Solar Panel Voc-MPPT?

Salvo wrote:
Is that a bunch of hot air, or are you going to provide analysis to prove your assertion? Talk is cheap! This isn't kindergarten.

I'll help you out. You'll need the following info for the analysis. Assume 95% efficiency for controller and cabling. Panel temperature is 75C. You'll have to calculate pwm current. It is NOT 6A.

Show me what you're capable of.

Sal

12thgenusa wrote:

Salvo wrote:
Careful when making a mppt to pwm comparison. Not only is mppt highly temperature dependent, but also battery voltage dependent. PWM can also be effected, but not as extreme.

For example, you got a mppt controller that outputs 100W. If battery voltage is 12.0V, charging current is:

I = P / V = 100W / 12.0V = 8.33A

If battery voltage rises to 14.0V, charging current is 7.14A, a 14.3% reduction.

Sal

OTH, assuming no losses from panel output to controller output, a 100W panel through a PWM controller will give you less than 6A all the time, 16% less than the MPPT at 14V and 28% less at 12 volts.

I just took the figures from your post that ignored everything except battery voltage. (8.33-6)/8.33=28% and (7.14-6)/7.14=16%. But you’re right, you wouldn’t probably get 6 amps through PWM, more like 5.5amps. Your own simple analysis shows that MPPT would produce much more even at 14 volts.

But since you insist:

Let's assume you have a 100w panel that produces 5.5 amps.
Let's assume you have a PWM controller that is 100% efficient.
Let's assume the wiring is 99% efficient.
Let's assume panel temp of 75C which degrades voltage and power to 80%

So for PWM you have:
5.5*.99 = 5.44 amps (all solar day long, well not quite. See below)

Let's assume a MPPT controller efficiency of 95%

So for MPPT you have:
100w*.8*.99*.95 = 75.24 watts (controller output)
@ 12 volts that is 6.27 amps (15% better than PWM)
The break-even point for amperage comparison is 75.24/5.44 = 13.83V.
However, at that battery voltage and with panel voltage degradation due to temp, the PWM will be struggling to contribute anything.

If you integrate the amperage curves over a whole solar day for both systems, the MPPT would win every time. Kindergarten indeed!