Where will the system live?
Search by city, state, postal code, or country—or use your current location. Place search is worldwide; solar results depend on available PVWatts climate data.
— design peak sun hours
The lowest month is used for year-round array sizing.
Recommended default: use the lowest month for a system expected to operate year-round.
Why would I choose a different month?
Keep the lowest month for dependable year-round operation. Select another month only when the system is seasonal, a generator will intentionally cover darker periods, or you accept reduced production and possible load shedding in lower-solar months.
Advanced location and solar settings
Use a conservative design-month value for year-round operation.
Build the load profile
Add each appliance once. Tell us how each appliance behaves: either it runs for about the entered hours each day, or it cycles on and off automatically. A refrigerator is a common cycling load—it may be available all day without running continuously. Evergreen estimates missing electrical values while keeping every assumption editable.
| Appliance | Qty | Running W | Starting W | Simultaneous starts | How it operates | Hours/day | Average running | Daily energy | Remove |
|---|
Starting scenario: Evergreen assumes recognized automatic cycling motors—such as refrigerators, freezers, pumps, and mini-splits—may restart together after power is restored. For multiple identical automatic motor loads, the simultaneous-start quantity defaults to the full equipment quantity.
Customize design assumptionsOptional controls for load behavior, system assumptions, and engineering details
Advanced motor-start assumptions
Leave this off unless the design includes controls that deliberately sequence compressor and motor starts after power restoration. When enabled, the inverter starting check applies only the largest automatic motor-start increment rather than adding all recognized automatic cycling motors.
Advanced hourly coincidence schedule
Model non-coincident loads by hour
Simple mode assumes every load can run at the same time. Turn on the hourly schedule to identify the highest coincident hour instead. By default, the schedule becomes the source of truth for both daily energy and coincident peak. You can switch it to peak-only mode when checked hours represent only the times an appliance could operate rather than its actual energy use.
Checked hours set each load’s daily runtime and also determine coincidence.
Uses checked hours. Loads that run for entered hours count each selected hour fully; cycling loads apply their visible average-running percentage.
Uses checked hourly windows to find coincident running and starting loads.
The hourly grid is the source of truth for daily energy and coincidence unless you choose peak-only mode.
When enabled for the first time, all 24 hours are selected for every load so the starting point remains conservative. Remove the hours when each load cannot operate. In Battery energy + inverter peak mode, each checked block counts as one scheduled hour. Loads set to run for entered hours count the full hour; cycling loads apply their average-running percentage. Choose peak-only mode when checked hours show only when equipment could run, while Hours/day provides a more precise energy estimate.
Engineering settings & calculations
Select a battery product for equipment-specific sizing and BMS current checks. Detailed module ratings remain available below.
Select a catalog product to verify battery-voltage class, continuous output, surge capability, AC configuration, and efficiency. An inverter/charger charges from an AC source; it does not replace a solar MPPT unless the product specifically includes an integrated solar charge controller.
Detailed battery module ratings
Defaults represent a generic 12.8 V, 100 Ah LiFePO₄ module. Replace every value with the selected battery manufacturer’s datasheet ratings before purchasing equipment.
DC cable length and voltage-drop check
Enter the one-way cable length. The battery-to-inverter engine applies material, ambient temperature, conductor-count adjustment and terminal-temperature limits, then selects the smallest listed conductor satisfying both ampacity and round-trip voltage drop.
Measure from the battery connection point to the inverter DC terminals. Return length is included automatically.
86°F
Inverter AC-output conductor settings
Sizes the preliminary feeder from the inverter AC output to a panel, transfer equipment, or other downstream distribution point. Enter the one-way length; return-path length is included automatically.
86°F
PV module and controller input check
Use this after choosing actual panel and controller models. Copy the values below from their datasheets. The calculator will recommend a series/parallel panel arrangement and check cold-weather voltage and controller input current.
Choose a catalog product for equipment-specific verification, or keep Evergreen assumptions for a quick preliminary design. Values remain editable.
Evergreen will attempt a weather-based suggestion after location lookup. Verify the site design criterion before installation.
158°F
Choose a catalog product for equipment-specific verification, or keep Evergreen assumptions for a quick preliminary design. Confirm all tracker-specific limits.
Minimum PV operating voltage: Enter the values exactly as the manufacturer publishes them. Use the fixed minimum field when a fixed MPPT floor is listed, or use the two “above battery voltage” fields when the datasheet gives startup and operating differences. Evergreen determines the method automatically.
Evergreen uses the startup requirement as the conservative stringing floor and reports the operating requirement separately.
Leave blank when the manufacturer publishes only maximum PV short-circuit current and PV-power ratings.
The optimizer applies the more restrictive of this allowance and the maximum array-power value.
Physical input terminals per tracker. Leave blank if not published. External combiners may still be possible when permitted by the manufacturer.
Balanced prioritizes exact module use, even tracker loading, practical string voltage, and lower current.
From the far end of a string to its combiner or controller input. Return length is included automatically.
From the combiner or array junction point to the controller input. Use 1 ft when no separate combined run exists.
104°F
A conservative preliminary factor. Confirm the governing code, equipment instructions, and any project-specific exceptions.
Enter or select module and controller datasheet values to begin validation.
Your system design
Clear numbers, visible assumptions, and a direct path to the engineering detail.
Transparent by design
Location-specific solar-resource and photovoltaic-production estimates are obtained using the National Laboratory of the Rockies PVWatts® V8 API. Evergreen Off-Grid independently performs the off-grid planning calculations.
Place lookup uses OpenStreetMap Nominatim data © OpenStreetMap contributors. Worldwide place search does not guarantee PVWatts climate data for every location; manual PSH remains available.
Evergreen Off-Grid is independent and is not affiliated with or endorsed by NLR, the U.S. Department of Energy, or the Alliance for Energy Innovation.
Methodology, data sources, and limitations
This calculator provides preliminary educational and planning estimates only. It is not a final electrical design, engineering document, equipment specification, or code-compliance determination.
NLR supplies location-specific PVWatts solar-resource and photovoltaic-production estimates. Evergreen Off-Grid independently applies load, storage, efficiency, reserve, inverter, and controller assumptions.
Actual performance may differ because of weather, shading, snow, hourly load timing, battery temperature, equipment behavior, installation conditions, and other factors.