September 22, 2026 · Energy · 7 min read

Solar Panel Sizing Explained: Panels, Inverter and Batteries

A solar system has three sizes that all have to match: the panel array, the inverter, and the battery bank. Get one wrong and the whole system underperforms — usually because two of the three were sized for different numbers. Here is the sequence professionals use, simplified.

Step 1: Add up your daily energy

List each appliance, its wattage, and how many hours per day it runs. Multiply and sum:

10 LED bulbs × 10 W × 5 h = 500 Wh
Refrigerator: 150 W average × 24 h ≈ 1,500 Wh (fridges cycle, so use average draw, not nameplate)
TV: 100 W × 4 h = 400 Wh
Laptop + phone charging: 60 W × 8 h = 480 Wh

Total: about 2,900 Wh (roughly 3 kWh) per day.

Step 2: Convert to array size using sun hours

Panels only produce at full rating in ideal conditions. Your location's peak sun hours (find yours online — it ranges from about 3 to 6 per day) tell you how many full-rating hours the array effectively delivers daily.

Array size (kW) = daily Wh ÷ (sun hours × 1,000 × system efficiency)

With 4 sun hours and a 75% overall efficiency factor (inverter losses, heat, dirt, wiring):

3,000 ÷ (4 × 1,000 × 0.75) = 1 kW of panels — for example, three 350 W panels.

Step 3: Size the inverter for the moment, not the day

The inverter must handle your largest simultaneous load, not your daily total. If lights (100 W), fridge (150 W average but 500 W surge) and TV (100 W) run together, a 500–600 W inverter might barely cope — but add a microwave (1,200 W) and you need 2 kW or more. Motors in fridges, pumps and air conditioners draw several times their rated power for a second at startup, so check the inverter's surge rating.

Heavy motor loads deserve their own arithmetic: the Water Pressure Pump Calculator estimates what a pressure pump draws, and the Heat Pump Calculator does the same for heating and cooling units.

Step 4: Size the battery bank

Battery (kWh) = daily Wh × days of autonomy ÷ depth of discharge

For one night of backup with our 3 kWh/day load:

Lithium (80% usable): 3 ÷ 0.8 = 3.75 kWh
Lead-acid (50% usable): 3 ÷ 0.5 = 6 kWh — one and a half times as much battery for the same service

This is the main reason lithium dominates new off-grid installs despite the higher upfront price.

Tip: enter your appliance list once in the Solar Load Calculator and it returns panel count, inverter size, battery capacity and estimated cost in one pass.

Don't forget the charge controller

The controller must handle the array's maximum current at your battery voltage. For a 1 kW array on a 24 V battery bank, that's roughly 42 A — so a 50 A MPPT controller fits. Undersizing it silently throttles your production on the sunniest days.

If air conditioning is part of your load, read Cooling Load Basics first — AC is usually the single biggest item on the list, and sizing it correctly matters twice: once for comfort and once for your solar budget. Work out that load directly with the Cooling Load Calculator; the BTU/h figure converts straight into the watts your panels must cover.