At 1 MW the job stops being an installation and becomes a power station, in the operator's eyes and in the standard's. EREC G99 calls it Type B, and Type B brings a compliance regime that Type A never asked for: a dossier before the switch-on, tests the operator witnesses, capabilities the inverters must prove, and monitoring the operator can see.
This is part 5 of DNO applications by size. It is the shortest part, because above 1 MW the paperwork is engineer's work rather than installer's. The aim is that you recognise the line, know what is on the other side of it, and price it.
The thresholds
G99 sorts generating modules by registered capacity and by the voltage at the connection point.
| Type | Registered capacity | Connection point |
|---|---|---|
| A | 0.8 kW up to, but not including, 1 MW | below 110 kV |
| B | 1 MW up to, but not including, 10 MW | below 110 kV |
| C | 10 MW up to, but not including, 50 MW | below 110 kV |
| D | 50 MW and above, or any size at 110 kV and above | any |
The type is set by the registered capacity of the module, not by the panel count. A 1.4 MWp array behind 999 kW of inverters is Type A on that reading. Some developers register just under 1 MW with an export limit for exactly that reason. Whether the operator accepts it depends on how the limit is engineered and declared, and it is the operator's call.
What Type B adds
The Standard Application Form is the same form, and now all of it applies. Parts 4 and 5 ask for the extended technical and compliance data: the module's control and protection design, its reactive capability, its behaviour through faults and frequency events.
Beyond the form, four things arrive.
The compliance document. Before the module first synchronises, the generator submits a document that shows how the module meets G99's Type B requirements, with the manufacturer's evidence behind it. The operator needs it at least 28 days before the first synchronisation. The forms move from the A family to the B family: the compliance document, the test schedule, and at the end the installation document, Form B3.
Witnessed tests. The operator witnesses the compliance tests, on at least 28 days' notice, and can agree a shorter period. Tests cover the protection, the fault ride-through where it applies, the frequency response and the reactive capability. The final operational notification follows the post-energisation test evidence, submitted within 28 days of synchronising.
Capabilities the inverters must prove. Type B modules must ride through defined network faults, reduce output when frequency rises, and provide reactive power on instruction. The inverters do this; the dossier proves it with the manufacturer's certificates and the site's settings.
Monitoring the operator can see. Many operators require SCADA or telemetry from 1 MW so the module can be observed and, in a constrained connection, controlled. Some add disturbance recording and power quality monitoring. The equipment and the communications are part of the connection works.
The studies
Above 1 MW the operator's assessment leans on studies you provide.
- Harmonics, under EREC G5, for the inverters' distortion at the connection point.
- Voltage step and flicker, under EREC P28, for switching and variation.
- Fault level, for the contribution the inverters make to the network's fault current.
- Earthing, for the HV installation and the transformer.
- Protection settings, for the interface protection at the connection point, against the operator's tables.
These are the work of a chartered engineer or a specialist consultancy. A design tool can carry them, attach them and keep them with the application. It cannot write them, and it should not pretend to.
The connection itself
A Type B connection is high voltage. The operator names a point of connection on its 11 kV or 33 kV network, and the works between the array and that point are contestable: a transformer or several, HV switchgear with the G99 interface protection, cables, and the operator's ring main unit and metering unit at the boundary. An independent connection provider designs and builds them under the operator's design approval.
The operator's own works, at its substation and on its network, are priced in the offer. At this scale the offer can name reinforcement that takes years, or a constrained connection that runs sooner with curtailment. A flexible connection is often the difference between a project that builds in eighteen months and one that waits five years.
The transmission step
Above a certain size a distribution connection also touches the transmission system. In England and Wales the threshold at the time of writing is 5 MW of export capacity, under the connections reform that came into force in 2025. Above it the project enters NESO's gated process on top of the operator's, with its own milestones and queue. In Scotland the threshold is lower. Confirm the current figure with the operator and NESO before the application goes in, because the reforms have moved it more than once.
Type C and Type D
Type C, from 10 MW, and Type D, from 50 MW or at 110 kV and above, follow the same shape as Type B with more of everything: wider studies, more capabilities to prove, more monitoring, and a formal operational notification procedure with interim and final stages. They are transmission-facing projects that happen to connect to a distribution network. Nothing in this series is aimed at them beyond naming the line.
Questions installers ask
Is a 1 MW roof really Type B?
If the registered capacity of the module is 1 MW or more, yes. Most rooftop projects that approach the line are designed to sit just under it, at 999 kW of inverter capacity, and stay Type A with the SAF's Parts 1 to 3.
Who witnesses the tests, and what does it cost?
The operator's engineer attends. Notice is 28 days for a Type B test schedule. Fees vary by operator and are set out in the offer or the operator's charging statement.
Can a design tool do Type B?
It can design the array, the strings and the LV side to 5 MW, draw the single line diagram, and carry the studies and certificates with the application. The compliance document, the studies and the protection settings are engineer's work by their nature.
Does MCS apply?
No. MCS stops at 50 kWp. Above that, and certainly above 1 MW, the G99 process and the electrical certification are the compliance record.
Solar Engine designs ground and roof arrays to about 5 MW and files the paperwork to 1 MW. Above that line the product says so plainly, names the Type B leg, and leaves the compliance dossier to the engineer who will sign it.