How much solar power should my new system produce?

by | Jun 29, 2021 | Solar 101 | 0 comments

This week’s blog post is inspired by a recent callout I received, and a part of solar world that’s sometimes not known or understood.

I received a called from Jason. He’d had recently had a new 6.6kW solar system installed at his property and was worried that his system wasn’t performing as expected. Luckily, we were able to pick up on the reason why before attending the callout 😉

I ran through the numbers with Jason over the phone. His solar system is East/West facing without any shading issues and comprises of 6.6kW worth of panels, yet his system is only peaking at a little under 4500W… So, what was the problem? Why wasn’t Jason’s new solar system reaching its rated power output of 6600 watts?

A common misconception in the solar industry is that your system will produce its maximum power rating at peak times. In Jason’s case, 20 x 330W panels equals 6600W. If you’ve had solar salesmen tell you your system will frequently reach these numbers at peak times, run…

The rating of each solar panel indicates the amount of power it could possibly produce under perfect conditions. But in reality, it’s impossible to hit these numbers.

Here’s Why:

In the real world there’s a variety of factors that impact a systems overall energy yield. The six main reasons are:

  • Solar panel efficiency losses – Each panel comes with a ‘power tolerance’ loss of around about 1% of its potential yield

 

  • Temperature losses: This one’s hefty, contributing to around 10% of expected system losses

 

  • Dirt Derating Factors – Yep, even the thin film of dirt and dust that magically appears on your panels a day after installing them has a detrimental effect. Around 5% on average. Birds and bats aren’t great for them either…

 

  • Wiring Losses – The wiring between your solar panels and your solar inverter also play a role in panel power loss. Due to the resistance in the wires, you’ll lose around 2% in voltage drop which in in turn effects your power output.

 

  • Inverter Efficiency – The process of inverting the DC electricity created by your solar panels into usable AC power comes at a small cost. Around the 4% mark generally, depending on the inverter brand and its specifications.

 

  • Panel Pitch and Azimuth – Panels aimed a little west of true north, and at a pitch of 27 degrees from flat (in South East Queensland) are spot on, and you’ll lose very little power. Finding a roof with these specs is as rare as hens’ teeth though, and you notice any variance to this will result in some loss depending on the angle and pitch of the roof.

 

So, looking at Jason’s solar we can actually calculate using the above percentage losses the amount of power the system is expected to generate at peak times.

Starting with 6600W of generated electricity, we’ll see pretty close to the numbers in the chart at the top of this article.

You’ll also notice once you start to dig a little deeper, that the majority of 6.6kW solar systems are packaged up with a 5kW inverter. Our good friends at Energex allow us to over-size our inverters by up to one third. Which is great, as we can reach higher production earlier and later in the day. Plus, as you’ll see in the above de-rating diagram, it’s rare our systems will ever peak much over the inverter’s rating in any case, so it makes sense.

After running through the numbers with Jason, he was satisfied that his solar system was working as it should, and he’s enjoying the huge reduction in his bills each quarter.

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When designing and quoting solar installations through South East Queensland, it’s important to make sure all elements are factored in when calculating expected yields and payback periods for our customers.

Not only should the system de-rating factors be calculated, but other (very important) aspects of design should be considered as well, including:

  • Possible shading issues now and in the future (we can calculate this too – ask us how)

 

  • Which electricity retailer is the best fit for each individual client (hint: the plan with the highest solar feed-in tariff isn’t always the best fit)

 

  • The power consumption habits of each individual client

 

  • Recommended system sizing – relative to expected solar system production and power consumption habits, as well as factoring in Energex solar export limitations.

The whole thing can be confusing, especially when you first start looking into solar. Don’t worry though, we’ve got your back!

Trav and I have spent a lot of time making sure we get the very best solution for each of our clients. We take into consideration all the above factors and more. And the best bit? We’re only a click away!

If you have any questions or you’re ready to see what you can save with a new system at your place, with actual, carefully considered data – click this link and we’ll get you started.

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