G99 Grid Connection for Manufacturing Solar: Realistic Timelines

Grid connection is the single most misunderstood part of a manufacturing solar project. Manufacturers plan the roof survey, the panel choice and the finance carefully, then discover that the connection agreement with the Distribution Network Operator is the item that decides when the array can actually run. On a constrained network that agreement can take longer than everything else combined.

This guide sets out the realistic timelines, explains why they stretch to 6 to 18 months above 100 kW, and shows how to keep the project moving through two levers: applying on day one, and phasing the design with battery storage when export capacity is slow. It is written for the operations director or plant manager who needs to give the board a programme they can trust rather than an optimistic sales estimate.

What G99 actually is

G99 is the Engineering Recommendation that governs how generation equipment connects to the UK distribution network. Any solar PV system that can export more than a threshold amount has to be assessed and approved by the DNO before it energises, so that the local network stays safe and stable.

For manufacturing sites the trigger is low. A G99 application is required for connections above 17 kW per phase, which almost every commercial rooftop array exceeds. So while a small domestic system connects under the lighter G98 notification process, a manufacturing install of 50 kW to 2 MW sits firmly in G99 territory and needs a formal application, a network study and a connection offer before it can go live.

G99 approval is not a formality you complete at the end. It is a separate workstream that runs alongside design and installation, and on a busy network it is usually the critical path.

Why 6 to 18 months is common above 100 kW

The headline figure manufacturers need to plan around is this: G99 grid-connection lead times of 6 to 18 months are now common for installs above 100 kW on constrained networks. That is not a worst case. It is the normal range on much of the UK network today.

Two things drive the timeline. First, the DNO has to run a study to work out whether the local network can accept your generation. Typical DNO study responses run to around 65 working days, which is roughly three months of working time before you even see a connection offer. Second, if the study finds the network is constrained, the actual connection date can push out considerably further while reinforcement work is scheduled or export capacity is found.

Several site conditions make the timeline worse. Many older manufacturing sites have legacy single-phase or capacity-limited supplies that cap PV size unless a DNO upgrade is undertaken, and that upgrade is itself a queued network job. Energy-intensive sites in industrial clusters often sit on parts of the network where a lot of other generation and demand is already competing for headroom. The busier the local network, the longer the queue.

The stages inside the timeline

It helps to see where the months go. A representative programme for a manufacturing install above 100 kW looks like this.

Stage	Typical duration	What is happening
G99 application prepared and submitted	Week 1	Submitted alongside the structural survey so the clock starts on day one
DNO study and connection offer	Around 65 working days	The DNO assesses network capacity and issues terms
Offer acceptance and connection agreement	2 to 6 weeks	Terms reviewed, connection cost agreed, contract signed
Any network reinforcement or supply upgrade	Highly variable	The main cause of the 6 to 18 month spread on constrained networks
Physical installation on site	4 to 10 weeks	Runs in parallel where possible, not gated by the connection
Final grid connection and commissioning	4 to 8 hours	Scheduled into a planned maintenance window or weekend

The physical build is rarely the bottleneck. Installation is usually 4 to 10 weeks once materials arrive, and the final connection outage is only 4 to 8 hours, scheduled into a planned maintenance window or weekend so production is not disrupted. The waiting is almost entirely in the DNO study and any reinforcement that follows.

Apply on day one, alongside the survey

The single most effective thing a manufacturer can do to protect the programme costs nothing and takes no extra time: submit the DNO application at the very start, in parallel with the structural survey, rather than waiting until the contract is signed and the design is final.

This matters because the connection is usually the longest item in the project programme. If you wait until the roof survey, the shading study and the finance are all complete before you apply, you have added three to four months of design time to the front of a 6 to 18 month connection queue for no reason. Applying on day one means the connection clock and the design work run at the same time, so the DNO study is often back before installation is due to start.

We submit the DNO application alongside the structural survey so the connection clock starts on day one. Most competitors wait until contract, which quietly adds months to delivery. The application does not need the final panel layout to be locked, it needs the connection point and the proposed export capacity, both of which are known early. Where the study later reveals a constraint, you find out months sooner and have time to react rather than discovering it days before you hoped to energise.

This is also why the full project timeline holds together. From contract signature to full commissioning, a manufacturing install typically runs 4 to 9 months, and most clients are generating their own solar within 6 to 9 months of the first call, only because the DNO application starts immediately after the survey rather than at the end.

Phasing with battery when export capacity is slow

Sometimes the study comes back and the network simply cannot accept your full export in the timescale you need. This is where a lot of manufacturing projects stall, and it is where the design should adapt rather than the project waiting.

The key insight is that a manufacturing site consumes most of its own solar. Manufacturing PV is sized to daytime baseload, not to roof area, and the working rule is to install 70 to 90 percent of peak daytime demand to maximise self-consumption. A correctly sized array self-supplies 30 to 60 percent of annual demand, with the best sites much higher. In practice that means most of the value comes from self-consumption, not from export, so a slow export agreement does not have to hold up the savings.

Where export capacity will not arrive in time, we phase the design with battery storage so you get immediate self-consumption while waiting for the export agreement. The site can be commissioned to run against its own load, using an export limitation device to stay within whatever the DNO permits in the interim, while the battery captures generation that would otherwise be spilled. When the full export agreement lands, the system is uprated to its final configuration.

Battery storage earns its place on several manufacturing profiles anyway. It starts to pay above roughly 250 kW of PV where night shifts run, where DUoS red-band charges are heavy, or where the site wants to trade flexibility. A continuous-process site such as food and beverage manufacturing, where refrigeration, chilling and ovens run close to 24/7, or a pharmaceutical site with cleanroom HVAC around the clock, has exactly the flat baseload that makes storage and high self-consumption work well. On those sites, phasing in a battery to bridge a slow connection is often a decision you would consider for its own sake.

A word of caution on sizing the battery to the network rather than the site: always pull at least 12 months of half-hourly meter data before final sizing, and model the load profile shift by shift rather than as an annual average. The battery that bridges a slow export agreement should be the same battery the site needs long term, not an expensive stopgap.

How this fits sector by sector

The connection challenge is not identical across manufacturing. Engineering and metalworking sites, with CNC machining, welding and induction-heating loads, need the G99 sizing to account for large motor-start and welding loads, which affects the study. Chemical and process sites in the industrial clusters most likely to be network-constrained often face the longest queues. Continuous-process food and pharmaceutical sites tend to have the strong daytime baseload that makes the phase-with-battery route most attractive when export is slow.

Whatever the sub-sector, the sequence is the same. Survey and apply together, design while the DNO studies, and keep a battery-phased fallback ready in case export capacity lags. That is how the connection stops derailing the project.

Getting the timeline right for your site

The honest answer to “how long will grid connection take?” is that it depends on your local network, and the only way to know is to apply and let the DNO study run. What you can control is when that clock starts. Start it on day one, plan the board case around a realistic 6 to 18 month window above 100 kW, and keep the battery-phased option in the design so a slow export agreement never means a stalled project.

For the numbers behind a specific system, see our full breakdown of manufacturing solar cost and the grants and funding that offset it, including the Industrial Energy Transformation Fund for larger decarbonisation projects. Export income under the Smart Export Guarantee is the secondary value stream once your connection agreement is in place, though for manufacturers self-consumption always comes first.

If you run a continuous-process operation, our food and beverage manufacturing page covers the high-baseload profile that makes phasing with battery especially effective. When you are ready, request a quote and we will submit the G99 application alongside the survey so your connection clock starts on day one.