PV Array Energy Calculator

A photovoltaic array must be assigned an expected energy production value before its output can be used for production estimates, utility-interconnection documentation, battery-storage planning, load-offset review, and preliminary feeder or service-energy analysis. The PV Array Energy Calculator produces estimated annual AC energy in kWh/year from the installed PV array DC nameplate and a documented Net site-specific yield.

The calculation is intended for a yield value already developed through PVWatts, SAM, measured production data, or another documented site resource. It does not derive solar resource from peak-sun-hours assumptions, panel wattage alone, or a national-average production estimate.

Net Specific Yield

Solar production is commonly expressed as net specific yield, measured in kWh/kWdc-year. It represents the expected annual AC energy delivered per installed kilowatt of DC nameplate capacity after the assumptions embedded in the cited model or measured record.

The Net site-specific yield input must identify a documented basis, such as:

• A PVWatts result with its selected weather data and configuration assumptions
• A SAM model result
• A measured production period from an existing comparable array
• Another named engineering, utility, or site-resource source

The calculator records that basis through Model or weather version and Resource and loss note. These entries preserve the production assumptions behind the resulting kWh estimate.

A net yield of 1,400 kWh/kWdc-year means each installed kWdc is expected to produce 1,400 kWh of AC energy annually under the documented resource, orientation, shading, loss, and weather assumptions.

Calculation Inputs

Field	Electrical and Production Use
Array or project label	Identifies the PV array, roof section, project, inverter context, or other production record.
PV array DC nameplate (kWdc)	The installed or proposed DC nameplate capacity of the array.
Net site-specific yield (kWh/kWdc-year)	Documented annual production yield per kWdc. This is the production basis for the energy calculation.
Model or weather version	Records the production model, weather dataset, station, location, or measured-data period supporting the yield.
Resource and loss note	Records relevant tilt, azimuth, shading, losses, station distance, and similar production assumptions.

The label and documentation fields do not alter the arithmetic. They establish traceability for the production assumption, especially where multiple roofs, array orientations, inverter groups, weather stations, or modeled scenarios are being compared.

Energy Formula

The calculator applies the documented net yield directly to DC array nameplate capacity:

\(\displaystyle \text{Estimated annual AC energy (kWh/year)} = \text{PV array DC nameplate (kWdc)} \times \text{Net site-specific yield (kWh/kWdc-year)}\)

It then converts annual energy into average monthly and daily values:

\(\displaystyle \text{Average monthly AC energy} = \frac{\text{Estimated annual AC energy}}{12} ] = [ \text{Average daily AC energy} = \frac{\text{Estimated annual AC energy}}{365}\)

The Net specific yield result repeats the entered yield value for use in project records and comparison between arrays of different DC capacities.

Calculation Example

For an array labeled PV array A, use the following documented planning inputs:

Input	Value
Array or project label	PV array A
PV array DC nameplate	8 kWdc
Net site-specific yield	1,400 kWh/kWdc-year
Model or weather version	PVWatts V8 / 2020 TMY or measured data
Resource and loss note	Record tilt, azimuth, shading, losses, and station distance

Annual AC energy is:

\(\displaystyle 8\text{ kWdc} \times 1{,}400\text{ kWh/kWdc-year} = 11{,}200\text{ kWh/year}\)

The resulting production values are:

Result	Value
Estimated annual AC energy	11,200 kWh/year
Average monthly AC energy	933.3333 kWh/month
Average daily AC energy	30.6849 kWh/day
Net specific yield	1,400 kWh/kWdc-year

These monthly and daily results are annual averages. They are not monthly production forecasts and do not represent the array’s expected output during a particular season, weather event, or hour of the day.

Electrical Planning Use

Annual AC energy is an energy quantity, not a circuit-current value. It supports energy-side planning tasks such as:

• Comparing projected PV production with annual utility consumption or load profiles
• Estimating the annual energy contribution of separate roof planes or array blocks
• Developing preliminary battery-storage energy targets in kWh
• Reviewing expected production for utility billing, net-metering, or project financial assumptions
• Comparing alternatives with different DC nameplate capacities, orientations, shading exposure, or modeled losses
• Establishing a documented production baseline for later comparison against monitored inverter or revenue-grade meter output

The result does not determine PV branch-circuit conductor ampacity, feeder ampacity, overcurrent protective device sizing, inverter output current, raceway fill, voltage drop, grounding and bonding requirements, or service/load-calculation treatment. Those decisions require the applicable equipment ratings, circuit topology, conductor characteristics, installation conditions, manufacturer instructions, and AHJ requirements.

Production Assumptions and Field Limits

The calculator assumes the entered Net site-specific yield is already a net AC production figure appropriate for the stated DC nameplate capacity. If a yield source uses different assumptions for system losses, module degradation, availability, clipping, curtailment, shading, snow, soiling, or array orientation, the resulting annual energy will reflect those source assumptions.

A valid project record should identify the production basis in Model or weather version and Resource and loss note. For example, a modeled yield should retain the selected weather dataset and location, while a measured yield should identify the measurement period and the array or system configuration it represents.

Production should also be verified against actual operating data when the system is commissioned or when substantial conditions differ from the documented model. Module additions, inverter replacement, changed tilt or azimuth, new shading, equipment downtime, curtailment, and changes to the monitored measurement point can make a prior yield value unsuitable for the revised array.