Eigg Electric

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 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.

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 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.

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

23 thoughts on “Eigg Electric

  1. Hello,

    As an Electrical Engineer, I followed this project closely when i was involved with the renewables industry having designed several off-grid hybrid systems at the time and then went into the Offshore oil & gas world, i became involved in load management within islanded electrical networks and i fully appreciate the challenges on the kW and MW scale.

    Being back in the renewables industry i thought i would read up on the project and was very pleased to hear its going so well.

    I believe there are things which you can do which would see there being no need to have to shut down any source of generation at times of surplus. Likewise, i would modify the battery management and interaction with the generators

    Finally, i believe you should take advantage of PV prices just now, with large scale PV at around £1100-1500/kW installed (having installed some 20-50kW systems) i think this would dramatically improve your summer system performance, and help your reserves on those lovely crisp clear windless mornings we get in Scotland.

    Finally, whilst people are aware of how much power their property is using, there are other ways the islanders could react and help balance your network if they knew about the supply & demand at any time.

    I would love to chip in if you needed any second opinions.

    Best regards,
    Stuart Graham

    • Thanks for your comments Stuart. It would be interesting to hear your thoughts on battery management and how that interacts with the generator.

      Re PV – we’ve already installed an additional 20kW on top of the original 10kW and are about to add a further 20kW, bringing that input up to 50kW. This will reduce our need for diesel back up to just a few percent of our overall generation.

      Would also be interested in how we could let people know about supply and demand in real time – very useful.

      Have you ever been to Eigg? Maybe you could come over some time this summer and we can talk more?

      • Hello,

        If your genset contribution is just a few % then there is probably little point in adjusting their regime. Unless an extended period renewables defect was expected i’d not charge the batteries so fully from the genset are you are limiting then the renewable charging potential.

        If you start at 50% DOD, id run up to about 60-70% at most then stop the genset at this point. This would still give the genset a good run each time it has to and give more room for the renewables to top you up.

        But as i say, its hard to improve upon a few %!

        How much surplus kWh are you dumping or not generation throughout the year when you have a surplus?

        Feel free to email on the address supplied,


      • Thanks for all that – will share with the electric team, who are in a better position to reply in any detail to your question about what do we do with any surplus. The broad answer is (of course!) that over the five years the scheme’s been up and running, the amount of surplus has varied with the weather and how much people are using at the time. Also, as we’ve been adding to and adapting the system in that time, the surplus (or not) has also varied. Will try and see if there’s a more definite answer than that. Thanks in the meantime for your interest again.

    • Hello Lewis. We currently pay 21p per kWh unit, which includes VAT and the daily standing charge. Consumers buy electricity cards, in £10 or £20 denominations. This helps people budget, but also cuts down on administration as there are no bills to send out.

  2. Facinating! Can’t wait to visit Eigg and hopefully see around the system. One question, if the output from each individual is 5Kw how can the total be 60 Kw. Alos is the current coverted to AC at the inverter or at the transformer stage?
    Great site !!

  3. I spent a few days on the island at the beginning of the month and was impressed by the system, particularly its unobtrusiveness. I would be interested in a few more statistics, such as; average energy produced per year; percentage contributions of the hydro, wind, solar, and diesel generators to the yearly energy output; grid voltage and maximum power rating; number of houses and businesses served; cost of energy to consumers.
    Michael Matthews

  4. Why do you only run your battery banks down to 50% capacity? This means you’re wasting half your available capacity – you might as well not have bothered installing half those batteries. You have the generators for backup should the batteries become exhausted but you’re actually using the generator to cyclically charge the batteries. Surely it would be better to allow the batteries to discharge, then start the generators and not recharge the batteries until excess energy was available again.

    • Hi James – The deep cycle lead acid batteries batteries perform overall at their best if if operated between fully charged and not less than 50% – they give their best power output at close to full charge – keeping the state of charge above 50% is associated with long battery life; the irreversible changes to the plates which limit the operational life of a battery take place more rapidly as the state of charge falls. If you discharge batteries completely they become quite resistant to re-charging and the irreversible chemical changes develop very rapidly – you can’t actually do this to a battery more than a very few times before it will not re-charge at all. So, in summary, over the range we use we get the best combination of power output and battery life. We should expect 15yrs or more from our battery bank through using it in this way.

Write Your Comment

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s