4kW Solar System: Installation Costs, Power Outputs, and More

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A 4 kW solar system could generate 6380 kW of solar energy annually, saving you about $1900 per year. All that while only costing you roughly $4500 in installation and about 2 and a half years to pay off.

Oh, and did I mention that modern solar panels last for around 25 years? If all goes well, you’re looking at 22.5 years of free energy!

Pretty sweet deal, eh? Well, now that I have your attention, here’s everything you need to know about 4 kW solar systems. Below is a list of topics I’m covering. Feel free to skip sections if you want, but I recommend reading from the top.

How much does a 4kW solar system cost in Australia?

On average, the cost of a solar systems in Australia is about $1000 per kW. Every state has its own averages, of course. It’s better to get quotes from CEC-certified installers for accuracy, but here’s a list of averages per capital city for your reference.

City1 kW (in $)4 kW (in $)

Again, it’s important to note that the 4kW solar system price shown here isn’t set in stone. The actual cost of installation will still be dependent on numerous factors, including the components you choose, the complexity of the installation, and the installer’s quote.

How much power does a 4kW solar system produce?

There’s also no one answer to this question, as there are also numerous things that go into how much solar power your system can produce.

We have a separate article for that if you want to read more into it, but, in summary, this includes the orientation (angle and tilt) of your solar panels, their power ratings, where you install them, and day-to-day weather conditions.

Although, to answer the question of “how much electricity does a 4kW solar system produce per day?” I listed the estimated daily, monthly, and yearly outputs for each Australian capital city below.

Keep in mind that these numbers were computed using the PV Watts calculator under the following settings:

  • Roof pitch: 22.5%
  • Inverter efficiency: 96%
  • Quality and type of solar panels: Standard
  • Installation type: fixed, roof-mounted
CityPer Day (kWh)Per Month (kWh)Per Year (kWh)

For further reading: How much solar power can your system produce?

How many panels are in a 4kW solar system?

To accurately calculate this, you will need the power ratings of the solar panels you plan to install. You then divide your system size (4 kW or 4000 watts) by said power ratings. The answer is how many panels you’ll need.

For example, let’s say you choose to install Canadian Solar’s HiHero, which has a rated capacity of 445 watts (W).

  • number of solar panels = system size ÷ solar panel rated capacity
    • 4000 W ÷ 445 W
    • ~9 solar panels

If you intend to install the more affordable but lower-capacity solar panels, you’ll also need to install more of them. For example, let’s say you’re installing solar panels with rated capacities of only 300 watts.

  • number of solar panels = 4000 W ÷ 3000 W
    • ~13 solar panels

For further reading:

How much roof space would you need for a 4kW solar system?

On average, a residential solar panel will be 1.65m tall and 1m wide. However, every brand and model will have its own set of dimensions.

Moreover, how much roof space you need also depends on how many panels you’ll need to complete your 4kW solar system. Refer to the section above if you skipped it, but, in a nutshell, you’ll need fewer solar panels if you also choose ones that have higher-rated capacities.

For this discussion’s purposes, let’s assume you chose solar panels with average dimensions and a rated capacity of 445 W. That means you’ll need 9 of those panels to get to 4kW. This means you’ll also need 14.85 square meters of space. Here’s how that calculation went down:

  • Step 1: Calculate the area of one solar panel
    • Area = height x width
      • 1.65m×1m
      • 1.65 m2
  • Step 2: Multiply the area of the solar panels by how many of them you need
    • Required roof space = solar panel area x number of panels
      • 1.65 m2 x 9
      • 14.85 m2

The financial implications of a 4kW solar system

There are multiple layers to investing in a 4kW solar system. One is cost, which we’ve already covered, and the others are how much money you save, your return on investment (ROI), and your payback period.

As usual, we have articles dedicated to those conversations, but let’s talk briefly about them here.

How much money can you save with a 4kW solar power system?

The broad estimates below show the monthly and annual savings you could get with each capital city. However, do remember that how much money you save also depends on how much it costs to get your system installed, how much energy you consume, and the cost of electricity.

CityMonthly Savings ($)Annual Savings ($)

What about ROI and payback periods?

If your potential savings didn’t wow you, I bet the ROI will. Your payback period, or the length of time it takes you to fully payoff your 4kW solar power system, is also shorter than you’d expect.

But, you guessed it, both of these also depend on other things, namely your installation costs and savings. Here are some easy equations you can use:

  • ROI = (total savings ÷ total cost) x 100
  • Payback period = total cost ÷ annual savings

You can use the numbers listed above if you want an estimate, or you could check the table below.

CityROI (%)Payback Period (years)

Combined, that’s an average ROI of just over 1000% and a payback period of just 2 and a half years! In full disclosure, though, these computations are overly simplified and assume the most optimal of conditions.

Realistically, your numbers probably won’t be this high. Even in average, if not terrible, conditions, however, you’d still be looking at a payback period of around 6–10 years. That leaves you with about two decades of free solar energy. That’s a huge win by any standard.

Conclusion: Would your household benefit from a 4kW solar system?

I say absolutely, especially if you’re a small- to medium-sized family. If you can afford a higher-capacity system and it makes sense for you to do so, go for it! But if your computations led you to a 4kW solar system, that’s great, too.

Now, if you’re not sure, you can always ask, How much power does a 4kW solar system produce per day? Per month? Maybe even per year? Then cross-reference that number to your own consumption habits by checking your bill.

Still confused? No worries. You can always ask a professional. In that case, we have a network of pre-vetted solar installers that can give you 3 FREE quotes right away.