Skip to main content

​
Summary

Plant-level calculations aggregate block outputs, apply equipment losses—HV and transmission lines in user-defined order—then apply and the grid limit () to produce the final power delivered to the .

​
Inputs

NameSymbolUnitsDescription
Block PowerPblockP_{block}WAC power per block (from Array-Level Aggregation & AC Losses)
Block Repeater Countnrep,blockn_{rep,block}—Number of identical blocks represented in the plant
HV Transformer RatingPHV,ratedP_{HV,rated}MVAHV transformer nameplate capacity
HV No-Load LossLNL,HVL_{NL,HV}%HV transformer no-load loss as a percentage of PHV,ratedP_{HV,rated}
HV Full-Load LossLFL,HVL_{FL,HV}%HV transformer full-load loss as a percentage of PHV,ratedP_{HV,rated}
Transmission Line Lengthℓ\ellkmConductor length
Transmission Line ResistanceRlineR_{line}Ω/1000 ftConductor resistance per unit length
Inverter Design Deratedid_i—Ratio of real power to apparent power (kW/kVA) for inverter ii
Inverter Repeater Countnrep,invn_{rep,inv}—Number of identical inverters per array
Array Repeater Countnrep,arrayn_{rep,array}—Number of identical arrays per block
Transformer High-Side VoltageVHSV_{HS}kVLine-to-line voltage on transformer high side
Conductors per PhaseNcondN_{cond}—Number of parallel conductors per phase
Availability Lossfavailf_{avail}%Percentage reduction for system availability
LGIA LimitPPOIP_{POI}MWMaximum allowed power at point of interconnection

​
Outputs

NameSymbolUnitsDescription
Grid PowerPgridP_{grid}WPower delivered to the grid

​
Detailed Description

​
Block-to-Plant Aggregation

Each plant may contain multiple blocks (with repeater counts). The total plant-level power before HV losses is the sum of all block outputs, weighted by their repeater counts: Pplant=∑blocksPblock×nrep,blockP_{plant} = \sum_{blocks} P_{block} \times n_{rep,block}

​
HV Equipment

HV equipment consists of one or more transformers and transmission lines connected in series. The user defines the ordinal (sequence) of each element. The prediction iterates through the elements in ordinal order, passing the output of each element as the input to the next. For example, a plant stepping up from 34.5 kV to 230 kV via an intermediate 115 kV bus might define:
  1. HV Transformer (34.5 kV → 115 kV) — quadratic transformer losses on PplantP_{plant}
  2. Transmission Line (at 115 kV) — I²R line losses at 115 kV current
  3. HV Transformer (115 kV → 230 kV) — quadratic transformer losses on the remaining power
  4. Transmission Line (at 230 kV) — I²R line losses at 230 kV current

​
HV Transformer

Each HV transformer applies the Transformer Loss Model. The calculation is identical to the transformer, using the HV transformer’s specific rating and loss fractions. When is enabled and triggered (see Inverter Operating Regions for trigger conditions), the HV transformer no-load loss is set to zero, eliminating standby core losses. Additionally, if any inverter in the plant triggers disconnect, the entire plant output after HV equipment is set to zero (see Transformer Loss Model for details).

​
Transmission Line Model

Transmission line losses are calculated from the I²R dissipation in the three-phase conductors. The model uses the line-to-line voltage on the high side of the preceding transformer (or the maximum MV transformer voltage if no HV transformer precedes the line), converted from kV to V. Resistance Calculation The line length is first converted from km to m. The total line resistance in ohms is then: Rtotal=ℓ×Rline304.8R_{total} = \frac{\ell \times R_{line}}{304.8} where Rline/304.8R_{line} / 304.8 converts from Ω/1000 ft to Ω/m (since 1000 ft = 304.8 m). Power Factor Calculation The inverter Design Derate (did_i) represents the power factor of each inverter—the ratio of its real power output (kW) to its apparent power rating (kVA). The PlantPredict logic tracks real (active) power throughout, but transmission line current accounts for active and reactive power and is, thus, proportional to the apparent power Pin/PFP_{in} / PF where PFPF is the power factor. PFPF is calculated as the repeater-weighted average of the individual inverter Design Derate values, computed once at the plant level (displayed as “Plant kVA Derate” in the UI): PF=∑blocks  nrep,block∑arrays  nrep,array∑inv  nrep,inv×di∑blocks  nrep,block∑arrays  nrep,array∑inv  nrep,invPF = \frac{\displaystyle\sum_{blocks}\; n_{rep,block} \sum_{arrays}\; n_{rep,array} \sum_{inv}\; n_{rep,inv} \times d_i}{\displaystyle\sum_{blocks}\; n_{rep,block} \sum_{arrays}\; n_{rep,array} \sum_{inv}\; n_{rep,inv}} Resistive Loss Calculation For a given input power PinP_{in} entering the transmission line, the three-phase line current is: I=Pin3 VHS PFI = \frac{P_{in}}{\sqrt{3}\, V_{HS}\, PF} The total three-phase dissipation, accounting for parallel conductors, is: Lline=3 I2 RtotalNcondL_{line} = \frac{3\, I^2\, R_{total}}{N_{cond}} The output power is: Pout=Pin−LlineP_{out} = P_{in} - L_{line} PinP_{in} can be negative during nighttime operation when the grid supplies power to keep transformers energized; in that case PoutP_{out} is also negative (further from zero due to the line loss).

​
Availability Loss

After all HV equipment losses, a flat percentage availability deduction is applied: Pavail=PHV,out×100−favail100P_{avail} = P_{HV,out} \times \frac{100 - f_{avail}}{100} This deduction represents estimated downtime due to maintenance and unplanned outages. It reduces power uniformly across all timesteps.

​
Grid Limit (LGIA)

The final step enforces the capacity constraint at the point of interconnection. If configured, any power exceeding the limit (converted from MW to W) is curtailed: Pgrid=min⁡(Pavail, PPOI)P_{grid} = \min(P_{avail},\, P_{POI}) The LGIA limit can be specified as:
  • Constant value: a fixed MW cap applied to all timesteps.
  • Time series: a timestep-varying MW limit loaded from a time series input.
  • Off: no cap is applied (Pgrid=PavailP_{grid} = P_{avail}).
The loss due to is reported as: LLGIA=max⁡(0, Pavail−PPOI)L_{LGIA} = \max(0,\, P_{avail} - P_{POI}) In practice, curtailment would reduce inverter setpoints and rebalance upstream losses (transformer loading, collection losses, etc.). The model applies the cap at the POI instead, which yields the same delivered energy while attributing the excess power entirely to curtailment loss rather than redistributing it across upstream loss categories.