Sizing solar need – Are you a small business owner?


Calculating solar power need – Are you a small business owner?

Producing your own energy to save money definitely seems appealing. But the sad reality is that solar is still a very mysterious subject to many business owners. Finding out how much solar power you need for your business can be a major pain point. And probably the most difficult hurdle to jump when you first start out.

Truth be told – for most people, one of the most crucially important things to get right when shopping for solar is – what size solar power system is needed? Finding someone that is good at sizing and trustworthy at the same time is no easy task.

I am here to tell you that you are the most reliable source to calculate your own solar power need. Yes, it is possible. And you will find out how simple it is in the next few minutes.

Other advantage of sizing – without solar company’s influence – is that you become aware of your true need. And because not all solar companies are created equal, you can put them to test with your knowledge when the time comes for buying one.

This article has one goal – size a system that is optimized just for your need. Nothing more, nothing less. And, ultimately, how big of a solar energy system you end up installing will likely depend on couple more factors such as your financial and/or physical (roof space) limitations.

So, let’s get started.

If you paid attention when I mentioned the one goal of this article, you’ll recall the word optimize. What is it and why is it important?

Need optimization in commercial solar

Even a small commercial solar system can be double the size of a residential system. This means couple of things:

  • Business solar is a much bigger system to operate and maintain.
  • The upfront cost is bigger as well.

At its heart, commercial solar is about payback period. And because these systems are large, there will be an on-going cost for operations and maintenance (O&M) as well. Size optimization helps with both.


There are three essential steps to finding out what size solar power system you need:

  1. Find out average daily consumption, in kWh, for your business.
  2. And, figure out what percent of that daily consumption is used in the daylight hours.
  3. Finally, calculate what size solar array will supply your daily need.

For this exercise, we will consider a grid-connected battery-less solar system because this is the most commonly installed system today. It is the cheapest and the easiest way to go about solar.

Find out your average daily consumption.

There are two sources to determine how much energy you consume in a day. No matter which source you end up using it is important that “average” daily consumption is truly an “average” value – for the entire year. Doing this will optimize your need by considering seasonal variations.

Source#1: Electricity bill


Your utility bill tells you how much you owe to the power company. It also has another vital piece of information – your total consumption measured in kWh. It may be a good time to look into your utility bill.

If you are lucky, your invoice will also have a historical bar graph that says what your average daily, monthly or quarterly consumption was for each of the past twelve months or four quarters. Whichever it may be, add all those up to 12 months and divide to get the daily average.

This is an important exercise, as it balances your consumption for high, low and average months. The result is an optimized solar system that you need for your business.

Source#2: Smart meter interval data


You are more likely to hear the term “interval data” if you live somewhere in Victoria. That’s because interval data is the half-hourly data on your energy usage that only a smart meter can capture. And a few years ago, everyone in Victoria was required to switch to smart meter, while in other states getting smart meter for your home or business is still only an option.

Interval data has your consumption data for every thirty minutes interval. That’s 2 readings per hour x 24 hrs x 365 days = 17,520 data points in a year.

The only downside of interval data is that there are 17,520 data points. You would need a special tool to interpret this data to find out your average daily consumption.

Next, in our goal to calculate solar power need, is:

Figure out what percent of the daily consumption is used in the daylight hours.

This is a difficult task in some cases. The nature of your business is going to dictate how much of your daily consumption comes from daytime.

For businesses that mostly operate in 8am-5pm hours, most of the consumption may come during the day light hours. If they also don’t have any heavy machines consuming power overnight, the energy profile may look similar to what I have shown below.


If you are working just off your electricity bill, the best approach to determine your daytime consumption out of daily consumption is through estimate.

It won’t be a very scientific approach but the shortcomings can be partially overcome by guessing to the best of your knowledge. Remember, no one is more qualified to estimate your afternoon usage closer to reality than yourself.

The upside of “guess-estimate” approach is that it is quick and easy – and for sizing smaller systems, it is still a safe approach.The downside is you can’t be certain how close you are to optimizing your solar need.

If you happen to have hourly interval usage data, you know precisely how much energy you use for any given range in time. The data is highly granular and it eliminates the guesswork from the sizing. For commercial system sizing, this is also my preferred choice of data when available.

So, if your interval data is just a phone call or an email away, this is a much better approach to size a system that can be well optimized resulting in shorter payback and high IRR.

Off course, I don’t expect you to toy around with 17000 data points. You can ask your solar company to analyze this data for you. All you have to do is make the data available to them.

And, finally..

If we knew how many kilowatt-hours (kWh) each kilowatt (kW) of solar panels produced in a day, we would know our need in Kilowatts.

Fortunately, Clean Energy Council (CEC), the Australian peak body for clean energy has provided the output guidelines for each kW of solar panels for various locations across Australia.

Which is as follows….

City 1 kW system daily production estimate
Adelaide 4.2 kWh
Alice Springs 5.0 kWh
Brisbane 4.2 kWh
Cairns 4.2 kWh
Canberra 4.3 kWh
Darwin 4.4 kWh
Hobart 3.5 kWh
Melbourne 3.6 kWh
Perth 4.4 kWh
Sydney 3.9 kWh


Calculate your Kilowatt need as below:

Average daily “daytime” consumption / kWh production by 1kW system for your location.

So, there you go. That’s all there is to sizing a solar power system that fits your requirement. 

Wrapping it up!

The reason I posted a separate “how to size solar power need” for small business owners is to highlight the importance of interval data. When systems get bigger, I believe interval data becomes more important to understand your consumption profile and accurately size your need. I hope you enjoyed reading this post.

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