DNO, G98/G99, and export limits: why your inverter may be capped
A practical UK guide to DNO rules, G98 vs G99, export limits, and what “capped at 3.68kW” really means for solar output, savings, and system design.
DNO, G98/G99, and export limits: why your inverter may be capped
If you are getting solar quotes in the UK, you will sometimes see a line like:
“Export limited to 3.68 kW”
or:
“G99 application required”
This is where people get spooked, because it sounds like a hidden restriction that will ruin your savings.
In most homes, it is not that dramatic. Export limits are common, and a well-designed system can still perform brilliantly.
If you want to sanity-check what “normal” looks like where you live, with local yield and tariffs baked in, start here: Find your postcode
Quick answer: is an export cap a deal-breaker?
- Export limits cap how much you can push to the grid at once. They do not stop your panels generating.
- Most homes lose only a small amount of annual kWh from a sensible export cap, because the cap only bites on peak sunny hours.
- G98 vs G99 is about grid connection rules, not “better” or “worse” solar. It depends on inverter power and your supply.
- The right response is not panic. It is to understand the constraint and design around it (inverter choice, export limit settings, or a G99 application).
Assumptions and variability
- We assume a domestic UK solar PV system on a typical single phase supply.
- We talk about system size in kWp and power in kW and energy in kWh (see Glossary).
- Export caps, approvals, and timelines vary by local network and by DNO (Distribution Network Operator, see Glossary).
- What shifts results most is inverter sizing, how often the cap bites on your roof, and your day time usage pattern.
- For the modelling assumptions behind SolarByPostcode yields, tariffs and savings, see: Data sources and methodology
The mental model: why export gets capped in the first place
If you remember only one thing, remember this:
Most export caps are about protecting the local grid from voltage issues, not about “punishing” solar.
DNO, in one paragraph
DNO stands for Distribution Network Operator (see Glossary). Your DNO runs the local electricity network in your area. They are not your energy supplier.
When you add solar, you are no longer only consuming electricity. You are also exporting it at times. Export changes local voltage and loading, especially in streets where many houses export at the same time on a sunny day.
That is why the DNO gets a say.
G98 vs G99: what actually decides which you are on
People often assume:
- small system = G98
- big system = G99
That is not quite right.
The rule trigger is usually about inverter AC power, and whether you are on single phase or three phase.
For most homes, the headline threshold people talk about is:
- 16A per phase, which is roughly 3.68 kW on a 230V supply.
If your inverter output per phase is within that, you are usually in the “simpler” bracket, commonly referred to as G98.
If you are above that, you are usually into G99, which generally means you apply and get approval before connecting.
Do not let the jargon scare you. The practical question is:
How much power can this inverter export to the grid at once, and what is the DNO willing to accept at my address?
If you have never seen kW vs kWh explained clearly, start here (it matters in this guide): Glossary.
What an export limit actually does to your system
An export limit is a cap on instantaneous power to the grid.
It is not a cap on:
- how many panels you can fit on your roof
- how much your house can consume
- how much your battery can charge from solar
- how much your system generates in the morning, evening, or winter
The cap only bites when all of these are true at once:
1) It is sunny enough that your inverter could push above the limit
2) Your household demand is low at that moment
3) Your battery (if you have one) is full or charging slowly
4) The export would exceed the limit
That “perfect storm” is real, but in many homes it is rare.
This is why an export limit is often a smaller deal than it sounds.
If you want the deeper “rated output vs real output” explanation, this guide helps build intuition:
The main ways installers handle export constraints
When an installer says “export limited”, they could mean slightly different design choices.
1) Keep the inverter under the threshold
This is the simplest approach in paperwork terms.
You might still have a larger array of panels (kWp), but the inverter AC output is limited.
That means:
- peak clipping can happen on very sunny hours
- but you often get a long, strong shoulder season output
- and you keep the grid approval process simpler
This is common in standard domestic installs.
2) Use a larger inverter and apply under G99
This can unlock a higher allowed export if your local network can handle it.
If it cannot, you may still end up capped, just with more paperwork.
It can be worth it in some cases, especially where:
- you expect to export a lot (low day time use)
- you have a very high-yield roof
- or you are building a larger system from day one
3) Export limiting device or settings (still with a larger system)
Sometimes the system is physically capable of more, but it is configured to obey a cap.
This is where homeowners get confused because the quote might show:
- “system size: 8 kWp”
- “export limit: 3.68 kW”
Those can both be true.
The system can still generate 8 kWp worth of DC power, but the grid export is kept within a limit.
4) Upgrade supply (rarer, usually expensive)
Occasionally, a DNO might require or suggest a supply upgrade for certain configurations. For normal homes, this is much rarer than installers make it sound, and it is not the default assumption.
If a quote quickly jumps to “you need a supply upgrade” without explaining why, treat that as a prompt to get a second opinion.
How export limits affect savings, in plain English
Most homeowners care about money, not grid rules. So translate it.
Your savings usually come from:
1) Self-use: using your own solar instead of buying electricity from the grid
2) Export: getting paid something for what you send out (SEG)
Export caps mostly affect the second bucket, and usually only at peaks.
The first bucket (self-use) often dominates savings. That is why:
- homes with day time usage do well even with export caps
- batteries can reduce the pain of export caps by soaking up peaks (when sized sensibly)
- and a slightly capped system can still be a great investment
If you want the sizing framework that links kWp, kWh, and self-use properly, this is the flagship:
What to ask your installer when “export limited” appears in the quote
This is the shortest set of questions that usually reveals whether the quote is thoughtful.
1) What export limit are you assuming in kW, and why?
2) Is that a DNO requirement at my address, or a default assumption?
3) How much annual kWh do you estimate is lost to clipping or export capping?
4) What is the inverter AC rating, and how does that relate to G98/G99 in this design?
5) If I add a battery later, will the export limit still apply, and will it matter less?
A good installer can answer those without getting defensive.
A weak installer will lean on jargon.
Postcode examples: click a few, then come back to your quote
Export constraints are a grid reality, but local context changes how likely the cap is to bite.
Use a wide spread to build intuition:
- Leeds: LS1 (Leeds)
- Liverpool: L1 (Liverpool)
- Nottingham: NG1 (Nottingham)
- Southampton: SO14 (Southampton)
- Norwich: NR1 (Norwich)
- Exeter: EX1 (Exeter)
- Swansea: SA1 (Swansea)
- Dundee: DD1 (Dundee City)
- Belfast: BT7 (Belfast)
You are not looking for “the right answer” in those pages. You are looking for a feel for what changes by location, and what stays the same.
Then use your own postcode and your own usage pattern.
Common misunderstandings (and what is actually true)
“If export is capped at 3.68 kW, my solar can never go above 3.68 kW”
Not necessarily.
That number is about export to the grid. Your house can consume solar at the same time.
Example: if your system is generating 5 kW and your home is using 1.5 kW, the export is 3.5 kW and you are still within a 3.68 kW cap.
That is why self-use matters so much.
“Export caps make big systems pointless”
Not true in general.
Big systems can still:
- generate a lot in shoulder seasons
- cover more of your annual consumption
- charge a battery faster
- and support future electrification (EV, heat pump)
The correct question is not “big or small”.
It is:
Does the extra kWp produce enough extra useful kWh (self-use + paid export) to justify the extra cost?
This guide helps with that decision:
“G99 is bad”
G99 is not bad. It is a process.
Sometimes it is required for a design that makes sense. Sometimes installers default to it unnecessarily, or they use it to justify complexity.
The right posture is:
- understand why it is being used
- and ensure the benefit is real
If you want a practical baseline on how quotes vary and what drives cost, read:
How this connects to MCS and SEG
Export payments are under SEG (see Glossary).
Many suppliers expect MCS documentation when you apply for SEG export payments.
MCS and DNO are different “systems”:
- MCS is certification and process
- DNO / G98 / G99 is grid permission and export constraints
You usually need both to have a clean experience.
If you have not read the MCS guide yet, read it next:
Bottom line
- Export limits are common. They protect the local grid, not the installer.
- G98 vs G99 is mostly about inverter AC rating per phase, not about how many panels you buy.
- A cap usually bites only at rare peak moments, so annual impact is often modest.
- The right response is to ask a few clean questions and compare quotes based on assumptions, not badges.
Next reads
- MCS certification in the UK: what it guarantees (and what it doesn’t)
- Planning permission and conservation areas: what UK solar installs are actually allowed to do
- Inverters explained (UK): what they do, what can go wrong, and what “clipping” really means
- Oversizing your solar system in the UK: when it pays off and when it does not
- How to compare solar quotes in the UK: a numbers-first checklist
- Do solar panels increase house value in the UK? The boring truth (and when it backfires)
Check your own home
Export caps are only scary when you do not have context.
Run your postcode, compare a couple of system sizes, and see how self-use and export play out with real local assumptions.