Power Limits and Curtailment
A plant is described by three different power figures, and only one of them is the ceiling it may actually feed into the grid. Mixing them up is the single most common reason a healthy plant looks like it is underperforming.
The Three Power Figures
All three live on the plant's Core data page, in the performance card.
| Figure | What it is | Typical relation |
|---|---|---|
| DC peak power (modules) | The DC nameplate of the panel field — the sum of what all modules can deliver under standard test conditions. | The largest of the three |
| AC peak power (inverters) | The combined AC limit of the inverters — the most the plant can convert to alternating current. | Usually below the DC peak |
| Grid connection limit (PAV,E) | The most the grid operator accepts at the connection point. | The plant's hard ceiling |
The card also shows the DC/AC ratio (DC peak divided by AC peak). A ratio above 1 means the array is deliberately oversized against the inverters — a normal design choice that trades a little clipping at midday for more yield in the morning, evening and winter.
Which one is the ceiling?
The lowest configured of the AC peak power and the grid connection limit. A plant with 83 MWp of panels, 63 MW of inverters and a 58 MW grid connection can never feed in more than 58 MW — and reaching 52 MW on a good day means it ran at roughly 90 % of what it is allowed to deliver, not 63 % of its nameplate.
The Same Value, Other Names
The grid connection limit is the figure most often asked about, and it travels under many names depending on the document it came from:
| You may see | Meaning |
|---|---|
| Netzanschlussgrenze, Netzanschlussleistung | Grid connection limit / connection capacity |
| Einspeisebegrenzung, Einspeisegrenze | Feed-in limit |
| Vereinbarte Einspeiseleistung | Agreed feed-in power |
| PAV,E (also written PAV,E or P_AV,E) | In the German grid connection rules (VDE-AR-N 4105 for low voltage, VDE-AR-N 4110 for medium voltage), the active power agreed with the grid operator for feed-in at the connection point |
They all refer to the same thing, and in Mirox they are all stored in the grid connection limit field. The value comes from your grid connection contract or feed-in permit — it is a contractual figure, not something the plant measures, so the platform only knows it once it has been entered.
If it is not set
With no grid connection limit and no AC peak power configured, the platform has no feed-in ceiling to work with: expected-production curves are calculated uncapped (and read high whenever the plant would really clip), and plant-wide curtailment cannot be quantified at all. Setting the two limits is part of plant onboarding.
Why a Plant Never Reaches Its Peak Power
Even without any limit, the DC nameplate is a laboratory figure — it assumes full standard irradiance on every module at once, at a module temperature no real summer day delivers. Real plants peak well below it. On top of that come, in order:
- Inverter clipping — output above the AC peak power is simply not converted.
- The grid connection limit — output above it may not be fed in.
- Curtailment — a temporary reduction ordered by the grid operator or your marketer, on top of everything above.
So a curve that flattens at a constant value is usually not a fault. Compare it against the ceiling, not against the nameplate.
Curtailment (Abregelung)
Curtailment is production you were deliberately prevented from delivering. Mirox tracks it separately from component losses and attributes it to the responsible party:
- Grid curtailment — the grid operator reduced the plant, typically feed-in management during grid congestion.
- Marketer curtailment — your direct marketer or trading party reduced the plant, typically on negative market prices.
How a Reduction Is Recognised
The plant reports its active power setpoint as a percentage. That percentage is taken against the plant's grid connection limit — or against the AC peak power when no grid limit is configured. So on a plant with a 58 MW grid connection, a 60 % setpoint means the plant is being held to about 35 MW.
A setpoint only counts as curtailment when it actually bites: it must fall below roughly 85 % of that reference. This threshold keeps normal control-system noise and permanent minor settings from being booked as losses every day. If no reference can be resolved at all, only a near-complete shutdown is recognised.
The energy foregone while a reduction is in force is recorded per minute against the responsible party, so a perfectly healthy plant that was told to throttle is never flagged as a defective one. How that energy then appears in the performance ratio is covered in Loss Detection.
Reading the "Power Limit" Curve
In the graphs and the raw metrics you will find a Power Limit series alongside the per-party ones (Power Limit by Grid, Power Limit by External, Power Limit by Local).
The Power Limit series is not the feed-in ceiling
It expresses the active setpoint percentages applied to the DC nameplate. Its unrestricted baseline is therefore the DC peak: a value equal to the DC peak power means no reduction is in force, not that the plant may feed in that much. For the actual ceiling, read the grid connection limit on Core data.
Where to Find and Set These Values
Open a plant and go to its Core data page — the performance card shows all three figures plus the DC/AC ratio, and the master-data form is where they are set. Open in Mirox — pick your plant from your plants and choose Core data.
Changing either limit re-deploys the plant's edge agent, so the new value is picked up by the curtailment calculation within a few minutes.
Related Features
- Loss Detection — how curtailment is separated from real component losses
- Digital Twin — the expected-production model these limits clip
- Graph Visualization — where the power and limit curves are shown
- Plant Onboarding — the step where these values are first entered
- Data Scraper — the edge agent that performs the curtailment calculation