I wanted to know what temperatures were typical for solar panels. Solar researchers developed a formula that the industry uses: Tcell=Tambient+G×(NOCT-20°C)/800Wm2. Where G is the irradiance at the instant when the ambient temperature is T_ambient. All calculations use °C and the results displayed using °F.
The formula provides the following chart of Tambient vs Tcell with G = 1000Wm2.
Although it’s well established that PWM and MPPT controllers produce virtually identical charging at higher temperatures and MPPT more at lower temperatures I wanted to graph the difference. The following chart is for the Grape Panel Model GS Star 180 W at 1000 Wm2 (SOC) and varying ambient temperatures. Tcell is used for the temperature coefficient calculations. The battery charging is for 14.8v and includes a 6% MPPT efficiency loss.
As posted above the PWM amps temperature % coefficient increase is much smaller than the MPPT power temperature % decrease. However, MPPT high ambient and cell temperature provides better charging (power and amps) because the PWM controller does not harvest any power above 14.8 V and the panel voltage, i.e. that power is lost which will be shown in the IR graph picture below. Notice that at 14.8V the PWM amps are about 9.6 A just little below Isc.
The vertical line on the IR graph is 14.8V or maximum charging voltage for a flooded battery. The power to the right of 14.8V is not harvested by a PWM controller unlike a MPPT controller. This accounts for the better MPPT charging across a wide range of ambient temperatures.
If you camp in the summer where temperatures can be 110 °F+ then consider a PWM controller. But it’s only that hot around noonish so your overall harvested charging may be less than MPPT.
OK I get it – PWM controllers cost less which is a factor. But 12V panels cost more for a given number of solar watts and take more square feet of space than 60 and 72 cell panels which are larger. Lots of variables and factors to consider. My 2014 costs for 3x 60 cell panels and a Morningstar MPPT 60 controller was the same as equivalent 12V panels and Morningstar PWM 60 controller. Your mileage may vary.
My search did not find a common 12V panel with both STC and NOCT specifications. If you know of one in the 150w range let me know and I’ll like to view the graphs for NOCT.
The formula provides the following chart of Tambient vs Tcell with G = 1000Wm2.
Although it’s well established that PWM and MPPT controllers produce virtually identical charging at higher temperatures and MPPT more at lower temperatures I wanted to graph the difference. The following chart is for the Grape Panel Model GS Star 180 W at 1000 Wm2 (SOC) and varying ambient temperatures. Tcell is used for the temperature coefficient calculations. The battery charging is for 14.8v and includes a 6% MPPT efficiency loss.
As posted above the PWM amps temperature % coefficient increase is much smaller than the MPPT power temperature % decrease. However, MPPT high ambient and cell temperature provides better charging (power and amps) because the PWM controller does not harvest any power above 14.8 V and the panel voltage, i.e. that power is lost which will be shown in the IR graph picture below. Notice that at 14.8V the PWM amps are about 9.6 A just little below Isc.
The vertical line on the IR graph is 14.8V or maximum charging voltage for a flooded battery. The power to the right of 14.8V is not harvested by a PWM controller unlike a MPPT controller. This accounts for the better MPPT charging across a wide range of ambient temperatures.
If you camp in the summer where temperatures can be 110 °F+ then consider a PWM controller. But it’s only that hot around noonish so your overall harvested charging may be less than MPPT.
OK I get it – PWM controllers cost less which is a factor. But 12V panels cost more for a given number of solar watts and take more square feet of space than 60 and 72 cell panels which are larger. Lots of variables and factors to consider. My 2014 costs for 3x 60 cell panels and a Morningstar MPPT 60 controller was the same as equivalent 12V panels and Morningstar PWM 60 controller. Your mileage may vary.
My search did not find a common 12V panel with both STC and NOCT specifications. If you know of one in the 150w range let me know and I’ll like to view the graphs for NOCT.
