Graham Brennan discusses the results of analysis and testing of the elements needed to build such an all-electric island using the Aran Islands as a model and examines whether the island of Ireland could one day benefit by applying this concept to its own energy system
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Author: Graham Brennan, transport programme manager, SEAI

Introduction


Imagine an island with no fossil fuel resources of its own situated in the wild Atlantic ocean with an abundance of wind and ocean power available to it. How could it break its dependence on ship borne supplies of fuels while turning its harsh environment into a valuable asset?

These were questions pondered by the Sustainable Energy Authority of Ireland (SEAI) when invited to meet the people of the Aran Islands a number of years ago. What started out as a discussion topic sowed the seeds for a longer-term exercise to answer this question through meaningful research and demonstration activities.

One obvious answer is to make the most use of the available wind and wave power. This could be achieved by ‘electrifying’ the demand for heat and transport by replacing existing fossil fuel systems with heat pumps and electric vehicles (EVs). These systems can store surges of renewable energy. An electrical interconnector could then be used to supply top-up electricity or trade any surplus energy generated on the islands.

This article discusses the results of analysis and testing of the elements needed to build such an all-electric island using the Aran Islands as a model and examines whether the island of Ireland could one day benefit by applying this concept to its own energy system.

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Fig. 1 Aran Islands’ wind resource and 3MW interconnection

The all-electric island model concept


The Aran Islands are rugged with little biomass growth potential and rely mainly on tourism, fishing and craft work for income. The population of the islands is 1,225 and there are an estimated 337 passenger vehicles in operation comprising mainly cars, 4x4s and minibuses. The heating systems include oil central heating and open coal fires.

A 3MW subsea interconnector links the islands to mainland Ireland and all three islands are linked together electrically (see Figure 1). On average, the islands consume a total of 1,493 tonnes of oil equivalent energy each year. Of this total, 13 per cent is used in transport, 23 per cent is used for electricity and 64 per cent of the energy is consumed heating the homes on Aran.

The first step in developing an all-electric energy system for the islands was to assess the scale of wind, wave and tidal resources available to the islands.  The tidal current speeds were considered to be too low and were discounted. Unsurprisingly, the theoretical wind and wave resources were found to be several hundred MWs in scale.

But when National Heritage Areas (NHAs) and Special Areas of Conservation (SACs) on or surrounding the islands were considered, the accessible resource reduced considerably to 18MW, most of which comprised offshore wave energy. This number was far in excess of the limit of 3MW set by the electrical cable and considered adequate in size in order to allow full electrification of the island’s energy demand.

Redevelopment of 675kW wind farm site


The best chance for onshore wind farm development within this planning regime was considered to be a redevelopment of a 675kW wind farm site which existed on Inis Meáin at the time. This study therefore assumed that any wind energy system would be located there and kept within a reasonable size. For each day of the year, hourly profiles of wind power and wave power were created.

Similarly hourly profiles for transport demand and heat demand were estimated for each day of the year and scaled using typical combustion efficiencies and known volumes of oil being shipped to the islands each year. This allowed the daily heat demand (kWh) and transport demand (km) profiles per household to be determined.

In the all-electric model, it was then assumed that heat pumps and EVs would be used to meet those daily demand requirements. By considering the efficiency, storage capacity and the power rating for each system, it was then possible to determine how much energy these systems needed and when they were available for storage.

An algorithm was created which determined how much power was required to meet both the normal electrical demand (e.g. lighting) and the power required by the combined number of EVs and heat pumps available each hour. The algorithm firstly optimised the timing of supply to the EVs and heat pumps to maximise the consumption of locally produced wind and wave power and then secondly, optimised the charging time to coincide with the time of cheapest imported electricity prices (i.e. night-time tariff rates). Any surplus power was then exported to the mainland.

When 100 per cent of the available vehicles and heating systems were converted to EVs and heat pumps, the all-electric model showed that the energy imports to the islands could be reduced by 84 per cent in the following stages (see Figure 2):

  • Firstly, with basic energy efficiency (thermal and electrical appliances) the energy imports from all sources fall by 23 per cent;
  • Secondly, as EVs and heat pumps are energy efficient and consume electricity instead of imported fossil fuels, they reduce energy imports with the ratio of 4:1 resulting in a substantial 48 per cent reduction in imports;
  • Thirdly, as EVs and heat pumps store intermittent renewable energy, they allow a greater amount of the energy demand to be supplied from local generators thus displacing energy imports by a final 13 per cent with respect to 2008 levels.

The above all-electric island system required only 1.8MW of wind power to be installed to power the islands. The remaining top-up energy required by the system would then come predominantly from imported electricity. However, there are times during the year when the production of renewable energy on the island exceeds the island’s requirement resulting in energy export.

When this volume of exported electricity is subtracted from the imports it was found that the island would have an annual net import of energy of three per cent indicating that the island is near self-sufficient on a net energy supply basis.

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Fig. 2 Energy imports reduced by 84% mainly for the all-electric Aran Islands model

Despite all of this conversion of demand to the local electricity grid, the overall electrical energy demand is predicted to rise by 28 per cent, most of which would occur during the night-time valley.

 

Electric Vehicle (EV) demonstration


It was decided to conduct an experiment to see if EVs would actually work on the islands and achieve the impact on energy imports predicted by the study. A trial of  eight vehicles began in 2011 and lasted a little more than three years. The vehicles were passed to a new set of drivers each year with a total of 30 drivers participating.

The Axiam Mega ECity (see main picture) vehicle was chosen for its use of regenerative breaks, corrosion-resistant aluminium chassis and ABS body panels. While the vehicle had only a range of 60km its energy efficiency is considered representative of modern EVs. The vehicle used maintenance-free gel-sealed lead batteries which was the only realistic option available at the time of the trial.

The performance of the EV was compared against that of a one-litre diesel vehicle. The vehicle chosen was a Citroen C1 which is of similar weight and dimensions. While the diesel vehicle was not tested on the islands, only the manufacturer’s information was used for comparison purposes.

As there are no wind turbines on Aran these days, all electricity is supplied from the mainland. The electricity supplied to the EVs was matched to the CO2 intensity and wind energy content of the national electricity system for each hour period of operation. The following results were obtained:

  • An equivalent new diesel car would require three units of energy for every one unit for the EV;
  • The EV energy cost was 1.9c/km and 8.7c/km for the diesel, giving a 78 per cent saving;
  • Wind energy content was 19 per cent, which compared with 2.8 per cent biofuels by energy in transport fleet in 2013;
  • CO2 reduction of 44 per cent was demonstrated.
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Smart Meter used to measure electricity consumption

The savings potential predicted for EVs by the all-electric study, where the old fleet of vehicles were considered to be replaced, are therefore confirmed by this trial. The islanders adapted very well to the use of the EVs and more than 90 per cent indicated that they would like to switch to electric drive when vehicle prices were favourable. The vehicles were leased and managed by Merrion Fleet, which removed the vehicles from the islands at the end of the trial.

 

Community energy efficiency programme


As part of their own activities, the islands established the Aran Islands Energy Co-Op, which has been busy promoting insulation upgrades and energy awareness on the islands. As of 2013, the community had achieved a 16 per cent reduction in imported heating fuels.

Once all measures are installed with funding from SEAI’s Energy Efficiency programmes, this figure is expected to rise to 24 per cent in 2015, thus falling in line with the assumptions of the all-electric study.

The co-op estimates that more than half of the properties have benefited from the installation of at least one energy-efficiency retrofit, leaving significant margin for further improvement in time. Going forward, it is envisaged that progress towards the development of a new community-owned wind farm will also be made.

Before realising the all-electric Aran Islands, further work is required to determine the ability of the local grid to operate with such a high number of EVs, heat pumps and renewable power. Smart grid components must be developed and tested to trigger the operation of these storage systems. Finally, a low-cost heat pump with high energy density storage suitable for retrofit is also required.

 

An all-electric Ireland?


The Aran All Electric concept has shown that an island with a large wind or wave resource could substantially reduce its energy imports by electrifying the demand for transport and heat. If this all-electric island model could be applied to all of Ireland, what benefits could it bring and what would our energy system look like?

In applying the results of the Aran model to Ireland, firstly we must recognise that energy demand on Aran is only representative of domestic and light commercial energy demand. The effect of heavy industry must therefore be added with industrial heating loads replaced with electrical heating systems.

Transport use in Ireland is approximately one-third of energy demand which is higher than Aran. Therefore with these differences in mind, an estimated energy import reduction of 50-60 per cent may be possible with a fully electric Ireland system. However, a more detailed study would be required before confirming the true scale of the saving. Instead of importing gas, coal and diesel, Ireland would seek to supply its energy demand from local renewable resources first and then import electricity from neighbouring electricity markets.

Alternatively, renewable power would be available for international trade in times of surplus generation. With the EU target of achieving a zero CO2 emitting electricity sector by 2050, any electricity imported when added to our own renewable power would result in a net energy import neutral economy with near zero emissions.

But what would such an energy system look like? Firstly we would become an island greatly interconnected to the UK and mainland Europe. We would have a highly developed onshore and offshore wind and wave energy resource. Increasing use of EVs and heat pumps would reduce our national energy demand and increase consumption from local renewable resources.

Conventional generators mothballed


Over the decades, Ireland’s conventional generators would all eventually be mothballed and displaced with DC electrical interconnectors to Europe such as the recently constructed state-of-the-art 500MW East-West interconnector joining Ireland to Wales (Figures 4 and 5). DC interconnectors themselves would provide convenient connection points for large offshore wind and wave farms.

The French and UK electricity markets are substantially bigger than Ireland’s. Using interconnectors, energy from these markets would be required for two main purposes 1) to supply planned daily power in cases of low renewable generation in Ireland and 2) to supply emergency power in cases of power failure conditions. Appropriate international agreements would be required to ensure Ireland’s market requirements are integrated into any future planning for those networks.

One major problem with this model of relying entirely on renewable energy and imported DC power however is frequency control. Under a conventional system which comprises a network of large power stations, should a generator suddenly fail, a power imbalance would be created and the AC frequency of the system shifts.

The spinning inertia of the remaining generators arrests this falling frequency thus buying time to increase power station output and recover control. Without this in-built inertia, the system could quickly become unstable and generators could shut down in sequence like a set of dominoes.

Renewable energy systems such as wind and solar PV system are currently considered by grid operators to reduce the amount of system inertia. In Germany in the summer of 2012, for one 45-minute period, 50 per cent of the generation capacity was supplied from wind and PV which worried the system operators greatly. Therefore, low system inertia is a growing problem for all electricity network operators.

Renewable generators with appropriate AC converter technology


Solutions to this problem may be at hand, however. It is considered that renewable generators with appropriate AC converter technology can in fact be configured to provide frequency control. A modern DC interconnector can quickly add or remove electrical energy from the national grid (see Figure 4) helping to restore energy balance if so configured. Similarly, smart grid controlled EVs and heat pump loads could be dropped out in emergency conditions until frequency is restored.

Battery storage systems in EVs and in homes could be rapidly switched on to provide power to the grid thus delivering ‘synthetic inertia’. To illustrate this particular contribution, it is estimated that 1.3 million EVs (equivalent to 50 per cent of 2030 cars stock numbers) each with 100kWh of battery storage could supply Ireland’s winter electrical energy demand for a single 24-hour period.

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Fig. 4 500MW Power Converter Station in Woodland, Co. Meath connecting Ireland and Wales– Banks of powerful transistor switches are digitally pulsed in sequence to convert 3 phase current from AC to DC or vice versa

This ‘all-electric Ireland’ concept may sound like a radical future energy system where conventional power stations are finally wound down in Ireland. However, if we follow the trends towards greater renewable generation, electric mobility, low thermal demand dwellings and a political desire for integrated markets offering greater consumer choice, we may already be on an inevitable path towards becoming an all-electric island.

Our larger European neighbours have a desire for more renewables without the space to accommodate them and may therefore need to rely more heavily on conventional power systems with carbon capture technologies and nuclear fission. Let us therefore take advantage of our small size and use our own ingenuity to unleash this large tradeable renewable energy resource which prevails at our doorstep.

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Fig. 5 AMC Connector cable laying ship was used on its maiden voyage to lay DC cable from Ireland to Wales

 

http://www.engineersjournal.ie/wp-content/uploads/2015/09/aev21.pnghttp://www.engineersjournal.ie/wp-content/uploads/2015/09/aev21-300x300.pngDavid O'RiordanElecelectric vehicles,fossil fuel,SEAI,wind farms
  Author: Graham Brennan, transport programme manager, SEAI Introduction Imagine an island with no fossil fuel resources of its own situated in the wild Atlantic ocean with an abundance of wind and ocean power available to it. How could it break its dependence on ship borne supplies of fuels while turning its...