Work backwards from monthly kWh or a variable energy charge to an indicative solar array and panel count.
Bill mode converts only the entered variable energy charge to kWh. Fixed charges and taxes remain outside the target.
Offsetting an energy charge does not necessarily offset fixed charges, taxes or the complete bill. Export and net-metering rules are not inferred. Trust level: engineering estimate; verify site and equipment assumptions before purchase or installation.
| Scenario | Array size | Panel count |
|---|---|---|
| Conservative | 3.85 kW | 8 |
| Expected | 3.08 kW | 6 |
| Optimistic | 2.567 kW | 5 |
Method: array kW = monthly target kWh ÷ 30.4375 ÷ (peak sun hours × (1 − loss))
Inputs used: 375 ÷ 30.4375 ÷ (5 × (1 − 20%)) = 3.080082135523614 kW
Assumptions: Target entered directly as energy Peak sun hours Combined system loss
Scope and warnings: Offsetting an energy charge does not necessarily offset fixed charges, taxes or the complete bill. Export and net-metering rules are not inferred.
National Renewable Energy Laboratory · PVWatts supported locations; use a location-specific model for a site estimate · effective PVWatts version 5 documentation · reviewed 2026-09-12
high confidence · Engineering estimate
Supports the transparent solar energy relationship and system-loss planning reference.
Exclusions: Not a structural, electrical or financing assessment. ToolMitra does not query PVWatts automatically.
For a kWh target, the calculator converts monthly energy to an average day and divides by peak sun hours and the usable fraction after losses. Bill mode first divides the entered variable energy charge by the flat tariff; it does not treat fixed charges as energy.
Offsetting 375 kWh per month at 5 peak sun hours and 20% losses requires about 3.08 kW on the expected case. With 550 W modules that rounds up to six panels; lower-resource scenarios require more capacity.
Not necessarily. Fixed charges, taxes, demand charges, timing, self-consumption and export-credit rules can remain. Bill mode targets only the energy charge represented by the tariff you enter.
Calculations run on your device. Review your results before exporting or sharing them.
Energy mode is the cleaner route when recent bills show kWh. Bill mode is a convenience for a variable energy charge and flat tariff; it cannot recover kWh accurately from a bill dominated by slabs, fixed charges or taxes.
Conservative solar resource produces the largest array because fewer equivalent sun hours must deliver the same target. Panel count rounds upward, but roof fit, inverter limits and export caps can constrain the practical system.
Published by ToolMitra — methods and editorial approach.