Can panels give you more power than rated?

[ThisBigRoadTrip]

I have 3 x 170w panels. They claim to be 8.9a rated each but sometimes I am getting 31+a from them. This has started recently when:
- In full sun
- At altitude, I have been over 2000m for the most part when this is happening. So, higher and cooler too.
- Now that I am closet to the equator, I am now further south than the tip of Baja, pretty much in line with Mexico City.

Here is the panel spec:

Solar cell type	Monocrystalline
Output power	170 W
Rated current	8.9 A
Rated DC voltage	19.1 V
Open-circuit voltage	22.5 V
Module efficiency	16.4%
Connectivity	MC4 connectors

Thoughts? Is the rating dependant on conditions? Are panels somewhat variable?

[jflorey2]

Thoughts? Is the rating dependant on conditions? Are panels somewhat variable?

Panels are rated at STC, which means "full" sea level sun and a panel temperature of 25C. High temperatures decrease the voltage a lot and increase current very slightly, so the net result is that high temps = lower power output. However, being above more atmosphere increases the solar flux. Add a few clouds near the sun and I could easily believe you are seeing higher than STC output.

[littleharbor]

Are your panels series wired into an MPPT controller? This will definitely give you increased amperage at altitude, in cooler conditions. while fluffy clouds float near the sun.

[ThisBigRoadTrip]

Ok, that makes sense. Temp is 21c and we are at 2,200m currently. Panel was tripping the 30a breaker we have between the panels and the controller. We have another 30a breaker between the controller and battery pack.

Our solar controller is a GoPower PWM rated for 30a. What happens if we get slightly over 30a coming in through that? Any idea?

[ThisBigRoadTrip]

Ignore that last comment. The GoPOwer controller is plated at 30 but rated to 37.5a.

".. The GP-PWM-30-UL is intended for use at 12 VDC system voltage and is rated for a maximum continuous DC input current of 37.5A and input voltage of 35VDC .."

Thanks for the replies.

[J.P.M.]

The short answer is yes. Cell current and power output are roughly proportional to POA (Plane Of Array) irradiance. there's more irradiance at higher altitude. Also, lower atmospheric temps will tend to decrease PV operating temps and so tend to increase power output.

Transmittance of solar radiation through the atmosphere increases (or more accurately is attenuated less) roughly inversely as atmospheric pressure which pressure decreases asymptotically with altitude above sea level. At 2 km and the same latitude, the global irradiance will be about 10 % more intense than at sea level, with a smaller portion of that irradiance being diffuse at altitude than at sea level due to less Rayleigh scattering at altitude. The intensity of the received irradiance will also increase as the solar zenith angle decreases in the summer. Some of the perceived increase you see above that 10 % will most likely be from less scattering of the shorter wavelengths as altitude increases. Reason: Current silicon based solar devices only use wavelengths below ~ 1.15 micrometers. If the shorter path length through the atmosphere results in less scattering of those shorter wavelengths (which is why clear the sky is blue BTW), that will also tend to increase PV device current and power in addition to the increased irradiance at altitude.

Lower PV device temps. will also tend to increase power production but that's because the device voltage will increase inversely as device temp. decreases. Countering that to some degree, the increased irradiance will tend to increase device temp. which will decrease device voltage either open circuit or operating voltage, as can be easily verified through an energy balance on the PV device.