Got Approval but Still Not Started Construction? SSE Upgrades Its Energy Storage Project from 2 Hour

<p>On August 13, SSE Renewables announced that its revised proposal for the Mullafarry energy storage project in County Mayo, northern Ireland, had officially received planning approval. After the modification, the project scale will reach <span style="color:rgb(56, 158, 13)"><strong>80MW/320MWh</strong></span><span style="color:rgb(56, 158, 13)">.</span></p><p>Interestingly, the project's power capacity has actually remained unchanged at <span style="color:rgb(56, 158, 13)"><strong>80MW</strong></span><span style="color:rgb(56, 158, 13)">.</span> The real change is the storage capacity, which has been directly increased from the previous <span style="color:rgb(56, 158, 13)"><strong>160MWh to 320MWh</strong></span>, meaning the duration of the energy storage system has been extended from the original <span style="color:rgb(56, 158, 13)"><strong>2 hours to up to 4 hours</strong></span>.</p><p><img src="https://energyplanet.oss-cn-shenzhen.aliyuncs.com/uploads/images/20260819173642_83aaefa1.png" alt="" loading="lazy" decoding="async" /></p><h2>Before Construction Even Started, the Project Was Upgraded from 2 Hours to 4 Hours</h2><p>As early as April 2025, SSE had already obtained planning permission. At that time, the project was planned as an <span style="color:rgb(56, 158, 13)"><strong>80MW/160MWh system, capable of continuous charging and discharging for around 2 hours.</strong></span> SSE stated at the time that the stored electricity from the system would be equivalent to supplying more than <span style="color:rgb(56, 158, 13)"><strong>75,000 households</strong></span> with power for approximately two hours.</p><p>Under the normal project development process, obtaining planning approval would typically be followed by moving ahead with construction. However, SSE did not proceed directly according to the original design. More than a year later, SSE decided to revise the project plan. In June 2026, the company submitted a new planning application to the local authority, adjusting the project to:</p><p><span style="color:rgb(56, 158, 13)"><strong>80MW/320MWh, with a maximum storage duration of 4 hours. </strong></span>The power capacity remained unchanged, but the energy capacity was doubled.</p><ul><li>Original plan: 80MW/160MWh, 2 hours</li><li>New plan: 80MW/320MWh, 4 hours</li></ul><p>Why was the project changed to 4 hours? When SSE submitted the modification application in June this year, the company explained that the change was made partly in response to the latest developments in energy storage technology, and partly because electricity system operators are seeing increasing demand for reliable and flexible power reserve capacity.</p><p>Previously, many storage projects were designed around a 2-hour duration. However, the current expectation is that storage systems should be able to store more electricity at once and provide support to the grid for a longer period. Therefore, the key purpose of this upgrade is not to make the energy storage system "discharge more powerfully", but to enable it to "discharge for a longer duration".</p><h2>Four Hours Matches Ireland's Current Energy Storage Policy Direction</h2><p>In recent years, Ireland has been continuously increasing the role of energy storage in its power system. In July 2024, the Irish government officially released the country's first <span style="color:rgb(56, 158, 13)"><strong>Electricity Storage Policy Framework</strong></span>, formally integrating energy storage into future electricity system planning.</p><p>Ireland aims to achieve <span style="color:rgb(56, 158, 13)"><strong>80% of electricity demand being supplied by renewable energy by 2030</strong></span><span style="color:rgb(56, 158, 13)">. </span>However, as wind and solar power continue to grow, having more renewable generation alone is not enough. How to store electricity when generation is high and release it when supply is insufficient has naturally become increasingly important. As a result, the role of energy storage has also grown.</p><p>Interestingly, one point in the storage policy framework closely aligns with the upgrade of Mullafarry. In <span style="color:rgb(56, 158, 13)"><strong>Action 6</strong></span><span style="color:rgb(56, 158, 13)"> </span>of the policy framework, Ireland clearly proposed advancing the procurement of long-duration energy storage services. Relevant storage systems should be capable of continuously supplying electricity to the transmission system for <span style="color:rgb(56, 158, 13)"><strong>4 hours or more</strong></span><span style="color:rgb(56, 158, 13)">.</span></p><p>Later, in October 2025, Ireland’s transmission system operator <span style="color:rgb(56, 158, 13)"><strong>EirGrid</strong></span> further launched a consultation on long-duration energy storage procurement mechanisms, beginning to explore how storage systems of <span style="color:rgb(56, 158, 13)"><strong>4 hours and above</strong></span> could be formally incorporated into procurement arrangements.</p><p>It should be noted that SSE did not state that the project modification was specifically intended to participate in this long-duration energy storage procurement mechanism. However, judging from the storage duration alone, the direct upgrade from 2 hours to 4 hours is clearly aligned with Ireland's current energy storage development direction.</p><p>Moreover, Ireland is not simply issuing policy documents without further action. In June this year, Ireland further eased restrictions on energy storage. The <span style="color:rgb(56, 158, 13)"><strong>Commission for Regulation of Utilities (CRU)</strong></span><span style="color:rgb(56, 158, 13)"> </span>adjusted transmission network charging rules for storage systems, aiming to make it easier for storage assets to participate in wholesale electricity markets. At the same time, the long-duration energy storage procurement framework continues to move forward.</p><p>Looking at this series of developments, Ireland's current goal is clear: as wind and solar capacity continues to expand, the country not only needs energy storage to participate more actively in electricity markets, but also needs more storage resources capable of supporting the power system continuously for several hours.</p><p>Against this background, SSE's decision to upgrade Mullafarry from a 2-hour project to a 4-hour project before construction even began becomes much less surprising.</p><h2>Located Next to SSE's Existing 104MW Power Station</h2><p>From a location perspective, Mullafarry is not an entirely independent new site. The project will be built on SSE-owned land, directly adjacent to the company's existing <span style="color:rgb(56, 158, 13)"><strong>104MW power station</strong></span><span style="color:rgb(56, 158, 13)">.</span> If SSE ultimately decides to move forward with construction, the latest official announcement estimates that the construction period will take up to approximately <span style="color:rgb(56, 158, 13)"><strong>two years</strong></span><span style="color:rgb(56, 158, 13)">.</span></p><p>However, it is important to note that <span style="color:rgb(56, 158, 13)"><strong>receiving planning approval does not mean the project will immediately enter the construction phase. </strong></span>SSE clearly stated in its announcement that whether Mullafarry will ultimately proceed to construction still depends on the company’s <span style="color:rgb(56, 158, 13)"><strong>Final Investment Decision (FID)</strong></span><span style="color:rgb(56, 158, 13)">.</span></p><p>The revised proposal has already received planning approval, but information regarding the final construction timeline, equipment suppliers, battery cell technology selection, and specific commissioning schedule has not yet been further disclosed by the company.</p><h2>Final Thoughts</h2><p>When SSE first obtained planning permission in 2025, Mullafarry was still an <span style="color:rgb(56, 158, 13)"><strong>80MW/160MWh, 2-hour energy storage project</strong></span><span style="color:rgb(56, 158, 13)">. </span>By 2026, before the project had even officially started construction, SSE had already redesigned the system and increased the storage capacity directly from 160MWh to 320MWh. Moreover, Mullafarry is not the only project undergoing this type of adjustment.</p><p>In Sweden, the <span style="color:rgb(56, 158, 13)"><strong>Vaggeryd project</strong></span> was originally approved with a storage capacity of <span style="color:rgb(56, 158, 13)"><strong>200MWh</strong></span><span style="color:rgb(56, 158, 13)">. </span>Ingrid later submitted a new permit application, doubling the capacity to <span style="color:rgb(56, 158, 13)"><strong>400MWh</strong></span>. The revised project scale became <span style="color:rgb(56, 158, 13)"><strong>100MW/400MWh</strong></span><span style="color:rgb(56, 158, 13)">,</span> corresponding to a <span style="color:rgb(56, 158, 13)"><strong>4-hour energy storage system</strong></span>.</p><p>In Northern Ireland, the UK, <span style="color:rgb(56, 158, 13)"><strong>ABO Energy</strong></span><span style="color:rgb(56, 158, 13)"> </span>is also redesigning an already approved <span style="color:rgb(56, 158, 13)"><strong>140MW, 2-hour Coolkeeragh energy storage project into a 140MW, 4-hour system</strong></span>. One project may simply be an individual case. However, when similar adjustments begin appearing in <span style="color:rgb(56, 158, 13)"><strong>Ireland, Sweden, and Northern Ireland</strong></span>, this trend deserves closer attention.</p><p>In the past, <span style="color:rgb(56, 158, 13)"><strong>2-hour energy storage systems</strong></span> were a common configuration for many large-scale projects. But now, project developers are clearly reconsidering a fundamental question: <span style="color:rgb(56, 158, 13)"><strong>For future energy storage projects, what duration will actually be the most suitable?</strong></span></p>