How long does a G99 application take? Clocks and delays

“How long will the DNO take?” has two honest answers: how long the operator has to reply, and how long the project takes. They are different numbers, and the second is the one that sets your go-live date. This page separates them, using the Energy Networks Association’s Distributed Generation Connection Guide (March 2025) and, for the equipment-evidence points, Electricity North West’s G98/G99 application guidance (December 2021, so check your own operator’s current process). For the full route, see the G99 application guide.

The operator’s clocks

For a formal quotation, the ENA guide gives these timescales:

Voltage of the connection	Operator does all the work	Independent connections provider does the contestable work
Low voltage (below 1 kV)	45 working days	30 working days
High voltage (1 kV to 22 kV)	65 working days	50 working days
Extra high voltage (22 kV and above)	65 working days	3 months

Most business batteries below about 1 MW connect at low voltage; larger ones, and any needing a high-voltage connection, take the longer clock. If you ask first for a budget estimate, the guide gives 10 working days below 1 MVA and 20 working days at 1 MVA or more, where the operator does all the work. A budget estimate is a desktop study: it is not open for acceptance and can change, so it helps you decide, but it does not start the formal process.

What is not in those clocks

• Preparing the application. Choosing the equipment, getting the type-test details, and working out your import and export capacities happen before the clock can start. Electricity North West’s own list of recurring problems is a good guide to avoidable delay: having the actual generator on the initial application helps the operator model it, and wrong forms or a missing manufacturer’s reference number slow the check.
• Network studies. For Type B and above the operator runs load flow, contingency, fault level and sometimes stability studies, and a connection at 11 kV can affect the 33 kV network. The guide notes this can take time.
• The acceptance window. A connection offer carries a defined period to accept, typically 30 to 90 days. Decision time on your side is project time.
• Reinforcement. If the offer includes network works, they take as long as they take; the guide notes that an operator can offer a curtailable connection, which allows an earlier connection with restricted export until the reinforcement is finished.
• Agreements and documents. Connection and, where an ICP is used, adoption agreements; a draft Power Generating Module Document at least 28 days before first synchronisation for Types B and above.
• Commissioning. The tests, and for Type A the Installation Document within 28 days of commissioning. See commissioning.

Faster routes, and where they stop

The guide describes a fast-track application process for some domestic-scale storage, which cuts the operator’s confirmation time from 45 days to 10 days or less. It applies to small, fully type-tested systems under the Small Generation Installation Procedure (G99 Form A1-2), and it does not apply if the storage is designed to run in island mode. It is not a route for a typical commercial battery. For a commercial site on a tight connection, the practical lever is design: a G100 export limitation scheme can let a battery connect inside the existing agreed capacity, if the operator accepts it, which can avoid a reinforcement wait.

How to protect the programme

• Apply early, with the real equipment named. Put the application in at feasibility stage, not after the order, with type-test register references for the inverters and batteries.
• Know your operator. Different operators publish different forms, portals and guidance, so find yours first (who is my DNO) and read its current process.
• Agree who submits. Settle in the contract who completes the application and answers the operator’s questions; a slow reply on your side is lost time on the programme.
• Plan planning in parallel. An outdoor container needs planning permission as well, and either process can end up setting the programme.
• Ask for the programme in writing. A good installer marks the DNO milestone as the critical path; our installation programme guide shows what a realistic end-to-end timeline looks like.

Next step

If you are not sure whether your battery is G98 or G99, start with the checker on the G99 application page, then read the jargon buster so the operator’s reply makes sense. If you want to talk it through, send an enquiry; we reply by email, and this site is not an installer.