Engineering
Solar Array and Battery Sizing Calculator
Size a DC solar array from daily energy, peak sun hours, and derate. Round to whole panels, calculate installed kW and roof allowance, and independently size nominal battery storage for a chosen autonomy period.
Required DC array size (kW)-
Whole panels required-
Installed DC array size (kW)-
Nominal battery storage (kWh)-
Usable AC-side battery energy (kWh)-
Roof-area allowance-
Estimated daily generation (kWh/day)-
Estimated generation minus target (kWh/day)-
Decision view
Solar array, daily energy, and battery capacity schematic
Solar array, daily energy, and battery capacity schematicWhole panels feed the daily AC target while the storage branch separates nominal battery capacity from usable delivered energy.
Exact scenario comparisonPeak-sun-hours reference changes while all other entered assumptions remain constant.
| Peak-sun-hours reference | Required DC array size (kW) | Whole panels required | Installed DC array size (kW) | Nominal battery storage (kWh) | Usable AC-side battery energy (kWh) | Roof-area allowance | Estimated daily generation (kWh/day) | Estimated generation minus target (kWh/day) |
|---|
How to use Solar Array and Battery Sizing Calculator
- Enter the daily energy target and peak-sun-hours reference.
- Enter system derate and module wattage.
- Choose autonomy days, usable battery percentage, and inverter efficiency.
- Review whole-panel generation margin, storage, and roof allowance separately.
Calculator guide
Understanding Solar Array and Battery Sizing Calculator
Solar array sizing must distinguish theoretical DC capacity, whole-panel installed capacity, expected daily generation, and battery energy. This calculator rounds only the panel count while keeping derate and storage conversions explicit.
Calculation method
How the calculation works
Size an idealized DC array from daily energy, solar resource, and derate, then round to whole panels and independently size nominal battery storage. Divide daily energy by peak sun hours and the retained system fraction, round watts up to whole panels, then divide autonomy energy by usable battery fraction and inverter efficiency.
Detailed calculation process
Size energy production and storage on separate conversion paths
The defaults target 28 kWh/day with 4.5 peak sun hours, 20% derate, 450 W panels, and 1.5 autonomy days.
General formula: P_req = E_d/[H_s(1-d)]; N = ceil(1000 P_req/P_panel); P_inst = NP_panel/1000; E_bat = E_d A/(u eta); E_gen = P_inst H_s(1-d) The array path converts daily energy to required DC power and rounds to modules. The battery path converts autonomy energy back through inverter efficiency and usable depth, so it must not be conflated with panel count.
What each symbol means
Worked substitution with the default inputs
The defaults require 7.778 kWdc, round to 18 panels and 8.10 kWdc, generate 29.16 kWh/day under the model, and require 55.851 kWh nominal battery storage.
Energy architecture
Trace sunlight to load and reserve
The engineering schematic separates the array and battery branches.
Worked situations
Practical examples
- A theoretical 7.778 kWdc becomes 18 whole 450 W panels.
- The installed array is 8.10 kWdc.
- A 1.5-day target requires 42 kWh usable AC-side battery energy.
Better inputs
Useful tips
- Use a site-appropriate solar-resource dataset.
- Apply shading and temperature losses inside a defensible derate.
- Check both energy capacity and instantaneous power limits.
Before relying on the result
Limitations and common mistakes
- Orientation, shading, temperature, snow, clipping, and seasonal variation are simplified.
- String voltage, inverter MPPT, battery power, and code requirements are excluded.
- Roof structure, setbacks, tariffs, and permitting need site-specific design.
Reference
Key terms
- Peak sun hour
- Equivalent hour at 1 kW/m2 solar irradiance.
- DC array size
- Sum of module nameplate wattage.
- Autonomy
- Days of target energy assigned to storage.
Important note
Calculated from the entered values using the displayed engineering relationship. Confirm design values, load cases, safety factors, standards, and field conditions with a qualified professional.
Frequently asked questions
Why round panel count upward?
A fractional module cannot be installed, and rounding down would miss the modeled target.
Is peak sun hours the same as daylight?
No. It is an equivalent full-irradiance energy measure.
Why divide battery energy by efficiency?
The nominal battery must supply losses before the AC-side target is delivered.
Does the battery size the inverter?
No. Inverter power and surge capability require separate checks.