200W vs 215W?

[yep]

HomeDepot has some deal on solar panel, and I'm in the market for a 200W-ish system. I wonder if there is any practical difference between 200W and 215W? Anything to consider?
200W
215W

 

[sunshine_eggo]

Slight size difference is consistent with a slight increase in power. With the same Imp (assuming Indonesia vs. Vietnam), they likely use the exact same cells, but the higher Vmp of the 215W indicates they have a few more cells in series for higher voltage/power.

These must be used on an MPPT controller to capture the additional 15W. If you use them on a PWM controller, they will perform identically.

7% more power for 4% more cost? Assuming the slight size difference isn't an issue, 215W is my choice.

 

[yep]

Actually this would be a more fair comparison in terms of cost 215W. However they add a PWM charger so it is not a good bundle.

Also it is confusing that 215W panel is slightly smaller... due to workmanship? Does it make sense...

 

[sunshine_eggo]

I would assume the size specs are swapped. The higher Vmp indicates more cells. That requires more space.

Missed the kit part of it. Sorry.

Complete waste of money to get the 215W. It will perform no better than the 200W due to the PWM controller. In fact, you'll never see more than 140W out of either due to the PWM controller. That's in perfect conditions at high noon, no clouds, panels perfectly perpendicular to the sun on the best day of the year for solar with at least 1000W/m^2 hitting the panels.

 

[yep]

Thanks for the note. Usually what can we get with MPPT controller in a perfect day?

 

[sunshine_eggo]

Thanks for the note. Usually what can we get with MPPT controller in a perfect day?

Panel rated power.

12V panels have an optimal power point. The Isc value above is the absolute maximum current you can possibly get from the panels if you short the leads. if you're operating at 12V or higher, you're going to be much closer to the Imp value.

Typical 12V battery peak voltage is 14.4V.

14.4V * 9.85A = 141.84W

An MPPT allows the panel to operate at the Vmp/Imp level and then uses a DC-DC converter to charge the battery with max power.

9.85A * 21.8V = 214.73W

214.73W / 14.4V = 14.9A, so the MPPT will reduce the voltage and increase the current to allow for maximum power delivery to the battery.

 

[yep]

understood. Thanks a lot!

 

[sunshine_eggo]

Caveat... there's always some losses somewhere even with MPPT. Hot panels produce less power; clouds, haze, dust, etc., all influence solar harvest.

It's just good to know where the STARTING theoretical max power is.