How To Choose the Right Size Solar System

Once you’ve decided that your house is suitable for solar, you’ll need to think about what size system to install.

The factors you need to consider are:

  • Roof sizeFirstly, you’ll need to determine how many panels you can fit on your roof. Solar installers can help you with this over the phone by using the mapping websites Nearmap or Google Earth, which allow them to accurately measure your roof. From there, you can get quotes for sizes up to the maximum allowable. Be aware that you can only use sections of roof between east, north and west, not south facing roofs. Keep in mind that smaller systems can have panels facing in only one direction (across multiple sections of roof is ok), whereas larger systems over 3kW can have panels facing in two different directions and across multiple sections (this is a feature of better quality inverters that use Maximum Power Point Tracking or MPPT).So, first of all, let us organise for three installers to get in touch so that they can figure out how many panels will fit on your roof. They’ll also be able to give you an idea of how much you’ll be looking at for a few different size options. If you’re not sure about all of this, you’re probably best organising for a few installers to get in touch so that they can give you a proper appraisal. If you’d like 3 quotes, we can organise this for you here. Some other questions you might be interested in:1. Is it worth going off grid just yet?
    2. Why is there a limit to how much solar we can connect to the grid?
  • BudgetDeciding what you can afford to spend is a major factor that will influence the system size that you’ll end up with on your roof. Do keep in mind that solar is first of all a financial investment and if you do the numbers and find that the return on investment is 15 -20% p.a or more, then its probably worth using equity from your mortgage or taking out finance. If you take this route, be doubly cautious and make sure you reduce your risk by choosing top quality components and a good reputable installer. The following table shows the out of pocket price averages for Australia in 2018:
    System size Number of panels Price range
    1.5kW approx 8 $2,724
    2kW approx 11 $3,400
    3kW approx 15 $3,500
    4kW approx 19 $4,900
    5kW approx 24 $5,000

    You can find some good advice about installer and components on the Whirlpool forum.

  • Household usageGenerally speaking, the bigger the household usage, the more benefit you’ll get from choosing a larger size system. Keep in mind the anticipated growth of your family or whether you have kids just entering their teenage years as they will start consuming more.

How to work out the best system size?

Once a solar installer gets in touch, they’ll look a few of your previous bills and figure out how many units (kWh) you use on average per day. From there, they’ll ask you a few questions about your lifestyle and family size to work out what percentage of that daily usage you use during the middle of the day.

Once they’ve figured this out they’ll suggest a system that will produce a similar amount to this or one that produces slightly more depending on anticipated growth in usage or how much power usage you can shift into the middle of the day such as washing machines and dishwashers.

From there, they’ll recommend a few sizes with different quality components depending on your budget.

Important: We recommend that you get a few different quotes so that you can tell if their numbers are overly optimistic.

Where in your solar journey are you?

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Understanding Batteries

Off-Grid Systems

For some households a battery system can be of great benefit and minimise a home’s reliance on the grid. However, it’s important to understand for a battery to be useful your solar system needs to be generating excess energy for the battery to store, which you can then use at night or when the sun is not out.

When selecting a battery, you’ll want to invest in a system that is most suited to your home and can drive the best return on investment (ROI). Despite a larger upfront cost, a higher quality battery may significantly increase your ROI.

    Battery systems start from $6,000 and costs can vary greatly based on the following factors:

  1. Cycle Life-Time

    The number of times a battery can fully charge and discharge.

  2. Battery Power (kW)

    How fast it can be charged or discharged.

  3. Storage Capacity (kWh)

    The maximum amount of energy a battery system can store.

  4. Battery Management System (BMS)

    An electronic ‘smart’ system that gathers data and manages the battery ensuring it does not overload or operate outside of its safe functioning zone..

  5. Inverter

    Battery systems require their own inverter if your solar system does not have a hybrid inverter.

  6. 'All-In-One Unit’

    A system which includes the battery, BMS and an inverter all in one unit.

  7. Warranty

    Length of time or cycles the battery system is under guarantee.

  8. Blackout Protection/Backup

    It’s important to note this is not a common feature of a battery system and could cost thousands of dollars to include. Blackout protection not only requires additional components but also a specialised installation and rewiring. For grid-connected homes, the cost for blackout protection can outweigh the benefit.

Additionally, if your purpose for adding battery is to go Off-Grid and become completely independent from the grid you will need to ensure your solar system can generate enough energy to power your home and your battery system is large enough to store this energy. For homes in metro areas going Off-grid is not cost effective and is only recommended for those in remote areas with limited access to the grid. Off-grid solar systems with battery start at approximately $30,000.