A rejected DNO application isn't just frustrating, it's expensive. Every resubmission resets the clock, pushes your install date back, and risks the customer losing confidence in the job. After processing thousands of G98 and G99 applications across all six UK DNOs, we've seen the same handful of mistakes come up again and again.
The good news: nearly every rejection is preventable. Here are the eight most common reasons applications get sent back, and exactly what to do about each one.
1. The Letter of Authority Doesn't Match the MPAN
This is by far the most frequent cause of delay. The Letter of Authority (LOA) names the customer authorising you to act on their behalf, but the DNO checks that name against the registered electricity account holder for that MPAN. If they don't match exactly, the application stalls.
Common mismatches include:
- LOA signed by one partner, account in the other partner's name
- Maiden name on the bill, married name on the LOA
- Property has changed hands and the MPAN hasn't been updated
- Landlord signs the LOA when the tenant is the bill payer
How to fix it: always verify the account holder against a recent electricity bill before the LOA is signed. If the names genuinely differ, the customer needs to update their supplier first, or the bill payer needs to sign instead. We carry out this verification on every application we process so the issue never reaches the DNO in the first place, and if the project is being scoped from scratch, a proper solar site survey captures the MPAN, cut-out photo and account details cleanly up front.
2. SLD Doesn't Match the Equipment List
The Single Line Diagram is one of the most scrutinised documents in a G99 application. DNO design engineers will reject an SLD if it shows different inverter quantities, different ratings, or a different protection arrangement to what's declared on the application form.
Typical SLD errors include:
- Inverter make or model on the SLD differs from the form
- Battery shown on the SLD but not declared, or vice versa
- Missing G99 type-tested protection relays on a multi-inverter system
- No clear indication of the export-limiting arrangement when one is required
How to fix it: treat the SLD as a single source of truth and build the application form from it, not the other way round. Our team draws every SLD from the equipment list itself, so the two cannot drift out of sync, and we use a library of approved templates that DNO engineers already recognise.
3. Wrong MPAN
A wrong MPAN routes the application to the wrong DNO, or to a property that doesn't exist on the network. New-build sites are especially prone to this, as are properties with multiple meters (outbuildings, annexes, commercial premises with sub-meters).
How to fix it:
- Always pull the MPAN from a current electricity bill, never from a previous quote or sales sheet
- Verify the first two digits map to the correct DNO region using a postcode-to-DNO lookup
- For new builds, confirm the MPAN has been issued before submitting (the DNO can't connect a generation system to a meter that doesn't exist yet)
4. Missing or Incomplete Equipment Specifications
Modern installs rarely contain just panels and an inverter. Batteries, EV chargers, hybrid systems and heat pumps all need declaring, and the DNO needs full make, model, and rated output for each one. A missing battery declaration is one of the fastest ways to get an application bounced back.
How to fix it: declare every piece of generation, storage, and significant load equipment, even if you think it isn't relevant. If a battery is going on the site at any point in the next 12 months, declare it now. Resubmitting later because the customer added a battery costs more than including it upfront.
5. Export Capacity Set Wrong
The proposed export capacity needs to reflect the maximum the system can push to the grid, not the panel capacity, and not what the customer would like. If you state 10 kW export on a system with a 5 kW inverter and no batteries, the DNO will reject it for being internally inconsistent.
On the flip side, if you understate export to avoid scrutiny and the actual system can do more, you create compliance issues at commissioning.
How to fix it: calculate export from the inverter's rated AC output (or the combined output across multiple inverters), not the DC panel capacity. If the customer wants to limit export to avoid network constraints, declare that explicitly and reference the G100-compliant limiting device in the SLD.
6. Wrong DNO Form for the System Size
Submitting a G98 notification when the system actually needs a G99 application is a guaranteed rejection. Remember the rule: G98 applies up to 3.68 kW per phase. Single-phase systems above 3.68 kW, or three-phase systems above 11.04 kW total, need a full G99 application before commissioning.
How to fix it: always check per-phase output, not total system size. A 10 kW three-phase system is G98 territory; a 4 kW single-phase system is G99. If you're unsure, our team will identify the correct route before any submission goes in.
7. Submitting Without Pre-Checking Supply Capacity
Some sites simply cannot accept the proposed export without network reinforcement. If the local network is already heavily loaded, the DNO may reject the application outright or come back with a costly offer letter requiring reinforcement.
How to fix it: on larger residential and commercial sites, request DNO heat-map or capacity data before designing the export figure. We routinely flag constrained areas before submission and design around them, so customers don't get hit with surprise reinforcement quotes weeks into the process.
8. Going Quiet During the Review Period
The final, often-overlooked cause of delay isn't really a rejection, it's a stall. The DNO requests information, the email lands in a busy inbox, days or weeks pass before anyone responds, and the application clock keeps running.
How to fix it:
- Set a 48-hour internal SLA for any DNO information request
- Keep a single, monitored inbox for all DNO correspondence
- Chase the DNO every 5 working days if you haven't heard back
This is one of the biggest reasons installers come to us. We chase every application proactively, log every comment from every DNO portal, and route information requests to a dedicated engineering team that turns them around the same working day.
Why First-Time Approval Matters More Than You Think
A rejected application doesn't just cost time. It costs:
- Customer confidence: every delay is a conversation the customer didn't sign up for
- Cash flow: jobs sitting in limbo can't be invoiced
- Installer reputation: word travels fast when projects slip
- Engineering capacity: rework eats the time you could spend installing
When you submit applications in bulk over a year, even a small rejection rate compounds into weeks of lost productivity. Getting it right first time isn't a nice-to-have, it's the single biggest lever you have on project velocity.
What We Do Differently
Every application we submit goes through a structured pre-submission review:
- LOA name and address checked against the MPAN account holder
- SLD drawn by real DNO experts, cross-checked against the equipment list
- Export capacity reconciled against inverter rated output
- G98 vs G99 routing confirmed against per-phase calculations
- Capacity constraints flagged before submission on larger projects
After submission, we chase the DNO every 5 working days, respond to information requests the same day, and give you a live dashboard so you can see exactly where every application stands without having to ask. The result is fewer rejections, fewer delays, and predictable approval timelines.
The Bottom Line
Most DNO rejections come down to the same handful of issues, and almost all of them can be caught at the desk before submission. Whether you handle it yourself or outsource the process, the cost of getting it wrong is almost always higher than the cost of getting it right.
If you'd rather not spend another afternoon redrawing an SLD because of a missing relay, that's exactly the kind of work we take off your plate. See our transparent pricing or read about our DNO application process to see exactly how we work.