Meeting Ireland’s 2030 solar targets

In order for Ireland – north and south – to meet its solar targets for 2030, transmission system operators (EirGrid and SONI) must establish new control strategies and invest in new infrastructure to ensure system security, researchers from EirGrid and University College Dublin (UCD) have claimed.

In Climate Action Plan 2023, the Government significantly increased its 2030 targets for solar energy generation to 8GW from a previously outlined target of between 1.5GW and 2.5GW of solar photovoltaic (PV) generation.

According to figures released by the Irish Solar Energy Association (ISEA), the Republic generated a total of just under 1.2GW of solar energy in 2023, a 42.6 per cent increase on what was generated in 2022.

In the North, 126GWh of electricity was produced by solar PV between July 2023 and July 2024. There is no specific target for solar energy in the North, although there are broader decarbonisation targets emanating from the Climate Change Act (Northern Ireland) 2022.

The paper – authored by five members of EirGrid’s Innovation and Planning Office, as well as Federico Milano, a professor at the School of Electrical and Electronic Engineering at UCD – outlines four key challenges related to solar PV which, while manageable at current solar penetration levels, will become more acute as the State expands its solar PV levels to meet the 2030 targets.

1. Dispatch down

The researchers assert that the rapid growth of solar PV, although currently at lower levels compared to wind, is already creating challenges for real-time grid management. Dispatch down occurs when grid operators order output reductions from renewable energy sources, either due to local network constraints or system-wide curtailment.

While wind power faces dispatch down challenges – mostly during the night when demand is low – solar PV output typically coincides with daytime demand peaks, reducing its frequency of curtailment.

Current dispatch down levels for solar PV are lower than for wind, but the gap is closing. In the North, solar PV dispatch down has been driven primarily by local network constraints. As more solar capacity is added, particularly distributed systems like rooftop PV, curtailment might increase, making grid management even more complex.

2. Frequency stability

Perhaps the most significant operational challenge introduced by solar PV is its impact on frequency stability. Unlike wind, solar PV can experience rapid fluctuations in output due to passing clouds, leading to more erratic supply profiles. These fluctuations are reflected in grid frequency, with deviations from the normal operating range (49.80 Hz to 50.20 Hz) becoming more frequent as solar PV penetration increases. Although solar accounts for a small share of Ireland’s total generation, its high variability is already driving an increase in the number of ‘violation minutes’, i.e. instances in which the grid’s frequency exceeds operational limits.

The challenge is compounded by the fact that most of Ireland’s solar generation is concentrated in specific areas, reducing the natural averaging effect seen with more geographically dispersed wind farms. Geographical aggregation of solar installations could mitigate this challenge, but it remains an area requiring further attention.

Moreover, the paper outlines how reductions in the minimum number of conventional units online (MUON limit) exacerbate the problem by reducing the amount of available reserve power to stabilise frequency.

EirGrid’s Operational Policy Roadmap 2023-2030, published in December 2022, reduced the MUON limit to seven units, which the UCD researchers assert has already contributed to a deterioration in frequency quality.

The researchers argue that increased solar penetration will require more sophisticated frequency control measures, including active power control in both solar and wind plants, to ensure stability as more non-synchronous generation is introduced.

3. Voltage magnitude variations

Solar PV also presents challenges for maintaining voltage stability. As demonstrated in the paper’s case study, rapid changes in solar output can lead to over-voltage conditions, especially in areas with high solar PV penetration. Voltage magnitude fluctuations, if left unmanaged, can damage electrical equipment and reduce the overall reliability of the grid. While reactive power control can mitigate these effects, additional voltage support infrastructure will be necessary as solar penetration increases.

Capacitor banks, static VAR compensators, and synchronous condensers are some of the solutions being mooted as solutions to local voltage challenges, particularly in areas with significant solar capacity.

4. Minimum operational demand

Another operational challenge highlighted by the researchers is the impact of minimum operational demand. As more distributed solar PV systems, such as rooftop installations, come online, the operational demand on the transmission system could, the researchers argue, drop to levels that make it difficult to maintain the MUON limit. During sunny days with high PV output, operational demand could fall so low that grid stability is threatened.

This ‘duck curve’ effect, where demand drops during the day due to rooftop PV generation but spikes in the evening as solar generation declines, is already becoming a challenge in regions with high solar penetration.

Energy storage systems, such as batteries, could provide a solution by storing excess solar power during the day for use in the evening. However, without sufficient storage capacity, grid operators may be forced to curtail solar PV output to maintain grid stability.

The EirGrid/UCD paper emphasises the importance of enhancing the grid’s visibility and controllability over distributed solar systems. Solutions such as advanced metering infrastructure (AMI) and smart grid technologies could provide the necessary tools to manage these fluctuations in demand and generation.

Conclusion

The integration of solar PV into the all-island power system (AIPS) introduces a new set of operational challenges, distinct from those posed by wind energy. While Ireland’s energy transition towards renewables is essential for meeting climate targets and legally binding, the rapid growth of solar PV requires grid operators and policymakers to rethink grid management strategies. Frequency stability, voltage control, dispatch down, and managing minimum operational demand will all require innovative solutions as solar PV continues to grow.

While the researchers accept that EirGrid and SONI are already taking steps to address these challenges, they nonetheless insist that further investment in grid infrastructure, control technologies, and storage solutions will be essential to ensure the long-term stability and reliability of the AIPS as it transitions towards a more sustainable future.