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PV system sizing: resource, kWp, strings, rows and PR

Size a solar system in one tool: your city's PSH against your consumption, the kWp and the inverter, the modules in series and the strings per MPPT at the site temperature, the row spacing without shading, the loss cascade with the performance ratio and, if stand-alone, the battery bank.

IEC 62548-1:2023maximum voltage and currents of the PV arrayNFPA 70article 690: maximum circuit voltage and currentIEC 61724-1:2021yields and performance ratioNREL PVWatts V5temperature model, losses and clippingDuffie y Beckmansun position and in-plane irradiation

Example cases
PV system sizing: resource, kWp, strings, rows and PR

Only the basic data; the rest is taken with typical values.

ALearn

E1Array

Empty: the maximum admissible.

Empty: the maximum.

Empty: all of the inverter's.

E2Site
°C

Lowest recorded: −6.4 °C.

°C

Mean maximum, warmest month.

R1Consumption and system
kWh

The one on your bill, a 12-month average.

%

Of the annual consumption.

kWp

Empty: the one required.

R2Solar resource
kWh/m²·día

Empty: the city's (NASA POWER).

M1Mounting
°
°

0 = south, 90 = west.

°
R3Consumption of each month
Consumption of each month

One row per month, January to December, from your bill. Empty: the monthly consumption above in all of them.

RowConsumptionkWhRemove

kWh
kWh
kWh
kWh
kWh
kWh
kWh
kWh
kWh
kWh
kWh
kWh
C1Array and inverters

The maximum it accepts.

Empty: the minimum values.

C2Module dimensions
mm
mm
E3Module (datasheet, STC)
W
V
V
A
V
A
%/°C
%/°C
%/°C
E4Inverter (datasheet)
V
kW
V
V
A
A
E5Assumptions and additional data
°C
W/m²
°C
%/°C
%
A
V
V
kWp
F1Tables and rows

Along the slope.

m

Pitch. Empty: the minimum.

°

Positive north. Empty: the city's.

F2Criterion and view
h

Around solar noon.

F3Soil
P1System
kWp

STC Pmax of the modules.

kW

Sum of the inverters.

P2Resource and temperature
kWh/m²

Of the period, in the plane.

°C

Irradiance-weighted.

%/°C

From the module datasheet.

P3Losses that depend on the hourly profile
%

From the simulation. Empty: not estimated.

%

Empty: no data.

%

From "Rows and shading". Empty: left out of the cascade.

P4Measured (optional)
kWh

At the point where the cascade ends. Empty: not compared.

P5Losses with a typical value
%
%
%
%
%
%
A1Battery bank
kWh

Empty: that of the highest-consumption month.

días

Consecutive days without sun.

V
%

The one the chemistry allows.

%
%

100 % a 25 °C.

%

Use a decimal point. The calculation runs in your browser and updates as you type.

Peak power required

— kWp

Annual production

—

Consumption coverage

— %

Mean in-plane PSH

— h/día

PR of the loss cascade

—

Lowest-production month

—

Modules

—

Installed DC power

— kWp

Inverters

—

DC/AC ratio of the array

—

Strings per inverter

—

Module area

— m²

Land with the rows

— m²

Modules in series

—

String Voc at minimum temperature

— V

Hot string Vmpp

— V

Strings per MPPT

—

1.25 · Isc per MPPT

— A

DC/AC ratio

—

Minimum and maximum cell temperature

— °C

Row spacing (pitch)

— m

Ground coverage ratio (GCR)

—

Shading limit angle

— °

Row loss over the year

— %

Sun in the view: elevation and azimuth

— °

Shadow on the row behind, in the view

— %

Expected performance ratio, Yf / Yr

—

Energy at the meter

—

Final yield Yf

— kWh/kWp

Reference yield Yr

— h

PR corrected to 25 °C

—

DC/AC ratio

—

Measured PR

—

Nominal bank energy

— kWh

Bank capacity

— Ah

Usable bank energy

— kWh

Total derating factor

—

Sunny days to recharge

— días

Expected production against consumption, month by month
  • Production
  • Consumption
Bars: what the array produces each month with the in-plane irradiation and the cascade PR. Line: your consumption.
Mean daily irradiation of each month
  • Horizontal (PSH)
  • In the plane of the modules
NASA POWER, 2001 to 2025 average, 1° cell around the airport station.
Array, strings and inverters
  • DC power
  • AC power
Each box is an inverter with its strings. The DC/AC ratio is the array nameplate power against that of the inverters.
String voltage against cell temperature
  • String Voc
  • String Vmpp
  • Max. Vdc
  • MPPT window
Voc rises when the cell cools: at the minimum temperature it must not cross the white line. Vmpp drops when it heats up: at the maximum temperature it must stay inside the yellow band.
Currents per MPPT
  • Group current
  • Inverter limit
Bars: the current of the strings connected to one MPPT. Yellow mark: the inverter datasheet limit.
Section of the rows with the sun ray
  • Table
  • Sun ray
  • Shadow on the ground
The ray leaves the top edge of each table; where it touches the table behind, the shadow begins.
The sun during the day
  • Profile or tracker angle
  • Without backtracking
  • Shading limit
There is shading when the sun's profile angle drops below the limit angle.
Row loss in each month
  • Geometric loss
  • Electrical upper bound
Loss of direct irradiation on the shaded part, on the mean day of each month.
Energy cascade, from resource to meter
  • Energy
  • Loss
Each gray bar is what is lost at that stage out of what the previous one left: that is why losses multiply and are not added.
AC power against available DC power
  • Inverter output
  • No limit
  • Rated PAC
The inverter delivers η · PDC up to its rated power and clips the rest.
Bank energy against days of autonomy
  • Nominal energy
  • Chosen days
Energy grows in a straight line with the days of autonomy.

Step-by-step calculation

What it means for your system

    Need it for a real project? We carry out the full study, with its report.

    Design and studiesSend via WhatsAppGo to the contact form

    What it is for

    Follow the whole sizing sequence of a solar system in one place: how much energy you need and how much sun the site has, how many kWp and which inverter, how the strings are built, how far apart the rows go so they do not shade each other, how much it produces with its losses and, if the system is stand-alone, which battery bank it needs. The tabs share their data: the city sets the irradiation, latitude and temperatures; the module and inverter in "Strings" build the array; the row geometry sets the in-plane irradiation and the shading loss; and the PR in "Production and PR" turns irradiation into energy.

    The "Strings" and "Production and PR" tabs are the string sizing and losses and performance ratio tools, with all their data, cases and results. In "Strings", when you choose the inverter and the module, the number of modules per string and strings per MPPT is defined, and a design you received is checked before buying or installing. A string with one module too many can stay within the maximum voltage under test conditions and exceed it on a cold early morning, when the sun is just rising and the cell is at air temperature: on the Bogotá plateau this happens with frosts. A short string, on the other hand, can leave the MPPT window at hot midday and lose energy.

    The "Strings" chart shows how the string's Voc and Vmpp change with cell temperature against the maximum input voltage and the MPPT window, so you can see how much margin is left at each end. For commissioning the PV array, Voc and Isc tests per string are described in the guide on testing to energize a solar plant.

    "Production and PR" builds the loss cascade of a PV system and shows how much each stage weighs between the solar resource in the plane of the modules and the energy reaching the meter, and calculates the expected performance ratio (PR) with the IEC 61724-1 definition. If you enter the energy measured over the same period, the tool calculates the measured PR and the difference against the expected one: a sustained difference points to a loss the design did not foresee, such as soiling above what was assumed, a disconnected string or unrecorded unavailability. What each loss is, how PR is measured so that it is comparable, and what it is used for in the acceptance and operation of a plant is explained in the guide on losses of a solar system and performance ratio.

    The battery bank of a stand-alone system is refined in the battery sizing.

    How it is calculated

    IEC 61724-1:2021yields and performance ratioNASA POWERmonthly irradiation

    Resource, consumption and kWp

    Emonth = P0 · Hplane,month · PR · P0 = coverage · Σ consumption / Σ (Hplane · PR)

    Each month's in-plane irradiation comes from the city's global and diffuse irradiation with the tilt, azimuth or tracker of "Rows and shading", and the energy is the nameplate power times that irradiation (in full-sun hours, the Yr of IEC 61724-1) times the cascade PR of "Production and PR". The PR includes the row loss: the one you enter in "Shading between rows" or, without that value, the one "Rows and shading" calculates. Grid-connected or hybrid, the array covers the part of the annual consumption you choose; stand-alone, it is set by the month in which production per kWp covers the least of your consumption.

    Module and inverter datasheetspower, dimensions and MPPT

    Array and inverters

    modules = Ns · ⌈P0 / (Pmax · Ns)⌉ · inverters = ⌈PDC / (DC/ACtarget · PAC)⌉

    Modules are rounded up to whole strings with the modules in series from "Strings". The number of inverters is the smallest that leaves the DC/AC ratio at the target or below; the tool checks that each inverter's strings fit in its MPPTs with the strings per MPPT from "Strings". The area is that of the modules, and the land is that area divided by the rows' coverage (GCR).

    IEC 62548ed. 2016, 7.2 y 7.3NFPA 70690.7, maximum voltage

    Maximum string voltage

    Voc,string = Ns · Voc · [1 + βVoc · (Tcell,min − 25 °C)] ≤ min(Vdc,max; Vsystem,module)

    IEC 62548:2016, in clause 7.2, takes as the maximum PV array voltage the Voc corrected to the lowest expected operating temperature, following the module manufacturer's instructions, and in 7.3 requires every component and the inverter input to have a rated voltage equal to or higher (text checked in the final draft, FDIS, of that edition; IEC 62548-1:2023, with its 2025 amendment, replaced it and its numbering was not consulted). Article 690 of NFPA 70 (NEC) defines the maximum circuit voltage as the sum of the Voc of the series modules corrected to the lowest expected ambient temperature, with the manufacturer's coefficient when given (text checked in the 2014 NFPA 70 and its commentary). Ns,max is the integer part of the quotient, rounded down.

    Module datasheettemperature coefficients and NOCT

    Hot voltage and MPPT window

    Tcell,max = Ta,max + (NOCT − 20 °C) · G / 800 W/m² · Ns,min = ⌈VMPPT,min / Vmpp(Tcell,max)⌉

    The hot cell temperature comes from the NOCT model with the conditions printed on datasheets (800 W/m², 20 °C air and 1 m/s wind), as presented by Duffie and Beckman (Solar Engineering of Thermal Processes, ch. 23), without the efficiency term, which would lower it by a few degrees: it errs on the safe side. Since datasheets almost never give the Vmpp coefficient, it is deduced from P = V · I: βVmpp = γPmax − αIsc, which comes out more negative than that of Voc and is therefore conservative at both ends. With the cold Vmpp, the tool checks that the string does not exceed the maximum MPPT voltage: the inverter starts, but does not track the maximum power point.

    IEC 62548ed. 2016, 7.3.13NFPA 70690.8, maximum current

    Strings per MPPT

    Np · Impp(Tcell,max) ≤ Imax,MPPT · 1.25 · Np · Isc ≤ Isc,max,MPPT · Np ≤ inputs

    IEC 62548:2016 (7.3.13) requires the inverter input to accept at least 1.25 times the STC Isc of the connected circuit, and NFPA 70 (690.8) sets the maximum circuit current as the sum of the parallel Isc times 125 %; Fronius writes it this way in its datasheets: Isc,max ≥ Isc(STC) · 1.25. If the check passes only without the 1.25 factor, the tool shows a warning; if it fails even then, a failure. An operating current above the maximum per MPPT does not damage the inverter, which limits it, but energy is lost. For bifacial modules, the current is multiplied by the rear-side gain.

    IEC 62548ed. 2016, 6.5.3 y 6.5.5.1

    String fuses

    (Np − 1) · Isc > Ifuse,module ⇒ fuse · 1.5 · Isc < In < 2.4 · Isc, In ≤ Ifuse,module

    If a string fails, the others in the group feed current back into it; when that current exceeds the maximum protection the module admits (the "maximum series fuse rating" on the datasheet), each string carries its gPV fuse in the indicated range.

    DC/AC ratio

    DC/AC = Ns · Np · MPPTs in use · Pmax / PAC

    It is the installed peak power against the inverter's rated power. There is no normative value: it depends on the resource, on the clipping you accept and on what the manufacturer allows. If you enter the maximum PV power from the datasheet, the tool warns when you exceed it.

    Duffie y Beckmanch. 1: sun position and profile angle

    Sun position and row spacing

    tan αp = tan αs / cos(γs − γ) · pmin = L · (cos β + sin β / tan αp) · fshade = 1 − sin αp / (GCR · sin(αp + β))

    The declination (Spencer), the equation of time, the hour angle, the solar elevation αs and the azimuth γs come from the equations of chapter 1 of Duffie and Beckman (Solar Engineering of Thermal Processes), with an error of a fraction of a degree; it is not NREL's SPA algorithm. In the plane perpendicular to the rows, the sun has the profile angle αp. The top edge of a table of width L tilted by β casts its shadow on the table behind, separated by the distance p (pitch): the geometry gives the shaded fraction fshade, which is zero while αp is above the limit angle, tan αlim = L sin β / (p − L cos β). The minimum spacing is the one that leaves all the chosen hours around solar noon on the criterion day free of shade; by default, the site's winter solstice and 4 hours (10:00 to 14:00 solar time), a common design practice and not a standard. GCR = L / p is the fraction of the land covered by the tables.

    Anderson y Mikofski 2020NREL/TP-5K00-76626, backtracking

    Single-axis tracker and backtracking

    θT = atan(sin θz sin γs / cos θz) · θ = θT − sign(θT) · acos(cos θT / GCR) if cos θT < GCR

    The north-south horizontal-axis tracker rotates toward the sun by the angle θT; with the sun low, neighboring tables shade each other and backtracking returns them toward the horizontal just enough for the shadow not to touch them, as presented by Anderson and Mikofski (NREL, 2020) for flat terrain. Without shading, some incidence is lost: that is the backtracking loss. The rotation is limited to the structure's maximum.

    Duffie y Beckmanch. 2: mean day, isotropic sky

    In-plane irradiation and annual loss

    Hplane = Σ [ Ib · cos θ / cos θz + Id · (1 + cos β) / 2 + I · ρ · (1 − cos β) / 2 ] · loss = Σ Ib,plane · fshade / Hplane

    The hours of each month's mean day come from the daily global and diffuse irradiation with the hourly fractions of Collares-Pereira and Rabl and of Liu and Jordan, and the in-plane irradiation with the isotropic sky model (Duffie and Beckman, ch. 2). The annual loss is the direct irradiation falling on the shaded part against the unshaded in-plane irradiation: it is geometric. The electrical upper bound counts all the direct irradiation of the hours with any shade, because a row of cells shaded at the lower edge cuts the bypass diodes of a vertically mounted module; the real loss lies between the two.

    IEC 61724-1:2021yields and performance ratio

    Yields and performance ratio

    Yr = Hi / Gi,ref · Yf = Eout / P0 · PR = Yf / Yr

    Hi is the in-plane irradiation of the period, Gi,ref = 1 kW/m², Eout the energy delivered and P0 the DC power installed at STC. Yr are equivalent hours of full sun and Yf equivalent hours at nameplate power, so the PR has no units. The cascade's reference energy is P0 · Yr: what the array would give at its nameplate power with all the irradiation of the period. The definitions were taken from IEC 61724-1:2021 as reproduced in Hukseflux's application note on PR calculation; the text of the standard was not consulted.

    NREL PVWatts V5equation 8IEC 61724-1:2021Temperature-corrected PR

    Temperature

    fT = 1 + γ · (Tcell − 25 °C) · PR25 °C = PR / fT

    NREL's PVWatts V5 manual (Dobos, 2014, equation 8) models DC power as Pdc = Itr / 1000 · Pdc0 · (1 + γ · (Tcell − 25 °C)). Because the equation is linear in temperature, over a period the energy is multiplied by a single factor if Tcell is the irradiance-weighted mean: the temperature of the high-sun hours weighs more than that of early morning. With a negative γ, a cell above 25 °C loses and one below gains. IEC 61724-1 defines the PR corrected to 25 °C by dividing each interval by Ck = 1 + γ · (Tmod,k − 25 °C); with the weighted temperature this equals dividing the PR by fT. It is useful for comparing months and sites without the effect of climate.

    NREL PVWatts V5equation 9

    Loss cascade

    Emeter = P0 · Yr · (1 − Lsoil) · (1 − Lshade) · fT · (1 − Lmis) · (1 − LcDC) · ηinv · (1 − Lclip) · (1 − LcAC) · (1 − Ltr) · (1 − Lavail)

    Each loss acts on the energy left by the previous one, so they multiply: the PVWatts V5 manual (equation 9) calculates total loss as 1 − Π(1 − Li) and warns that it is not the sum of the losses. The order follows the path of the energy: soiling on the irradiance reaching the cell, row shading if you enter it, temperature, mismatch and DC wiring of the array, inverter, clipping, AC wiring, transformer and availability. So PR = Emeter / (P0 · Yr) is the product of the factors.

    NREL PVWatts V5equation 11

    Clipping

    PAC = min(η · PDC; PAC0) · clips if PDC / P0 > 1 / (η · DC/AC)

    When the inverter output would exceed its rated power, it is limited to it (PVWatts V5, equation 11). This gives the fraction of nameplate power above which the inverter clips. The clipped energy is not calculated here: see the section "DC/AC ratio and clipping".

    IEEE 1013stand-alone system batteriesIEEE 1562stand-alone systems guide

    Battery bank of a stand-alone system

    Enominal = Edaily · days / (DoD · η · ktemperature · klife) · Ah = Enominal / V

    It is the same calculation as the "Stand-alone PV" tab of the battery sizing tool: the bank supports the load for the chosen days of autonomy, with the energy corrected for depth of discharge, battery–inverter path efficiency, capacity at minimum temperature and aging. Without a daily energy entered, that of the highest-consumption month is used. The recharge days are the usable energy divided by what is left over each day of the lowest-production month, after covering the load.

    Solar resource of the cities

    The monthly global and diffuse irradiation comes from NASA POWER: averages from January 2001 to December 2025 of the SYN1deg source, in a 1° cell (about 110 km) around each city's airport station. The cell averages valleys and mountains: Medellín and Rionegro, Pereira, Armenia and Ibagué, and Bucaramanga and Barrancabermeja fall in the same cell and have the same values. For a detailed design, use a site measurement or the IDEAM and UPME Solar Radiation Atlas; if you enter the site's PSH, the tool keeps the city's yearly shape and scales it to that mean.

    City (station)Mean PSHLowest monthHighest month
    Bogotá (El Dorado)4,64 kWh/m²·díaApr: 4,45Jan: 4,92
    Medellín (Olaya Herrera)4,93 kWh/m²·díaNov: 4,42Aug: 5,55
    Rionegro (José María Córdova)4,93 kWh/m²·díaNov: 4,42Aug: 5,55
    Cali (Alfonso Bonilla, Palmira)4,21 kWh/m²·díaDec: 4,01Sep: 4,45
    Barranquilla (Ernesto Cortissoz)5,41 kWh/m²·díaNov: 4,71Feb: 6,03
    Cartagena (Rafael Núñez)5,31 kWh/m²·díaNov: 4,6Feb: 5,88
    Santa Marta (Simón Bolívar)5,71 kWh/m²·díaNov: 4,92Mar: 6,34
    Riohacha (Almirante Padilla)5,51 kWh/m²·díaNov: 4,75Jul: 6,07
    Valledupar (Alfonso López)5,27 kWh/m²·díaNov: 4,62Feb: 5,9
    Montería (Los Garzones)5 kWh/m²·díaNov: 4,56Aug: 5,39
    Cúcuta (Camilo Daza)4,3 kWh/m²·díaApr: 3,9Sep: 4,77
    Bucaramanga (Palonegro)5,08 kWh/m²·díaNov: 4,56Feb: 5,54
    Barrancabermeja (Yariguíes)5,08 kWh/m²·díaNov: 4,56Feb: 5,54
    Pereira (Matecaña)4,55 kWh/m²·díaNov: 4,3Sep: 4,86
    Armenia (El Edén)4,55 kWh/m²·díaNov: 4,3Sep: 4,86
    Ibagué (Perales)4,55 kWh/m²·díaNov: 4,3Sep: 4,86
    Neiva (Benito Salas)4,24 kWh/m²·díaJul: 4,01Jan: 4,62
    Villavicencio (Vanguardia)4,31 kWh/m²·díaJul: 3,93Jan: 4,78
    Arauca (Santiago Pérez)5,04 kWh/m²·díaJun: 4,46Feb: 5,8
    Pasto (Antonio Nariño)4,03 kWh/m²·díaJun: 3,9Sep: 4,18
    Ipiales (San Luis)3,7 kWh/m²·díaJun: 3,36Oct: 4,17
    Quibdó (El Caraño)3,98 kWh/m²·díaDec: 3,59Aug: 4,35
    Leticia (Vásquez Cobo)4,55 kWh/m²·díaMay: 4,2Sep: 5
    San Andrés (Sesquicentenario)5,35 kWh/m²·díaNov: 4,23Mar: 6,49

    Source: NASA Langley Research Center (LaRC), POWER project, Climatology API v2.10.1, parameters ALLSKY_SFC_SW_DWN and ALLSKY_SFC_SW_DIFF, accessed 28 October 2026. These data were obtained from the NASA Langley Research Center POWER Project, funded through the NASA Earth Science/Applied Science Program. Station coordinates: NOAA's GHCN-Daily station list.

    Design temperatures in Colombia

    When you choose a city, the tool proposes two values from the airport station. For Voc, the lowest temperature recorded in NOAA's GHCN-Daily daily series (SYNOP station data, records without a quality flag): it is a raw value from a series with gaps, not a statistic, and it errs on the safe side. For the hot cell, the IDEAM 1991-2020 climate normal of the mean maximum temperature of the warmest month: an exceptional day is hotter. As a reference, the normal of the mean minimum of the coldest month is also shown; it is an average and must never be used as the design minimum. If you have the series of a station closer to your project (IDEAM, DHIME) or the minimum from a site study, enter it.

    City (station)HeightMean min. of coldest monthLowest recordedMean max. of warmest month
    Bogotá (El Dorado)2547 m6,4 °C−6,4 °C (15/02/1995)20,2 °C
    Medellín (Olaya Herrera)1490 m17,4 °C8,3 °C (15/02/1963)28,7 °C
    Rionegro (José María Córdova)2157 m12,1 °C3,9 °C (01/02/2018)22,7 °C
    Cali (Alfonso Bonilla, Palmira)970 m18,5 °C12,8 °C (21/04/1965)31,1 °C
    Barranquilla (Ernesto Cortissoz)14 m23,8 °C16,4 °C (01/09/2005)33,5 °C
    Cartagena (Rafael Núñez)2 m24 °C18,9 °C (07/01/1968)32,3 °C
    Santa Marta (Simón Bolívar)4 m22,6 °C12 °C (29/12/1976)33,9 °C
    Riohacha (Almirante Padilla)4 m22,6 °C10 °C (24/02/1974)35,4 °C
    Valledupar (Alfonso López)138 m23,1 °C17 °C (09/01/1974)36,2 °C
    Montería (Los Garzones)20 m22,6 °C17 °C (16/08/1974)34,6 °C
    Cúcuta (Camilo Daza)250 m21,4 °C13,9 °C (05/01/1965)34,4 °C
    Bucaramanga (Palonegro)1189 m18,4 °C13,3 °C (18/02/1984)26,3 °C
    Barrancabermeja (Yariguíes)126 m23,1 °C17 °C (02/08/1991)33,4 °C
    Pereira (Matecaña)1342 m17,4 °C10 °C (10/10/1964)27,4 °C
    Armenia (El Edén)1229 m16,8 °C7,2 °C (25/02/1968)28,8 °C
    Ibagué (Perales)943 m19,1 °C12 °C (14/09/1981)31,6 °C
    Neiva (Benito Salas)439 m22,4 °C13,9 °C (05/08/1966)34,9 °C
    Villavicencio (Vanguardia)422 m20,4 °C12 °C (22/01/1974)32,5 °C
    Arauca (Santiago Pérez)128 m21,1 °C15 °C (07/01/1965)34,6 °C
    Pasto (Antonio Nariño)1796 m14,5 °C5 °C (04/09/1961)26,1 °C
    Ipiales (San Luis)2961 m4,6 °C−3 °C (15/06/1974)17,2 °C
    Quibdó (El Caraño)75 m23,2 °C18,8 °C (27/10/1994)31,2 °C
    Leticia (Vásquez Cobo)84 m21,6 °C14 °C (20/07/1975)32 °C
    San Andrés (Sesquicentenario)1 m25,2 °C16,8 °C (12/09/1999)30,8 °C

    Sources: IDEAM, Standard climate normals 1991-2020 (minimum and maximum temperatures, file published on 8 May 2025), airport stations with their IDEAM code. NOAA NCEI, Global Historical Climatology Network – Daily, stations of the same airports, accessed 26 October 2026.

    Typical values and their sources

    In Essential mode, losses that do not depend on the hourly profile take the defaults of NREL's PVWatts V5 manual (A. P. Dobos, PVWatts Version 5 Manual, NREL/TP-6A20-62641, 2014). In Advanced mode they can all be changed. Clipping, transformer, cell temperature and γ have no typical value: they depend on your plant.

    StageTypicalSource
    Soiling2 %PVWatts V5, table 6. IEA PVPS (report T13-21:2022) gives 4 % to 7 % as the world average; it depends on rain, dust and cleaning, and must be measured.
    Mismatch2 %PVWatts V5, table 6.
    DC wiring2 %PVWatts V5, table 6. In V5 this 2 % covers all the wiring; the DC derate of PVWatts V1 was 0.98.
    Inverter efficiency96 %PVWatts V5, section 12 (default nominal efficiency). Use the weighted one from your inverter datasheet.
    AC wiring1 %AC wiring derate of PVWatts V1, 0.99, cited in table 6 of the V5 manual.
    Unavailability3 %PVWatts V5, table 6.
    Clipping, transformer—No typical value: they come from the hourly simulation and the transformer datasheet.
    Shading between rows—No typical value: "Rows and shading" calculates it from your array geometry.

    PVWatts also includes horizon shading (3 %), connections (0.5 %), initial light-induced degradation (1.5 %) and nameplate tolerance (1 %), which this tool does not separate: if you want to include them, add them to the mismatch with the multiplication rule.

    DC/AC ratio and clipping

    The DC/AC ratio is the array's nameplate power against the inverters' rated power. An array larger than the inverter makes it work more hours near its rated power, in exchange for clipping the hours of maximum production. The "DC/AC and clipping" view of "Production and PR" shows from what fraction of its nameplate power the array starts to clip, but not how much energy is lost: that depends on how many hours of the period the array delivers more than that fraction, and only an hourly (or finer) profile from a simulation or from measurement gives it. Since in practice the array rarely delivers its nameplate power (temperature, irradiance below 1000 W/m², array losses), clipping is usually smaller than the DC/AC ratio alone would suggest. Enter the clipping your simulation gives. The guide on inverter DC/AC ratio and clipping explains the consequences for the connection and protection.

    Example cases

    The data for the "Strings" cases come from the manufacturers' public datasheets. Always verify the datasheet version of your equipment: values change between revisions and model suffixes.

    • JinkoSolar Tiger Neo JKM590N-72HL4-BDV: datasheet JKM575-600N-72HL4-BDV-F9-EN (590 W, Voc 52.90 V, Isc 14.07 A, Vmpp 44.17 V, Impp 13.36 A, −0.25 / +0.045 / −0.29 %/°C, 1500 V, 30 A fuse, BNPI Isc 15.37 A; 2278 × 1134 mm).
    • LONGi Hi-MO 6 LR5-54HTH-430M: datasheet LR5-54HTH 420~440M, version 20230926V19 (430 W, 39.13 V, 14.15 A, 32.84 V, 13.10 A, −0.230 / +0.050 / −0.290 %/°C, NOCT 45 ± 2 °C, 1500 V, 25 A fuse).
    • Huawei SUN2000-115KTL-M2: technical specification at solar.huawei.com (1100 V, MPPT 200 to 1000 V, 30 A and 40 A per MPPT, 10 MPPTs with 2 inputs, 115 kW).
    • Huawei SUN2000-330KTL-H1: specifications at solar.huawei.com (1500 V, MPPT 500 to 1500 V, 65 A and 115 A per MPPT, 6 MPPTs with 4 or 5 inputs, 300 kW). The case uses 4 inputs, those of the MPPT with the fewest.
    • SMA Sunny Tripower X 25 (STP 25-50): SMA manual, DC input technical data (1000 V, MPP 150 to 1000 V and 430 to 800 V at rated power, 24 A and 37.5 A per input, 3 MPPTs with 2 strings, 37,500 Wp).
    • The "Production and PR" cases use the numerical example from the losses and performance ratio guide (illustrative figures) with the γ of the Jinko datasheet.
    • The resource, rows and storage cases are examples built with this equipment and NASA POWER irradiation; they are not real projects.

    Limits of the calculation

    • It is a design check with datasheet data; it does not replace the design of the plant or the conditions each manufacturer sets for its warranty.
    • Month-by-month production uses the mean day of each month and a constant PR: it is for sizing and comparing, not for guaranteeing output. NASA POWER irradiation is from a 1° cell; in mountain areas the site's may differ.
    • A stand-alone system is sized here with the mean-day balance of the worst month; several cloudy days in a row are covered by the bank with its days of autonomy, not by the array.
    • The temperature correction is linear, as datasheets write it. At low irradiance Voc drops a little: assuming it at full irradiance in the early morning errs on the safe side.
    • The hot Vmpp is calculated at the design irradiance; with clouds or in the late afternoon it drops, and the inverter can leave the MPPT window earlier than the chart shows.
    • The proposed minimum temperatures are from airport stations. A project in a valley or on a hillside may have colder or milder nights; on the Bogotá plateau and the highlands, frosts vary widely from one site to another.
    • The datasheet tolerances (±3 % on Voc and Isc in several brands) and the initial degradation are not added; if the string sits right at the limit, leave it some margin.
    • It assumes identical strings and the same number per MPPT in use. With different orientations, shading or asymmetric MPPTs, check each input separately.
    • For systems of 100 kW or more, NFPA 70 allows another documented method prepared by an engineer; this tool does not replace it.
    • Rows are assumed long, parallel and on flat terrain. Shading from obstacles or the horizon, shading at the row ends and the shadow the rows cast on the sky's diffuse irradiation are not calculated; the tracker is a north-south horizontal-axis one.
    • It is an energy cascade with average losses for the period, not an hour-by-hour simulation. It helps you understand the weight of each stage and check a PR, not guarantee output.
    • The temperature loss uses the PVWatts linear model with the weighted cell temperature you enter. If you enter the simple daily mean or the air temperature, the result is optimistic.
    • Inverter efficiency is an average value. The real one changes with load and voltage; a weighted efficiency from the datasheet represents it better than the peak.
    • The transformer has no-load losses all the time, also at night if it stays energized, and load losses according to the square of the current: its energy loss depends on the profile and is entered here as a percentage that you calculate.
    • Low irradiance, angle of incidence, degradation and power limits ordered by the grid or the plant controller are not separated. If you know them, include them in the nearest stage.
    • The measured PR is comparable with the expected one only if irradiation, energy and period are measured as IEC 61724-1 requires and at the same point of the cascade.

    Frequently asked questions

    How do I calculate how many solar panels I can put in series on an inverter?

    Correct the module's open-circuit voltage to the site's lowest temperature with the datasheet Voc coefficient, Voc(T) = Voc · (1 + β · (T − 25 °C)), and divide the inverter's maximum input voltage (or the module's system voltage, whichever is lower) by that value, rounding down. The minimum comes from dividing the minimum MPPT voltage by the module's Vmpp at the highest cell temperature, rounding up.

    What minimum temperature should I use for Voc in Colombia?

    The lowest expected at the site, not the average. On the coast and in the warm valleys the lowest recorded value is between 10 and 19 °C, but on the Bogotá plateau and the Nariño highlands there are frosts: the El Dorado station recorded −6.4 °C. The IDEAM normals give each month's mean minimum, which is an average and sits above the design minimum; the tool proposes the lowest recorded value of the nearest airport station.

    How many parallel strings can an MPPT accept?

    Those that meet three conditions from the inverter datasheet: the group's operating current must not exceed the maximum current per MPPT, 1.25 times the sum of the Isc must not exceed the maximum short-circuit current per MPPT (IEC 62548 and NFPA 70 690.8), and there must be physical inputs to connect them. With three or more strings in parallel, also check whether string fuses are needed.

    How is the performance ratio of a solar plant calculated?

    With the IEC 61724-1 definition: PR = Yf / Yr. The final yield Yf is the energy delivered in the period divided by the installed DC power (kWh/kWp); the reference yield Yr is the in-plane irradiation of the same period divided by 1 kW/m², in hours. A 1000 kWp plant that delivers 4180 kWh on a day with 5.5 kWh/m² in the plane has Yf = 4.18 h, Yr = 5.5 h and PR = 0.76.

    Are the losses of a photovoltaic system added?

    No. Each loss acts on the energy left by the previous one, so they multiply: total loss = 1 − Π(1 − Li). NREL's PVWatts V5 manual shows it with its default values: added they would give 15 %, multiplied they give 14 %.

    How does the DC/AC ratio affect the performance ratio?

    With a high DC/AC ratio, the inverter clips power during the sunniest hours, and that clipped energy lowers the PR. How much is lost depends on how many hours the array delivers more power than the inverter accepts, and only an hour-by-hour simulation or measurement gives that, not the DC/AC ratio alone.

    How many kWp do I need to cover my consumption?

    Divide the annual consumption by the energy each kWp delivers at the site: the annual in-plane irradiation (kWh/m²) times the performance ratio. In Bogotá, with about 4.6 peak sun hours a day in the plane and a PR of 0.8, each kWp gives around 1350 kWh a year; a consumption of 15,000 kWh a month calls for about 130 kWp. In a stand-alone system the month with the least sun governs, not the average.

    What distance should I leave between rows of solar panels?

    The one that prevents a row from shading the one behind it during the hours you choose on the worst day. With tables of width L tilted by β and the sun at a profile angle αp, the minimum row spacing is L · (cos β + sin β / tan αp). Near the equator the midday sun is high all year and rows can sit closer together than at high latitudes, but in the morning and afternoon the angle drops and shading appears.

    We design your solar plant and leave it ready to operate

    We design the PV array, the inverter and the grid connection, with documented calculations for solar resource, voltage, current, shading and protections, and we test the plant before energizing it.

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    Related guides

    Solar Plant Commissioning Tests: IEC 62446-1 and ProtectionTests a solar plant needs before energizing: IEC 62446-1 string and insulation tests, inverters, MV/HV equipment, interconnection protection.Solar Plant Losses and Performance Ratio (PR)Which losses separate the solar resource from the energy a PV plant delivers, and how performance ratio (PR) is defined in IEC 61724-1.Inverter DC/AC Ratio and ClippingWhat the DC/AC ratio is, why the solar array is oversized, what gets clipped and which AC capacity is stated to the utility for interconnection.Huawei SUN2000 Inverter and SmartLogger 3000 ExplainedWhat the Huawei SUN2000 inverter (330KTL, 215KTL, 100KTL) and the SmartLogger 3000 are, how they integrate with SCADA and what to check at commissioning.

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