A resilience installation is defined by the critical load, not by the headline capacity. The question is which circuits must ride through an outage and for how long, because that sets both the battery energy and the transfer design. Done well, it is cleaner, quieter and lower-maintenance than a diesel standby generator, and it can earn its keep with daily arbitrage and solar self-consumption between the outages it exists to cover.
The engineering centre of gravity is the changeover. Islanding requires anti-islanding protection compliant with G99, an automatic transfer or changeover arrangement designed to BS 7671, and careful separation of the must-run circuit so that only the critical load is carried. UPS-grade, zero-interruption designs (to BS EN 62040) are available where even a brief break is unacceptable.
How Backup & Resilience Install (Islanding) is delivered
Delivery normally runs: define and schedule the critical load; design the automatic transfer/changeover and anti-islanding protection; separate and re-feed the must-run circuit; install the battery indoors or outdoors as siting dictates; commission the islanding function under a simulated outage; then witnessed testing and O&M handover.
What this installation includes
- Islanding or UPS-grade design that rides a critical load through grid outages (cold chain, data, process, life-safety)
- Automatic transfer/changeover engineered into the existing distribution, cleaner and quieter than diesel standby
- Stacks daily arbitrage and solar self-consumption between outages
- Critical-load circuit sized and separated during install
Typical backup & resilience install (islanding)
- Power / capacity
- 50 kW / 100 kWh-1 MW / 2 MWh
- Siting
- plant room / external
- Published cost range
- Priced by capacity, plus islanding switchgear
What a backup & resilience install (islanding) costs
A resilience battery is priced by capacity on the same published UK ranges (about £20,000–£40,000 for 100 kWh, £80,000–£250,000 or more for 200–500 kWh, and around £140–£240 per kWh for containerised systems above that), plus the islanding switchgear and protection that let the site run through an outage. Qualifying plant gets the Annual Investment Allowance on up to £1m of spend a year; whether spend above that qualifies for full expensing or the 50% special-rate first-year allowance depends on the battery’s classification. General commercial premises do not get the 0% VAT relief, which runs to 31 March 2027 for residential and charitable buildings. These are published budget ranges, not quotes: the cost guide gives the sources. See also capital allowances and grants and funding.
Fire strategy and standards
Whether the battery sits indoors or outdoors, the fire design should follow the IET Code of Practice, BS EN/IEC 62619/62933 and the insurer’s requirements, with fire detection integrated so the resilience system does not itself become a risk.
Anti-islanding protection compliant with G99; transfer/changeover to BS 7671; BS EN 62040 for UPS-grade designs. Fire detection/suppression integration to the insurer's requirements and the IET Code of Practice. BS EN/IEC 62933/62619. Careful sizing of the must-run critical-load schedule.
The fire safety standards map shows which rules apply to a commercial battery, from BS 7671 Chapter 57 to the NFCC guidance.
DNO connection and witnessed commissioning
The connection sets the programme on any backup & resilience install (islanding). The G99 application should be lodged early, with a G100 export/import limitation where capacity is tight, and the metering and CT design proven so that peak-shaving works from day one. 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.
Backup & Resilience Install (Islanding): at a glance
| Attribute | Typical for this installation |
|---|---|
| Power / capacity | 50 kW / 100 kWh-1 MW / 2 MWh |
| Siting | plant room / external |
| Published cost range | Priced by capacity, plus islanding switchgear (sources) |
| Connection | G99 (G100 limitation where constrained) |
Request installer quotes: Backup & Resilience Install (Islanding)
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- 1. Tell us about the site: what you want the battery to do, your supply, and any half-hourly data you have.
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- 3. Compare what comes back against the installer checklist before you commit to a survey.
Common questions
What certifications should a commercial battery installer hold?
Ask for competent-person registration (NICEIC, NAPIT or ELECSA, searchable on one register), MCS certification where it applies to your system and its size, and evidence of G99/G100 applications taken through your DNO. Check that the design follows the IET Code of Practice for Electrical Energy Storage Systems and BS EN/IEC 62619/62933. For container and larger installs, ask who takes the CDM 2015 principal-contractor role. Asking to see a commissioning pack and a fire risk assessment from a comparable job is a good test.
How is half-hourly metering set up for a battery install?
Behind-the-meter control and settlement depend on accurate half-hourly measurement. The CT and metering arrangement should let the control system see site import, export, generation and the battery correctly, and any meter change is coordinated with the supplier or meter operator. Getting the measurement design right at installation is what makes peak-shaving and G100 limitation work in service.
What ongoing maintenance does an installed battery need?
A planned O&M regime: remote monitoring with alerts, periodic electrical inspection, firmware updates, thermal-management and cell-balancing checks through the battery management system, and fire-system checks. O&M agreements are often aligned to the cell warranty period. Check whether software optimisation of charge and discharge is included, because tariffs and DUoS bands move over the life of the system.
How long do the batteries last once installed?
Commercial LFP cells are commonly warranted to a stated number of cycles or years down to a stated share of retained capacity; the exact terms vary by manufacturer, so read the warranty document rather than a summary. A good proposal sizes the system with end-of-life capacity in mind, shows the warranted cycle count and degradation assumption, and says whether augmentation (adding cells later) is planned.
Can battery storage support new EV charging?
Often, yes. Rapid and ultra-rapid chargers create short, severe demand spikes that can trigger a grid upgrade. A battery can buffer those spikes, charging off-peak and from any on-site solar, so more chargers fit on the existing connection, and a G100 scheme can hold the combined site within its agreed capacity. Compare the cost against the DNO's reinforcement quote before deciding.