A Complete Guide to Purchasing a 6.6kW Solar System


6.6kW solar systems have become a common sight on the rooftops of busy Australian households. This is due to several factors, including their cost-effectiveness, ample size, ease of approval for grid connection, plummeting costs of solar energy products, decent subsidy and feed-in tariffs. This article will take you through 6.6kW solar panels costs, energy production, payback period and nearly everything you need to know about 6.6kW solar power systems.

6.6kW Solar Systems in Australia: A Summary

6.6kW solar system is an affordable way to produce your endless supply of clean energy through the sun. As the solar systems in Australia are becoming progressively affordable, the average size of solar systems keeps increasing. This means Australians are getting really quick returns on their solar investments and slashing money on their power bills thanks to generous amounts of sunshine, low solar panel installation costs, financial incentives and tariffs. A 6.6kW solar system package usually comprises 18-24 CEC approved solar panels, a 5kW solar inverter, roof mounting and electrical kit approved for Australia.

Do you need a 6kW or 6.6kW solar system?

If we use 370W panels to make a 6kW solar system, it would require 16 solar modules, which is a little under 6kW. Based on the installation location, array orientation and component quality, a 6kW PV system produces 24kWh of electricity per day. A professionally installed excellent-quality 6kW solar power system costs $5,000-$9,000. You should be able to pay off its initial costs in 4-5 years, assuming a good installation and a significant level of energy self-consumption.

Recently, 6kW systems have grown in popularity, although thinking a little bigger and installing a 6.6kW solar system would be a smart choice. Here’s why:

  • There is hardly a slight difference between the pricing, including installation costs, while the 6.6kW system provides an extra 0.600kWh to the mix.
  • Going for the slightly bigger 6.6kW system will enable you to get more STCs compared to the 6kW system. For example, a customer in Western Shore, Tasmania will receive 78 STCs for a 6kW system. On the contrary, the same customer would receive as much as 86 STCs for a 6.6kW solar power system.
  • Although the 6kW system has a shorter payback period, it hugely depends on your energy consumption numbers like the ratio between solar energy self-consumption vs. energy coming from the grid. And a 6.6kW solar system would ensure that you have enough power to self-consume in the daytime.

Going over 6.66 kilowatts: why not even larger?

Apart from the rooftop space constraints, there are limitations around the 6.66kW solar system for homes with single-phase connection. Most Australian homes have single-phase power and installation guidelines by Distributed Network Service Provider (DNSP) normally allow for a maximum inverter capacity of 5 kilowatts. Installation guidelines also allow only 133% oversize of the panel’s capacity against 5kW of inverter capacity.

This means 5kW x 133% = 6.65kW is the maximum system capacity for 5kW solar inverter capacity.  While you may not get the system exactly 6.65kW in size, you can aim for as close to it as possible, but not more than that, to comply with the approved oversizing limits.

Close to 6.66 kilowatts is often practical

Considering the number of panels that can be installed on a typical rooftop, people’s budget and what they expect from their solar systems, installing a system close to 6.66kW seems the most practical option. You can choose the number of solar panels to install depending on the wattages of power they produce, which ranges between 250 watts to 400 watts.

Most solar power systems these days comprise panels with 260W to 310W of output capacity. Those panels with higher capacity than this are often larger 72 cell panels that are scarcely used in residential roofs. Although if you are ready to pay for premium quality solar panels, you can get high capacity 60 cell solar panels that produce 360 watts of power.

Best solar panel wattage for maximum system output

Considering the solar panels ranging from 260W to 310W, there are mainly three best wattages to get as close to 6.66kW as possible:

  • 265 watts — maximum capacity 6.625kW
  • 275 watts — maximum capacity 6.6kW
  • 300 watts — maximum capacity 6.6kW

If you want to go for 6.6 kilowatts precisely, you will need 370W panels, as 18 of them will make a 6.6kW system.

While it makes sense to get close to 6.66 kilowatts, you don’t need to stress out over a couple of hundred watts. Paying a little more for a little more capacity may be worthwhile, but if your installer cannot achieve optimal solar panel wattage for you, it doesn’t make much sense to pay a great deal for them.

Is a 6.6kW solar system the right choice for your needs?

The primary measure to use while selecting the right solar system size for your home has to be your current daily energy consumption. You can readily access this information from your recent quarterly power bill.

  • Your household’s power consumption

Some people prefer sufficient renewable energy with which they can afford to reduce their electrical bills and contribute to the green initiative. If you are from this category, then a 6.6kW solar system could be the best size for you.

A 6.6kW solar power system can be the right choice for your household if your average daily power consumption is between 22 and 28kWh. To maximise the return on your solar power system, you must audit your current electricity consumption habits. Once you identify activities that consume a significant amount of electricity, action a plan to ensure you conduct these activities when the sun is out.

  • Location

If you live in zones with above-average and all-year-round sun radiation, higher wattage of the solar system would make more sense. The favourable weather will not only make the system cheaper to install, but will also give better returns with surplus energy for export.

For instance, if your average daily power consumption is about 10kWh per day, a 6.6kW solar system in Brisbane can yield you an extra 17kWh of energy for selling back to the grid. Though small, feed-in-tariff rates of about 8c per kWh will help you recoup the installation charges.

How much roof space is required for a 6.6kW solar power system?

A typical 370-watt panel measures approximately 1.8 meters x 1 meter. So, the installation of 18 such solar panels will require an area of over 32 m2. You may require more space depending on how your roof is laid out and whether you will need tilt frames. Because tilt frames need to be more spaced out than solar panels flush-mounted on the rooftop.

1.   Oversizing solar systems

The installation of solar panel capacity greater than the inverter capacity is known as oversizing. It is rather normal these days, totally safe and doesn’t harm the inverter. As Australia’s solar rebate is based on panel capacity rather than inverter size, you can extract the best level of incentive possible.

2.   6.6kW solar power systems with 5kW inverter and not 6kW inverter

The first obvious reason could be that a 5kW inverter is cheaper than a 6kW inverter. Apart from that, solar panels rarely produce as much energy as their rated capacity for many reasons. Heat in warm climate regions is one of the many factors that lessen solar panel efficiency. Most solar panels will lose 10% of their power rating on a day with 25°C temperature and more if it is hotter.

The dirt and grime on the panels and wiring losses are some other factors that also affect the output of solar panels. So, by installing a 5kW inverter with a 6.6kW solar system, you will ensure your inverter is working at its designed performance level for most of the time.

Another important reason for installing a 5kW inverter is, 6.6kW solar panel system is legally the maximum size you can put on a 5kW solar system. Installing a bigger inverter or a second inverter will drive up the price, making it hard for obtaining a high turnover. 

Your solar power system can’t produce its total capacity for the number of factors mentioned above, not to mention the site-specific factors like panel orientation. That’s why a 5kW system on a 5kW inverter generates less than a 6.6kW solar system on a 5kW inverter, while the cost difference is not much if you consider STCs.

3.   6.6kW solar system price

In Australia, the average retail price of a mid-range quality installation of a standard PV system is slightly under $1 per watt, after taking into account the federal government solar rebates. This means a 6.6kW solar system will cost you around $5,510 on average, significantly less than what it would have been a few years ago. However, solar system prices vary depending on the quality of products offered. A 6.6kW solar PV system from a cheap brand is made of low-end products and will cost much less, while premium-quality offerings will be costlier.

You may want to buy a cheaper system with low-end components, which will save you money on the initial outlay. But you will most probably spend the money you saved many times over on expensive repairs due to short equipment lifespans. So, it is recommended that you invest in a good-quality solar system, because anyway, government subsidies will significantly reduce the initial cost—by $3,250 for a 6.6kW solar system.

4.   How much electricity can you expect to generate from a 6.6kW solar system?

The amount of solar energy produced by a solar system varies depending on the location they are installed and other such factors. For instance, a 6.6kW solar system installed in Hobart will produce an average of 22kWh of electricity per day, while the same system will produce 27kWh per day in Brisbane. On average, you can expect your 6.6kW solar power system to generate 24kWh per day. 

A range of factors that can influence the total power production from solar power systems includes:

  • Number of peak sunlight hours
  • Shading
  • Temperature extremes
  • Panel orientation and tilt
  • Solar system quality
  • Inverter setup and efficiency
  • Panel maintenance

5.   How long is the payback period on a 6.6kW solar system?

The criterion by which most solar consumers measure their panel’s performance is the payback period, which is the number of years the system takes to pay for itself through power bill savings and feed-in-tariff credits. The results, however, depend on how efficiently you utilise the solar energy being produced from your system and how much you get for the unused excess solar power you sell back to the grid according to the feed-in-tariff agreement you have in place with your electricity retailer.

A good-quality 6.6kW solar system will allow you to pay back your solar investment in less than 4 years. Now, let’s say you installed a 6.6kW solar power system for your home in Brisbane, which cost you $4,860. You are paying 21c per kWh of electricity from the grid and your retailer is paying 5c per kWh energy exported. Assuming you are self-consuming 50% of the solar energy generated, you will pay off the 6.6kW solar system price in 3.4 years with a 30% internal rate of return (IRR).

6.       Do you need battery backup?

Solar power systems can only generate energy during daylight hours. Adding a battery backup can offer significant benefits. You can store solar power for night-time use and you don’t have to pay peak rates for electricity. However, its relatively high costs stretch the payback period to about 10 years. Battery storage for 6.6kW solar power systems usually cost $1,300-$2,000 per kWh. So, if you go for a 13kWh premium-quality lithium battery, you pay at least $10,000.

ConclusionWith a 6.6kW solar system, you can generate enough electricity to reduce your power bills to zero. So, you no longer have to worry about the rising electricity prices when you’ve got a lot of visitors who need lengthy hot showers or prefer running AC all day during hot weather.

Author: Harsh Patel

Date: August 13, 2021


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