What this calculator does
Solar arrays are routinely installed with more panel capacity than the inverter can pass through. This sounds like a mistake and is usually deliberate. Panels almost never produce their rated output, so an inverter matched exactly to the panel rating sits underused for the entire year.
The trade is that on the few brightest hours the inverter caps the output and the surplus is lost. That loss is called clipping, and the question is whether the extra generation on every ordinary day is worth more than the peak lost on the best ones. Usually it is, up to a point.
The formula
The ratio is simply array DC rating ÷ inverter AC rating. What reaches the inverter at full sun is the array rating reduced by system losses, so peak = DC × efficiency, and anything above the inverter rating is clipped. Dividing the inverter rating back by the efficiency gives the array size the inverter would exactly accommodate with nothing to spare.
| Term | Meaning |
|---|---|
| DC to AC ratio | Array rating divided by inverter rating. Also called the inverter loading ratio. |
| Clipping | Output the inverter cannot pass, lost at the brightest moments of the brightest days. |
| System efficiency | Combined losses from wiring, dust, heat and the inverter itself. Panels in the field rarely exceed 80 per cent of their rating. |
| Peak output | The most the array can deliver after those losses, which is what the inverter actually sees. |
The inputs explained
| Field | What to enter |
|---|---|
| Array size (DC) (kW) | Total panel rating, which is panel wattage times panel count. |
| Inverter size (AC) (kW) | The inverter's continuous AC output rating. |
| Average peak sun hours per day (h) | Average peak sun hours a day for your location, used only for the yearly yield figure. |
| System efficiency (%) | System efficiency. 80 per cent is a common planning figure and covers heat, dust, wiring and inverter losses together. |
When to use it
Checking an installer's quote
Enter the panel total and the inverter rating. A ratio between about 1.1 and 1.35 is the normal design range. Below 1 the inverter is larger than the array can ever fill, which is money wasted on the inverter.
Deciding whether to add panels
Adding panels to an existing inverter raises the ratio. Watch the clipped power figure: a little is fine and expected, but once a quarter of the peak is being thrown away the extra panels are earning much less than they cost.
Sizing an inverter for a planned array
The last output gives the array size the inverter exactly fits at your efficiency. Going somewhat above that is the normal choice, not an error.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
When does an array start clipping?
The inverter is fixed and the array grows.
| Array size | DC to AC ratio | Power clipped at full sun | Share of peak output clipped |
|---|---|---|---|
| 5 kW | 0.833 | 0.00 kW | 0.000% |
| 6 kW | 1.000 | 0.00 kW | 0.000% |
| 7 kW | 1.167 | 0.00 kW | 0.000% |
| 7.5 kW | 1.250 | 0.00 kW | 0.000% |
| 8 kW | 1.333 | 0.40 kW | 6.25% |
| 9 kW | 1.500 | 1.20 kW | 16.7% |
| 10 kW | 1.667 | 2.00 kW | 25.0% |
How much does system efficiency change the picture?
The hardware is fixed and the loss assumption changes.
| System efficiency | Peak output after losses | Power clipped at full sun | Yearly yield before clipping |
|---|---|---|---|
| 70% | 5.60 kW | 0.00 kW | 9,198 kWh |
| 75% | 6.00 kW | 0.00 kW | 9,855 kWh |
| 80% | 6.40 kW | 0.40 kW | 10,512 kWh |
| 85% | 6.80 kW | 0.80 kW | 11,169 kWh |
| 90% | 7.20 kW | 1.20 kW | 11,826 kWh |
Questions
Is clipping bad?
Not by itself. Losing a little peak output on the brightest afternoons is usually a good trade for generating more on every other day. It becomes bad when the ratio is high enough that a large share of peak output is lost.
What ratio should I aim for?
Between roughly 1.1 and 1.35 is the usual design range. The right figure depends on your climate: cloudier places can push higher because full sun is rarer.
Does this calculate how much energy clipping costs me per year?
No, and it deliberately does not guess. Working that out needs an hour-by-hour irradiance profile for your site, because it depends on how often the array actually reaches peak output. This page gives the peak clipped power, which is the part you can know from the ratings alone.
Why use 80 per cent efficiency?
It is a common planning figure covering heat, dust, wiring and inverter losses together. Panels are rated under test conditions a roof rarely matches.
Can the inverter be damaged by an oversized array?
No. Inverters limit their output by design and simply cap at their rating, though there is usually a maximum DC input the manufacturer specifies, which is a separate limit worth checking.
For sizing the array itself there is solar system sizing, and solar energy yield estimates annual output. What that output is worth depends on self-consumption.