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DIY Solar - Battery Sizing

Updated: Jun 24, 2020

For DIY Solar enthusiasts, solar PV systems with batteries or off-grid solar PV systems are one of the most exciting things to build for our own use. Its main advantage over typical on-grid solar PV systems is that it is not required to be connected to our house’s main utility supply, allowing for a safer installation.

To determine the proper size of the battery system that we need to power a certain appliance or appliances, we will need to start with a simple load analysis. It is very simple and straightforward. You will first need to multiply your appliance’s power rating with the number of hours that you will use it in a day. The result is the total energy consumption of that appliance in one day Kindly see the table below for a sample computation:

Getting the sum, we will have the total energy demand that we need to meet every day. This also means that we need to have a battery system with at least 276Wh of energy storage capacity. I said at least because we will still need to consider some things. First is the efficiency of the battery in storing and releasing energy. This is also called round-trip efficiency and is typically around 80%. We will