De-rating the 230w

That'll Learn Ya ! :)

That sounds like a great panel. Could you PM a where to buy link?

I hear occasional squealing but so far no piggy bank. That is one crafty little dude.

Mex

I don't even know if SchottPolys are still around. I'd love to find two more in place of the three mono panels I have.

I knew better than to test the Isc in those conditions. Normal conditions produce over 9a.

Thanks for that test. I am surprised it took that big of a cell covering to get the Voc down, but at least the idea works.

My 230w Hanwha panel has an Isc of 8.3a which it does in full sun if not 8.4 Voc rides around 34v of its 36.8Voc as soon as the sun gets on it, it warms up fast, which drops the Voc. I see solarblvd has a Hanwha 235 going for $160! Mine cost me $260 last year up here :(

I still don't know if the Isc of a 24v panel like that has any meaning at all for what amps you get with the buck MPPT controller.
I am suspecting the Isc has nothing to do with it, and it is all about the wattage at the controller output divided by the battery voltage.

OTOH, the 12v panel gets Isc in full sun and you can use Isc as your "expected amps" with the usual PWM controller.

I went looking for Schottpoly panels and they are discontinued. The few I found were over $500 except for a scratch and dent at $251, and it had different specs than mine did.

I would imaging any 230w poly panel will be close to the same for far less money.

JiminDenver wrote:
I hauled the 230w Schottpoly out to see if I could tone down the voltage by turning it or partially shading it.

How many cells 60? Have you looked at rewiring the cells to have half in parallel with the other half?



Not sure how to best incorporate the bypass diodes. Looks like you clip the left middle connection and bring wire to the other end.

Give Vmp of 15 volts.... might be a little low or might be perfect with PWM.

I'd be happy to do it to the Canadian solar 220w as long as it was reversible. I am assuming it would just be moving the wires around in the junction box. That's going to drop the Voc of that panel down to 17v or so in bright light. Will that be enough for bucking? Would it even convert the panel for use as a PWM system?

On edit, neither easy or reversible. Too bad too because it accrued to me it could be a way to mate a cheap PWM controller to a cheap 24v panel. Halving the Voc would mean halving the working voltage too, right? That would be dropping below 15v for the 220w.

I only want to derate my 230w for a test of a buck gizmo that has an intake limit of 32v with maybe fry it at 36v. Panel Voc is 36.8 but rides at 34v once out in the sun. After that it is back onto the regular controller at full 230w

Jim kindly tested an idea to just shade some cells to get the Voc down.

You could short the middle string in the J-box. You would lose 33% power and voltage. Not sure if that helps or hurts to use the buck converter.

Test it an hour before sunset?

Just thinking out loud. . .

Why not get a controller rated at the correct voltage? I bought a 20 amp PWM controller for $13. Some MPPT controllers are getting pretty low cost nowdays.

Aliexpress.com

Fred.

$50 MPPT controller. http://www.aliexpress.com/item/LCD-30A-MPPT-Solar-Panel-Regulator-Charge-Controller-12V-24V-380W-760W-With-USB/959502350.html it is the first one that came up when I looked up MPPT controller. You can look around the site, it offers many manufactures and sales places. .

Fred.