Solar Panel and Battery Calculator

A combined solar panel and battery calculator helps size both sides of an off-grid power system. The solar array must generate enough energy during available sun hours, and the battery bank must store enough energy to cover nights, cloudy periods, or the number of autonomy days you want.

This calculator estimates solar array watts, approximate panel count, battery capacity in Ah, and battery storage in kWh. It is meant for early planning and comparison, not as a final engineering design for code, wiring, or inverter surge sizing.

Short answer: First calculate daily energy use, then size solar panels from sun hours and system efficiency, and finally size the battery bank from daily load, autonomy days, usable depth of discharge, and battery voltage.

Solar + Battery Sizing Calculator

Estimate panel wattage, number of panels, battery Ah, and battery kWh for an off-grid system

Use a label such as cabin, RV, shed, backup, or off-grid home.
Add up the watt-hours used by all loads over a full day.
Use your local average for the worst useful season when possible.
Accounts for charge controller, wiring, temperature, dust, and other losses.
How many days of storage you want without meaningful solar input.
LiFePO4 is often sized around 80% to 90% usable DoD depending on the design goal.
Higher voltage reduces current and often simplifies larger systems.
Used to estimate panel count from total solar watts needed.

Combined Solar + Battery Sizing

Step 1: Daily load

Calculate total daily energy use in watt-hours by adding the energy used by all appliances over a day.

Step 2: Solar panels

Size the array from daily watt-hours divided by peak sun hours and system efficiency.

Step 3: Battery bank

Size the battery from daily load, autonomy days, usable depth of discharge, and system voltage.

Step 4: Practical rounding

Round panel count and battery capacity upward so the finished system has realistic headroom.

Example system design

Design ItemExampleResult
Daily load2000 WhBase daily energy need
Solar array2000 ÷ 5 sun hours ÷ 0.80500W solar panels
Battery bank2000 × 2 days ÷ 0.8 ÷ 48V104 Ah battery
Rounded systemReal-world purchase sizeAbout 500W solar + 48V 120Ah LiFePO4

Typical setup notes

A small off-grid cabin can sometimes work with around 1kW of solar and a 48V 100Ah-class LiFePO4 battery, but the right answer depends on daily load and how much cloudy-weather reserve you want. In many systems, battery autonomy and winter solar conditions drive the design more than the average summer load.

It is also common to pair lithium batteries with monocrystalline solar panels and an MPPT charge controller because MPPT controllers generally make better use of array voltage and changing solar conditions in off-grid systems.

Practical warning: The FAQ example for charging a 200Ah 48V battery using 5 sun hours gives 1920W as a simple minimum energy-equivalent array, but real systems usually need extra headroom for charging losses, weather variation, and battery absorption time.

Frequently Asked Questions

How many solar panels for a 200Ah battery?▼
At 48V, a 200Ah battery stores about 9.6kWh. Dividing that by 5 sun hours gives about 1920W as a simple energy-equivalent minimum, but practical systems usually size above that to account for losses and real charging conditions.
What is the best solar + battery combination?▼
For many off-grid systems, LiFePO4 batteries paired with monocrystalline panels and an MPPT charge controller are a strong practical combination because they balance cycle life, efficiency, and ease of system design.
Why do off-grid systems often use 48V?▼
Higher voltage reduces current for the same power level, which can help reduce cable size, heating, and losses in larger systems.
Should I size from average sun hours or worst month?▼
For dependable off-grid design, many installers size around poorer solar months rather than optimistic yearly averages.
Is battery Ah enough to compare systems?▼
Not by itself. Always consider voltage too, because 100Ah at 48V stores much more energy than 100Ah at 12V.

Practical rule: Size the battery for nights and cloudy days, then size the solar array so it can both run daytime loads and recharge the battery with realistic efficiency losses.

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Disclaimer: All calculator results are estimates based on standard formulas. Always verify with manufacturer specifications for critical applications.