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--- electrical:solar:output [2025/04/05 18:25]
frater_secessus [panel temperature]
+++ electrical:solar:output [2025/06/18 22:30] (current)
frater_secessus [panel temperature]
@@ Line 51: / Line 51: @@
 ===== panel temperature =====
-Solar panel voltage((and therefore output on MPPT controllers)) varies as cell temperature goes up (in the sun) or down (in very cold ambients).
+Cell temperature affects the voltage part of the panel's I/V curve; warmer temps drive voltages down and very cold temperatures drive it up.  This is why Voc+20% or similar rules of thumb are used when assessing how much voltage "headroom" the solar charge controller has -- a cold snap could, for example, put a 48Voc rated array over a 50v controller input limit.
+For this reason the array's real-world Vmp is rarely the Vmp given on the lab rating.  It doesn't matter much to PWM but you will observe your MPPT finding a Vmp that does not match rated Vmp.  And since with MPPT ''Vmp * Imp = Mpp'' lower Vmp means lower harvest.  Hence the panel mounting airgap;  it allows cooling airflow underneath.
+==== high cell temperatures ====
-Usually the problem is increased cell temperature which drives down panel output.  This is the main reason panels are mounted with an airgap;  it allows cooling airflow underneath.
 The data below, derived from [[http://digivation.com.au/solar/tempderate.php|this calculator]], show power from a 100W mono/poly panel dropping off as ambient temps rise:
@@ Line 72: / Line 76: @@
 So a [[camping:snowbirding|snowbird]] who "chases 60" will be losing ~10% of panel output during the warmest part of the day.  Snowbirds chasing 70 will be losing ~13% of panel output.
-Note:  sub-freezing temperatures can push Voc/Vmp above their rated values.  If you will use solar in sub-freezing conditions leave plenty Voc headroom in your solar charge controller spec. +20% margin is traditional.
 Note: that [[hvac:insulation#heat_from_solar_panels|radiated heat from the underside of panels can raise temperatures inside the camper]].
+==== low cell temperatures ====
+Sub-freezing temperatures can push Voc/Vmp above their rated values.  If you will use solar in sub-freezing conditions leave plenty of Voc headroom in your solar charge controller spec. +20% margin is traditional.

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