In this article, we will explore the accuracy of using your Eskom or municipal bill and WHY it isn’t recommended to use only your Eskom utility bill to determine what size your solar system should be. Calculating your electricity consumption is an essential step in making an informed decision about the exact output your solar system should be able to provide you with. Even though the number of PV system installations has been steadily increasing – even booming – over the years, only a few installers truly understand how to calculate your electricity consumption. Most companies just request the customer’s Eskom bill and do their calculations based on that.
Your Eskom bill can be misleading. It only reflects the TOTAL consumption of energy over a period of a month. It doesn’t give you an indication of the specific times when the electricity is actually being used. What you really need to accurately calculate the size of your PV system should be is a load profile.
A load profile is essentially a graphic representation of your electricity consumption throughout a specified time period. The load profile differs depending on if you have a residential property, a business or a farm. Because of this, it is beneficial to acquire a device that can track your energy consumption for you. The data you receive from this device you can use to plot a graph, this graph will be an accurate representation of your energy consumption and at what times the consumption takes place.
Below is an example of a 7-day load profile that indicates very clearly that most of the electricity used is on the 6th and 7th day, and almost none on the preceding 5 days.
According to the graph above the total kWh used for these 7 days is 3400 kWh. Most PV system installers will simply take that consumption and divide it by the number of days it was recorded on. So in this example, it would be 3400kWh ÷ 7 days = 385kWh per day. This number and the number of sun-hours available to you will then be used to calculate how much the output of your PV system should be.
Even though your Eskom utility bill shows how much energy you consume during a certain period, it is evident in this example that you shouldn’t just use the average rate of consumption to calculate the size of your solar system. The required size of your PV system would be calculated wrongly and won’t do you any good. The motivation for installing a grid-tied system is the realisation of saving money on your electricity bill during the day. The electricity generated by the sun is much less expensive than the municipality and Eskom’s cost for electricity.
In the graph below, we show the “calculated” solar system that indicates the following:
Point no. 1 – Day 1 to 7 we see the green curve that indicates the daily generated energy the PV system produces.
Point no. 2 – The coloured green curve shows the time of the day the consumer potentially receives no benefits.
Point no. 3 – The first time that week the consumer actually benefits from the solar system is on day 6 and 7. This is indicated by the blue area underneath the thick blue line.
A professional measurement of your load profile will include the use of an energy meter. The most practical energy meter used by most solar companies is called Efergy. Energy meters work by connecting directly to your power supply and measure your daily usage throughout the day, giving you the most accurate reading for your system requirements. The Efergy system can be monitored via an app and daily, weekly and monthly readings can then be used to create a solar system that will cater for your energy usage and lifestyle needs.