Solar System Sizing Basics
Estimate your energy needs, translate them into panel and battery capacity, and understand the assumptions behind the numbers.
Sizing a solar system means matching generation and storage to how much energy you use and when you use it.
Step 1: Estimate daily energy use
Use your electricity bills to find monthly consumption in kilowatt-hours (kWh) and divide by the number of days. Alternatively, list each appliance's power in watts and multiply by its daily hours of use.
Example: ten 10 W LED lights for 6 hours use 10 × 10 × 6 = 600 Wh (0.6 kWh) per day.
Step 2: Consider local sunlight
Solar resource is often expressed as “peak sun hours” — the equivalent number of hours per day of full-strength sunlight. Dividing daily energy needs by peak sun hours gives a first estimate of array size, before losses.
Step 3: Allow for losses
Real systems lose energy through heat, dust, wiring, inverter conversion and battery charging. Designers add a margin to account for these.
Step 4: Size batteries (if needed)
Estimate the energy needed after sunset or during outages, then divide by the battery's usable depth of discharge.
Step 5: Check space and budget
Finally, confirm the array fits the available area and adjust priorities if needed.
These steps give an estimate only. A professional design uses site-specific data and detailed calculations.
