How To Use Your Electricity Bill To Size Your Required Solar System

Eskom's mismanagement has resulted in rolling and recurring load shedding periods which have driven South Africans to investigate solar energy as a viable and trustworthy substitute.

In determining your home's average electricity consumption, your electricity bill typically reveals information about your residential or commercial property's total monthly energy consumption.

From this value alone, it is possible to approximate the required size of a Photovoltaic (PV) system that offsets monthly energy usage.

1. Calculate Your kWh Usage

Gather the kilowatt-hours (units) usage from your electric bill. You'll want to have full 12 months of usage to be able to look at peaks and valleys in usage over a year. Energy consumption spikes in the summer and winter with heavy use of your A/C and heating units.

Determine your average monthly kWh usage. Add up your kWh usage for 12 months and divide by 12 to figure out your average monthly consumption. i.e. Total consumption for the year is 5400 divided by 12 = 450kWh/month

Figure your daily kWh usage. Divide by 30 to determine your daily kWh usage 450 divided by 30 = 15.

2. Peak Sun Hours

Average peak sun hours vary greatly depending on your location and local climate. You'll want to determine how may peak hours of sunlight you'll get so you can make the most of the solar power. Western Cape peak sun hours are 4.7-6.1. You make your calculation on the lower winter peak of 4.7SPH.

3. Calculate the Size of Your Solar System

To figure out how to size your solar system, take your daily kWh energy requirement and divide it by your peak sun hours to get the kW output. Then divide the kW output by your panel's efficiency to get the estimated number of solar panels you'll need for your system.

Here is a written example:

You live in Cape Town, Western Cape and your monthly electricity consumption is 450kWh. Your area's monthly peak sun hours are 145 (4.7 x 31 days) and you want to use 400 watt solar panels to make up your solar system.

(450kWh ÷ 145) = 3.1 x 1000 = 3100 watts. You will need a 3.1kW solar system to offset your monthly energy consumption. 3100 watts ÷ 400 watts = 8 panels needed.

If you need more information, please contact David Raath (details below).