained operators, and time to adapt and optimise the system after each development stage. While small island power systems are generally very similar one to the other, medium island power systems start diverge and there are no off-the-shelf solutions which suit all islands. A tailor made approach including multi-stage plans for reaching high renewable energy penetration is necessary. Fig 4 presents such an approach for the medium-size island of Aitutaki. At the moment, Aitutaki is a power system 100% supplied by diesel generators (3 x 600 kW). During Stage 1, 1 MW of solar PV will be installed on the island which will run in parallel with the existing diesel generators. At this stage, instantaneous renewable energy penetration will be up to 70%. A 300 kW diesel generator will also be purchased and installed to enable higher solar PV output. And a control system will be installed to quickly control the output of solar PV plant and schedule diesel generation. By having a smaller diesel generator, slightly higher instantaneous RE penetration can be achieved (in Aitutaki’s case, up to 80% instantaneous). Stage 2 will see the addition of RE sources (solar PV or wind) along with enabling technologies including storage and inertia. With all those technologies, the system might be ready to switch off diesel generators for limited periods of time. Finally, Stage 3 would see installation of even more RE and larger energy storage for load shifting. With Stage 3 completed, the system will be able to operate without diesel generation for several days.

Fig 4. – Multi-stage approach to reaching 100% renewable energy Typical small system schematic, with four main components: renewable energy source, energy storage, backup generation and connection/control system.

The approach described works for Aitutaki, but may not necessarily work for every medium size power system. What can be concluded is that the road to achieving 100% RE penetration on medium size power systems is more challenging that the road for small island power systems, and can be divided into three critical stages: ƒ Initial RE generation (plus limited enabling technologies), ƒ Installation of dedicated enabling systems to boost reliability and improve cost effectiveness, ƒ Installation of energy storage (and additional RE). 2.4.

Large scale island projects (over 1MW average load)

The main difference between medium and large systems is in distributed generation and management of the distribution grid. In large systems, renewable generation can be distributed and connected across the power system. The distribution grids will have to manage power flows in two directions, and upgrades including smart technology may become necessary. In terms of the 100% RE energy journey, large island power systems may follow a similar 3-stage principle outlined for medium island power systems. However, in the case of large systems, enabling technologies would include distribution automation, system-wide control and communication systems. Large systems might also incorporate significant consumers, who will look at their own energy needs


Dusan Nikolic et al. / Energy Procedia 103 (2016) 207 – 212

separately. An example of this Rarotonga International Airport, which has the potential to generate (and possibly store) a significant portion of its own energy needs on site. This micro-grid will integrate with the larger power system and the two will support each other in different scenarios. Thus larger strategic plans, involving key stakeholders are necessary, and are similar to requirements of conventional interconnected power systems. Because of this complexity, large power systems require time to transition to 100% renewable energy as they plan, implement, measure outcomes and adjust plans progressively. This is best viewed as a journey, requiring a long term commitment by all stakeholders. Large island power systems may be limited to RE in the range of 50 to 60%. This is mostly due to the current cost of battery energy storage, which is difficult to justify economically if existing unit costs of energy (from diesel) are relatively low. Islands with existing energy storage facilities (hydro power) can access to cheaper, pumped hydro storage, and consequently, can achieve higher RE penetration levels more easily. Islands with no hydro potential will need to rely on continued decreases in new battery energy storage technologies. 4. Project economics, renewable contribution, and scale

10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0

$0.90 $0.80 $0.70 $0.60 $0.50 $0.40 $0.30 $0.20 $0.10 $0.00 0


40 60 Renewable energy (%)


Enabling technologies capital investment ($M)

Cost of Energy (NZ$ / kWh)

Adding a small amount (typically less than 15%) of RE into a system is very cost effective. There is no spill or required enablers, so the cost of energy is at a minimum. However, with more generation, this situation unravels, and the cost of energy increases as shown in Fig 5. The initial trajectory of declining total cost of supply lasts only briefly, before the cost of enablers and spilt energy becomes critical. Total cost of energy supply Reference cost of energy (diesel only) Solar PV generation cost Energy Storage Capex Enabling technology Capex


Fig 5. Example of impact of increasing renewable energy contribution on the cost of electricity supply (real case studies based on one of the scenarios for Aitutaki power system and current tehnology prices)

The point at which the total cost of supply exceeds the levelized cost of electricity (LCOE) of diesel is typically the maximum portion of renwable energy that can be economically achieved in that system. This point is sensitive to factors such as LCOE of solar vs diesel, transport costs, the cost of planning and design, and available technology, each of which varies with the isolation and size of the island. 5. A Collaborative, Multi-disciplinary approach The technical and economic drivers for each island have been mapped out in the Cook Islands Renewable Energy Chart Implementation Plan. Delivery of this plan requires a comprehensive team approach,that cuts across a range of traditional boundaries. Delivery of a high contribution renewable energy system requires increased community energy literacy; buy-in from utilities, landowners, private capital, and various government agencies; and access to technical assistance and capacity building. The team for the Cook Islands is shown in Fig 6.


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Fig 6. Cook Islands Southern Group Renewable Energy team

6. Conclusions Getting to 100% is a journey. More so than just a simple application of technology, it takes time to understand local requirements (social, environmental, technical and economic) and these vary widely with electricity use on the island. Successfully navigating this path creates buy-in from stakeholders and investment in systems which have a significant place in local communities for many years. Acknowledgements We would like to thank both Asian Development Bank and European Union for providing a loan and a grant for the Cook Islands Renewable Energy Sector Project (Project). We also want to thank the Government of the Government of the Cook Islands, particularly the Office of Prime Minister for providing great support to the Project. ADB extends its sincerest gratitude to all partners of this Project. 7. References [1] M. Piekutowski, S. Gamble, and R. Willems, "A Road towards Autonomous Renewable Energy Supply, RAPS case," in CIGRE 2012, Paris, France, 2012. [2] D. Kottick, M. Blau, and D. Edelstein, "Battery energy storage for frequency regulation in an island power system," Energy Conversion, IEEE Transactions on, vol. 8, pp. 455-459, 1993. [3] N. Hamsic, A. Schmelter, A. Mohd, E. Ortjohann, E. Schultze, A. Tuckey, and J. Zimmermann, "Increasing Renewable Energy Penetration in Isolated Grids Using a Flywheel Energy Storage System," in Power Engineering, Energy and Electrical Drives, 2007. POWERENG 2007. International Conference on, 2007, pp. 195-200. [4] ABB-PowerCorp. (2012). Low-Load Diesel (LLD) product. Available:

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