GUIDE · FOR UK SOLAR INSTALLERS · 10 MIN READ

G99 Application for Commercial Solar: An Installer's Guide

Every rule and figure below comes from the official ENA and DNO sources listed at the end.

G98 vs G99 at a glance

Both are Energy Networks Association (ENA) Engineering Recommendations: G98 for generation under 16A per phase, G99 for everything else.

When a commercial job needs G99

The 16A-per-phase line is the test: 11.04kW combined on a three-phase supply, so nearly any commercial roof is a G99 job. Batteries count too — NGED's guidance treats storage as generation when it exports.

The G99 Type sets the compliance work:

• Type A — 0.8kW to under 1MW, below 110kV. Most commercial roofs.
• Type B — 1MW to under 10MW. Adds a Power Generating Module Document (PGMD) and a Final Operational Notification.
• Types C and D — 10MW and above, or a connection at 110kV or more.

For inverter-connected solar, the Type is set by the total of all inverters behind one connection point: NGED's example of three 500kW PV inverters makes 1.5MW, so Type B. Units added to an existing G99 installation count with what's there; units added to an older G59 installation count separately.

The G99 fast track (Forms A1-2, A3-2, A3-3) tops out at 60A per phase with export capped at 32A by a G100 scheme, per SSEN and NGED — below most commercial jobs.

Which network operator handles it

Usually the regional DNO, but sometimes an Independent Distribution Network Operator (IDNO), which typically builds networks for new developments such as business parks. The ENA guide says the IDNO process is almost identical.

To check, take the first two digits of the site's MPAN from the bill: 10 is UK Power Networks (Eastern England), 15 Northern Powergrid, 16 Electricity North West, and so on in the ENA's table. No meter? Ask the DNO whose area you think the site is in.

The G99 application, step by step

The Type A route from the ENA's March 2025 connection guide. DNOs have their own forms and portals, so check with yours.

1. 1

   Talk to the DNO early

   The ENA guide says to discuss plans with the DNO before starting work, as early as possible. Use its capacity maps and surgeries. A budget estimate, or a paid feasibility study, can flag reinforcement before the customer commits.

2. 2

   Decide who builds the connection

   The DNO does non-contestable work on its existing network. Contestable work, such as new infrastructure, can go to an Independent Connections Provider (ICP) for a competing quote.

3. 3

   Apply before installing

   Below 50kW three-phase (17kW single-phase) there is a simplified form in Annex A.1 of EREC G99; larger systems use the ENA standard application form, which all DNOs use. The ENA guide expects the installer to submit it for the customer.

4. 4

   Prove the equipment complies

   For Fully Type Tested inverters registered on the ENA's Connect Direct portal, quote the Product ID. Otherwise send a Compliance Verification Report (Forms A2-1 to A2-3) before arranging commissioning.

5. 5

   Accept the connection offer

   It sets out the works, any reinforcement, whether the connection is constrained, the costs and any witness testing. It is open for a set period, typically 30 to 90 days, and can be withdrawn if the project stalls.

6. 6

   Sign the agreements

   Typically a Connection Agreement, an Adoption Agreement if an ICP was used, and an operating agreement for the interface. Some must be in place before construction.

7. 7

   Commission and notify

   Test to section 15 of EREC G99. If the DNO is witnessing, send the scope, time and date at least 15 days before. Submit the Installation Document (A3-1), plus Form A2-4 if on-site compliance tests were needed, within 28 days of commissioning.

NGED says it normally witnesses some commissioning tests where a site's total capacity exceeds 50kW, and charges for witness tests.

What to gather before you apply

The fuller the application, the more accurate the quote and the faster the assessment. From what SSEN and NGED ask for, plus what you need to size the system, have ready:

• Site address, MPAN(s), and a letter of authority if the applicant isn't the landowner or occupier (SSEN asks for one).
• A site boundary plan and a layout plan with the point of supply marked.
• The supply: single- or three-phase, low or high voltage.
• Existing generation or storage on site — it can change the G99 Type.
• The proposed system: inverter make, model and rating, total capacity, any battery.
• Inverter Product IDs from Connect Direct, or the manufacturer's compliance information.
• Full export or a limit, and where a limiting device would go.
• The site's consumption pattern, to size the system and any export limit.
• When the customer wants to be connected.

Nearly all of this comes from the site visit, which is why a proper commercial solar survey matters: miss the supply, the point of connection or the consumption data and you're back to the customer for it. Our commercial solar survey checklist covers what to capture.

Export limitation and G100

Export limitation caps what a site sends to the grid, and any scheme must comply with EREC G100.

Full export isn't always available. Where a connection would breach equipment ratings or statutory limits, the ENA guide says the DNO may reinforce the network, or offer a restricted connection such as a maximum export level, which a customer can also ask for. DNOs must also consider curtailable connections, restricted until reinforcement is done, to connect projects sooner.

For a site that uses most of what it generates, a limit can beat a reinforcement bill. The ENA's 2025 guide adds that G100 devices for G99's small-installation procedures now need to be Fully Type Tested. The acceptable level is the DNO's call, so raise it early.

G99 timescales and your sales cycle

Published standards and deadlines for individual stages, not a connection date: reinforcement or a transmission assessment can add far more. Check your DNO's current timescales.

So the connection runs alongside the sale, not after it:

• raise G99 at the first meeting, so a wait or charge isn't a surprise;
• check capacity maps, and get a budget estimate on larger jobs;
• make the proposal conditional on the connection offer;
• time the customer's decision to the offer's acceptance window.

Why G99 applications stall

• Incomplete applications. The ENA guide asks for as much information as possible so the DNO can assess promptly. Gaps mean questions and delay.
• No compliance evidence. Inverters not on Connect Direct need a Compliance Verification Report and possibly site tests. Check Product IDs at design stage.
• Reinforcement. If the network can't take the connection, reinforcement may be needed, which the ENA guide warns could be prohibitively expensive.
• Interactive applications and transmission impact. Other projects nearby can make applications interactive, and some need an Evaluation of Transmission Impact from NESO.
• Lapsed offers. An offer not accepted in time expires, with no guarantee of the same terms again.
• The wrong route. Fast-track forms need every condition met; NGED says an SGI-3 application failing its network study becomes a full G99 enquiry.

How G99 fits into winning commercial work

To the customer, the grid connection is part of the purchase. An installer who explains G99 at the survey and submits a complete application looks more credible than one who finds a constraint weeks after the proposal.

That conversation belongs in a survey with the decision-maker present. If filling the diary with those is the bottleneck, our guide to how to get commercial solar leads compares the channels, and solar leads UK explains booked surveys vs form fills.

Solar Surveys UK lists booked commercial solar survey appointments for installers, qualified by phone with the decision-maker, roof ownership, energy consumption and intent confirmed. It's pay per appointment, priced by system size (see how much commercial solar leads cost), and no sit, no pay: if the customer doesn't sit for the survey, you don't pay. See the commercial solar leads we list or how solar survey leads work.

G99 for commercial solar: FAQ