Key Takeaways
- G98 covers solar systems up to 16A per phase (3.68kW) — install first, notify DNO within 28 days
- G99 applies to larger commercial systems (50kW+) — requires DNO pre-approval taking 2–8 weeks
- MCS certification is not legally required but is needed for export payments and funding
- MCS 2025 standard requires MCS 012 certified mounting for flat roof installations from August 2025
- Wire Now is MCS-certified and handles all DNO applications as part of our solar installation service
What Is the Difference Between G98 and G99?
G98 and G99 are Engineering Recommendations published by the Energy Networks Association that govern how generation equipment (including solar PV) connects to the UK electricity grid. G98 covers small-scale systems with an inverter rating up to 16A per phase, equivalent to 3.68kW on single-phase supply. Under G98, you can install the system first and then notify the DNO within 28 days — no pre-approval is needed.
G99 applies to larger systems, typically commercial installations of 50kW and above. G99 requires a formal application to the Distribution Network Operator before installation begins. The DNO assesses whether the local grid can accommodate the additional generation capacity, which may involve network studies and potentially grid reinforcement works.
How Long Does DNO Approval Take?
For G99 applications, timelines vary depending on the complexity and the DNO's workload:
- Simple G99 (under 1MW, no network issues): 2–4 weeks
- Standard G99 (network assessment required): 4–8 weeks
- Complex G99 (grid reinforcement needed): 3–6 months or more
The key takeaway for commercial projects is to factor DNO approval into your project timeline from the outset. Wire Now submits G99 applications early in the project to avoid delays.
Is MCS Certification Required for Commercial Solar?
MCS (Microgeneration Certification Scheme) certification is not a legal requirement for installing solar PV. However, it is required to access the Smart Export Guarantee (SEG) for export tariff payments, and most business funding, grants, and incentive schemes require MCS-certified installations.
The MCS 2025 standard, now mandatory for MCS-certified contractors, introduced updated requirements including:
- Flat roof solar systems must use mounting systems that are MCS 012 certified (from 10 August 2025)
- Updated design and installation quality standards
- Enhanced documentation and handover requirements
Choosing an MCS-certified installer ensures your system meets these quality benchmarks and qualifies for available financial benefits.
What Happens If You Skip DNO Approval?
Installing a solar PV system that requires G99 approval without obtaining it is a breach of the connection agreement. The consequences can include:
- The DNO can require disconnection of the system
- You may be liable for costs of any network issues caused
- The system will not qualify for export tariff payments
- Insurance coverage for the installation may be compromised
There is no scenario where skipping DNO approval is worth the risk. The application process is straightforward when handled by an experienced installer.
Wire Now Is MCS Certified
Wire Now holds MCS certification for solar PV installation, complementing our NICEIC-approved contractor status. We handle the complete regulatory process for every commercial solar project:
- G98 notification or G99 application to your DNO
- MCS-compliant system design and installation
- Full commissioning documentation and MCS certificate
- Registration for Smart Export Guarantee payments
View our Solar PV services → | View our accreditations →
Part of our [Commercial Solar PV Guide](/blog/commercial-solar-pv-installation-guide-uk) series.
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