The significance of energy load profiles for designing efficient photovoltaic systems

A load profile is a record of a site’s power consumption over time, typically logged at 1- to 15-minute intervals for at least a week. In commercial solar design, it shows when and how much power is actually used, so the PV array, inverters, and batteries can be sized to real demand instead of estimates.

In this article, I will explain in more detail the significance of energy load profiles in commercial solar PV System designs.

Load profiles are important when designing bigger commercial systems, to ensure that you avoid overcapitalizing and yet have a system large enough to meet the energy and power demands.

So, what is a load profile? If you look at the following picture, you will see a typical load profile. It is basically a plot of power over time, which then gives you the energy. In other words, it is a log of your energy consumption over a period of time. In the graph, you can see the hours of a day on the bottom X-axis from zero to 23, and on the Y-axis, you can see the power in Watts from zero to 60 kilowatts.

A load profile is typically measured over a period of a few days, a week or two. This is to give you a good indication of how a company uses electricity over various days, weekends and at what time of the day.

Here is an example of power consumption that was measured at a company from Thursday to Tuesday. One can see clearly the weekend when they were not operational. The X-Axis indicates the days and hours, and the Y-Axis indicates the power.

When planning a solar system, one would ideally get the load profile of only the days they were operational. The following graph is a graph with only the operational days selected.

You will also see that each day is a bit different. It is difficult to design a system if each day is different. Ideally, one would like to get to an “average load profile per day for operational days”.

And finally, one would like to get an average load profile of an operational day. So the average load profile of the four days would look like this.

A line graphs gives one a good idea of a trend over time, but a bar graph gives one specific values for each datapoint. So, to make the graphs easier to read and get a specific value for each hour, one can change the graphs to a bar graph like this.

Why  is it necessary to use a load profile to design a solar system

So, people do design and install solar systems without using load profiles. They just look at the electricity bill and the main breaker size of the incoming supply. It is possible, but if you would like to design an efficient solar system, which is not too small or too big, then it is important to know what the consumption is.

• The system must not be too big
  • One would like to maximise the self-consumption of generated energy and minimise the amount of energy exported to the grid as the economic value of a kWh self-consumed is much higher than a kWh exported to the grid.
  • Over-capitalising on a solar system will increase the pay-back period.
• The system must not be too small.
  • Not designing a system to the maximum possible size causes the client to lose out on potential savings and the solar system supplier on potential profit.
• Optimise energy consumption for specific time periods
  • The system must be able to supply energy at the time it is being used, how much energy is used during the day and how much energy is used at night, so how big should the energy storage be to optimise for specific consumption patterns.
  • An electric bill just tells you the total consumption per month; it does not tell you when that energy is being consumed.
• Optimise energy consumption for specific use cases
  • Different companies have different operations, high seasons or low-seasons. Being aware of their consumption patterns will allow one to optimise the design to maximise economic return of a system
• Identify potential problems in supply and loads.
  • Having detailed energy logging data will help you identify the following.
  • Over or under-voltage in the supply
  • Power factor
  • Phase imbalances.

Without a load profile, everything is basically guesswork.

Conclusion

So, one can see how having access to energy logging data enables one to see exactly what is going on at a specific site with their energy consumption and other electrical parameters important in designing a solar system. 

One of the most important of these parameters is power factor, because it determines the relationship between real power (kW) and apparent power (kVA) — and that ratio drives how you size inverters and how the network operator bills you. For the underlying math and how to measure it on a live three-phase circuit, see Power Factor Formula: How to Calculate Power Factor (With Examples).

In the next article, we will see how to use energy load profiles and energy generation profiles of solar systems to design a solar system to maximise generated energy self-consumption.

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Useful links

Click here to see a list of portable energy loggers that can be used for these functions as explained above.

Click here to see the template used to analyse the data from the energy loggers and create the graphs seen here. (This template is included free of charge when purchasing an energy logger from us)