Panel outputs

[admiralslater]

Originally Posted by StuM

That's max Amps out.

Amp hours out is limited only by the working life of the panels. You should get many thousands of Amp hours out of a 200 Watt panel.

Stu I knew I could count on you. Where do I use the short circuit amperage value of the panel 10.79 against the specifications of the controller? The only place that I can think of is that it should not be higher than the output amps .
Does that make sense?

[a64pilot]

Originally Posted by StuM

No, it's the ratio of panel output to what the controller can handle.

If you "over panel", the controller will either "load limit" the input or shut down temporarily - depending on how it is built.

Assuming you have a good controller that will load limit by moving away from "maximum power point", the advantage of over-paneling lies in the morning and evening and in overcast conditions when the panels are not putting out full power.

The attached shows what happens when a good MPPT controller is over paneled. The green area is additional energy when output is not high, the brown area is lost energy when the panels are putting out close to their rating. As long as the green area is larger than the brown area, it's a net gain. If the brown area is larger than the green area, then you need to go to a bigger controller to get the most out of your panels.

I'm coming in the middle of this, but why would you want to overpanel at all?
Wouldn't it be better to have a controller that can handle all of the panel output?
By maxing out a controller isn't it likely to get hot, and possibly shorten its life?

Are controllers really actually amp limited, and not watt limited? Can you really double the amount of power a controller can handle by doubling the output voltage?

[john61ct]

There are a variety of designs, but using the Victron MPPTs as an example

Originally Posted by a64pilot

I'm coming in the middle of this, but why would you want to overpanel at all?

Because the higher capacity controllers are much more expensive, 75/15 for $80-90, 100/30 well over $200.

Ideal for shading is one SC per panel.

Peak conditions around noon hold for a relatively short period, in some climates relatively rare.

Some may want to get the max practical output per SC overall, increasing the output earlier in the day and in cloudy weather.

In peak conditions capturing every watt is less important.

Originally Posted by a64pilot

By maxing out a controller isn't it likely to get hot, and possibly shorten its life?

Are controllers really actually amp limited, and not watt limited? Can you really double the amount of power a controller can handle by doubling the output voltage?

Yes to the last two.

wrt the first, the Victrons are only "maxed out" from an input capacity POV with a ridiculous level of overpaneling, like triple the max output.

A reasonable level, say up to double the output amps rating, doesn't even come close to the max amp input spec.

The voltage limit has no leeway though, be conservative with that or you will damage the SC quickly.

And yes, a 24V bank setup doubles the controller's (potential) power output.

[a64pilot]

Why is individual controllers superior to parallel wiring from a shading perspective?

[john61ct]

The finer the granularity the MPPT algorithm is run, the greater the total output advantage.

The ideal is actually microinverters, or embedded MPPT, like Maxim's technology implemented by Jinko and others, where each string within a panel gets its own little SC on a chip.

I also like redundancy if one SC goes out brings down a lower proportion of total output, and cheap enough to carry a spare.

Multiple banks, different chemistries, easy to reallocate output as needed.

Finally with Victron's pricing model, actually can work out cheaper to go that way, used to be you'd have to pay a premium.

[foggysail]

Originally Posted by john61ct

Forget watts to start with.



I advocate one controller per panel, and that often works out with Victron's pricing model.

That is subjective. Individual controllers require additional wiring along with real estate to locate the controllers. And wiring can get very messy. Personally....and again subjective..... I would never go with individual controllers to save a couple bucks nor do I recommend it.

[foggysail]

Originally Posted by a64pilot

Why is individual controllers superior to parallel wiring from a shading perspective?

They are not!

[john61ct]

They are, objective fact that anyone can easily test.

I did not say saving money was the primary advantage, just that the pricing model made doing so more possible than in the past, when the much greater expense of this approach made it largely impractical.