Calculate a transparent solar-array nameplate and energy scenario from entered panel count, peak sun hours, losses, and annual site electricity.
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Create a transparent DC-nameplate and peak-sun-hours energy arithmetic record from exact entered module/count/resource/loss inputs without forecasting site production, bill offset or system suitability.
Reproduce the proposal nameplate and high-level energy arithmetic from exact inputs.
Enter module rating, whole count, cited resource, total loss and 12-month site electricity, then save the record.
Can reconcile DC nameplate, modeled annual energy and ratio without treating them as a guarantee.
See how a documented loss or resource basis changes the same candidate array.
Hold module/count constant, change one source-led assumption, and compare the retained inputs and outputs.
Does not choose the favorable assumption or confuse system loss with module efficiency.
Receive a clearly bounded handoff into a site-specific model and design review.
Inspect all arithmetic and omissions, then verify weather, tilt, azimuth, shading, array type, equipment, clipping, structure, code and interconnection separately.
Uses the result only as an auditable preliminary record.
Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.
This tool is part of these guided projects. Each project provides step-by-step instructions with checklists and all the tools you need in one place.
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Multiply the selected module datasheet rating by a whole candidate panel count. Nameplate capacity is not AC output and does not prove that the panels fit the roof or comply with structural, electrical, fire-access, permitting, or utility constraints.
DC nameplate kW = panel W × whole panel count ÷ 1,000Peak sun hours are an equivalent-full-sun assumption, not clock daylight. Enter a documented site, month, or annual basis and a total-loss percentage whose included categories are known. NREL PVWatts treats losses separately from module efficiency and uses location/weather, tilt, azimuth, array type, inverter, and other inputs.
Modeled daily AC kWh = DC kW × entered peak sun hours × (1 − entered loss %)The tool multiplies one daily scenario by 365 and divides by 12 for an average month. Optional site electricity produces only a modeled ratio. Weather sequence, shading, snow/soiling, temperature, clipping, degradation, outages, curtailment, tariff and export rules are not simulated.
Modeled annual kWh = modeled daily kWh × 365; ratio = modeled annual kWh ÷ entered annual site kWhUpdated: August 2026
Twenty 400 W modules equal 8.000 kW DC. With 5 entered peak sun hours and 14% entered total loss, the arithmetic is 34.400 kWh/day and 12,556.00 kWh/year. Against an entered 10,000 kWh site total, the modeled ratio is 125.56%—not a bill-offset promise.
Twelve 425 W modules equal 5.100 kW DC. At 4.2 entered peak sun hours and 14% losses, the model returns 18.421 kWh/day and 6,723.74 kWh/year. Confirm the resource and loss basis before comparing this record with a proposal.
The same 8 kW and 5-hour inputs model 13,140 kWh/year at 10% loss and 11,680 kWh/year at 20% loss. That 1,460 kWh gap is a reminder to document included losses and use a site-specific model rather than choose the favorable input.
Keep module efficiency, inverter behavior and total modeled losses distinct. Record the source, version and included loss categories so another reviewer can reproduce the scenario.
Run a site-specific weather and system model, preserve its uncertainty/range, verify roof and electrical constraints, and apply the actual utility tariff before authorizing a design or purchase.
Build a bounded solar-array arithmetic record from an exact module nameplate rating, whole panel count, cited peak-sun-hours assumption, and entered total system loss. Optional annual site electricity adds a modeled generation-to-usage ratio. The result does not choose a system, model a site, or predict a bill.