Why the 6.6 kW Solar System Size is Optimal

Australia’s Renewable Energy Target established the Solar Credits program as an incentive for individuals to install solar energy systems on their houses. This initiative provides renewable energy certificates (RECs) for every megawatt hour of energy generation. Small Scale Technology Certificates (STCs) are calculated based on the solar system’s size, the state or territory where it is installed, and the deeming period of the STCs. The result of these initiatives is a high demand for solar energy systems in Australia and a quest to find the optimal size to maximise energy efficiency and cost effectiveness.

Why Bigger is Better

Solar power systems are getting progressively bigger. Just five years ago, most buyers were choosing 3kW solar systems. However, the current trend is toward 6.6 kw solar system size. Selecting the optimal size for your needs depends on your budget, available space on the roof, amount of electricity use, and future energy plans. If you have the space and budget, bigger is better for several reasons.

  • Solar power systems are declining in cost, making larger systems more affordable.
  • The government offers more small-scale technology certificates (STCs) for more panels.
  • Larger solar sytems are needed for adding battery charging; 6.6kW is ideal.
  • Economies of scale result from the labour costs required in installing the unit. A 6.6kW unit will not cost much more to install than a 3kW system.
  • Larger systems generate higher feed-in tariffs (rebates from excess energy sent to the grid).
  • The larger the system, the lower the price per kilowatt. For example, in Sydney a 3kW system costs $4,223 and a 5kW system costs $5,538. Per kilowatt, you pay $1,407 for the 3kW system and the additional 2kW are only $657.
  • Additional kilowatts offer fast payback. With the price per kilowatt of $657 and a feed-in tariff of approximately 11.1c per kilowatt hour of energy sent to the grid, it will take just 4 years to recoup the cost of the additional 2kW. If you consume all the solar power yourself instead of exporting excess to the grid, you will recoup the money even quicker.

Benefits of a 6.6kW System

Solar suppliers and customers today have realised that 6.6kW of solar panels on the roof provide a better value when paired with a 5kW inverter. This is in compliance with the Clean Energy Council guidelines and network distributors. Legally, you can oversize your solar power system by 133%, enabling 6.6kW of solar panels with a 5kW capacity inverter (5kWx133%=6.6kW). This provides a number of benefits.

  • STCs are maximised without upgrading the inverter to 6kW. This saves money upfront and lowers the cost per watt of your system.
  • There is a wider selection of 5kW inverters available on the market than 6kW inverters.
  • Certain network distributors will not allow an inverter over 5kW.
  • 6kW is a great overall size solar system for supplying battery power for electric vehicles.

Specifics of a 6.6kW System

Once you realise the benefits of a 6.6kW system, you will want to opt for that size to handle your current energy needs and any upsizing or additions you plan for the future. Here are some specifics about a 6.6kW system.

  • How many panels do I need? While solar panels range in output, you’ll generally find 300-400 watts per panel. The total of all the panels determines the cumulative size of a solar system. If one panel contains 330w, you will need 20 to comprise a 6.6kW system.
  • How much space will the panels need? Household solar panels have a standard dimension of 1.70m x 1.00m. With 15-20 panels (depending on the wattage output you choose), you’ll need approximately 25.5-34 square metres of roof space to house the panels.
  • How much power will it generate? The solar system generates electricity during the daylight hours. This power is first fed into the home. You will save the most money by utilising the power straight from your system. Excess electricity not consumed in your household is sent to the grid. The power retailer will provide you a credit (feed-in tariff) for this excess energy.
  • How much does a 6.6kW system cost? Generally, you should expect to pay from $800-$1200 per kW in Australia. A high-quality solar system of this size should cost $5,000-$9,000, installed.

Ultimately, there are multiple factors to consider when determining the best solar system for your needs. Keep in mind that this investment is for the long-term and that the money you save over time will far outweigh the initial cost of installation.

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