A containerised outdoor BESS is the workhorse of commercial battery installation. The battery, inverters, protection and thermal management arrive as a factory-integrated, tested container or skid, so the on-site work is groundworks, a crane lift, terminations and commissioning rather than a build-up from components. For sites with yard or hardstanding but little internal plant-room space, it is almost always the right answer, and it is the only practical route to multi-megawatt capacity.
The engineering that matters happens before the container arrives. We confirm the incoming supply capacity and available fault level, design the foundations or reinforced hardstanding, settle the separation distances and firefighting access, and fix the connection route with the DNO. Get those right and the physical install is short and low-risk; get them wrong and the container sits on site waiting for a connection or a fire-authority sign-off.
How we install containerised outdoor bess
Delivery runs: reinforced hardstanding or foundation slab poured to structural design; ducting and cable routes laid; the container craned into position with NFCC-compliant separation from buildings, boundaries and escape routes; LV or HV terminations into your switchgear; protection and G100 limitation commissioned; then witnessed testing. Bunding, ventilation clearances and firefighting access are set by the fire strategy agreed at feasibility.
What this install includes
- Factory-integrated container or skid landed on a prepared hardstanding, craned into position, and terminated into the site LV/HV supply
- Fastest route to multi-MWh capacity with the fewest inside-the-building fire and space constraints
- Fire separation, bunding, ventilation, and firefighting access designed to NFCC guidance and insurer requirements
- Ideal where indoor plant-room space is scarce but external yard or hardstanding is available
Typical containerised outdoor bess installation
- Power / capacity
- 250 kW / 500 kWh-2 MW / 4 MWh
- Siting
- external compound / hardstanding
- Project value
- £180,000-£2.4m
- Payback
- 7 years
Cost, funding and how it is paid for
A containerised outdoor bess installation typically runs to £180,000-£2.4m, with a 7-year simple payback once the demand-charge, self-consumption and resilience value is engineered in. As plant and machinery it attracts 100% AIA on the first £1m then a 50% first-year allowance on the balance — special-rate, so AIA, not full expensing. The 0% VAT relief covers only residential or relevant-charitable buildings. See the cost guide, capital allowances and grants and funding.
Fire safety, siting and compliance
Outdoor siting is the containerised system’s biggest safety advantage: a thermal event is outside the occupied building. We still design to PAS 63100:2024 principles and NFCC grid-scale guidance — separation distances from buildings and boundaries, firefighting access, detection and, where required, deflagration venting — and engage the fire and rescue service and your insurer before the container is ordered.
G99 connection agreement (G100 limitation where the DNO connection is constrained). Siting and separation to NFCC BESS planning guidance and PAS 63100:2024 principles; BS EN 62619 cells and BS EN/IEC 62933 system safety. Foundations/hardstanding to structural design; DSEAR assessment where relevant. CDM 2015 principal-contractor duties on most container installs.
Grid connection and commissioning
For a containerised outdoor bess installation, the DNO is the critical path. We submit the G99 application at survey, engineer a G100 limitation scheme where the network is constrained, and design the half-hourly metering so the control strategy and settlement are correct. Every install ends with a documented, witnessed commissioning and an O&M handover pack. Read our honest view on whether it is worth it.
Containerised Outdoor BESS Installation: at a glance
| Attribute | Typical for this install |
|---|---|
| Power / capacity | 250 kW / 500 kWh-2 MW / 4 MWh |
| Siting | external compound / hardstanding |
| Project value | £180,000-£2.4m |
| Simple payback | 7 years |
| Connection | G99 (G100 limitation where constrained) |
Get a free containerised outdoor bess installation feasibility
Responds within one working day
- 1. Free desk feasibility from your meter data and roof, no obligation.
- 2. Site survey and a fixed-price proposal, itemised in writing.
- 3. Install and aftercare by MCS-certified engineers.
- MCS Certified
- NICEIC
- RECC
- TrustMark
Common questions
How long does a commercial battery storage installation take?
Physical installation is typically 1-6 weeks on site for a behind-the-meter system. The overall programme, however, is set by the DNO: a G99 study and connection can run 3-18 months depending on network capacity in your area. We submit the G99 application alongside the survey so the clock starts immediately, and use a G100 limitation scheme where it lets the project proceed sooner. Grid-scale standalone projects run 18 months to several years including planning.
What is the G99 process and why does it drive the timeline?
G99 is the Energy Networks Association connection agreement required for storage above 16 A per phase, which covers almost every commercial system. The DNO reviews the connection, may require a network study, and sets the protection and metering requirements. Because network capacity is limited in many areas, the study and connection offer are usually the longest item on the programme. We prepare the application, single-line diagrams, and protection proposals, liaise with the DNO, and, where the network is constrained, engineer a G100 export/import limitation scheme so the site can connect within its existing agreed capacity.
Containerised outdoor BESS or an indoor cabinet, which suits my site?
It comes down to space, capacity, and fire strategy. A containerised outdoor system is usually the fastest route to multi-MWh capacity and keeps the fire and space constraints outside the building, but it needs prepared hardstanding, separation distances, and firefighting access. An indoor cabinet suits smaller systems (roughly 60-500 kWh) at sites with a suitable plant room or switchroom, but the room must be compartmented, ventilated, and fire-detected. We assess both against your available space, target capacity, and insurer requirements at the survey.
What fire safety standards apply to a commercial battery installation?
We design to PAS 63100:2024 principles for installation and fire protection, BS EN 62619 for cell safety, and BS EN/IEC 62933 for system safety, with NFCC guidance for larger and grid-scale sites. We specify lithium-iron-phosphate (LFP) cells for their thermal stability, and engineer separation distances, detection, thermal monitoring, and appropriate compartmentation or bunding. A fire risk assessment is produced and the insurer, and where necessary the fire authority, engaged before installation.
Do you handle the DNO application and grid connection, or do we?
We handle it as part of our scope: the G99 application, single-line diagrams, protection settings, half-hourly metering arrangement, DNO liaison, and witness-test coordination, plus the G100 limitation design where the network is constrained. You get one accountable contractor across survey, design, connection, install, and commissioning rather than having to coordinate a battery supplier, an electrician, and the DNO yourself.