Proposals for a Battery Energy Storage System in Elstree

This website will share more information on BW ESS’ proposal for a Battery Energy Storage System (BESS), located at Hilfield Lane, Aldenham, Watford, WD25 8DD. The site, proposing a 170MW/425MWh BESS and associated infrastructure, would be accessible via Hilfield Lane.

This webpage will be updated as the project progresses. The local community matters to us and we look forward to your feedback, views and suggestions. This will help us refine our plans before submitting the planning application.

The Elstree development was originally proposed by Penso Power, a leading developer of BESS projects in the UK. Penso Power merged with its main shareholder, BW ESS, in October 2024. The Penso Power projects continue to be managed and delivered by the same team, integrated within the broader BW ESS platform.

BW ESS brings decades of expertise in energy infrastructure investment, delivery and operation, working alongside best- in-class developers, suppliers, contractors and financial institutions. Like Penso Power, BW ESS is committed to the long-term ownership and operation of its sites, which now includes all of Penso Power’s existing and future projects in England, including this project. As a result of being the long-term owner and operator of the projects we develop we look to establish and maintain good relationships with our neighbours and local communities.

Our UK BESS pipeline totals almost 2GW of connection capacity across 10 sites and the team’s track record includes development and deployment of the Minety project in Wiltshire, the largest in Europe at the time of its energisation in early 2021. Construction is currently underway on the 100MW/331MWh Bramley project in Hampshire and the 400MW Hams Hall project in North Warwickshire. Works will commence on our 200MW Berkswell project in Solihull later this year. BW ESS sites use top tier suppliers. Our fully warranted battery systems meet the latest safety and regulatory standards.

The site covers 6.1 acres/2.5ha of low-grade agricultural land (as classified by DEFRA mapping) and is within close proximity of the Elstree 400kV National Grid electricity substation, enabling connection with a minimum of disruption.

Whilst the site falls within the Green Belt, it does not fall within any protected national or local landscape designations or conservation areas. A Very Special Circumstances case, to justify what would be considered as inappropriate development in the Green Belt, will be submitted as part of any planning application.

The site is already well screened with existing trees and hedgerows, though new landscaping is proposed to further reduce any visual impact. This will take the form of planting of new native trees.

The facility does not need staff onsite; it is monitored remotely. Visits will be made to the site approximately once a month.

The existing footpath which lies adjacent to the site would not be impacted throughout construction or operation and would remain open.

A new access track would be constructed for construction and maintenance purposes.

The UK’s Electricity System was designed to carry electricity from the local coal and gas-fired power stations to local consumers. We are now replacing these local power stations with wind and solar generation, often a long way from customers.

The transition to distributed wind and solar electricity generation creates two issues. First, intermittency – the wind doesn’t always blow and sun doesn’t always shine. Second, network constraints, meaning the inability of the UK grid to transport electricity from where it is generated to where it is needed.

Battery storage solves these two key challenges:

• Batteries store excess electricity when generation is higher than demand and release it when demand is This can help balance our electricity system and mitigate grid constraints, lessening the need for expensive and disruptive network upgrades.
• Battery storage supports energy security and enables the addition of more renewable generation to our electricity system; thereby supporting lower emissions, lower costs and lower energy prices leaving current and future generations more prosperous.

This is why batteries are seen as a critical part of our electricity mix and why the Department for Energy Security and Net Zero and National Grid see battery storage as essential electrical infrastructure and a critical enabler of the energy transition.

Locating energy storage within those areas of highest energy demand, such as the South East of England, supports the resilience of our electricity system and provides security of supply to ensure there is sufficient capacity available to meet periods of peak demand.

The Elstree National Grid substation (approx. 300m to the north of the site) is a major grid supply point and has near term connection capacity available for a BESS project of this size.

This site has been chosen following an extensive site selection process (previously developed land and undeveloped sites have been considered in this search). The close proximity to the Elstree substation means the site can be connected with minimum disruption.

Whilst the site is in the Green Belt, it is free from restrictive planning constraints such as any protected national or local landscape designations or conservations areas or other constraints such as proximity to housing.

This project presents an opportunity to deploy much needed battery storage to support energy security both locally and nationally. It will also assist the Council’s commitment to achieve net zero carbon emissions no later than 2050.

Road access
Access to the site for construction and maintenance will be proposed by a new access track off Hilfield Lane.

Traffic
Construction is expected to take approx. 18 months with, on average, two deliveries per day. Once built the local traffic implications of the site are very low; typically, one van movement per month.
A Planning, Design and Access Statement, a Transport Assessment and a Construction Traffic Management Plan (setting out the avoidance of deliveries at peak times or weekends) will be submitted with any planning application.

Footpaths
The existing footpath that lies adjacent to the site will not be impacted by the proposal and will remain open both during construction and once the site is operational.

Like all of the land surrounding the sub-station, the site falls within the Green Belt. However, it does not fall within any protected landscape areas. A series of landscape and ecological enhancements will be made. The existing on site trees and hedges will be retained.

There will be no harm to protected species, and significant biodiversity net gain enhancements will be proposed, in excess of the 10% standard. This could include additional hedge & tree planting, bird and bat boxes, beehives, ponds, hibernacula, sowing of native wildflowers & grasses.

Landscaping
The hedgerows and trees will be retained and enhanced. New tree planting will be included in the landscape design and a number of ecological enhancements will be implemented. New native tree planting is proposed to infill gaps and help screen the site from views from the footpath. All of these improvements will be detailed when the planning application is submitted.

Visibility
The site is well contained within the wider landscape. As the battery units are around 3m in height, they are well shielded by existing and new vegetation surrounding the site.

Noise
Battery storage projects make little noise and they only operate for certain parts of the day. At times of peak output, the noise level experienced is still low. Studies have shown that the level of noise generated by battery storage units is the equivalent of a domestic dishwasher.

Ecology
A preliminary ecological assessment survey has been carried out which identified no requirement for further detailed surveys. The proposals will include mitigation during construction, where needed, to ensure no harm to flora or fauna, as well as Biodiversity Net Gain enhancements.

Flooding
The site falls within Flood Zone 1, with a low risk of flooding.

Enable clean energy transition

• Deployment of up to 170MW/425MWh of energy: Equivalent to powering 1 million homes for 1 hour.
• Contribute towards energy security and the UK Government’s commitment to reach net zero carbon emissions by 2050 and Hertsmere’s commitment to achieve net zero carbon emissions no later than 2050.

Enhance biodiversity

• Delivers biodiversity net gains onsite with the planting of new native trees and hedgerows. Other ecological enhancements could include bird and bat boxes, beehives, ponds, hibernacula sowing of native wildflowers and grasses.

Strengthen energy resilience for the UK

• Will enhance energy security and system resilience, ensuring there is sufficient capacity available to meet periods of peak electricity demand.
• Battery storage helps balance variable electricity demand with intermittent supply to enable the addition of more renewable generation to our energy system, supporting lower emissions, lower costs and lower energy prices.

Contribute to the local economy

• Payment of business rates to Hertsmere Council over the lifetime of the project, providing valuable revenue to help the Council deliver vital public services.
• Provide a monetary contribution to a local community fund on a yearly basis (for the duration of the project lifespan).

We are currently preparing a planning application, which is anticipated to be submitted in January 2025.