Solar Panel Load Calculator

Estimate off-grid solar array size from daily watt-hours, inverter loads, peak sun hours, real system losses, roof orientation, panel wattage, battery voltage, and controller headroom.

⚡Real Off-Grid Presets

📊Load and Solar Inputs

Direct DC or already measured load (Wh/day)

Use daily watt-hours for DC lights, routers, controls, or measured appliance energy.

AC inverter running load (watts)

Enter the typical simultaneous AC load that runs through the inverter.

AC inverter runtime (hours/day)

The calculator converts AC watt-hours to DC battery-side Wh using inverter efficiency.

Peak sun hours (PSH/day)

Use the weaker season you want the system to survive, not the annual best month.

Battery or array nominal voltage

Controller output amps are estimated from installed array watts divided by this voltage.

Solar module wattage

Panel count is rounded up, then installed watts are recalculated from the rounded count.

System loss profile

Includes controller, wiring, battery charge, temperature, and inverter efficiency assumptions.

Tilt and azimuth derate

Multiplies peak sun hours before array sizing, so poor orientation increases panel count.

Formula path: daily load Wh = direct Wh + AC watts × runtime / inverter efficiency. Required array watts = load Wh / (peak sun hours × tilt derate × harvest efficiency).

Daily Solar Load

0 Wh

battery-side energy per day

Panel Count

modules rounded upward

Charge Controller

0 A

with 125% headroom

Installed Array

0 kW

rounded module capacity

Full Calculation Breakdown

🔌Solar Module / Inverter / Spec Comparison

100 W

Compact Module

Often 18 Vmp class, useful for vans, gates, cameras, and small 12 V battery banks.

200 W

RV / Portable

Good balance for mobile roofs and folding kits; two panels make a practical 400 W starter array.

400 W

Home Module

Common modern full-size module; pairs well with 24 V and 48 V MPPT off-grid systems.

2×

Inverter Surge

Motors, pumps, and compressors can need brief surge capacity above running watts.

☀Peak Sun Hour Planning Table

Planning Condition	Typical PSH	Use When	Sizing Effect
Cloudy winter northern site	2.0 to 3.0 h/day	Critical loads must work year-round	Largest array for same Wh load
Mixed-season temperate site	3.5 to 4.5 h/day	Cabins, sheds, and backup loads	Moderate array with useful reserve
Sunny inland or summer RV use	5.0 to 6.0 h/day	Seasonal mobile or fair-weather systems	Fewer panels, less winter margin
High-sun desert planning	6.0 to 7.0 h/day	Dry climates with open exposure	Strong daily harvest if heat losses are managed

💡Common Off-Grid Load Reference

Load Type	Typical Running Watts	Example Runtime	Daily Energy
LED lighting circuit	20 to 60 W	5 h/day	100 to 300 Wh/day
WiFi router and modem	10 to 25 W	24 h/day	240 to 600 Wh/day
Efficient DC fridge	35 to 60 W cycling	Duty-cycle averaged	500 to 900 Wh/day
Laptop and monitor work block	70 to 140 W	6 h/day	420 to 840 Wh/day
Small pressure or well pump	500 to 900 W running	0.5 to 1 h/day	250 to 900 Wh/day

⚙Derate and Loss Factors

Factor	Typical Range	Calculator Use	Why It Matters
MPPT harvest efficiency	92% to 98%	Included in loss profile	Controller conversion and tracking losses reduce usable charge energy.
Battery charge efficiency	80% to 98%	Included in loss profile	Lead acid systems need more array for the same delivered Wh.
Wiring and connection loss	2% to 5%	Included in loss profile	Voltage drop rises with current, long cable runs, and small conductors.
Tilt / azimuth derate	70% to 100%	User-selected multiplier	Flat, east/west, shaded, or off-angle arrays receive less daily sun.
Controller headroom	125% common	Installed W / V × 1.25	Headroom covers high irradiance moments and rating selection margin.

📋Common Project Sizes

Project	Daily Load	Typical Array	Notes
Security camera and router node	300 to 700 Wh/day	200 to 400 W	Use winter PSH because loads run overnight and in storms.
Weekend cabin essentials	900 to 1800 Wh/day	400 to 800 W	Lighting, charging, modem, fan, and short inverter use.
RV fridge and electronics	1200 to 2600 Wh/day	600 to 1200 W	Flat roof derate usually matters more than panel nameplate watts.
Tiny home essential loads	3000 to 6000 Wh/day	1200 to 3000 W	48 V systems lower controller current and cable size pressure.

✅Solar Sizing Notes

Use the right sun month. Peak sun hours are not daylight hours. For critical systems, enter the lowest practical month for your location, then compare whether the rounded array harvest still exceeds daily load.

Separate AC loads from DC loads. A 250 W AC load running three hours is 750 Wh at the outlet, but the battery must supply more because the inverter is not perfectly efficient.

Calculating the size of an off-grid solar array are a complex calculation because there are a variety of variable that will impact the amount of energy that the solar array will produce. There are many different variables that must be accounted for in order to ensure that the solar array can provide enough energy for the electrical loads of an off-grid home, as well as to compensate for the energy that is lose by the solar array. The energy that the solar array lose can be lost during the DC to AC power conversion process, due to the electrical losses of the wiring of the solar system, and due to the efficiency of the batteries that is used to store the energy produced by the solar array.

The calculator that is provide above will automatically calculate each of these variables for you once you have entered your own specific variable into the calculator. Each of these variable includes the type of electrical loads that the solar array is to supply, the amount of peak sun hours that is available to your panels each day, the efficiency of your hardware and wiring (represented by the loss profile), the angle of your solar panels (represented by the tilt derate option), the size of your charge controller, and the size of your solar array. Each of these factor are important to ensure that you have a solar array that can supply the energy requirement of your off-grid home.

Solar Panel Load Calculator