Isle of Eigg

The Isle of Eigg, at 8km by 6km, is the second largest of The Small Isles 16km off the Western Coast of Scotland south of the Isle of Skye.

With just over 100 inhabitants, it is also the most populous. Eigg boasts a wide variety of coastal scenery, ranging from beaches and spectacular cliffs, to historic caves.

Once boasting a population of 500, the island was left with just 64 inhabitants before local residents completed their ambitious £1.5million purchase of the land in 1997, after decades of mismanagement by absentee landlords. Since then, the depopulation trend has been reversed, with Eigg now thriving and home to 105 residents, thanks in large part to the work of the Isle of Eigg Heritage Trust, (a partnership between the residents of Eigg, the Highland Council, and the Scottish Wildlife Trust) which was set up to drive through the deal. New homes have been built, tenants have been given security of tenure, and the island generates virtually 100% of its electricity using renewable energy.

Visit www.isleofeigg.org for more information.

Prior to 2008 the Isle of Eigg was not served by mains electricity, with most properties relying on ageing diesel generators for power.

In 2008, the Isle of Eigg became almost totally independent from oil imports from the mainland and from fossil power sources by switching on a unique hybrid system. This pioneering Sunny Island system was designed & installed by Wind & Sun and enabled over 90% of the island’s power to be generated from renewables - ensuring 24 hours energy for the first time to all 46 households, 21 businesses and 6 community facilities on the island.

The Isle of Eigg Electrification project has provided an electricity supply for the island which is sustainable both environmentally and economically. The Isle of Eigg Heritage Trust formed a company, Eigg Electric Ltd, to procure and operate a mains-type electrical network system for the islanders, to provide an electrical supply similar to that enjoyed by people living on the mainland with the aims of the generation of predominantly renewable electricity and the supply of a reliable 24 hour electricity supply for all islanders.

Various renewable sources distributed around the island were incorporated to allow diversity of energy supply, - solar PV , three hydro turbines (6 kW, 6 kW & 100 kW) and a 4 x 6kW wind turbines all supported by standby diesel generation and batteries to guarantee continuous availability of power. Properties on the island are connected using a 3.3 kV three-phase distribution system. Load management is used to ensure optimal use of the renewables. The battery/inverter system provides the basis for the island mini-grid together with system control. Wind & Sun worked with Econnect Ventures to design this alongside SMA and this became the world's first Sunny Island Multicluster system.

This scheme provides encouragement for operators of other isolated off-grid systems to adopt these technologies, both in the UK and overseas.
It also demonstrates that high proportions of renewable energy can be accommodated within distribution networks, encouraging attempts to integrate increasing proportions of renewable energy into existing networks to help the UK achieve its CO2 reduction targets.

Listen to the BBC audio link which describes the background to the electrification project (RealPlayer required).

Synergy Scotland managed the electrification project using Scottish Hydro Contracting as main contractors and Wind & Sun worked for them as specialist sub-contractors.

In January 2007 we undertook the installation of the PV array, battery store and Sunny Island inverters. Installation of the island grid was carried out by Scottish Hydro Contracting over the summer months, which involved the laying of several km of cables together with the associated transformers and switchgear as well as the updating and testing of the wiring to all the properties on the island. G.G.Mackenzie Contractors Ltd undertook all the groundworks and laying of cables.

Scottish Hydro also installed the new 100kW water turbine, pipeline and weir.

Power was switched on to the island on 1st February 2008.

Residents of the Isle of Eigg now have 24 hour a day electricity powered by renewable energy and have gone from lacking a technology that defines the modern age, to possessing one that the rest of us are still struggling to develop. It is an inspiring example.

The main battery inverters are the heart of the system and provide a reference grid to which all loads and generation is connected. They control the system voltage and frequency, and manage the balance between loads and generation by controlling the power into and out of the batteries.

Additional system control is provided by load management at times of high renewable generation.

Twelve Sunny Island SI-5048 5kW inverters are used connected in four three phase clusters to give a total output rating of 60kW.

A MultiCluster Box MC-Box-12 is used to combine the cabling from each of the Sunny Island inverters and provides contactors for the connection to the island grid and the back-up generator.

Each cluster is connected to a 48V 2242 Ah (C10) battery bank consisting of 24 Rolls Solar RB 4KS25PS batteries fitted with Hydrocaps to reduce maintenance.

Total energy storage is approx. 212kWh to 50% DOD.

The main benefit of the PV array is during the summer months when its output is high, complementing the lower output that is expected from the hydro generation and the wind turbines (due to low summer rainfall and low summer windspeeds). Because of the uncertainty regarding the load profile and the intermittency of the renewable sources, diesel generation will provide backup power to ensure a reliable supply for the island is maintained.

The PV array is located close to the power house which houses the batteries, inverters and standby diesel generators. It consists of 60 BP Solar BP3165S PV modules mounted on an aluminium ground mount support frame. They are wired in six series strings of 10 modules with three pairs of strings each connected to an SMA Sunny Boy SB-3000 inverter.

The PV array is connected to the low voltage side of the AC network via these grid-connect inverters. This will allow the PV output to feed the island loads directly. Surplus output is stored in the batteries.

A new 22 kWp PV array was added in April 2011 to increase generation over the summer months.

Four Proven 6kW wind turbines on 15m towers each connected to SMA Windy Boy WB-6000A inverters are sited at the Southern end of the island where the best wind exposure is obtained.

These give best output over winter months and have potential to work 24 hours per day.

These were installed by Energy Renewed Ltd a local Proven installer based in Aberdeen who were well placed to deal with the logistics of getting the equipment to the island and the construction there. Maintenance is carried out by the Eigg Electric team.

The new grid electricity supply connects every property on the island. Households are limited to 5kW and businesses 10kW. Electricity is purchased using pre-payment cards and every property has a wireless 'Owl' energy monitor so people can see how much electricity they are using.

Nearly every light bulb on the island is low energy and the islanders are well used to energy conservation and understand much more about energy than on the mainland.

Some properties used to have their own small power system (generator and inverter etc...) and have a change-over switch so they can switch over from Eigg Electric to their own private supply if required. In the community buildings (Tea Room, Community Hall and Churches) plug-in load controllers (Frequency Controlled Switches) are used to switch on background heaters to utilise surplus renewable energy in times when the battery store is full.

In May/June 2010 there was very little rain on Eigg, resulting in reduced hydro generation & increased diesel generator support. So a new 22 kWp PV array was proposed with this being installed in April 2011.

This had always been planned for in the original electricity scheme design but due to constraints of budget the funds available were spent on installing a larger hydro turbine. This made sense since the hydro could not be increased in size at a future date but PV’s because of their modular nature and the flexibility of the Sunny Island system could be added to very easily.

Eigg were successful in obtaining funding from the Nesta Big Green Challenge (a national competition with three finalists each receiving £300,000 to develop further their community-based carbon reduction schemes); and the Ashden Awards which are given to sustainable energy projects.

After an abortive trip in February (when strong winds meant the ferry failed to make the last 100m to the pier on Eigg!) Wind & Sun installed the new PV system in March 2011 in snow with help from the Eigg Electric team! The new PV system was sited adjacent to the existing arrays and consisted of

126 x BP Solar BP4180 180Wp PV modules, connected to 3 x SMC-7000HV inverters and mounted on three Schletter PVMax-3 ground mounting frame.

Following the success of the previous upgrade, the islanders decided to add more PV’s which Wind & Sun installed in July 2013 – bringing the total PV contribution on Eigg to just over 50kWp.

The new 22.5kWp PV array used 90 x REC Solar REC 250PE 250Wp PV modules connected to 3 x SMC-7000HV inverters. The PV arrays are mounted on Schletter PVMax ground mounting frames.

Successfully Powering The Island

The life for the people has changed dramatically. They now can enjoy the luxury of modern living by using almost only renewable power sources. This unique system is entirely stand-alone and almost all the energy is made locally.

The system has now been running almost seamlessly for over 5 years and has proved that large scale off-grid applications are possible and that photovoltaic power can give an extremely productive valuable contribution, even in the north of Scotland.

Although the island population and loads are constantly increasing, the integration of new power sources such as additional PV has enabled sufficient renewable power to be provided to this growing community. Further steps to upgrade the system are under consideration.

In addition to the availability of 24hr power one of the greatest benefits is the reduction in diesel used to generate electricity. Fuel consumption has been reduced from 51,000 litres to 7,800 litres per year. This is a total saving of 85 %. Depending on the household or business, costs are between 25 % and 40 % now compared to before the electrification scheme. In addition, they no longer have noise or maintenance issues.

The extra PV array reduces this fuel consumption further increasing reliability and reducing costs even more.

As the island developed it was realised that further battery storage and Sunny Island inverter power would be required in future so it was decided to upgrade the system's central battery inverter system.

The original system had used an SMA MultiCluster MC-Box 12 (for use with 12 x Sunny Island inverters) - so this was replaced with a new MC-Box 36. At the same time an extra new cluster of 3 x SI-8.0H-12 6kW Sunny Island inverters and an additional battery bank was fitted.

The new MC-Box 36 was then successfuly commissioned with the existing 4 x clusters of Sunny Island SI-5048 5kW inverters and the new Sunny Island Cluster.

The monitoring system was also upgraded from the existing Sunny Webbox to new Sunny Data Manager.

To further reduce the island's carbon footprint and to take advantage of the potential offered by the new MC-Box the original power control building was extended to double the size of the battery room and provide a new space to fit further Sunny Island inverters. At the same time funding was obtained for the addition of extra PV systems.

Contractors based on Eigg first made the concrete footings required for the ground mount frames over winter in difficult conditions with consistent rain and boggy ground conditions. All the equipment needed was shipped to the island, then after a bumpy journey to the island on the Spanish John landing craft (due to ferry cancellation because of stormy weather) Wind & Sun installed the PV systems with help from our good friends Solar Kinetics and ProFit Energy.

The additional PV consisted of two components:

a) Ground Mounted alongside existing PV arrays on the hillside above the power building

Five South Facing 9.36kWp arrays each consisting of 2 x Schletter PVMax ground mounting frames with 22 x REC Solar REC-440AA 440Wp PV modules on each connected to SMA STP-20000TL 20kW inverters.

b) Roof Mounted on the Eigg Electic power control building

One East and one West Facing 10.56kWp array each consisting of 24 x REC Solar REC-440AA 440Wp PV modules connected together to a SMA STP-20000TL 20kW inverter.

Eigg’s population has increased by 70% since 1997 to 110 strong and visitor numbers have more than doubled in the past 10 years to 11,000 per annum. The increasing number of households and businesses has meant that the 78kW Sunny Island inverter capacity would soon be limited in meeting the needs and demands of Eigg’s growing population. Planned development of the An Lamrhig pier centre with improved tearoom, shop, offices and workshops would further increase power demand.

Increasing the inverter and storage system aims to tackle these pressures to improve opportunities for Eigg’s residents, its economy and environment allowing full benefit to be obtained from the recently expanded PV system

The upgrade of the system on the neighbouring Isle of Rum to use lithium-ion batteries(see here) resulted in their old Sunny Island inverters becoming available, so these were shipped to Eigg for re-use.

These three clusters each of 3 x SI-5048 were then installed in the extended power control building along with three new Rolls battery banks.

The installation was completed in time for the June 12th 25th anniversary celebration of the community buyout of the island.

Following on from this two more clusters (one of 3 x SMA Sunny Island SI-5048 and one of 3 x SMA Sunny Island SI-8.0H inverters) and two further battery banks were added in February 2023.

This brings total Sunny Island Battery inverter power to 156 kW (10 x 3 phase clusters) and total battery storage of approx. 530 kWh to 50% DOD.