The Difference Between Max Power at STC and Max Power at NOCT
We’re often asked the difference between Max Power at STC and Max Power at NOCT, which are figures you will find quoted on a solar panel’s spec sheet. This blog will define both Max Powers, the difference between the two, and why they’re important pieces of data you should consider when deciding on your solar panel of choice.
Max Power at STC
Max Power at STC means the maximum power of the panel when tested under Standard Test Conditions. (This is not to be confused with Small Technology Certificates, also known as STCs, which are government solar rebates.)
If you’ve read our previous blog on Power Tolerance, you’ll already know that Standard Test Conditions are the lab conditions solar panels are tested under:
- Irradiance (sunlight) of 1000W per square meter
- Cell temperature of 25°C (This is usually achieved with an air temperature of 0 to 2°C)
These test conditions simulate peak sunshine, zero cloud cover, a low air temperature to prevent solar panels from overheating, and a panel position that directly faces the sun. This is an ideal world for your panels but is not a good reflection on ‘real world’ conditions.
Max Power at STC is the number that both consumers and those within the solar industry refer to as the size of the solar panel. For example, a 327W SunPower solar panel has a Max Power at STC of 327W.
This nameplate value makes it easy for different panels and system sizes to be compared.
Max Power at NOCT
Max Power at NOCT is the Wattage that more realistically reflects the Max Power of your solar panel. NOCT stands for Nominal Operating Cell Temperature, and refers to testing conditions that are much closer to the real world conditions your solar panels will face every day:
- Irradiance (sunlight) of 800W per square meter
- Panel surface temperature of 45 (+/- 3) °C
- A wind speed of 1m/s
- Air temperature of 20°C
The Difference Between Max Power at STC and NOCT
Test conditions at NOCT have an irradiance 200W less than STC, take into account wind, and factor in higher ambient and panel temperatures. Max Power at NOCT reflects your panel’s performance in a more realistic environment, with cloud cover and hotter temperatures.
Looking at a panel’s Max Power at NOCT is a great way to help you choose between two panels of the same or similar STC Max Power. By choosing the panel with the highest NOCT Max Power, you’ll be choosing the panel that will perform better in Australian conditions.
Solar Panels at Infinite Energy
SunPower E20-327W Module
SunPower panels are designed to perform exceptionally well in the harshest of conditions, and are backed by industry leading warranties.
It should then come as no surprise that SunPower’s 327W panel has a Max Power of 243W NOCT, delivering an impressive 74% of its STC Max Power.
WINAICO WSP-310M6 PERC Module
Manufacturing some of the highest performing crystalline photovoltaic panels in the world, WINAICO products deliver incredible reliability and bang for buck.
WINAICO’s award-winning 310W panel has a NOCT Max Power of 230W, an equally remarkable 74% of its nominal STC Max Power.
WINAICO WST-280P6 PERC Module
WINAICO’s WST-280P6 PERC Module has a NOCT Max Power of 205W, 73% of its STC Max Power.
Canadian Solar CS6K-260|265|270|275W Modules
Boasting enhanced system reliability and more system power yield over its lifetime, Canadian Solar panels perform outstandingly well in Australian conditions. All panels in the CS6K series deliver NOCT Max Powers over 70% of their STC Max Powers.
| Max Power at STC | Max Power at NOCT | % |
| 260W | 189W | 73% |
| 265W | 192W | 72% |
| 270W | 196W | 73% |
| 275W | 199W | 72% |
The difference between Max Powers is one of the reasons it’s sometimes ideal to oversize your solar PV system. Installing 5kW of panels with a 5kW inverter may mean your inverter does not perform to its full rating. By overloading our panels, taking into account their Max Power at NOCT rating, you’re ensuring your inverter works at a higher average efficiency, making up for whatever power your panels are losing.
The Bottom Line
Max Power at NOCT is the maximum power of a panel when tested in harsher, more realistic conditions than STC Max Power. In a good quality panels, it’s between 70-75% of the STC Max Power, and at Infinite Energy we recommend not investing in solar panels with anything less.
While your solar panel spec sheet is a great place to start when choosing your solar panel brand, there are also many other important factors, including warranties and a significant Australian presence to consider.
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