What Size Solar System Do I Need?
March 13, 2020

What size solar system do I need?

Trav and I spend a lot of our afternoons assessing potential solar projects, and designing systems to suit the needs of a variety of different energy usage profiles.

A common question we get asked is, “what size solar system do I need?”

One day, for instance, we’ll meet a family of 5 living in a large house. They’ll have a pool, air conditioning units, multiple fridges, large electric hot water systems and electric cooking appliances. The kids are young so Mum’s at home with them through the day with the air conditioning full blast most of the day.

Then the next project we assess might be a young professional couple living in a townhouse, with gas appliances, a single small refrigerator and a couple of ceiling fans. They’re out of the house from early in the morning through until the early evenings, so they use barely any electricity through the day.

Both are very different cases and require very different designs to get the best economic outcome for each client.

So, what’s the process to knowing what size solar system you need?

1. Assessing the Roof

The first step we’ll generally take is checking your roof to assess what limitations there might be up top. Here’s what we’re looking for –

    • The actual size of the roof space and the material it’s made of.
    • The structural integrity of the roof, making sure it can handle the load of the solar
      panels, especially in strong tropical-Queensland wind conditions
    • The different roof aspects – roof angle/pitch, as well as which direction each aspect
      face (north, south, east, west) for optimum production at the right times
    •  Possible shading hinderances which could affect production, including potential
      future shading issues.

2. Create an energy usage profile, and design to suit:

Once we’ve got a good idea of the canvas we have to work with up-top, we’ll need to ascertain how much electricity you’re using, and more importantly when you’re using it. Then we’ll be able design the right size system to suit.

In many cases, we find a standard 6.6kW system is the optimal size for homes in South East Queensland given the solar export limit put in place by Energex, as well as the current solar feed- in tariff rates available (more on that here).

So, broadly speaking, a larger system (10kW or bigger) is more financially beneficial if your home is:

    • Three-phase, or
    • Single-phase (most are) and,
    • using larger amounts of electricity (25kWh or more/day) and,
    • you’re self-consuming 50% of that power or more through sunlight hours when your
      solar system is producing electricity.

Tip: You’ll find your daily usage in kWh’s on your electricity bill. Be sure to average it out over the whole year for an accurate indication, as usage can wildly differ from season to season.

It’s worth noting that a property with a 3-phase supply can export excess solar energy of up to 5kW per phase – which is three times the amount a single-phase property is allowed, so different design principals can apply. In most instances with feed-in tariffs of up to 17c currently available, bigger is better.

If you’re unsure about any of this stuff or just want to know more about your own personalset-up, click here to book in a phone chat. We’re more than happy to answer any burningquestions you may have

Here’s a bit more info on the solar export limit and how it can affect sizing:

The export limit in South East Queensland is set at 5kW per phase. This means that at any one time, your inverter must be programmed by your solar installer to only draw enough electricity from your solar panels to supply your house with what it’s consuming at that point in time, plus a maximum of 5kW which is then exported back to the grid.

Therefore, if a larger single-phase system (say a 12kW system) is installed on your roof, and you’re at work all day and consuming minimal electricity during sunlight hours, your 12kW solar system may only ever produce a little over 5kW max! This means your solar system has been grossly over-sized in relation to your individual needs, and your payback period will be lengthy.

3. Solar Budget and Hardware Selection

The final factor at play when deciding on the right size for your solar system, is your budget!

There’s lots of different hardware on the market and prices can wildly vary, so finding the sweet spot between the quality of the gear you want installed, and selecting the size of your solar system can take a bit of thought.

We’ve put some serious hours into selecting the best gear for our customers to satisfy a range of different price points.

It’s also important we make sure to work within the parameters of our customers personal budgets for solar, and deliver the best bang for their buck, whilst also delivering a quality product that will stand the test of time!

Ready to book a consultation and system design for your project? Click here to book a consultation.

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