One of the biggest misconceptions people have when sizing up a solar system is to think that a 5kW solar system will produce 5kW of power at any one time.
The reality is a 5kW system will output a bit less than that, with ‘peak output’ on a good day being somewhere between 4kW and 4.7kW during the middle of the day, and a less in the morning and afternoon:
Peak output can also vary depending on what angle your panels are installed.
A system installed on a flat roof will perform better in summer and worse in winter compared to the average, whereas a system installed on a steeper roof will perform better in winter because the panels will be tilted towards the lower winter sun.
A system installed on a steep roof or with tilt frames can actually reach a higher peak-output in winter compared to summer.
Peak output will always be less than the panel’s rating because a panel’s rating is based on its performance in ‘flash test’ in a testing laboratory where conditions are perfect. In the real world, there are a whole number of factors that slightly reduce a panel’s output such as the angle of the panel in relation to the sun (the time of year), the time of day, the weather including pollution or haze in the air, the temperature (heat actually reduces efficiency), patchy shade, and dirty panels.
Furthermore, the output from a panel is reduced by efficiency loss as it is converted from DC to AC by the inverter. Most inverters have an efficiency of around 97% or so, but already that takes output in perfect conditions from 5kW down to 4.85kW.
So why doesn’t any of this matter?
Because with solar we want the daily output to cover most of your household’s energy usage, which means we size up a solar system based on a system’s daily output, not the peak output.
A solar system in Sydney will output around 4 times its size, so a 10kW system will output around 40kWh on an average day. But there are large variations based on the weather and the time of year, so it is a matter of getting it right most of the time, and by using averages to roughly work out what will be a good fit.
Here is an example of output across a day with morning shade, illustrating how real-world output varies significantly. On this day the peak output of our 5kW system was only 4.06kW, however, the system produced 24.2kWh of power across the day, significantly higher than the Clean Energy Council’s guideline for a solar system’s output in Sydney, which is 19.7kWh:
Sizing Up The Solar System
Once we understand the output curve of a solar system, we can then try to size up a solar system so that you use most of the solar power over the course of the day to maximise the benefit of the system.
Most households will use more power than the solar system generates early in the morning and later in the afternoon, and a lot less than what the solar system outputs during the middle of the day. We expect most households will be able to use up to around 70% of the solar power in the home as it is produced, although many households do a lot better than this.
Having installed thousands of smart solar systems with online monitoring, we now have a very clear picture of how households tend to use electricity:
- The baseload: fridges, freezers, lights, fish tanks and anything else left running most of the time
- Daily usage: pool pumps, air conditioning, appliances such as the dishwasher, washing machine etc.
- Peaks: the toaster, hairdryer, heat lamps in the bathroom, a big air conditioner turning on
Typically when sizing up a solar system, we try to cover all of the baseload, plus as much of your daily usage as is practical/affordable.
The big spikes in power usage won’t be covered by the solar system as it just isn’t worth it. As an example, doubling the size of your solar system to cover a 10-minute spike of power usage from the bathroom heat lamps doesn’t make financial sense.
The other factor to all of this is managing when you use your power.
Once you have the solar installed, running appliances during the day will help you use more of the solar power as it peaks during the middle of the day. This can be done by using a timer, especially with the air conditioner and pool pumps.
By spending just a little bit of effort managing your power usage, you can save a lot of money on your power bill, especially now with smart solar systems where you get such detailed insights into your power usage and the system’s output.
Installing A Larger Solar System
If you are worried that you will use a lot more power than what the solar system generates, the answer is of course to install a few extra panels. Solar panels are so cheap these days, getting a slightly larger system than what you need is common practice, especially because the government incentive is based on the size of your system, so the more panels you install the more money you get back as a part of the STC program.
So, for example, if you want to aim peak output of 5kW to cover your household’s peak energy usage, the answer is to simply install a larger system, such as a 6kW system rather than a 5kW system. The price to oversize the system is a lot less than what most people expect.
Installing a larger system will mean most of your home’s energy usage will be powered by the solar system, but more power will potentially be sent back to the grid if it isn’t used as it is generated.
This isn’t such a bad result these days, because feed-in tariffs in NSW are now up around 20 cents per kW with many energy retailers. We now have many customers getting their quarterly power bills down to well under $100 thanks to an oversized solar system, or even in credit:
Interested in more information on sizing up a system? Detailed info is available here: How to Size Up A Solar System, or call the Solaray Team today on 1300 221 586.
Battery Storage Is Changing The Ballgame
The big game-changer this year is battery storage, the number of households installing storage has skyrocketed compared to even just two years ago.
We are now able to install battery storage to capture any excess solar power for you to then use in the evening. We leave you connected to the grid so you can use the grid it as a backup, however, we now have many customers essentially running on solar power 24/7.
More information on battery storage is available here: The price of solar storage
The Smart Solar & Storage Experts
The Solaray Team can help you accurately size up a solar system based on what you want to achieve, whether it be a fast return on your money, minimising your power bills, or just doing your bit for the planet. For personalised advice and pricing, please contact us today. We’d love to hear from you.