MPPT “overclocking”

[Solar_Mann]

Question. A "40 Amp" solar controller might show "520 Watts" output in the specs. 520 W would be 40 amps at 13 V. Is such a controller limited to 40 amps or 520 W when the battery voltage hits, say, 14.0 volts on the way to being fully charged? A 40 amp rating would suggest 560 W at 14.0 V. A 520 W rating would suggest 37.1 amps at 14.0 volts. Which is it? I've never loaded my solar controller high enough to see it limit.

My instinct is that that 40 amps is the determining specification. Any other thoughts?

Another question, it seems that the input clipping should occur when the input power is higher than the output power by the amount of the losses. I.e., for 96% efficiency, clipping should start at 542 W with 520 W output (520/0.96).

This may seem like splitting hairs, but it looms significant when looking at "over paneling."

Not sure about all brands but EPever it is 40amp limit no matter voltage.

 

[hclarkx]

Not sure about all brands but EPever it is 40amp limit no matter voltage.

Thank You. My brand indeed is Epever, the Tracer BN series. I have three of them. This was the confirmation I was hoping for. My 40 amp unit then should be good for up around 560 Watts output (toward the end of the bulk charge stage in my situation) and 560/0.96 or 583 Watts input given that the ~4% losses are covered by the power input. As such, 800W of panels is only 37% above output rating.

Using 37% and comparing that with a "fully rated" solar converter (array Wattage matches controller) provides the following results in PVWatts. The maximum monthly wasted potential energy is 5% at this particular location (Central California Coast). Of course, most of that occurs on the best sun days when clipping is greatest. So an average of 5% for the month might be 10% on the 15 best days.



It's interesting that in winter production is actually higher with the smaller solar controller/inverter. The simulation does take into account a typical inverter loss profile so the smaller inverter may be operating in a more efficient range in winter.

 

[Solar_Mann]

I have 2 tracer 40amp units. One running 800watts @12v and the other 1300 watts @24v

 

[MichaelK]

I'm considering this too.
Have a photo by chance?

The first pic is of my first-generation, V1.5 design. Each of the five arrays holds three 300W panels. My latest V4.0 design is shown in pic two and three. Pic two is the bare frame to let you see the construction, and pic three is with four 250W panels. If I had rotated the panels horizontally, I could have mounted six panels, but I sort of fixed on 120VDC, so I put up just four. Now the five V1.5 arrays are positioned on the east side of my home, but the V4.0 version is on the west side. This array faces due West to harvest late afternoon sun, up to about 6pm.

 

[eprotiva]

in the grid tie biz they call it "over dimensioning" the solar