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Part of the Assessment To Size A Solar Power System – Just The Usual, Thanks!

Although this topic is very basic, I believe it to be really important. I have an issue with how some solar power systems are sized, and that it is too basic. There is a limited assessment of actual energy consumption, behaviour patterns, and expectations. Each client’s case and requirements are different and questions need to be asked, which is valuable to ask yourself in the early stages when considering going solar - why you want it and what are your expectations.

If we can’t take the time to consider this, then why can’t we just ring a solar company and say “ Just the usual, thanks!” This would save a lot of time.


Up until recently, a 5kW system seemed to be the favoured size recommended for residential systems, who came up with that arbitrary number I am not exactly sure but that was the going size for a while. The Clean Energy Council’s updated report shows the average size now has increased to 7kW. This to me feels a bit generic, if you don’t want to think about it too much, then, by all means, have a system sized the typical way and that is fine in some cases, a couple of questions and show of your power bill and you’re done. What bugs me about this though is the cost associated with solar power systems, I believe this provides merit to take the extra time to think about your energy needs, consider your energy usage patterns, and discuss this with your consultant, you may not need such a big system; saving you money.

I encourage clients to consider why they want solar, which again brings me back to the whole expectations of a system – if you know why you want it, then your expectations will be more aligned with how your system performs.


Just to theorise for a moment, let us consider the following scenarios:

Do you want to have solar so you never ever have to pay for electricity ever again, whilst still connected to the grid? Then we firstly need to really bring your expectations into check! If this were to be your why then at least we can size your system and create an energy management strategy plan that will enable you to minimise what you draw from the grid, minimising your electricity costs by consuming most of the generated electricity onsite. Unless you really don’t want to pay for any electricity at all, ever again, you may consider including batteries in your system, and going as far as being off grid, in which case, your payback period will be significantly longer, however, people are doing it.


Or are you a person who expects to turn on every appliance in the house and expect your solar to be generating enough electricity to cover that? If so, the design needs to accommodate the parameters of these peak loads, you may require a larger system if this is what you want. Or are you someone who is prepared to stagger usage over the day, this would enable you to have a smaller system as opposed to sizing for the peak load client.


If your purpose is environmentally driven and just want to do your bit, but let’s say works fulltime. Then you will be doing your bit, but you will be exporting a lot of generated power, rather than consuming onsite. By doing your bit does not necessarily mean consuming whatever is generated, but you will also be contributing to the grid, providing some green power to be redistributed elsewhere, reducing the pressure to burn more coal – even if the reduction is minuscule.


There is a lot to think about when deciding whether or not to install solar, transparency between the client and the consultant is a must, that way the system is uniquely designed to suit the requirements, expectations are realistic, and you will get the most from your system.

There are other details that need to be considered that will set the parameters for sizing and meeting expectations:


o Do you want a system with the longest product warranties

o Add value to your home

o Electricity price security

o Budget restrictions

o Initiate independence from the grid

o Are you planning on purchasing an electric vehicle in the future

o Limited or unlimited roof space/property space

o Does your energy consumption change significantly between seasons

o Are you prepared to modify your energy behaviour to consume as much of the solar generated electricity on site, rather than export


There are other considerations, but the point is your home, your energy consuming behaviour, and expectations you have should dictate the size of your solar system.

Consider signing up to your distributors’ energy portal, if available, this will give you readings of your energy consumption, and give an overview of when and how much energy you use. This will provide you with more insight to help you decide and have an input into the system you are potentially getting.


I strongly believe, and I will probably bring it up time and time again, that an energy strategy plan for reference after the install is a critical element in installing a solar power system, encouraging you how to use energy in your home in relation to the size of the installed system, and what expectations you have.


It is also really important to note that to financially optimise any system is to consume as much of the generated power onsite rather than exporting, as feed-in-tariff rates are a lot less then what you pay for electricity. Also remember there are cloudy overcast days, which will reduce how much your system outputs, the change of the suns position throughout the day impacts the output, even a bird poo can impact it. There are constant variables that will change the output, so note this in your subconscious list of expectations that you have of your system. Don’t let this deter you though, some days your system will generate an abundant amount of power so don’t fret.





Next time I will aim to talk about the rated output of panels, how to compare panels, and reading important items on the specifications/data sheets of solar panels to help you compare, and provide you with information to make an informed decision.

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Melinda Glew