A procurement-focused guide to grid connection routes, export limitation, type-test evidence and the documents that should be checked before equipment is ordered.
Today I want to talk you through the grid connection compliance issues you can't avoid when it comes to solar and battery storage projects in the UK. While putting this guide together, I found that most procurement pitfalls actually come down to a few concepts people don't keep straight. So let me walk you through G98, G99, G100 and MCS from the ground up, the way I understand them.
Start at the point of connection. Add the AC output of every generating device at the premises, then verify the applicable G98 or G99 route, any G100 export control, the exact equipment evidence and the separate MCS installation requirements.
- Where Does the G98 Calculation Start?
- Which Projects Qualify for G98?
- Which Projects Need G99?
- Why Can't You Assess Solar and Storage Separately?
- What Is the G100 Export Limit?
- What Does MCS Certification Actually Prove?
- What Documents Should You Check Before Buying?
- Is My Project G98 or G99?
- Common Procurement Mistakes
- What Do You Need to Send for a UK Project Review?
- Quick Answers to Common Questions
01 /Where Does the G98 Calculation Start?
The first step is to work out the total AC output of every generating device at the same premises. Don't just focus on the new inverter - existing solar inverters, AC-coupled battery inverters, hybrid inverters and vehicle-to-grid equipment all count if they're there.
Here's a point people often get confused about: the battery's capacity (kWh) determines how long it can run, but which connection route you take depends mainly on electrical power, current, system topology, export behaviour and the conditions in the relevant engineering recommendation - not so much on kWh.
Keep two screening numbers in mind: 16 A per phase is roughly 3.68 kW on a single phase at 230 V; on three phases, 16 A per phase adds up to about 11.04 kVA. These are handy for quick estimates, but they don't replace the actual current-based rule, the exact phase arrangement or the DNO's review.
When you're planning the system, keep power in kW separate from stored energy in kWh. You can look at SINELINK's full BESS article for the equipment boundary, but this article focuses on UK connection and certification evidence.
02 /Which Projects Qualify for G98?
G98 is the simplified connection route for microgenerators, provided the equipment has passed full type testing, the aggregate rated current is no more than 16 A per phase, and it operates in parallel with a public low-voltage distribution network.
Eligible projects usually follow a "connect and notify" process, but don't think that means you're off the hook - the installer still has to follow the current G98 procedure and the submission requirements of the relevant DNO.
- The combined AC output of every generating device at the premises, not just the new inverter;
- The number of phases, per-phase current and proposed phase allocation;
- The exact manufacturer, model, rating and applicable firmware or software version;
- A matching entry and type-test evidence in the ENA equipment database where the route relies on registered type testing;
- The single-line diagram, protection settings, commissioning record and responsibility for notifying the DNO.
When checking specific equipment, always use the ENA Type Test Register. Don't assume a device is covered just because the model family name looks similar, a higher-rated sibling model exists, or a certificate covers a different firmware version.
03 /Which Projects Need G99?
When a project exceeds the G98 threshold, connects at a higher voltage, hasn't been fully type-tested for G98, or otherwise falls outside the G98 conditions, it goes down the G99 route.
The biggest difference is timing.
G99 requires approval before connection. The DNO may assess voltage rise, thermal capacity, fault level, protection, power quality, export constraints and any network reinforcement needed.
Your commercial schedule should therefore treat the DNO application and approval as a formal gate. If you order an inverter before the accepted connection design is known, you risk redesign, firmware, protection or delivery problems down the line.
According to ENA's G99 Type A summary guide, projects above 16 A per phase and below 1 MW fall within Type A scope. Larger or more complex projects have extra requirements - remember, the DNO application pack defines the accepted equipment and settings, not the marketing material.
04 /Why Can't You Assess Solar and Storage Separately?
The most common procurement mistake is assessing the PV inverter and the battery inverter separately.
The current MCS battery installation standard is clear: the 16 A-per-phase threshold uses the total aggregated AC output of all generators. The standard's example is easy to follow - a 3 kW solar PV system plus a 3 kW battery storage system sharing a single-phase supply has a combined theoretical output above 16 A, so G99 applies.
Either way, tell the DNO about the complete system. An existing PV approval does not automatically cover a newly added battery inverter or a replacement hybrid inverter.
Existing PV + new battery inverter → aggregate AC output at the point of connection → confirm the applicable G98 or G99 route.
05 /What Is the G100 Export Limit?
When the network can't accept the full theoretical export, the DNO may accept an export limitation scheme under G100: power is measured at the point of connection, and generation or storage is controlled so export stays within an agreed limit. The limiter, sensing arrangement, control response and fail-safe behaviour must all match the accepted design.
- Setting export to zero does not automatically remove G98 or G99 obligations.
- An export limit does not automatically reduce installed aggregate capacity to the G98 threshold.
Some storage projects may qualify for a G99 fast-track - for example, the ENA application form describes conditions involving G98 type-tested equipment, aggregate capacity no more than 32 A per phase and export limited to 16 A per phase - but you must confirm eligibility and documentation with the relevant DNO.
06 /What Does MCS Certification Actually Prove?
MCS sets standards for certified small-scale renewable installations, products and contractors. For battery storage, MIS 3012:2025 covers electrical energy storage systems permanently installed in buildings with a maximum power output of up to 50 kW, and it must be read alongside the IET Code of Practice for Electrical Energy Storage Systems. The standard requires the contractor to follow G98, G99 or G100 as applicable and to use fully type-tested generating plant.
Buyers should treat four things separately:
Check the current MCS standards library and installer directory rather than trusting a logo in a brochure. MCS certification does not grant DNO connection permission, and DNO acceptance doesn't by itself make an installation MCS-certified.
07 /What Documents Should You Check Before Buying?
I've turned the things you should verify before purchasing into a checklist - go through it item by item:
Also make sure your equipment schedule identifies solar DC cables, PV connectors and AC cables by exact construction and rating. An inverter's grid compliance doesn't prove the cables, connectors or protection devices were chosen correctly.
Treat the approved design, equipment evidence and commissioning record as one connected document set.
08 /Is My Project G98 or G99?
Equipment scale and topology change the evidence and connection path; battery energy capacity alone does not determine the route.
09 /Common Procurement Mistakes
10 /What Do You Need to Send for a UK Project Review?
For an initial technical and commercial review, you'll need: project postcode, DNO, supply voltage and phase, existing generation, proposed PV and storage power, battery energy, required export limit, inverter models, single-line diagram, target commissioning date and required documentation. For retrofit work, include the previous DNO letter or notification, plus photos of the meter, consumer unit and installed equipment labels.
Request a UK Project Document Review
Send the complete site, equipment, export-control and evidence package so the requested products and documentation can be reviewed against the proposed project scope.
11 /Quick Answers to Common Questions