Solar Panel Voc-MPPT?

Salvo wrote:
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

You’ve made your point using extreme worst case scenario. Let’s try again with a more realistic example. The Kyocera panel you list has a max operating temp of 90C, and you chose 75C which would be on the high end of what the (or any) panel is capable of. Ktmrfs found in his tests that the panel temp rose to 46C. My panels for instance list 44.4C as the operating temperature. Your Kyocera example gives an operating temp of 45C. Let’s use 50C as a much closer representation of what one might expect in real life. We’ll use your 5.59A as benchmark PWM output.

25*.45% = 11.25% or 11.25 watts

100-11.25 = 88.75 watts from panel

88.75*.99*.95 = 83.47 watts to battery

83.47/12 = 6.96 amps to battery @ 12V (24.5% better than PWM)

83.47/5.59 = 14.93V break-even point (where PWM amps = MPPT amps if PWM amps are still that high; improbable and both would have moved to Abs before that point anyway)

Don’t think the surface charge story will work here.

Let’s take it a step further and find the break-even panel temp @ 14V output.

5.59*14 = 78.26 watts
78.26/(.99*.95) = 83.21 watts
100–83.21 = 16.79 watt loss
16.79/.45 = 37.3C temp rise over 25C standard
37.3+25 = 62.3C panel temp (144F) 17.3C over NOT

Do the same for 12V

5.59*12 = 67.08 watts
67.08/(.99*.95) = 71.32 watts
100–71.32 = 28.68 watt loss
28.68/.45 = 63.8C temp rise over 25C standard
63.8+25 = 88.8C panel temp (192F) 43.8C over NOT

MPPT simply out-performs PWM at any realistic panel temp. And even though MPPT amps decrease as battery voltage increases, it is still greater than PWM.

Your attempt to prove your point by using an extreme case falls short in real life use.