Solar System Sizing Chart

Record load, target coverage, peak sun hours, system losses, performance ratio, array kW, panel count, first-year production, year-25 production, roof fit, and electric utility follow-up.

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Quick reference table

A solar system sizing chart records monthly load, target coverage, system losses, array size, production, roof fit, inverter limits, and battery assumptions in one worksheet.

Solar system sizing worksheet

Solar system sizing worksheet
Item	Record from calculator	Follow-up
Load basis	Monthly kWh and target coverage	Confirm bill and critical loads
PV array	Panel count, required kWdc, and rounded kWdc	Check layout, shade, and roof area
Production	Average monthly, first-year annual, year-25 annual, capacity factor	Compare with NREL PVWatts, metered data, or site model
Losses	System losses and performance ratio	Review shade, soiling, temperature, wiring, inverter, and availability
Inverter	AC rating and surge notes	Verify product and interconnection limits
Battery	kWh or Ah basis	Review backup loads and autonomy target

Solar system sizing follow-up record

Solar system sizing follow-up record
Follow-up item	Record on worksheet	Why it controls the next step
Load profile	Monthly kWh, target coverage, critical load, seasonal peak	Array and battery choices should follow the actual load shape
Roof or site limit	Usable area, shade, structural or ground-mount note	Physical layout can cap panel count
Production model	Peak sun hours, losses, degradation, year-25 kWh	Production assumptions should stay visible before ROI or battery sizing
Inverter strategy	String, hybrid, microinverter, export limit	Inverter choice affects clipping, backup, and electric utility review
Battery role	Backup-only, self-consumption, outage autonomy	Battery capacity is different for each operating goal

Formula basis

Required kWdc = target daily solar kWh / peak sun hours / performance ratio. First-year kWh = rounded kWdc x peak sun hours x 365 x performance ratio.

Load is the monthly or daily kWh target entered in the calculator.
Target coverage is the share of load intended to be served by the PV system.
System losses cover soiling, shade, mismatch, wiring, inverter conversion, and availability before deriving performance ratio.
Array kW is the DC size of the module group.
Annual degradation estimates year-25 production from the first-year result.
Inverter and battery values should be checked against product data, site conditions, AHJ requirements, and electric utility rules.

Worked examples

PV plus battery sizing recordRecord monthly usage, target coverage, system losses, panel count, array kW, first-year production, inverter rating, battery capacity, critical loads, and electric utility interconnection follow-up.

Critical-load backup sizing recordDocument main-panel load profile, critical-load subpanel, roof area, target coverage, annual degradation, hybrid inverter rating, battery autonomy, and electric utility export limit before design review.

Assumptions. Balanced load and line-to-line voltage assumptions behind this chart.

Solar system sizing depends on load data, site conditions, product selection, utility rules, and installation constraints.
This chart uses calculator-entered peak sun hours and losses; NREL PVWatts or a site-specific model should be used for production proposals.
The worksheet is a sizing estimation record and does not replace engineered drawings or permitting review.

Code and standard notes. Planning limits that should be checked before final equipment selection.

Use this chart as a sizing estimation record; verify adopted NEC PV and energy-storage installation requirements, electric utility interconnection rules, manufacturer data, site conditions, AHJ expectations, and qualified project review before procurement.

How to use this chart

1Start with loadRecord usage, target coverage, critical loads, and bill period before sizing equipment.

2Record production basisDocument peak sun hours, system losses, performance ratio, first-year kWh, year-25 kWh, capacity factor, and NREL PVWatts comparison notes.

3Connect PV and inverterDocument panel count, array kW, inverter rating, and clipping or export notes.

4Add storage contextList battery capacity, autonomy target, backup load, and interconnection follow-up.

Worksheet checklist. Record source basis, review gaps, and assumptions before using the chart result.

Capture load and coverageRecord monthly kWh, target coverage, daily load, and critical load notes.
Capture productionWrite peak sun hours, system losses, degradation, first-year kWh, average monthly kWh, and year-25 kWh.
Capture equipmentWrite panel watts, count, array kW, inverter size, and battery capacity.
Capture review itemsList site survey, electric utility, AHJ, manufacturer, and qualified project follow-up.

Common mistakes to avoid. Review these before turning chart current into an equipment decision.

Sizing PV from average load without checking roof area, shade, seasonal production, losses, and utility limits.
Treating one peak-sun-hour value as a PVWatts-grade site model.
Adding battery capacity without defining the backup load and runtime target.
Choosing inverter and battery sizes before separating whole-home offset goals from critical-load backup goals.

Frequently asked questions

These answers explain how to use the chart without turning a quick reference into a final design decision.

Should the system be sized from one monthly bill?

One bill can start the estimate, but annual usage and seasonal production usually give a better sizing basis.

Does battery capacity equal backup time?

Not directly. Backup time depends on load watts, usable capacity, inverter efficiency, battery limits, and reserve settings.