The Distribution Network Operator (DNO) is the company responsible for the electricity cables and infrastructure that deliver power to your home. When you install solar panels, the DNO needs to know about your system because you’re no longer just consuming electricity – you’re also generating it and potentially exporting it back to the grid.
For most residential solar installations, DNO involvement is straightforward: your installer simply notifies the DNO after installation, and no approval is required. For larger systems, a formal application and approval process is needed before installation can begin. Understanding how this process works helps set realistic expectations and ensures your installation proceeds smoothly.
This guide explains what DNOs do, why they’re involved in solar installations, how the notification and approval processes work, typical timelines, what can cause delays, and how to ensure your application succeeds.
DNO Approval at a Glance
| What is a DNO? | Company managing local electricity network |
| Why involved? | Solar exports power to their network |
| Small systems (≤3.68kW) | Notification only – no approval needed |
| Larger systems (>3.68kW) | Formal application and approval required |
| Who submits? | Your MCS installer |
| Cost to you? | Usually nothing |
What Is a DNO?
DNO Role
| Responsibility | Details |
|---|---|
| Own infrastructure | Cables; substations; transformers |
| Maintain network | Repairs; upgrades; safety |
| Deliver electricity | From transmission to homes |
| Manage connections | New supplies; generation |
| Network planning | Capacity; future needs |
DNO vs Energy Supplier
| DNO | Energy Supplier |
|---|---|
| Owns the wires | Sells the electricity |
| Maintains infrastructure | Bills you monthly |
| Regional monopoly | You can switch |
| Approves connections | Pays for your export (SEG) |
| Examples: UKPN; WPD; NPG | Examples: Octopus; EDF; British Gas |
UK DNO Regions
| DNO | Areas Covered |
|---|---|
| UK Power Networks (UKPN) | London; South East; East of England |
| National Grid (formerly WPD) | Midlands; South West; Wales |
| Electricity North West (ENW) | North West England |
| Northern Powergrid (NPG) | North East; Yorkshire |
| SP Energy Networks | Central/South Scotland; North Wales; Merseyside |
| Scottish and Southern (SSEN) | North Scotland; Central Southern England |
Finding Your DNO
| Method | How |
|---|---|
| Electricity bill | Shows distribution charges |
| MPAN number | First two digits indicate area |
| ENA postcode checker | energynetworks.org |
| Ask your installer | They’ll identify it |
G98 and G99 are the formal Engineering Recommendations published by the Energy Networks Association, the trade body for the UK’s electricity and gas network operators. They replaced the older G83 and G59 standards in 2019 and are the documents your installer’s compliance work is measured against.
Why DNO Involvement Matters
Network Safety
| Concern | Why Important |
|---|---|
| Voltage regulation | Export can raise local voltage |
| Cable capacity | Infrastructure has limits |
| Transformer loading | Can’t exceed ratings |
| Safety isolation | Engineers need to know generation exists |
Network Capacity
| Issue | Consequence |
|---|---|
| Too much local generation | Voltage rises too high |
| Reverse power flow | Network designed for one-way |
| Transformer overload | Equipment damage risk |
| Cable thermal limits | Overheating risk |
Why Small Systems Are Simpler
| Factor | Explanation |
|---|---|
| Limited export | 3.68kW won’t stress network |
| Self-consumption | Much used on-site |
| Diversity | Not all exporting simultaneously |
| Historical data | Network tolerates this level |
G98: Notification Process
What G98 Covers
| Aspect | Details |
|---|---|
| System size | Up to 3.68kW per phase |
| Single phase | Up to 3.68kW |
| Three phase | Up to 11.04kW total |
| Process type | Notification – not application |
| Approval needed? | No |
G98 Timeline
| Stage | When | Who |
|---|---|---|
| System installed | Day 1 | Installer |
| System commissioned | Day 1 | Installer |
| Notification submitted | Within 28 days | Installer |
| DNO acknowledges | Usually automatic | DNO |
| Added to database | After notification | DNO |
What’s in a G98 Notification
| Information | Purpose |
|---|---|
| Installation address | Identify location |
| MPAN (supply number) | Link to supply point |
| System capacity | kW rating |
| Inverter details | Make; model; G98 compliance |
| Commissioning date | When connected |
| Installer MCS number | Certification verification |
G98 Submission Methods
| Method | Details |
|---|---|
| Online portal | DNO’s website – most common |
| MCS database | Auto-notifies some DNOs |
| Email form | Some DNOs accept |
| Bulk upload | For installers doing many |
G99: Application Process
What G99 Covers
| Aspect | Details |
|---|---|
| System size | Above 3.68kW per phase |
| Single phase | Above 3.68kW |
| Three phase | Above 11.04kW total |
| Process type | Formal application |
| Approval needed? | Yes – before installation |
G99 Application Stages
| Stage | Description | Timeline |
|---|---|---|
| 1. Application | Submit to DNO | Day 0 |
| 2. Validation | DNO checks completeness | 5 working days |
| 3. Assessment | Technical evaluation | Up to 45 working days |
| 4. Connection offer | Terms and conditions | After assessment |
| 5. Acceptance | Customer accepts offer | Within 90 days |
| 6. Pre-connection | Any required works | Variable |
| 7. Installation | System installed | After approval |
| 8. Commissioning | Final connection | May need witness |
For a step-by-step walkthrough of preparing and submitting a G99 application – including what each form looks like and which DNO portals work best – see our companion DNO solar application guide.
Application Documentation
| Document | Contents |
|---|---|
| Application form | Site details; contact info |
| Single line diagram | Electrical schematic |
| Inverter datasheet | Technical specifications |
| G99 compliance | Protection settings |
| Site plan | Location of equipment |
| Installer credentials | MCS certification |
What DNO Assesses
| Check | Purpose |
|---|---|
| Network capacity | Can local network accept export? |
| Voltage impact | Will voltage stay within limits? |
| Fault level | Impact on protection systems |
| Thermal capacity | Cable and transformer loading |
| Protection settings | G99 compliance |
Connection Offer
Types of Offer
| Offer Type | Meaning |
|---|---|
| Unconditional | Connect at full capacity; no constraints |
| Conditional | Connect with conditions/limitations |
| Curtailment | Export may be limited at times |
| Reinforcement required | Network upgrade needed first |
Offer Contents
| Item | Details |
|---|---|
| Connection capacity | Approved export limit |
| Connection point | Where you connect |
| Technical requirements | Protection settings; equipment |
| Any conditions | Limitations; requirements |
| Costs (if any) | Connection charges |
| Validity period | How long to accept |
Accepting the Offer
| Step | Action |
|---|---|
| Review terms | Understand conditions |
| Sign acceptance | Formal agreement |
| Pay any fees | If required |
| Within validity | Usually 90 days |
Timelines in Detail
Regulatory Timescales
| Stage | Target Time |
|---|---|
| Application validation | 5 working days |
| Connection offer (simple) | 45 working days |
| Connection offer (complex) | 65 working days |
| Offer validity | 90 days |
Real-World Timescales
| Scenario | Typical Duration |
|---|---|
| Simple approval | 6-8 weeks |
| Standard assessment | 8-12 weeks |
| Complex assessment | 12-16 weeks |
| Constraints identified | 16-26 weeks |
| Reinforcement needed | 6-18 months |
What Causes Delays
| Cause | Impact |
|---|---|
| Incomplete application | Returned; resubmit |
| Missing documents | Clock stops until provided |
| Complex assessment needed | Extended timeline |
| Network constraints | Additional studies |
| High application volume | DNO backlog |
| Reinforcement design | Engineering work |
Network Capacity
Checking Capacity
| Method | Details |
|---|---|
| DNO heat maps | Online capacity maps |
| Pre-application enquiry | Ask DNO before applying |
| Installer experience | Know local issues |
| Neighbour experience | Others installed nearby? |
Constraint Types
| Constraint | Cause |
|---|---|
| Voltage constraint | Too much local generation |
| Thermal constraint | Cables/transformer at limit |
| Fault level | Protection coordination |
| Reverse power flow | Network design limits |
High Constraint Areas
| Area Type | Why Constrained |
|---|---|
| Rural | Long cable runs; weak network |
| End of line | Distance from transformer |
| High solar uptake | Many existing systems |
| Old infrastructure | Limited capacity |
Possible Outcomes
G99 Application Results
| Outcome | What It Means |
|---|---|
| Approved – unconditional | Full capacity; no restrictions |
| Approved – export limited | Capped export capacity |
| Approved – curtailment | May be limited at peak times |
| Requires reinforcement | Network upgrade needed |
| Deferred | Queue for capacity |
| Refused | Cannot connect at requested capacity |
If Export Limited
| Option | Consideration |
|---|---|
| Accept limit | Proceed with reduced export |
| Add battery | Store excess rather than export |
| Reduce system size | Match approved capacity |
| Appeal/negotiate | Discuss with DNO |
For the technical detail of how export limiting actually works – and why it’s increasingly the default approach for systems just over the G98 threshold – see our guide to export limitation. If you’re considering battery storage as a way to soak up curtailed export, our battery retrofit guide covers the practicalities.
If Reinforcement Required
| Aspect | Details |
|---|---|
| What it means | Network upgrade before connection |
| Cost | May be charged to you |
| Timeline | Months; potentially years |
| Alternative | Accept lower capacity instead |
Costs
G98 Costs
| Item | Cost |
|---|---|
| Notification | Free |
| DNO assessment | N/A – not required |
| Connection | Free – existing supply |
| Total DNO cost | £0 |
G99 Costs
| Item | Typical Range |
|---|---|
| Application fee | Usually free; up to £300 |
| Assessment | Usually included |
| Connection (simple) | Often £0 |
| Witnessing | If required: £200-500 |
| Reinforcement | If needed: £100s-£10,000s |
Who Pays What
| Cost | Typically Paid By |
|---|---|
| Application/assessment | Usually covered by DNO |
| Simple connection | Usually free |
| Minor reinforcement | Often shared |
| Major reinforcement | Customer or shared |
Commissioning
G98 Commissioning
| Aspect | Details |
|---|---|
| DNO attendance | Not required |
| Witness | Not required |
| Testing | Installer performs |
| Documentation | Installer provides |
G99 Commissioning
| Aspect | Details |
|---|---|
| DNO witnessing | May be required |
| When required | Usually larger systems |
| Booking | Arrange with DNO |
| Cost | May be charged |
| Testing witnessed | Protection settings verified |
Commissioning Documents
| Document | Purpose |
|---|---|
| G98/G99 form | Confirms compliance |
| Test results | Protection settings verified |
| Electrical certificate | BS 7671 compliance |
| As-built diagram | Final configuration |
Your Installer’s Role
What Installer Does
| Task | Details |
|---|---|
| Determine standard | G98 or G99? |
| Prepare application | Technical documentation |
| Submit to DNO | Through proper channels |
| Respond to queries | Additional information |
| Accept offer | On your behalf or with you |
| Arrange commissioning | Book witnessing if needed |
| Submit completion | Final notification |
Your Role
| Task | Details |
|---|---|
| Provide MPAN | From electricity bill |
| Confirm supply type | Single or three phase |
| Sign if required | Some applications need signature |
| Accept offer | May need your approval |
| Pay fees | If any apply |
If you’re using a quote-comparison process to find an installer, make sure DNO application handling is explicitly included in the price – some cheaper quotes leave it as the homeowner’s responsibility. Our solar quote checker walks through what should be itemised in a compliant quote.
Different DNO Processes
Portal Variations
| DNO | Online System |
|---|---|
| UKPN | G99 online portal |
| National Grid (WPD) | Connection portal |
| Northern Powergrid | Online application |
| ENW | Self-service portal |
| SP Networks | Connection portal |
| SSEN | Online services |
DNO Performance
| Metric | Variation |
|---|---|
| Processing times | Vary by DNO; workload |
| Portal usability | Different quality |
| Communication | Varies in responsiveness |
| Fees | Slight variations |
Troubleshooting
Common Problems
| Problem | Solution |
|---|---|
| Application rejected | Check missing info; resubmit |
| Taking too long | Chase via portal/phone |
| Capacity refused | Request lower capacity or limit |
| High reinforcement cost | Reduce capacity; use export limit |
| DNO non-responsive | Escalate; contact Ofgem if serious |
Avoiding Delays
| Action | Benefit |
|---|---|
| Complete application | No back-and-forth |
| Correct documentation | Passes validation |
| Check capacity first | Avoid surprises |
| Experienced installer | Know the process |
| Respond promptly | Keep clock running |
Escalation
| Stage | Action |
|---|---|
| Initial query | DNO customer service |
| Persistent issue | DNO complaints team |
| Unresolved | Energy Ombudsman |
| Regulatory breach | Ofgem |
If escalation reaches the regulator, the body in question is Ofgem – the gas and electricity markets regulator. Their guidance on resolving energy disputes covers the route from supplier or DNO complaint through to the Energy Ombudsman, which handles unresolved cases after eight weeks.
After Approval
What Happens Next
| Step | Timeline |
|---|---|
| Accept connection offer | Within validity period |
| Schedule installation | With installer |
| Installation proceeds | As planned |
| Commissioning | Day of completion |
| Final notification | Installer submits |
| System generating | Immediately |
Documentation to Keep
| Document | Why Important |
|---|---|
| Connection offer | Proof of approval |
| Acceptance confirmation | Agreed terms |
| Commissioning certificate | Compliance evidence |
| MCS certificate | SEG eligibility |
| DNO reference number | For future queries |
If you ever plan to add more panels to your existing system, your DNO reference number is the starting point for the new application. The DNO will need to know what’s already approved on the connection.
Frequently Asked Questions
Process Questions
| Question | Answer |
|---|---|
| Do I contact the DNO myself? | No – installer handles it |
| How do I know which applies? | Installer determines |
| What if application refused? | Reduce size or export limit |
| Can I appeal? | Discuss with DNO; options exist |
Practical Questions
| Question | Answer |
|---|---|
| Does G98 delay installation? | No – notification after |
| Does G99 delay installation? | Yes – approval before |
| What’s an MPAN? | Meter Point Admin Number – on bill |
| Will DNO visit my property? | Usually not for residential |
Summary
| Aspect | G98 (Small) | G99 (Larger) |
|---|---|---|
| Process | Notification | Application |
| Timing | After installation | Before installation |
| Approval | Not required | Required |
| Timeline | No delay | 45-90+ working days |
| Cost | Free | Usually free; possible fees |
| Your involvement | Minimal | May need to sign/accept |
The DNO approval process ensures that solar installations connect safely to the electricity network. For most residential systems under 3.68kW per phase, this is straightforward – your installer simply notifies the DNO after installation, and no prior approval is needed. This means no delays to your installation timeline.
For larger systems requiring G99 approval, the process takes longer. Applications must be submitted before installation, and the DNO has 45 working days to assess and provide a connection offer. In practice, this often extends to 8-16 weeks, and longer if network constraints exist. Your installer handles the application, responds to queries, and manages the process through to completion.
Understanding the difference helps you make informed decisions about system sizing. Many homeowners choose to stay within G98 limits by using export limiting, allowing larger inverter capacity while capping export to 3.68kW. This avoids G99 delays while still providing full system power for self-consumption and battery charging.
Your MCS installer manages the entire DNO process as a standard part of installation. They know which standard applies, prepare the necessary documentation, submit through the correct channels, and ensure commissioning paperwork is completed. You may need to provide your MPAN number and sign certain documents, but the technical process is handled for you.
Sizing your system around the G98 line. The 3.68 kW per-phase threshold is the single most consequential number in UK domestic solar. A 4 kW or 5 kW inverter triggers G99 with its 6-16 week pre-approval wait, while a 3.68 kW inverter (or a larger one with export limiting set to 3.68 kW) lets you stay G98 and install in days. For most UK homes, an export-limited 5-6 kW system makes more sense than a non-limited 3.68 kW one – you get more generation for self-consumption and battery charging, while the grid-side limit keeps you in G98 territory.
Ask your installer up front: is this G98 or G99, and if it’s G99, what’s the timeline and likelihood of any reinforcement charges in your postcode? An experienced installer will already know the local capacity picture and can flag risks before you commit. Decisions on how many panels and which inverter to fit are best made with the DNO position already understood.
