How long does a commercial battery installation take? The G99 timeline explained

Ask most people how long it takes to install a commercial battery and they picture the crane: a container arrives, it is lifted into place, it is wired in, done. That part is real, and it is quick: usually a few weeks on site for a behind-the-meter system. But it is not what sets the timeline. The programme for almost every commercial battery storage installation is set by the Distribution Network Operator, and specifically by the G99 connection process.

The physical install is the short part

For a typical behind-the-meter system (say a 250 kW / 500 kWh peak-shaver or a containerised 1 MW / 2 MWh unit), the on-site work runs to a few weeks: groundworks and hardstanding for a container (or room preparation for an indoor cabinet), cable routes, the crane lift or cabinet installation, terminations into the switchgear, and commissioning. Even a large containerised system is usually installed within weeks once everything is on site and the connection is agreed.

The catch is in that last clause: once the connection is agreed.

Why the DNO sets the real timeline

Any storage system above 16 A per phase (3.68 kW), which is essentially every commercial battery, needs a G99 connection agreement with the DNO. The DNO reviews the proposed connection, may require a network study, and sets the protection and metering requirements. Because network capacity is limited in many parts of the UK, that study and the resulting connection offer are usually the single longest item on the programme. The G99 process can take months, and considerably longer where the network needs reinforcement; the DNO can give an indication for your site.

This is the part that catches businesses out. A battery quote may say “installed in weeks”, but the system cannot be energised until the DNO says yes. A quote that talks only about the crane, and not the connection, is not showing you the real programme.

How to compress the timeline

You cannot make the DNO move faster, but you can start the clock earlier and avoid adding to it:

• Submit G99 at survey. The most effective single lever is to lodge the G99 application at the feasibility stage, not after the design is signed off. This runs the DNO study in parallel with your internal approvals rather than after them.
• Use a G100 limitation scheme where the network is constrained. A G100 export/import limitation scheme holds the site within its existing agreed capacity, which can let a project proceed without waiting for a network reinforcement if the DNO accepts it. That can be the difference between connecting soon and waiting for the network to be upgraded.
• Settle the fire and siting strategy early. Fire and insurer sign-off can also add time if left late. Separation, detection and access should be settled at feasibility so they are not a surprise near go-live.

A realistic programme

For a behind-the-meter commercial installation, a realistic end-to-end programme looks like this: feasibility survey and G99 submission in the first weeks; the DNO study and connection offer over the following months (the variable part); fire siting and design freeze in parallel; then an installation of a few weeks and commissioning once the connection is agreed. An outdoor container usually needs planning permission too, which runs alongside the connection; grid-scale standalone projects are a different order entirely once planning is included.

The honest version

A good installer will hand you a programme with the DNO milestone marked plainly as the critical path, and will give you the realistic range for your specific network rather than quoting only the install weeks. When you ask for quotes, ask each installer for that programme. Request installer quotes (your enquiry is passed to installers who cover your area; this site is not one of them), and compare what comes back with the containerised and indoor cabinet guides.