What Size Solar System Do I Need?

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Understanding the answer to the question 'What size solar system I should get?' should be a high priority if you’re looking at installing solar power. 

With the price of panels coming down, feed in tariff rates going up, and grid electricity going up in price in recent times, the answer might surprise you!  

Over the past year or two we've seen a trend with the majority of households opting for larger systems than just a standard 5kW inverter with 6.6kW of solar panels. In fact our average system size is now around 8.2kW. Now this might seem counter intuitive for those of you currently consuming well under that level of energy. The truth is that current market conditions and future energy demand projections for homes are encouraging many people to cover their roofs with as many panels as possible. 

In this blog I want to talk about value for money and why making a smart investment in solar power for your home is well worth your time and effort. 

Important Considerations
 

1. Your budget. 

How much can you afford to spend? 

2. How much energy your household uses.

People often assume they should calculate how much energy their household consumes, then purchase the smallest size system possible to match their energy consumption, thinking it will generate enough power to supply their demand. 

We can understand this line of thinking, because of course: who in their right mind wants to waste money on an oversized system?

A word of warning though - this can be an overly simplistic calculation, as rates of energy generation vary according to sunlight conditions and power usage at different times of the day and year, so if you match your solar system size to your energy consumption needs, (quite sensibly) thinking you are being economical, you are likely to be disappointed in the performance of your system and energy bill savings. The reality is the usual logic you would apply to other household purchases doesn't always stack up when it comes to solar systems, because there are a number of specific variables at play.

Solar Quotes have a handy guide to calculating your current energy consumption, which is a great starting point for discussing your solar needs with us at Goliath Solar & Electrical.

3. How soon do you want to see the return on your investment?

If you are planning on living in your house for the next 3 / 5 / 10 years, and you want to see your investment paid off sooner rather than later, the smaller sized systems may not serve you as well as a 6.6kW system or larger.

 
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3kW Solar Systems 

Assuming you've done your homework on your energy consumption and decided a 3kW system is adequate for your needs, without being under or oversized, we have a few pointers on why a quality 3kW system may not be the optimal value it appears to be. We actually feel these are expensive relative to the value a larger system offers.

Whilst the price of a 3kW system will certainly come in under a comparable 6.6kW system, it will not be 50% of the 6.6kW size price as you might expect. The main reasons for this are:

Cost of Inverter

Most 3kW inverters are only a couple of hundred dollars cheaper than a 5kW inverter, due to the fact that they are essentially the same - just with different programming and compliance stamps to cater to the energy load.

STCs / 'Rebate'

The more panels you install, the greater the STCs 'rebate' from the government, so a 6.6kW system obviously attracts a far greater $$ value 'rebate' than a 3kW system does. 

Installation Labour

Other than the inverter and solar panels, the other thing you are paying for is the installation service from our team. You might expect a 6.6kW system install would take twice as long as it does to install a 3kW system. But it doesn't! Regardless of what size system we install we still need to do the core work of setting up the switchboard and running the cables between the panels and the inverter.

So the extra time involved comes down to getting the extra panels on the roof, which for a 6.6kW system, can often be done in an extra couple of hours on the same day.  Also we employ all our own tradesmen and apprentices, NO SUB CONTRACTORS, so we pay our guys to be there for one day whether they are installing a 3kW, 6.6kW or 13kW solar system.

This sets us apart from other solar companies who sub contract out their work, and normally pay the installer per panel or per Watt they install, so their installation prices usually rise with the larger system installs. Therefore the additional costs you're looking at for a 6.6kW system installed by Goliath Solar are the extra panels & railings (which are mostly covered by STCs), plus the extra inverter cost.

In our opinion the wise thing to do is to put the largest system you can fit on your roof! 5kW inverter with 6.6kW of panels, 8.2kW inverter with 10.71kW of panels, and 10kW inverter with 13.23kW of panels are our most popular systems these days. 

 
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Most Common Size Solar System For An Average House

The most popular sized system we have been installing on single phase power homes in recent years is without a doubt the 6.6kW system.

Yet we still get queries all the time from folks whose thinking is 'Why would I pay for extra capacity to generate energy that my home won't use?'

A few years ago, when the feed-in tariff was as low as 6 cents, you would have been right to think this way, but with the current feed-in tariffs now sitting between 10 - 14 cents, it makes economic sense to invest in a larger system and feed your excess energy back into the grid. With current tariffs, an average SA home should pay off the extra investment cost of the 6.6kW system within a few years, and from there turn their energy production into profit.

The other thing I want to mention is it's far easier and cheaper to add more panels from the get go, rather than down the track. And our energy consumption is predicted to grow with the introduction of electric cars and home battery storage in the not to distant future. With battery technology coming in the next few years, you want to make sure you have enough power on your roof to charge that battery.

In our opinion the 6.6kW system (or larger) is far better value for the average home than a 3kW system, so long as your budget allows for it.  

 
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Fill Your Roof Now While Panels Are Cheap & Government Rebates Are High! Super Size Is Always Better

Single Phase Power Homes

In recent years many people have been tricked into thinking that a 5kW inverter with 6.6kW of panels was the maximum size allowed on single phase residential properties. The truth is that the maximum you can feed into the grid on single phase is 5kW. However you can actually install a 10kW inverter with 13.33kW of panels on a single phase home. This will help you in two ways:

1. You can use 5kW of power in your home and still feed in 5kW into the grid.

2. When you get a battery in a few years time you can feed 5kW into your battery, then 5kW into the grid.

Three Phase Power Homes

On three phase power homes you can go supersize and install a 30kW inverter with 39.9kW worth of panels, however you can only feed in 15kW to the grid at anyone time, so the same principle applies here:

1. You can use 15kW in your home and 15kW into the grid.

2. Or feed 15kW into your battery and feed 15kW into the grid.

Most people with three phase homes are now installing a 10kW inverter with 13.23kWw of panels, a 12.5kW inverter with 16.25kW of panels or a 15kW inverter with 18.9kW of solar panels.

If you have the space we would recommend installing a 20kW inverter with 25.83kW of panels!

As inverter technology improves, feed-in tariffs rise and customers begin future proofing their homes for battery storage and electric cars, the regulators have begun allowing these supersize systems to be installed. 

Whilst this makes sense in many cases, bear in mind the 10kW inverter limit for homes with single phase power, which is the most common type of phase throughout Adelaide. There is also a 33% oversize limit to how many panels we can install with any inverter. In practise this means we are only limited by your roof size and budget. Exciting times for renewables!

However, before you go bananas and super size your solar to the max, please reach out to our team for a chat. Pricing wise, there is always a tipping point where going above a certain size for your property may not be optimal economically. We will always do our best to talk you through the best solution for your property and budget, to help you get the most out of your investment now and set you up for your needs down the track.

To learn details specific to your property, please contact us.


 
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WRITTEN BY

Ben Gordon

Joining Goliath after 10 years as a team leader with Coca-Cola, Ben transitioned into solar sales and customer service, receiving great praise from our customers due to his honest nature.