In my last post I covered why you have to tell the DNO. This one is the how: picking the right route, gathering what the DNO asks for, and sending it without it bouncing back.
It covers Great Britain. Northern Ireland has its own process through NIE Networks.
Step 1: work out whether it's G98 or G99
Add up the AC rating of every generating device on the installation: solar inverters, battery inverters, and anything that's already there. Use the inverter's continuous rated output, not the panel kWp. Then divide by 230V for each phase.
- G98 if every device is fully type tested to G98 and the total is 16A per phase or less. That's about 3.68kW on single phase or 11.04kW on three phase. This is "fit and inform": install, commission, then notify the DNO within 28 days, counting commissioning day as day one.
- G99 if the total is over 16A per phase, or any device isn't fully type tested to G98. You apply before you install and wait for the DNO to say yes.
The total is what catches people out. National Grid's own example: a 4kW single-phase inverter is 4,000 ÷ 230 = 17.39A, so it's G99. And MCS gives the example of a 3kW PV system plus a 3kW battery on one single-phase supply: together they're over 16A, so G99. A battery added to an existing G98 solar system can tip the whole installation into G99.
One more G98 trap: if you've done, or will do, other G98 installs in the same close geographic area within 28 days, the notify-after route doesn't apply. Use the multiple-premises process and talk to the DNO first.
Step 2: pick the G99 route
G99 isn't one form. The common routes for domestic and small commercial jobs are:
- Fast track. Most DNOs offer a quicker route for small, fully type-tested generation and storage on existing premises, using the integrated micro-generation and storage application (Form A1-2), then a notification within 28 days of commissioning. ENA's G99 guide says this route was set up for domestic-scale storage and reduces the connection time from 45 days to 10 days or less. The eligibility limits are set out as categories (SGI-1 to SGI-3) and vary slightly in how each DNO words them, so check your DNO's page. ENA says it doesn't apply if the battery will run in island mode during a power cut.
- Simplified application (Form A1-1). For generation under 50kW three phase or 17kW single phase. If every device is fully type tested and on the ENA register, you quote the reference. If not, the manufacturer's compliance verification report (Form A2-3 for inverters) goes in with it.
- Standard application form. For anything bigger. That's a much heavier job, with site plans, a detailed design and more data for the DNO's network studies.
After commissioning, you send the installation document (the A3 forms) within 28 days. On every G99 route, the DNO decides, and its connection offer can come with conditions, such as an export limit, or a charge for network work.
Step 3: gather the information
Most rejected or delayed applications are missing something. Have this ready before you start:
- Site and customer: the installation address and postcode, the customer's name and contact details, and the MPAN. The first two digits of the 13-digit core MPAN tell you which DNO area it's in.
- Supply: single or three phase, the cut-out fuse rating, the earthing arrangement and any existing generation or storage on site. A clear photo of the cut-out is worth taking on every survey.
- Each device: manufacturer, model, the ENA device reference (the type-test reference from the ENA register), rated AC output in kW, which phase it's on, and for batteries the capacity and charge and discharge rating.
- Export: whether the system is export limited and, if so, to what. That needs the G100 information too.
- Installer: your company details, your contact name and your accreditation, such as your MCS number.
- Drawings: a circuit or single line diagram of the installation. ENA lists supporting information such as circuit diagrams for the installation documents, and a single line diagram is mandatory on the standard application form. If the diagram doesn't match the data on the form, expect delays.
- Dates: the commissioning date for G98, and the planned installation date for G99.
The ENA register used to be the Type Test Register. It closed in April 2024 and moved into ENA Connect Direct, where you can still search devices and download the type-test reports.
Step 4: send it the right way
You've got two ways to send it:
- ENA Connect Direct. ENA's free online platform for installers making domestic low carbon technology applications, covering solar, batteries, EV chargers and heat pumps. It's the same process for every GB and NI network operator and most iDNOs. It runs the DNOs' decision checks and can approve in minutes when they pass, or escalate to a DNO engineer when they don't. You'll need the make and model of each device from its register, the customer and installer details, and a photo of the cut-out. For non-domestic jobs, ENA says to use the G98, G99 and G100 forms.
- The forms. The ENA publishes the G98 and G99 forms, and each DNO lists where to send them. Many DNOs also have their own online forms. The paper route is still accepted.
Where EV chargers fit
A normal EV charger is a load, not a generator, so it isn't a G98 or G99 job at all (a V2G charger that can export is different). It still needs telling. Under ENA's process for existing properties, if the premises' maximum demand, including the charger, is 60A per phase or less and the supply is adequate, you install and notify within 28 days. Otherwise you apply first. Heat pumps follow the same process, and both go through ENA Connect Direct.
If a job has solar, a battery and a charger, count the battery inverter in the G98 or G99 total and the charger in the maximum demand.
Common mistakes
- Counting one device instead of the installation. The 16A is the total of all generation, including what's already there.
- Using the panel kWp. It's the inverter's AC rating that counts.
- Installing a G99 job before the DNO says yes. That's the one that comes back to bite you.
- Assuming an export limit makes it G98. G98 says a new generator plus a battery with a G100 export limitation scheme should go down the G99 route. (A manufacturer can restrict an inverter's rating with settings the customer can't access, and G98 accepts that. An export limit is different.)
- Wrong or missing ENA reference. Check the exact model on the register, including the variant, and its G98 or G99 status.
- No cut-out photo, or a poor one. Connect Direct checks it automatically, so an unclear photo can fail the application.
- Missing the 28 days. It runs from commissioning day, for G98 notifications and for the G99 installation document.
- Forgetting the customer. They'll need the DNO's acceptance for their export tariff and when they sell the house. Hand it over with the MCS certificate.
Doing it from the job in CircuitHQ
I built CircuitHQ because I was typing the same details into DNO forms that I'd already put on the certificate.
CircuitHQ searches the ENA register for inverters, batteries and other generation devices, and fills in the ENA reference, compliance status, kW, phases and G98/G99 type-test status where the field is blank. It prepares the G98 and G99 forms from the job.
For G98 and G99 solar and battery applications where every device is on the ENA device register, and EV chargers, all under 17kW per phase, you review the application and press Submit to send it to ENA Connect Direct from the app. For G100, export-limited systems and changes to existing applications, it prepares the forms for you to check and send yourself. The DNO still decides.
It sits alongside the rest of the solar paperwork: the job, the certificates and the handover. Solo is £29 a month + VAT, and there's a 14-day free trial with no card needed to start. See pricing or start your free trial.
Phillip Mills, Director, PPM Electrical Ltd