ORKNEY'S ENERGY FUTURE
RESULTS
ELECTRICITY DEMAND AND GENERATION
This section will consider the results in the context of the generation and future infrastructure scenarios (Figure 1).
Figure 1: Electricity generation and transmission scenarios.
CURRENT ELECTRICITY DEMAND AND GENERATION
(SCENARIO 0)
Based on a current electricity demand of approximately 157 GWh and wind data from years 2014 to 2018, the average potential electricity generation from onshore wind is 291 GWh, resulting in an average annual electricity surplus of 134 GWh.
Table 1: Annual potential electricity generation and surplus based on current 157 GWh electricity demand.
Due to the limitations in the Orkney electricity network, not all this generation can be realised and a significant percentage – 38% in 2018 – is lost through curtailment (Figure 2). Due to the large onshore wind capacity, Orkney is a net exporter of electricity and just 1.8% of its electricity needs is calculated to be imported in Scenario 0. A primary aim of this project was to determine how far this electricity surplus could go to decarbonise the most fossil fuel intensive sectors of Orkney’s economy – domestic buildings, road transport and marine transport – in line with its ambition to decarbonise by the end of 2030.
Figure 2: Hourly electricity demand and generation profile for January 2018 showing curtailed electricity generation and surplus.
CURRENT ELECTRICITY GENERATION WITH DECARBONISATION
(SCENARIO 1)
The technologies identified as most suitable and technically feasible to decarbonise domestic heating, road transport and marine transport were air source heat pumps, electric vehicles and battery ferries, respectively. Calculated annual electricity demand for decarbonising all domestic heating, cars and 12 ferries totals 68.9 GWh. The current average annual surplus is 134 GWh. Therefore, it is possible to fully decarbonise these with the current electricity surplus (Figure 3). This would leave approximately 65.1 GWh remaining which could be used to decarbonise the energy system further although the magnitude of that demand is untested.
To test the robustness of this conclusion, the worst-case generation year between 2014 and 2018 was also considered. This was 2018 where 277 GWh could have been generated from onshore wind leaving a surplus of 120 GWh which would still be sufficient to decarbonise the sectors. The high case annual electricity demand of EVs – 18.7 GWh – was also considered and in this case the total demand would increase from 225.9 to 230.5 GWh leaving 60.5 GWh surplus.
Figure 3: Electricity demands arising from decarbonising domestic heating, cars and 12 ferries compared to annual average electricity generation.
The result of increasing the electricity demand while still relying on climate-based and therefore intermittent sources of electricity is that more electricity would be required to be imported to Orkney. The proportion of electricity demand being imported was calculated to be 7.1%.
FUTURE WIND FARMS
Connection of the planned wind farms would increase Orkney’s renewable generation capacity significantly (Figure 4). Adding the four and eight planned wind farms to the current installed capacity would generate 473 GWh and 925 GWh of electricity annually, respectively. These would create even greater electricity surpluses; 247 GWh and 699 GWh, respectively based on the current electricity demand of 157 GWh plus the calculated 68.9 GWh from decarbonisation of the sectors studied. With greater generation potential, less electricity would be required to be imported from the National Grid. With four additional wind farms the import rate has been calculated to be 1.5% and with eight additional wind farms it has been calculated to be 0.2%.
Figure 4: Energy generated from current installed wind capacity, current installed plus 4 more wind farms and current installed plus 8 more wind farms based on average generation using 2014-2018 weather data. Average total annual electricity generation is annotated (based on 2014-2018 weather data).
WASTED ELECTRICITY
Connecting further onshore wind capacity will increase Orkney’s renewable generation potential. However, its value could be limited depending on the infrastructure in place. ‘Wasted electricity’ is defined here as the electricity that can potentially be generated but in reality, has to be curtailed due to grid constraints. In Scenario 0, the calculated curtailment was 41%, which is consistent with values found in literature [1]. The wasted electricity and curtailment were calculated for all scenarios (Table 2).
Table 2: Electricity wasted per year in each scenario and corresponding level of curtailment.
To put this into context, the wasted electricity in Scenario 0 would be enough to heat a further 31,000 homes, based on the calculated electricity demand of the homes being decarbonised in Orkney.
The result for Scenario 1 shows that by increasing electricity demand, more of Orkney’s renewable electricity can be utilised therefore alleviating curtailment because any surplus electricity can be exported using the current 40 MW capacity cables (Figure 5).
In Scenarios 2a and 2b, generation is increased but no new transmission cable is built, meaning that only power up to a limit of 40 MW can be exported and when the export limit is reached, wind turbines are curtailed. Scenario 2a wastes 17.5 GWh per year - enough to supply power to almost 16,000 EVs in Orkney. In Scenario 2b, wasted electricity was calculated to be 363.2 GWh/year; this is enough to meet Scotland’s total electricity demand for almost 4 days [2]. If Scenarios 2a and 2b became a reality it is likely that the current curtailment problem will be exacerbated.
Figure 5: Surplus and deficit for January based on average generation using 2014-2018 weather data and demand after decarbonising domestic heating, cars and 12 ferries. The current surplus and deficit can be managed with the existing 40 MW cables but increased surpluses arising from additional onshore wind capacity exceed the 40 MW capacity which would result in curtailed turbines and wasted electricity.
HOURLY PROFILES
On an annual basis, there is sufficient surplus electricity to decarbonise domestic heating, cars and 12 ferries. However, it must be considered that the electricity system is dynamic and wind-based sources are inherently intermittent and unpredictable. When analysing hourly electricity demand and generation profiles, it is observed that there are instances where demand exceeds supply (Figure 6). The current distribution network allows power of up to 40 MW to be imported but when peak load is greater than 40 MW and generation is low, additional power would be required. At present this is provided primarily by Kirkwall power station but to avoid burning fossil fuels, the use of batteries could be considered. The modelling workflow to quantify the battery storage requirement in this case is presented here.
In scenarios where the electricity infrastructure network is upgraded and capacity increased (3a and 3b), it is considered that the supply deficit could be met by importing from mainland Great Britain.
Figure 6: Electricity demand and generation for one week in December based on 2018 weather data.
Another motivation to discharge batteries instead of importing from the National Grid is that electricity from the Grid has associated carbon dioxide emissions, while batteries have zero-emissions at the point of use. However, the National Grid has ambition to operate a zero-carbon system by 2025 [3]. Therefore, in this instance importing electricity would still align with Orkney’s goal to have an energy system free from fossil fuels.
AVAILABLE DOWNLOADS
The spreadsheet with the demand and generation calculations is available here.
REFERENCES
[1] Orkney Islands Council, "The Orkney Hydrogen Economic Strategy," Seafuel, 2019.
[2] Scottish Government, "Total final energy consumption by sector," [Online]. Available: https://scotland.shinyapps.io/Energy/?Section=WholeSystem&Chart=EnConsumption. [Accessed 13 April 2021].
[3] National Grid ESO, "Zero-carbon explained," 2021. [Online]. Available: https://www.nationalgrideso.com/electricity-explained/zero-carbon-explained. [Accessed 16 April 2021].