Solar Panel Voc-MPPT?
Wondering if there is any relationship between measured Voc and MPPT performance with a 24v panel. My 12v panel has a Voc rating of 21.9 and Isc of 8.2, but I often see 8.2ish when Voc is only 20....
Forum Discussion
Not bad, but improvements are necessary.
Looking at a Kyrocera 135W spec, I get numbers that reflects better for pwm.
135W Kyrocera
135W Kyrocera spec:
Isc = 7.63A
Ptc = -0.45%/C
A 100W panel has Isc= 5.65 A
PWM charging current is 5.65A * 0.99 = 5.59A
A 50C temp rise decreases power by: -0.45%/C * 50C = 22.5%. We now got a 77.5W panel.
Power to the battery is: 77.5W * 0.99 * 0.95 = 72.89W
At 12.0V, charging current is 72.89W / 12.0V = 6.07A
At 14.0V, charging current is 72.89W/ 14.0V = 5.21A
MPPT takes a 14% performance degradation when going from 12V to 14V.
The break even point is 13.04V
Due to battery surface charge, battery voltage quickly moves into the 13V region. Here mppt performs worse than pwm!
Your original projections are way off base.
BTW, my original analysis stated the mppt controller outputs 100W. You've modified the calculation by making the panel 100W, but that's ok. That's why I believed the pwm current is greater than 6A.
Sal
Looking at a Kyrocera 135W spec, I get numbers that reflects better for pwm.
135W Kyrocera
135W Kyrocera spec:
Isc = 7.63A
Ptc = -0.45%/C
A 100W panel has Isc= 5.65 A
PWM charging current is 5.65A * 0.99 = 5.59A
A 50C temp rise decreases power by: -0.45%/C * 50C = 22.5%. We now got a 77.5W panel.
Power to the battery is: 77.5W * 0.99 * 0.95 = 72.89W
At 12.0V, charging current is 72.89W / 12.0V = 6.07A
At 14.0V, charging current is 72.89W/ 14.0V = 5.21A
MPPT takes a 14% performance degradation when going from 12V to 14V.
The break even point is 13.04V
Due to battery surface charge, battery voltage quickly moves into the 13V region. Here mppt performs worse than pwm!
Your original projections are way off base.
BTW, my original analysis stated the mppt controller outputs 100W. You've modified the calculation by making the panel 100W, but that's ok. That's why I believed the pwm current is greater than 6A.
Sal
