Solar Calculator: how much solar do you need?

Short answer: work out how many watt-hours you use per day, divide by your peak sun hours and a 25% system loss, and that gives the array size in kWp. A typical South African home using 10 kWh a day needs roughly a 2.4 kWp array (about 5 standard panels) and around 12.5 kWh of lithium battery for one day of backup.

The calculator below does this for your own appliances, and the tables further down show the common sizes so you do not have to calculate anything.

Work out your own system

Tick what you want to run, or add your own row. Leave the hours at 0 if an item should not count.

Appliance	Watts (W)	Hours / day	Wh / day
LED lighting			200
Refrigerator			1200
Wi-Fi router			240
Television			400
Laptop			480
Water pump			750
Kettle			500
Washing machine			500
Air conditioner			0
Electric geyser			0

Peak sun hours per day

Most of South Africa is 5–6. Port Elizabeth averages about 5.

Days of backup (autonomy)

1 day covers overnight; 2–3 covers cloudy spells.

Battery type

Lead-acid needs roughly twice the capacity for the same usable energy.

Panel wattage

550 W is the common residential panel today.

Everything is calculated in your browser — nothing is sent anywhere.

Your estimated system

Energy needed—

Solar array size—

Panels needed—

Battery capacity—

Inverter size—

Array area—

An estimate for budgeting, not a design. Shading, roof direction, roof angle and your actual usage all change the result — we quote against your real figures.

Get a quote for this size

Common solar system sizes

If you would rather read off a table than calculate, these are the sizes we are asked for most. Figures assume 5.5 peak sun hours, a 25% system loss and one day of battery backup.

Daily use	Array size	550 W panels	Lithium battery	Typical home
3 kWh/day	0.7 kWp	2	3.8 kWh	Small flat, lights + fridge + TV
5 kWh/day	1.2 kWp	3	6.3 kWh	Couple, essentials only
10 kWh/day	2.4 kWp	5	12.5 kWh	Family home, no geyser on solar
15 kWh/day	3.6 kWp	7	18.8 kWh	Family home with pump and TV
20 kWh/day	4.8 kWp	9	25.0 kWh	Larger home, evening cooking
30 kWh/day	7.3 kWp	14	37.5 kWh	Large home or small office

How the numbers are worked out

Every figure above comes from the same four steps, so you can check it yourself:

Daily energy — add up watts × hours for everything you run. A 60 W laptop on for 8 hours is 480 Wh.
Array size — divide the daily energy by your peak sun hours and by the system efficiency. We use 25% losses (inverter, cabling, heat, dust) as a realistic South African figure:
kWp = daily kWh ÷ (peak sun hours × 0.75)
Battery — daily energy × days of backup, then divided by how much of the battery you may actually use: 80% for lithium, 50% for lead-acid.
Inverter — sized from the largest simultaneous load, with 25% headroom, because motors and compressors draw several times their running current for a moment when they start.

Why we quote rather than publish prices: panel, inverter and battery prices move with the rand and with import cycles, so the calculator sizes the system and we price the actual bill of materials. Send us your numbers and we will come back with a costed system.