Hot Solar Panel MPPT vs PWM Results

[BFL13]

This test is a follow-up to a bunch of earlier tests in various threads.

Background: last summer I got fewer amps to the battery than I expected with my MPPT and it turned out to be temperature related.
When PWM would have been 14.5a, I got 15.5a in the Spring, but only 13.5a in the Summer. I decided this year to see if I could get at least that 14.5a in the summer by using PWM, but that meant going to a 24v battery bank since I only have one 24v panel.

First tests with 230w panel same set-up as last year: (cool panel)
Reading: panel- batt, battv, amps to batt, controller output watts

24-12 MPPT 12.7, 14.97, 190w
24-24 MPPT 25.4, 7.95, 203w (like 15.9a at 12v)
24-24 PWM--25.5, 7.99, 204w (like 15.98a at 12v)

Today's tests with 255w panel (replaced the 230w) and hot panel same as last summer 25C ambient, 51C panel

24-12 MPPT 13.0, 15.85, 206w
24-24 MPPT 27.0, 7.95, 215w (like 15.9a at 12v)
24-24 PWM--27.0, 8.0, 216w (like 16a at 12v)

My 255w panel, if two 12s at 255w total, should get 255/130 x 8.2 = 16 amps at STC, so that 16 amps is my "standard" for comparison. Today, panel Isc was 9.20 amps and its rated Isc is 9.0, so insolation was up to STC and I should get the 16 amps with 12-12 PWM

I got 16 amps with the 24-24 PWM, so that works out. The MPPT results with the hot panel are much better than I got last summer, also being close to 16.

By comparison with that 13.5 I was getting with the 230w vs 14.5 PWM, today I would see 15 vs 16 but instead I got 15.9. I don't know what is different this year, but I'll take it 🙂

Where the hot vs cool panel shows up is comparing the cool 230's vs the hot 255's amps with MPPT.

24-24 MPPT cool 230 was at 15.9
24-24 MPPT hot 255 was at 15.9 (255/230 x 15.9 = 17.6, 1.73 more)

1.73/17.6 = 9.8% less than it 'should be' because it is hot (typical power loss at 50C panel compared with 25C panel is 10%)

However, since I am now getting the same with MPPT vs PWM instead of less like last summer (no idea why, could be several reasons) there is no point in going to 24v bank and use the PWM instead of 24-12 MPPT . So I am off the hook for that hassle if I was ever going to do that.

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EDIT: Trying to account for the difference from last year where now get "15.9 vs 15" as described above. I notice that the power temp coefficient for the 255w panel I have now is lower than the 230's used last year. This accounts for just some of the difference.

255's- 0.43%/C x 25 degrees = 10.75%
230's- 0.45%/C x 25 degrees = 11.25%

with the voltages only to a single decimal place, ratios are not accurate enough for doing this
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A curiosity:

Eco-Worthy MPPT controller-- with 24-12 the Demo amps are the same as panel Isc amps taken with the panel disconnected, so you can just take the Demo amps as your current Isc when estimating insolation.

But-- with 24-24, the Demo amps are less than measured panel Isc. EG panel 9.16 and Demo 8.02. So you can't go by the Demo amps for actual Isc in 24-24.

Meanwhile, in 24-24 the Solar30 amps would not go above 8.1 in the same situation with panel Isc at 9.22 (With 12-12 it does same amps as Isc)