Solar Panel Calculator

Written byOleh Soloninupdated 25 September 2026

Daily consumption, kWh

Peak sun hours

Hours a day in which the sun delivers 1 kW per square metre, for your place and month — from an insolation map.

Panel rating, W

Days of autonomy

Advanced options

Bank voltage, V

System losses, %

Panel heating, cables, the charge controller and the inverter. 25% is the calculator's example, not a standard.

Allowed depth of discharge, %

How much of the battery's capacity you may use — from its datasheet. 50% is an example.

Result

Panels5
Installed capacity, W2,000
Capacity required, W1,905
Daily yield, kWh5.25
Battery capacity, Ah417
Working
5,000 Wh ÷ (3.5 h × 0.75) = 1,905 W; 1,905 ÷ 400 = 4.76 → 5; bank 5,000 Wh ÷ (24 V × 0.5) = 417 Ah

From kilowatt-hours a day to a panel count

Works out how many panels cover a daily consumption at your sun hours and losses, what they yield and how big a battery bank the days of autonomy need at the allowed depth of discharge.

The panel power needed is daily consumption divided by the peak sun hours and by what is left after losses: P = E ÷ (hours × (1 − losses)). For 5 kWh a day at 3.5 sun hours and 25% losses that is 1,905 W — five 400 W panels. Sun hours for your place and month come from an insolation map.

Batteries have to see you through the night and cloudy days. Bank capacity is daily consumption × days of autonomy ÷ (bank voltage × allowed depth of discharge). The depth of discharge is on the battery's datasheet; the calculator's 50% is an example.

How to use

Enter daily consumption in kilowatt-hours, the peak sun hours where you are and one panel's rating.
Set the days of autonomy; the advanced fields hold the bank voltage, system losses and allowed depth of discharge.
Read the power needed, the number of panels, their daily yield and the battery capacity.

400 W panels under different sun

Each row is a separate run with 25% losses.

All rows come from the calculator on this page.
Consumption	Sun hours	Power needed	Panels	Daily yield
3 kWh	3.5	1,143 W	3	3.15 kWh
5 kWh	2	3,333 W	9	5.4 kWh
5 kWh	3.5	1,905 W	5	5.25 kWh
5 kWh	5	1,333 W	4	6 kWh
10 kWh	3.5	3,810 W	10	10.5 kWh
10 kWh	5	2,667 W	7	10.5 kWh

Battery capacity

For 5 kWh and one day of autonomy on a 24 V bank at 50% depth of discharge you need 417 Ah; at 80%, 260 Ah; on a 48 V bank at 50%, 208 Ah. Two days of autonomy double it to 833 Ah.

What this calculator shows

Array capacity required and how many panels of your chosen rating that is
Battery capacity for the days of autonomy you want
The average daily output of the chosen number of panels

What to keep in mind

Sun hours, losses and depth of discharge are yours to set; the defaults are examples.
The yield is a daily average for the sun hours given; day-to-day weather is not modelled.

FAQs

How many solar panels does a house need?

It depends on consumption and sun. For 5 kWh a day you need five 400 W panels at 3.5 sun hours and nine at 2 hours, with 25% losses.

What are peak sun hours?

The day's solar energy per square metre, expressed as hours at 1 kW per square metre: 3.5 hours means 3.5 kWh per square metre per day.

What losses should I allow for?

The calculator defaults to 25% — panel heating, cabling, the charge controller and the inverter. It is an example: at 14%, the same 5 kWh needs 1,661 W instead of 1,905.

How do I size the battery bank?

Daily consumption × days of autonomy ÷ (bank voltage × depth of discharge): 5,000 Wh × 1 ÷ (24 V × 0.5) = 417 Ah.

Why does winter need more panels?

There are fewer sun hours: at 2 hours instead of 3.5, the same 5 kWh needs 3,333 W instead of 1,905.

What inverter do I need?

The calculator does not size one: an inverter is sized by the largest load running at once, in watts, motor starts included — not by daily energy. The generator sizing calculator helps with that estimate.

Worked example

A home using 5 kWh a day

Input: 5 kWh, 3.5 sun hours, 400 W panels, 1 day of autonomy

Output: 5 panels, 5.25 kWh a day, 417 Ah of batteries

Note: A 24 V bank, 50% depth of discharge and 25% losses are the defaults.

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Result

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