Friday, December 20, 2013

1243. Experiments: Eigg Electric

By Island Go Green, March 2013

Eigg Electric is a community owned company which provides electricity for all island residents from the renewable sources of water, sun, and wind.
Watch a short film about 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.

Renewable power systems

Three hydroelectric generators produce electricity from running water.  The biggest hydro above Laig produces 100kW, with two smaller 5-6kW hydros on this side of the island.
Four small wind turbines below An Sgurr produce 24kW maximum.
Photovoltaic cells produce 30kW electricity from the sun.

11km of cable was laid for our Grid
From the renewable sources, this high voltage grid delivers electricity around the island, and 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.

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.

Can you take the 5kW challenge?

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!

Eigg Electric is community owned, managed and maintained.

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.

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 30kW. The total generating capacity of the whole system is approximately 164kW.

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.

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.

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.

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 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.

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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