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 usually the right answer, and it is the only practical route to multi-megawatt capacity.
The engineering that matters happens before the container arrives. The installer should 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 installation is short and low-risk; get them wrong and the container sits on site waiting for a connection or a fire sign-off.
How Containerised Outdoor BESS Installation is delivered
Delivery normally runs: reinforced hardstanding or foundation slab poured to structural design; ducting and cable routes laid; the container craned into position with the separation from buildings, boundaries and escape routes that the fire strategy sets; LV or HV terminations into the switchgear; protection and any G100 limitation commissioned; then the G99 commissioning tests, which the network operator may choose to witness. Bunding, ventilation clearances and firefighting access follow the fire strategy agreed at feasibility.
BESS installation, step by step
The sequence for a containerised system on a UK business site, from data to handover. The network connection and, outdoors, planning set the programme; the physical installation is the short part.
- Feasibility from your data. Twelve months of half-hourly meter data sets the power (kW) to the peaks the battery must shave and the energy (kWh) to how long it must run. The incoming supply capacity and available fault level are checked at the same time.
- The grid connection. A G99 application goes to the network operator. The registered capacity decides the G99 type: below 1 MW is Type A, 1 MW to under 10 MW is Type B, and the commissioning route follows the type (see G99 types).
- Planning. In England the permitted development rights for renewable energy do not include batteries, so an outdoor container usually needs planning permission. For 1 MWh or more, national guidance encourages you to talk to the local fire and rescue service before applying. See battery storage planning permission.
- Fire design and siting. The installation is designed to BS 7671, which gained a battery chapter (Chapter 57) in 2026, and the IET Code of Practice. For open-air lithium systems of 1 MWh or more, NFCC guidance proposes an initial 30 m between battery units and occupied buildings before mitigation is considered. Your insurer should see the layout now, not later.
- Civils. Foundation slab or reinforced hardstanding, cable ducts, drainage and a crane route, all designed before the container is ordered.
- Delivery and placement. The container or skid is craned onto its base, levelled and fixed, and the LV or HV terminations are made into the switchgear.
- Commissioning. Safety systems first, then the battery and power conversion, then the protection and G99 tests. Below 1 MW the Installation Document reaches the network operator within 28 days of commissioning; at 1 MW and above the operator needs details of the tests at least 28 days in advance. See battery storage commissioning.
- Handover. Electrical Installation Certificate, G99 records, settings, manuals, warranty registration and training, then the maintenance regime starts.
What is inside a battery container
A containerised BESS is a set of systems in one enclosure. Knowing them helps you read a quote and check what the warranty covers.
- Battery racks, usually lithium iron phosphate (LFP) cells built into modules, with a battery management system watching cell voltages and temperatures.
- Power conversion: the inverter or power conversion system that charges and discharges the battery, either inside the container or on its own skid alongside.
- Controls: the energy management system that decides when to charge and discharge, and the metering it relies on.
- Thermal management: air conditioning or liquid cooling to keep the cells in their operating range.
- Fire safety systems: detection and, depending on the design, suppression and deflagration venting.
- Switchgear, and for a high-voltage connection a transformer, usually as separate equipment beside the container.
What this installation 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
- Published cost range
- About £140–£240 per kWh at 500 kWh and above
Cost, funding and how it is paid for
Containerised systems of 500 kWh and above are published at around £140–£240 per kWh installed, so a 1 MW / 2 MWh container works out at roughly £280,000–£480,000 before any major grid works. Hardstanding, cranage and the separation the fire strategy needs are the site costs most likely to move a containerised quote. As plant and machinery, a containerised outdoor bess installation can qualify for the Annual Investment Allowance, which gives 100% relief on up to £1m of qualifying spend a year; above that, the treatment depends on how the battery is classified, so confirm it with your adviser. The 0% VAT relief (to 31 March 2027) covers only residential or relevant-charitable buildings. These are published budget ranges, not quotes: the cost guide gives the sources. See also 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. The design should still follow the IET Code of Practice for Electrical Energy Storage Systems and, on larger sites, NFCC guidance: separation distances from buildings and boundaries, firefighting access, detection and, where required, deflagration venting, with the fire and rescue service and your insurer engaged before the container is ordered.
G99 connection agreement (G100 limitation where the DNO connection is constrained). Siting and separation to the IET Code of Practice for Electrical Energy Storage Systems, NFCC guidance where it applies and the insurer's requirements; BS EN/IEC 62619 cells and BS EN/IEC 62933 system safety. Foundations/hardstanding to structural design; DSEAR assessment where relevant. CDM 2015 duties apply to the construction work.
Which standards apply, and what each one covers, is set out in the commercial battery fire safety guide.
Grid connection and commissioning
For a containerised outdoor bess installation, the DNO is the critical path. The G99 application should go in at survey stage, with a G100 limitation scheme proposed where the network is constrained, and the half-hourly metering designed so that the control strategy and settlement are correct. A proper installation ends with documented battery storage commissioning and an O&M handover pack. Read an independent view on whether it is worth it.
Containerised Outdoor BESS Installation: at a glance
| Attribute | Typical for this installation |
|---|---|
| Power / capacity | 250 kW / 500 kWh-2 MW / 4 MWh |
| Siting | external compound / hardstanding |
| Published cost range | About £140–£240 per kWh at 500 kWh and above (sources) |
| Connection | G99 (G100 limitation where constrained) |
Request installer quotes: Containerised Outdoor BESS Installation
Free and no obligation. This site is not an installer.
- 1. Tell us about the site: what you want the battery to do, your supply, and any half-hourly data you have.
- 2. Your enquiry is passed to installers who cover your area. This site is not one of them and takes no part in the work.
- 3. Compare what comes back against the installer checklist before you commit to a survey.
Common questions
How long does a BESS installation take?
The physical work for a containerised system is short once the civils are ready: the container is craned in, fixed and terminated, then commissioned. What sets the overall programme is the grid connection under G99 and, for an outdoor container, planning permission, so both should start at feasibility stage.
Does a containerised BESS need planning permission?
Usually, yes. In England the permitted development rights for renewable energy (Part 14 of the General Permitted Development Order) do not include battery storage. On industrial land a narrow right for plant used in an industrial process may apply if the container does not materially change the appearance of the premises; a lawful development certificate confirms it.
Who witnesses the commissioning of a BESS?
Under G99 the commissioning tests are the owner's obligation and the network operator may choose to witness them. For systems of 1 MW and above, the operator must receive details of the tests at least 28 days before the commissioning date so it can decide.
What is the G99 process and why does it drive the timeline?
G99 is the Energy Networks Association engineering recommendation for connecting generation and storage above 16 A per phase, which covers almost every commercial battery. 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. The installer normally prepares the application, single-line diagrams and protection proposals, and, where the network is constrained, may propose 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 at sites with a suitable plant room or switchroom, but the room must be compartmented, ventilated and fire-detected. A survey should assess both against the available space, target capacity and insurer requirements.
What fire safety standards apply to a commercial battery installation?
For commercial systems the main references are the IET Code of Practice for Electrical Energy Storage Systems, BS EN/IEC 62619 for cell safety and BS EN/IEC 62933 for system safety, with NFCC guidance for larger and grid-scale sites and your insurer's own requirements. PAS 63100:2024 is written for battery systems in dwellings, so it is useful context rather than the commercial standard. Lithium-iron-phosphate (LFP) cells are generally preferred for thermal stability. A fire risk assessment should be produced, and the insurer engaged, before installation.
Who handles the DNO application and grid connection?
Usually the installer, but check the contract. The G99 application, single-line diagrams, protection settings, metering arrangement, DNO liaison and witness-test coordination (plus any G100 limitation design) are often included in an installer's scope. If they are not itemised in the quote, you may end up coordinating a battery supplier, an electrician and the DNO yourself.