Home › Guides › Why your inverter is smaller than your panel array, and why that is correct
SolarWhy your inverter is smaller than your panel array, and why that is correct
Almost every good UK solar design puts more panel capacity on the roof than the inverter can pass through at once. It looks like an error on paper, but it is a deliberate design choice that puts more electricity into your house across the year.
Updated 4 August 2026 · written by the Clearline guidance team
Two different numbers, doing two different jobs
Your panel capacity, measured in kWp, is what the array could produce under laboratory test conditions. Your inverter rating, measured in kW of AC output, is the maximum the system can push into your house at any one moment. They are not the same measurement and they are not supposed to match.
The relationship between them has a name: the DC to AC ratio, sometimes called the inverter loading ratio. Divide installed panel kWp by inverter AC rating. The industry norm is 1.10 to 1.30, with most systems landing between 1.15 and 1.25. A 4.4kWp array on a 3.68kW inverter is a ratio of 1.20, which is squarely mainstream.
Around 4kWp on a 3.68kW inverter is the standard UK single phase build
It is the default for a reason. 3.68kW per phase is the ceiling for connecting under the simple notify-afterwards process rather than applying for permission first, and the panels above that line still earn their keep for most of the year.
What clipping actually is
When the array produces more DC power than the inverter's AC rating can pass, the output is capped at that rating and the excess is lost. That is clipping. It sounds like waste, and on a spreadsheet showing a single perfect summer noon it is. Across a year on a British roof, it is a rounding error.
The reason is in the test conditions. Panel ratings assume standard test conditions including a 25C cell temperature, and UK roofs rarely sustain the combination of full irradiance and moderate temperature that would put an array at its nameplate figure. The windows in which a well-designed array actually exceeds its inverter rating are short and clustered around the middle of clear summer days.
What you gain by loading the inverter
Every hour that is not a clear summer noon, the extra panels are doing straightforward useful work. Oversizing the array relative to the inverter lifts yield in mornings, evenings and through the winter, which is precisely when a British household is at home and using electricity. Extra panels are usually cheaper than a bigger inverter, and the added annual production typically outweighs the clipping losses.
There is a second, less obvious gain. A smaller inverter starts generating earlier in low light, because it reaches its start-up threshold at a lower input. On dull mornings that is real generation you would otherwise not see.
| Time of year | What the extra panels do | Clipping risk |
|---|---|---|
| Winter | Lift a weak output substantially, exactly when you are home using it | None |
| Spring and autumn | Extend the useful generating window at both ends of the day | Minimal |
| Summer mornings and evenings | Add generation in the hours either side of the peak | None |
| Clear summer midday | Produce more than the inverter can pass | Output capped at the inverter rating |
Based on DC to AC ratio guidance and UK clipping analysis, accessed August 2026.
The regulatory reason for 3.68kW
The 3.68kW figure is not an engineering constant, it is a connection threshold. Under G98 a system of 3.68kW per phase or less, which is 16A per phase, can be fitted first and notified to your Distribution Network Operator afterwards. Above that, G99 applies and the installer needs approval before the work happens, which takes roughly four to eight weeks in a standard determination.
Crucially, the threshold governs the inverter's AC rating, not panel kWp. You can hang well over 4kWp of panels on a 3.68kW inverter and stay firmly within G98. That single fact is why UK solar design looks the way it does, and it is explained in full in G98 versus G99 explained.
Three phase changes the arithmetic entirely
The same connect-and-notify rule applies per phase, so a three phase home can fit up to 11.04kW without prior approval. If you are not sure which you have, our single phase versus three phase guide covers the sixty-second check at your fuse board.
When the ratio is genuinely wrong
Loading an inverter is good practice, but overloading it is not. Past roughly 1.30 the clipping losses start to bite into the summer months in a way the winter gains do not repay, and you are buying panels whose output you will systematically throw away. A quote showing a ratio well above that range deserves a question.
- Below 1.10: you have paid for inverter headroom you will almost never use, which does no harm but is money that would have bought generation elsewhere.
- 1.15 to 1.25: the mainstream band, and where most well-designed UK systems land.
- Above 1.30: worth asking why. There can be a good reason, such as a battery-focused design or a deliberately export-limited system, but it should be a decision rather than an accident.
The other thing the inverter decides
If you have or want a battery, the inverter choice is also the storage choice. A hybrid inverter runs the panels and the battery in one unit. Our battery storage guide covers what changes, and microinverters versus optimisers versus string covers which architecture suits your roof.
It also affects how much you can export and when, which feeds directly into which export tariff makes sense for you. Our tariffs guide carries the current rates with the date each was checked.
Not sure whether the ratio on your quote is sensible? Bring it to a free design call and we will run the arithmetic with you in ten minutes.
Get your free quote →Checking your own quote
Find total panel kWp
Panel wattage multiplied by panel count, divided by 1,000. Twelve 440W panels is 5.28kWp.
Find the inverter AC rating
It is on the quote as a kW figure, often 3.68kW on single phase. This is what your network operator regulates.
Divide the first by the second
5.28 divided by 3.68 gives 1.43. That is above the mainstream band and worth asking about.
Ask what the answer is
There may be a perfectly good reason for a high ratio, such as an export-limited design or a battery absorbing the surplus, and your installation team should be able to name it without hesitating.
Every county page on this site carries a calculator for that area, built on the same model our guidance uses, so you can test different configurations before anyone visits. Start at your county page. Installations are carried out by an MCS-certified installation team for your area.
Inverter sizing, answered
Why is my inverter smaller than my solar panels?
Because the panels rarely all hit their rated output at once on a British roof, and because extra panels are cheaper than a larger inverter. Loading the inverter this way lifts generation in mornings, evenings and winter, and the added annual production typically outweighs what is lost to clipping at summer peak.
What is inverter clipping?
It is what happens when the array produces more DC power than the inverter's AC rating can pass through. The output is capped at the inverter rating and the excess is lost. On a UK roof the clipping windows are short and concentrated around clear summer middays.
What is a good DC to AC ratio?
The industry norm is 1.10 to 1.30, and most well-designed systems land between 1.15 and 1.25. Below 1.10 you have bought inverter capacity you will not use. Above 1.30 the clipping losses start to outweigh the low-light gains, and the design deserves an explanation.
Can I fit more than 3.68kW of panels?
Yes, easily. The 3.68kW threshold applies to the inverter's AC output per phase, not to panel capacity. You can install well over 4kWp of panels on a 3.68kW inverter and remain within the simple connect-and-notify process.
Would a bigger inverter generate more electricity?
Only during the short periods when the array would otherwise be clipping, and it may generate less on dull mornings because a smaller inverter reaches its start-up threshold at lower light. It also pushes you above the G98 threshold, which means applying to your network operator before installation rather than notifying afterwards.
Does a battery change the inverter sizing?
It changes what happens to surplus generation rather than the ratio itself. With a hybrid inverter, power the array produces above household demand can charge the battery instead of being exported or clipped, which strengthens the case for a fuller roof. The sizing conversation and the storage conversation belong together.
See the numbers next: LONGi 530 W panels, installed, or the solar panels guide.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- DC to AC ratio norms of 1.10 to 1.30 and the definition of clipping aurorasolar.com
- UK convention of around 4kWp on a 3.68kW inverter, short real clipping windows, earlier low-light start blog.spiritenergy.co.uk
- Inverter oversizing versus undersizing: yield gains in mornings, evenings and winter freedomforever.com
- G98 applies at 3.68kW per phase or less, which is 16A per phase sunsave.energy
- G99 standard determination takes roughly four to eight weeks sunsave.energy
- The threshold governs inverter AC rating, not panel kWp sunsave.energy
- Three phase connect-and-notify limit of 11.04kW blog.spiritenergy.co.uk
Read next
How long does a solar inverter last, and when does replacing it make sense?
The one component you should expect to replace, and the decision tree when it goes.
Read the guide →Are solar panels worth it in 2026? Here is the actual maths
Roughly £1,000 per kWp installed, offsetting electricity at 26.32p a unit. The real arithmetic.
Read the guide →Adding a battery to solar panels you already own
Retrofitting a battery to working solar is straightforward. The paperwork is where people trip up.
Read the guide →