How Many Solar Panels Do I Need? – Quick Calculation Guide

Using this informational guide, you can quickly estimate how many solar panels you need for your particular setup.

It’s important to note, that on a home/grid solar setup, you are always going to have mains electricity available to power your house – so you can theoretically have as many or as few solar panels as your roof and equipment can support.

Checking the capability of your structural roof supports, isolator, cables and inverter are key in this instance.

The calculations below are particularly valuable for off-grid and remote setups, whether it’s a cabin, in an Rv, on a boat etc.

Knowing your solar panel number and requirements will help keep your DC batteries charged at all times in the event of an emergency for example.


How Many Solar Panels Do I Need? – The 5 Minute Calculation Guide

NOTE: this guide is for informational purposes only – to give you an idea of where you can start with your solar panel purchasing decision.

You should always check the solar panel, solar panel equipment, and battery instructions – and confirm with the manufacturer correct sizing and number of panels before purchase.


Step 1

List all the devices that use DC power, OR count the number and total voltage of DC batteries your system runs on


Step 2

Estimate how many A/h your devices use per hour, and how many hours they run a day. OR, you can just find out the total A/h of your batteries per hour or per day – which should be in the product instructions on the battery


Step 3

Multiply your total A/h of all devices by 12v (common DC power voltage – but, if you have a bank of batteries, it could be higher like 24v for example) = total watts you use in a day (watt hours)


Step 4

Divide the total watts by number of available sunlight hours in a day (say 6-8 on average = the total wattage of solar panels you need


Step 5

To be safe, increase that number by 20%.



If I have 1 x 12v battery that runs at 100 A/h that I want to charge, and I have 8 hours of direct sunlight available to me per day. I would go:

1. 100 x 12v = 1200 watt hours

2. 1200/8 = 150 total watts I need from solar panels

3. 150 x 1.2 = 180 watts with a 20% buffer added

So, 2 x 100 Watt panels would work in this instance (as long as they are rated for total voltage of your battery, or the battery bank – you may need an inverter or regulator for a 24v battery bank and you only have 12v rated panels, OR you would charge the 2 x 12v batteries separately off of each panel.

A full 12 volt battery will top up at 12.6 volts – so your incoming solar panels will need to exceed this voltage, and be controlled with a solar controller (18 volts is common for standard off grid panels).

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