Grid connection applications are often the single biggest source of anxiety and delay in commercial solar projects. Asset managers tell us they struggle to get straight answers about timelines, costs, and whether their site will even be approved.
Lynx Sustainable Solutions has navigated hundreds of DNO (Distribution Network Operator) applications across multiple network regions. In this blog, Nick Kennedy, Joint Managing Director, will demystify the process, explain what you’re dealing with, and show you how to avoid the most common pitfalls.
G99 vs G100: Understanding Which Application You Need
The first critical question: which type of grid connection application does your project require?
G99 Applications
G99 covers the connection of all generating equipment to the UK’s distribution network, from small commercial PV arrays to multi‑megawatt solar farms. It applies to any generation above 3.68 kW (single‑phase) or 11.04 kW (three‑phase), up to around 16.5 MW on high‑voltage distribution systems.
For most commercial solar installations, this means you’ll submit a G99 application along with inverter models, export capacity, and protection settings. The DNO assesses local network capacity, and if sufficient capacity exists, approval usually arrives within the standard 90‑day window.
To support the application, several technical documents must be submitted to the DNO so they can properly assess the proposed system and its impact on the local electricity network. These typically include:
- Provisional layout of the PV system
- Single line diagram
- Letter of Authority from the client
- ENA application form for the generation
- Datasheet for the type-tested inverters to be utilised at the site
- Type Test certificates for the inverters specified
G100 Export Limitation Schemes
G100 adds an extra layer when the DNO restricts how much generation your system may export to the grid. A G100‑compliant export limitation scheme uses certified control equipment to ensure exports never exceed the agreed Maximum Export Capacity (MEC).
You’ll encounter G100 requirements when the DNO confirms limited network capacity but still offers a “non‑firm” or constrained connection rather than full reinforcement. Implementing export limitation can secure a cost‑effective connection much faster than waiting for network upgrades.
What Triggers G100 Requirements?
Export limitation may be required for:
- Sites in network‑constrained areas
- Projects on weak rural feeders or long cable runs
- Situations where total installed capacity exceeds available export headroom
Understanding whether your project needs G99 alone or G99 plus G100 controls is essential for realistic programme planning and compliance with your DNO’s connection offer.
Realistic Timeline Expectations
Here’s the timeline most clients expect: submit application, wait 90 days, receive approval, proceed with installation.
The reality is that 90 days is the minimum for straightforward G99 applications. For G100 or applications requiring network studies, expect it to take 4-6 months sometimes longer.
Why Does It Take So Long?
DNOs are managing thousands of connection applications across their networks. With solar, battery storage, EV charging, and heat pumps demand for grid connections has exploded. They’re working through significant backlogs, particularly in areas with high renewable energy adoption.
Additionally, your application isn’t assessed in isolation. The DNO must consider all existing and pending connections in your network area. A large solar farm application submitted the week before yours could consume available capacity, forcing your project into a reinforcement queue.
The DNO Process Breakdown
Once submitted, your application moves through several stages:
- Initial assessment (2-3 weeks) – Basic feasibility check
- Capacity allocation (4-6 weeks) – Determining if network capacity exists
- Network studies (6-12 weeks for G100) – Detailed impact analysis
- Offer preparation (2-4 weeks) – Cost calculations and connection terms
- Offer acceptance and contracting (varies) – Your timeline to review and accept .
Each stage has dependencies. If the DNO identifies network constraints, you might receive a “non-firm” connection offer or be told reinforcement is required. This can add months to your programme.
We always tell clients to budget 3 months from DNO application to feedback or an approved connection, even for apparently straightforward projects. This realistic timeline prevents programme disappointment and allows proper coordination with installation schedules.
Cost Implications: Connection vs Reinforcement
DNO connection costs vary dramatically based on network conditions. Understanding the difference between connection costs and reinforcement costs is essential for accurate budgeting and this is an area where Lynx Sustainable Solutions are proactive with early assessment.
If network capacity exists at your connection point, you’ll pay for several components. Understanding these upfront prevents budget surprises.
Initial Application Assessment Fee
This covers the DNO’s technical review of your proposed generation before a formal connection offer is produced. The assessment includes:
- Review of G99/G100 application documentation
- Network capacity checks at your proposed connection point
- Initial constraint identification
- High-level fault level and voltage analysis
- Allocation of network study engineers
Assessment fees vary significantly based on project size and complexity:
- Small G99 Fast Track applications: £300–£1,500
- Standard G99 projects (under 1MW): £1,500–£5,000
- Large projects (multi-MW or high voltage): £5,000–£20,000+
Some DNOs bundle assessment fees into overall design costs, while others itemise them separately. Always clarify the fee structure when requesting a connection quote.
Connection Design and Administrative Costs
Beyond initial assessment, you’ll pay for detailed connection design work, protection settings calculations, and administrative processing to formalise your connection agreement.
Physical Connection Work
The final cost component covers the actual installation: cabling from your system to the connection point, installation of protection equipment, and metering infrastructure. These costs vary based on the distance to your connection point and any required switchgear modifications.
For straightforward G99 applications with available network capacity, total standard connection costs typically range from £5,000–£15,000 depending on site-specific requirements.
Reinforcement Costs
When network capacity doesn’t exist, the DNO may offer connection subject to network reinforcement. This is where costs escalate significantly.
Reinforcement might involve:
- Upgrading transformers at local substations
- Installing new cables between substations
- Enhancing protection systems across wider network areas.
Who Pays for What?
You pay for reinforcement costs if your project triggers the need. The DNO isn’t required to upgrade their network at their expense to accommodate your generation.
However, if reinforcement benefits multiple users (for example, several solar projects in the queue), costs may be shared. The DNO should explain their cost-sharing methodology in the connection offer.
Spotting Problematic Grid Connections Early
Experienced solar developers learn to spot sites where grid connection will be problematic. Here are the warning signs:
Geographic Red Flags
- Rural locations far from major substations
- Areas with significant existing renewable generation (solar farms, wind, AD plants)
- Weak agricultural networks designed for low demand, not generation
- Island or spur networks with limited connection to the wider grid.
Site-Specific Red Flags
- Three-phase supply but with small service fuse ratings (suggesting limited network capacity)
- Existing voltage issues reported by the tenant (lights flickering, equipment sensitivity)
- Recent DNO correspondence about network constraints in the area
- Multiple generation connections visible nearby (other solar installations, wind turbines).
DNO-Specific Intelligence
Some DNO regions have published constraint maps showing areas with limited capacity. These aren’t always easy to find, but they exist, and we have deep knowledge of which networks are heavily constrained based on our project experience across different regions.
If your project ticks multiple red flag boxes, commission a DNO capacity enquiry before investing in surveys and design. A simple pre-application enquiry can reveal whether your site faces fundamental grid constraints.
How Asset Managers Can Streamline the Process
You can’t control DNO processing times, but you can avoid delays caused by incomplete applications or avoidable issues.
Submit Complete, Accurate Applications
Incomplete applications go to the back of the queue. Ensure you provide:
- Accurate single-line diagrams showing your proposed connection
- Correct Maximum Export Capacity (MEC) figures
- Proper equipment specifications (inverter models, protection settings)
- Site location information with accurate MPAN/Supply Number.
Engage Early with DNO Account Managers
For large or complex projects, request a pre-application meeting with the DNO. These meetings can reveal constraints early, clarify requirements, and sometimes identify alternative connection points you hadn’t considered.
Build DNO Timeline into Project Programme
Build realistic DNO timelines into your project programme from day one. Managing expectations early prevents difficult conversations later. The critical path of a project requires the DNO to be submitted at the earliest opportunity. We try to do this pre-contract under an LOI to ensure all licences are in place prior to agreeing a contract.
This includes enagagement with the DNO to review constraints following submission.
Work with Experienced Partners
Solar delivery partners, like us, that regularly navigate DNO applications understand regional variations, know which arguments work with specific DNOs, and can spot application issues before submission. This experience accelerates approval and reduces cost.
Sometimes a bespoke solution to free up fault level contribution can be agreed with the DNO. We have had success with decoupling gensets to free up headroom.
Final Thoughts
DNO applications aren’t the exciting part of solar development, but they’re often the critical path item that determines programme success. Understanding G99 vs G100 requirements, budgeting realistic timelines, anticipating cost implications, and spotting red flags early separates successful projects from stalled ones.
Planning a commercial solar project? Contact our team to discuss grid connection feasibility before you invest in detailed development.