Eigg Electric

Eigg is not connected to the mainland electricity supply.  After decades of diesel generators, Eigg Electric provided 24 hour power for the first time in February 2008. 

Eigg Electric is a community owned, managed and maintained company which provides electricity for all island residents from the renewable sources of water, sun, and wind.   No more pouring smelly and expensive diesel into noisy generators, just clean, reliable electricity for everyone. 

Why take power from 3 renewable resources?

The system was designed to take power from renewable resources sufficient to provide the island with a continuous reliable electricity supply with minimal us of fossil fuel generators, at all times of the year. No burn (stream) on the island has sufficient bulk flow of water throughout the year to provide our needs through hydroelectric generation alone. Wind generation provides the complement through most months of the year. The photovoltaic panels might appear to be the lowest yielding, least cost effective, component of the system, when their output is viewed as a contribution to the annual supply of electricity.  However, it is in the summer months that they come into their own and make a significant energy saving contribution to the overall economics of running the system.

To provide electricity we have:

Renewable power generators

Three hydroelectric generators produce electricity from running water.  The biggest hydro above at Laig on the west side of the island is 100kW, with two smaller 5-6kW hydros on the east side.

Four small 6kW wind turbines below An Sgurr

50kW Photovoltaic array producing electricity from the sun.

Although the capacity of the scheme is around 184kW, not all renewable resources produce their maximum output all the time or at the same time.   However, by having a balanced scheme of all three, we can maximise the available renewable resources and ensure there’s enough to provide all or most of the island’s electricity needs.  Renewable sources have provided around 95% of our electricity since the scheme was first switched on in 2008.

The remaining 5% is generated by two 80kW diesel generators to provide back up when renewable resources are low or during maintenance.

Distribution

Power is distributed from the renewables via 11km of underground cable that was laid to form an electricity grid for Eigg.   This high voltage grid delivers electricity around the island, while transformers convert the power to domestic voltage into homes and businesses.

A control building

Where power is regulated and stored.   Nearby are back-up generators, for periods when renewable sources are in short supply.

To watch a short film about Eigg Electric, click here.

Enough for everyone

We can only use what we make.  To ensure nobody goes short, each house has a maximum use limit at any one time of 5kW, each business 10kW.

5kW is enough for an electric kettle and washing machine, or fifty 100w light bulbs!  Spreading our use throughout the day is easy, and OWL meters tell us how much we’re using moment by moment.

More than we need

Sometimes Eigg Electric produces more electricity than we can use, so we use the excess to heat community buildings.  If you see a fan heater on in the community hall or the waiting room, we’re not wasting electricity, we’re making too much!

The Big Picture – Isle of Eigg Electrification scheme, in detail

The new Isle of Eigg electrification scheme was a community inspired project to electrify the whole island and was the biggest project of our first ten-year plan for the sustainable development of the island.

When the system started generating power on 1st February 2008, our achievement was a double first. Continuous power was made available for the first time to all residents and businesses on the island. Until then, we were each dependent upon making our own electricity, mainly using costly and inefficient generators. Further, for the first time, the renewable resources of wind, water and solar generated electricity were integrated into a grid system designed to supply an isolated and scattered small community.

Our electricity system is entirely stand-alone. It has no external input from a mainland utility and is operated and maintained for the community by Eigg Electric Ltd. a wholly owned subsidiary of the Isle of Eigg Heritage Trust. Repair and servicing is the responsibility of a trained maintenance team of island residents.

The initiative and energy of the community in driving this unique project to its successful conclusion was recognised by the award of Best Community Initiative at the 2008 Scottish Green Energy Awards. Our unique concept and the environmental efficiency and sustainability of the project were recognised by the Scottish and Southern Energy Innovation and Energy Efficiency award 2009 at the Scottish Energy and Environment Conference 2009.

Overview

The system consists of three hydroelectric generators a group of four small wind generators and an array of solar electric panels sited at different locations around the island as determined by optimum availability of resource. The hydroelectric capacity is approximately 110kW, the maximum output of the wind farm is 24kW and the solar electric panels can produce up to 50kW. The total generating capacity of the whole system is approximately 184kW.

The output of all the renewable energy generators is brought together, controlled and distributed to all households and businesses on the island by way of an island-wide high voltage grid of approximately 11km length. Consumers are supplied via transformers which convert the grid voltage to domestic voltage and which are located in close proximity to clusters of properties. These same transformers provide the means of access to the grid for the energy produced by the renewable generators.

A bank of batteries, capable of providing power to the whole island for up to 24hrs, has been designed into the scheme to enable us to optimise our usage of energy from the renewable resources. To cover occasions when renewable generation is low, the system is supported by a pair of 70kW diesel generators, which act alternately as back up and reserve, and can be switched into the system automatically as a part of the control strategy.

It was an essential consideration in the design and development of the whole project that it should impact upon the natural beauty of the island as little as possible. The whole of the cable routes, both grid and domestic, are buried, and the only parts of the system that are visible above ground are the generators themselves, the transformers and the control building, where the whole system is integrated and controlled.  At all locations, the aerial structures have been positioned with due sensitivity for the visual environment and we have overcome obstacles of complex engineering to achieve this..

Photovoltaic (power from the sun)

The photovoltaic array is of 50kW capacity, and is located on the south-facing hillside above the Control Building and Telephone Exchange. The array is angled at 20 degrees to the horizontal, and the choice of location and orientation optimise the output of a static array over the whole course of the year. The output of the photovoltaic panels is dc and this is converted to ac power via inverters located in the Control Building, before entering the grid at the Control Building transformer.

Hydroelectric (power from water)

The hydroelectric component of the system consists primarily of a 100kW Gilkes generator located on the burn near Laig Farm, at the north west of the island. It is a 3phase machine and its output, which is regulated on site, is passed direct to the grid via an adjacent transformer.  In addition, there are two small pre-existing generators of 5-6kW capacity each. They are located in the south east of the island and have been upgraded and brought into the system, where they provide a useful supplement to the hydroelectric generation in circumstances of low water flow at Laig.

The generator at Laig is supplied via a 300mm buried pipeline from a weir on the burn at approximately 800metres distance and with over 100metres head. The weir is accessible via a newly constructed track from the forestry area in the centre of the island, or by following the track above the course of the pipeline, from the hydroelectric building at Laig. The weir is located amid spectacular scenery, with views across Laig Bay to Rum and Skye, and its position on the burn was carefully chosen for minimum visual impact.

Wind

The wind turbines are located to the south of An Sgurr, along the track leading to the ruined settlements of Upper and Lower Grulin, just beyond the Piper’s Cairn.  There are four turbines, each with a capacity of generating 6kW, or 24kW in total.

The four wind generators stand at the head of a long view over the southern slopes of the island and across the sea to Muck and Coll, Ardnamurchan Point, Mull and the Treshnish Isles. During the winter months, the sun sets over Muck and the turbines make a spectacular contribution to the whole scene. This location was chosen because, of all possible sites on the island, it offered the best combination of exposure to wind with minimal turbulence, accessibility and best fit in the landscape, with minimal visual impact from all directions.

The wind generators are each 6kW, 3 phase Proven machines.  The voltage generated by these varies with wind speed and so their output cannot be fed direct into the grid. Instead, it is rectified on site and the direct current power produced is fed through inverters to produce alternating current power at the required stable output voltage needed for transformation up to grid voltage. A transformer at the site connects the wind generators to the grid and supplies also the domestic properties in the Galmisdale area.

Control of the system

It is at the Control Building that the whole system is regulated, to ensure a continuous supply of electricity to the island. The basic parameters of the control of the system are the state of charge of the batteries and the frequency, when it rises above the normal operating frequency of the system.

There are ninety-six 4volt batteries at the control building. They occupy half of the building and are housed under well-ventilated conditions separate from the control room. The batteries are organised into parallel arrays of 48volts each and connected to the system via four clusters of three inverters each. The clusters each convert battery power to mains 3-phase ac power and this connects to the grid via the transformer at the control building. By this means the grid also connects to the batteries and power can flow in either direction – to the batteries or from them. Each inverter has a maximum output capacity of 5kW and so the maximum power that can flow in or out of the batteries is 60kW.

When the renewable resources together are producing more electricity than is being consumed by the island, then the excess flows into the batteries via the inverters and they become charged. When the renewable resources produce insufficient power for the needs of the island power flows out of the batteries and they progressively discharge.

The inverters monitor continually the state of charge of the batteries. If this falls to 50%, the inverters signal for the standby generator to start. This supplements the power produced by the renewable resources and the batteries become re-charged.

When the charge of the batteries reaches 90%, the inverters signal for the generator to be disconnected and turned off. A separate control system ensures that the generator and main hydro run together in phase. If any or all of the renewable resources are out of commission for any reason, the generator alone can power the island.

If the renewable resources produce more power than is consumed by the island, then the batteries eventually become fully charged and will accept no more power. At this point, the frequency of the system rises and a sequence of frequency controlled regulatory measures is initiated. As a first means of absorbing surplus power, a series of frequency controlled switches activates space heaters at community facilities – the Community Hall, the Pier Centre and the churches. Most circumstances of surplus power production are in winter and the space heaters provide a useful and energy saving complement to existing arrangements. For the churches, these heaters are the only source of warmth presently in place, and they play a useful role in helping to keep the fabric dry during the winter months. If there is still surplus power and the frequency continues to rise, then a control system comes into play at the wind farm that progressively diverts the output of each wind generator into heaters, which dump their power to the atmosphere. Finally, the output of the main hydroelectric generator is restricted at a fixed upper frequency limit and the system runs in balance until renewable output falls, and the above procedure is reversed.

Limitations

The system has been designed to provide at least 95% of the power consumed on the island, from the three renewable resources, and to allow for growth in the population.

However, it is of limited capacity, especially in the summer months when we may have little wind or rain. To avoid the possibility of overload and to ensure that electricity was always available equally to all consumers, without the need for excessive running of the generators, a decision was taken early in the design of the project to cap the supply to all outlets. Domestic and small business premises were to be capped at 5kW and for larger business premises at 10kW. All consumers were provided with energy meters to measure power consumption and indicate when the cut off point was approaching. The residents supported the concept unanimously, from the outset, and in operation, it has been a total success.

Acknowledgements

This has been a technically challenging and unique project. It owes its success not just to the individual specialist capabilities of all who have contributed to the project, but to the way in they have co-operated, jointly discussed every aspect of the project as it progressed, and worked together as a team throughout.

Our thanks go to:

Our Main Contractor for the Design and Build –     Scottish Hydro Contracting Ltd.

Our Project Manager throughout                          –     Synergie Scotland Ltd.

Sub Contractors

E-Connect Ventures Ltd
Wind and Sun Ltd
Energy Renewed Ltd
G.G. MacKenzie Contractors Ltd
The residents of the island who gave of their time and skills.

The project would not have come into being without the financial support of:

European Regional Development Fund

Big Lottery Fund

HIE Lochaber

Highlands and Islands Community Energy Company

Scottish Households Renewables Initiative

Energy Saving Trust

Highland Council

Isle of Eigg Heritage Trust

The Residents of the Isle of Eigg

We thank all of these organisations and individuals for seeing merit in our project and for supporting us so well.

For further information about any aspect of the island electricity system, please contact:  Eigg Electric Ltd. An Laimhrig Isle of Eigg PH42 4RL

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