MPPT Max Solar Input Power and Voltage

[rack04]

Quick question. Looking at the Renogy RVR40 MPPT solar charge controller I see that the specification states the max solar input voltage is 100v and the max solar input power at 12v is 520w. I assume both conditions have to be met and I couldn't put four (4) 200w panels in series with a VOC of 24.2v since 800w exceeds 520w. Is that correct?

 

[Bud Martin]

24.2V VOC x 4 = 96.8V (way too close to the limit), then you factor in 20% for cold weather condition = 116V, so 4 panels in series should not be used, I suggest 2S2P.
As for power, the SCC should throttler down the power and limit it to 520W.

 

[rack04]

24.2V VOC x 4 = 96.8V (way too close to the limit), then you factor in 20% for cold weather condition = 116V, so 4 panels in series should not be used, I suggest 2S2P.
As for power, the SCC should throttler down the power and limit it to 520W.

So the business case for investing more in a 800w array is as follows? A 800w array in 100% sun (perfect conditions) will be limited to 520w by the MPPT. A 800w array in 50% sun will pull in 520w (hypothetical) while a 520w array (sized for the MPPT) will pull in 300w.

 

[Bud Martin]

The reason you over panel is to be able to get the most power as possible when the sun condition is not perfect, I.E. in winter time or cloudy day.

 

[MichaelK]

A good rule of thumb is you almost never see rated output from a panel, mostly from what Bud mentions above, but also because the panels are tested in temperature controlled conditions, and in the hot sun, panel voltage goes down.

For perfectly aligned panels expect 85%.
For panels at a acute angle, say 8am sun on south facing panels, expect 10%.
For panels laying flat on a roof, maybe 60%.

So, to get an honest 520W of power, you'll need 520W/.85% = 612W of panels. Adjust those numbers accordingly for panel orientation.