Vicaya GlobalCalculator · Solar · inverter clipping
How much is your inverter clipping?
When an array can out-produce its inverter, the excess is simply lost. This works out how much, in which months, and what it is worth — from every hour of a simulated year.
What do kWp and kWh mean?
- kWh — kilowatt-hour
- A unit of energy, and the thing your electricity bill charges you for. A 1,000-watt heater running for one hour uses one kWh. A typical home uses somewhere between 2,000 and 10,000 kWh a year depending on where it is and how it heats.
- kWp — kilowatt-peak
- A unit of capacity — how big the solar array is, not how much it makes. It is the output the panels would produce under standard test conditions: bright, cold and perfectly aimed. Real roofs rarely see those conditions, which is why a 4 kWp array does not generate 4 kW for most of the day. One modern panel is roughly 0.4 kWp, so 4 kWp is about ten panels.
- Putting them together
- kWp is the size of the system; kWh is what it produces over time. The ratio between them — kWh generated per kWp installed, per year — is the honest way to compare locations, because it strips out how big the system happens to be. It runs from roughly 700 in cloudy high latitudes to over 1,800 in sunny deserts.
12 × 450 W at 21% is 2.14 m² per panel — about 26 m² of roof.
This array loses 4.71% of its potential output to the inverter ceiling — about £97 a year.
Recovering it means an inverter of 5.40 kW, which costs about £327 more and would take 4 years to repay that difference out of the energy it rescues.
When the clipping actually happens
| Month | kWh |
|---|---|
| Jan | 33 |
| Feb | 58 |
| Mar | 88 |
| Apr | 78 |
| May | 51 |
| Jun | 23 |
| Jul | 0 |
| Aug | 6 |
| Sep | 27 |
| Oct | 66 |
| Nov | 40 |
| Dec | 14 |
| Total | 485 |
Why clipping is smaller than it sounds
An array reaches its nameplate rating only when several things coincide: full sun, a low angle of incidence, and cold modules. Panels are rated at 25°C and spend most of a sunny afternoon well above that, losing roughly 0.38% of their output per degree. So a 5.40 kWp array does not produce 5.40 kW on a hot clear day — it produces meaningfully less, and the gap between nameplate and reality is headroom the inverter never has to pass.
That is why the loss is bounded. Even an inverter well below the array's rating can only lose the energy in the hours that would have exceeded it, and a year contains few of those. The cost of clipping is real, but it is a slice off the top of the best hours of the best months, not a percentage taken from every kilowatt-hour.
It also depends almost entirely on where you are. This page opens in Phoenix, because that is where the effect is worth seeing. Move the location control to London and the same array, on the same inverter, clips essentially nothing — a maritime climate delivers its annual total through a great many mediocre hours, and mediocre hours never reach a ceiling. If you have been told your array is oversized for its inverter, the first question is not how big the gap is but what your sky does with it.
What this does not model
- Every day in a month is modelled as that month's average day. Cloudiness comes from long-run monthly climate and is applied to all of that month's hours, so the 8,760-hour series holds no individually clear day. Annual energy is a sum and is unaffected; clipping is driven by peaks and is not. Modelled peak AC for a 5.4 kWp array in London reaches 57% of nameplate where a real clear, cool day approaches 85%. Treat the clipping figures here as a floor rather than an estimate — the effect is largest in cloudy climates, where this model reports zero clipping up to a DC:AC ratio of 1.6 and the recommended ratio rises accordingly.
- Inverter efficiency is constant at 96%. A real inverter's efficiency varies with load, so the energy recovered by a larger unit is slightly overstated here.
- No inverter thermal derating. A hot inverter reduces its own output, which looks like clipping and is not modelled.
- No export limit separate from the inverter. Where a connection agreement caps export rather than generation, a system can self-consume through the cap and lose less than this page shows.
- Shading is declared as none. A shaded array clips less, because it rarely reaches the ceiling in the first place.
Frequently asked questions
What is inverter clipping?
When the array briefly produces more DC power than the inverter can convert, the excess is “clipped” and lost. This calculator shows how much that costs, month by month, for an inverter smaller than the array it serves.
How much energy does inverter clipping lose?
Usually a small fraction of the year’s output, because the peaks that get clipped are rare — and often less than the money saved by fitting a smaller inverter. The tool quantifies the lost energy so you can weigh it against the cheaper inverter.
Is inverter clipping bad?
Not necessarily. A little clipping is normal and often economic, since it trims only the brief, rare peaks. The calculator shows whether a bigger inverter would ever repay the difference, so “bad” becomes a number rather than a feeling.