The Isle of Muck is part of the Small Isles off the West Coast of Scotland. Muck is just under 4km long by 2km wide and has a population of 38. The island is not connected to the mainland grid but, like it’s neighbour the Isle of Eigg, has its own 3 phase 3.3kV grid that has 20 domestic properties, a school, a community hall, 3 workshops, and a guest house connected to it.

Isle of Muck, Scotland

The islanders have had ‘island grid’ electricity supplied to them since 2000 via two Vergnet 20kW wind turbines backed up by a diesel generator. However, by 2011 the turbines were no longer operational and the islanders had their electricity use restricted to the hours of 07.30 to 11.30 am and 16.00 to 23.30 pm and relied solely on the ‘back-up’ generator.

The aims for the replacement system differ from what might be expected of a conventional mainland grid-tied system. Aside from providing a reliable supply of electricity to the islanders, the system had to: be easily maintained using the skills of local residents with minimal requirement for specialist support; use technology that had been proven to be robust enough to survive in such an exposed environment and achieve a high renewable penetration to minimise the cost incurred from the diesel generator.

System design

The system was designed around an estimate demand of 150kWh/day and was aided by weather and generation data from the system on the nearby Isle of Eigg. To meet this demand, the system includes six 5kW wind turbines (Evance R9000) and 33kWp of solar PV (132 x REC Solar 250PE 250 W) which are backed up by two diesel generators (40kW & 25kW). Variations in resource mean that the system sometimes relies on a single generating source and so to minimise diesel use, each generating option was sized to be able to supply total demand independently.

In order to balance demand with the variable generation supply, energy storage was designed into the system in the form of deep cycle lead acid batteries (4KS25PS Rolls Solar deep cycle batteries). The storage capacity was sized to provide 24-hours autonomy (150kWh) to the network and avoid battery degradation, should there be no wind or solar resource. In addition, demand management was factored into the system in the form of storage heated that were installed in all properties except the workshops. During periods where the batteries are fully charged and there is wind generation surplus to demand, the storage heaters can be turned on to control system frequency and avoid curtailment.

Scottish Supply Chain

The system provides a range of benefits to the islanders including reduced carbon emissions, reduced cost (less diesel consumption), lower maintenance, attractive to new business and it will also allow the population to grow and so safeguard their future.

The project was developed and delivered by Scottish companies and is now owned and operating under the care of the local community, the Isle of Muck Community Enterprise Ltd (IoMCE) and Isle of Muck Power Ltd.

Edinburgh based Synergy Scotland successfully managed the project with Aberdeen based Senergy Econnect providing the initial system design.

The primary contractor was Perth based SSE Contracting who are one of the UK’s largest mechanical and electrical contracting businesses. They integrated the new generating plant with the electrical network and installed the new backup generator. Civil Engineering contracting was provided by Ross-shire based GG Mackenzie Contractors ltd.

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