Morningstar MPPT Controller's Maximum Input Power Rating

BFL13 wrote:
Also don't forget their other advice about oversizing the array. They warn you are just wasting your money since the controller will just clip the amps.

You are not wasting your money because you are getting more amp-hours with the same controller.

True, to squeeze every possible AH out of the larger array, you also need a larger controller. Not $5 larger. Once you are in big arrays, then MPPT comes with the territory, and the difference in price of 45A and 60A MPPT is $100 or more, plus - possibly - a beefier cable, while panels are cheap. But this is a different subject. The issue that they raised was to oversize or not, and the answer is - yes, you can, and there can be benefits to this.

At some point down the road it won't make sense to oversize anymore, because of diminishing returns. Then you will need a bigger controller. And then you can oversize again :)...

This a plot of my home system with the oversize PV modules mentioned in previous post. Notice how it is flattish on top? To get the next size up for both inverters would have cost around $1500-$1700 total.

Almot wrote:
Not a news, really. I believe most (any?) MPPT can be used with oversized array. Benefits are well known: the I/t curve (t=time) becomes flatter with larger array, the tip is clipped but shoulders are wider. Better production in early hours and/or on cloudy days.

Oversizing "might" have a detrimental effect due to more heat in controller operating near max output. Though I have a gut feeling that after you've arrived to clipping point, it doesn't matter how much you exceed it, heat is still the same. Perhaps somebody who understands the clipping better will correct me.

I've been saying this for years on here and people either argue or don't understand what I said. Maybe I should have been as eloquent as you! Well said! My last two home installs were like this as well as my residential installer is the one that clued me into this trick.

One was 8kw array with 7kW inverter, currently I have a 15kw array with 13 kw of inverters.

Too funny! They say if you oversize your array you get more amps in low light than if you had a smaller array. Gosh! Who knew! :) What has that got to do with fancy MPPTs? No idea.

Some have posted that MPPTs generally do better than PWM in the shoulder hours, but cannot show how that could be. Seems dubious to me. I have MPPT and PWM and see nothing along those lines. Perhaps somebody can explain that business better, then maybe I can find it.

However, here we have them showing just that for the shoulder hours but only by oversizing the array so it flat tops mid-day. The PWM will also get the higher shoulder hour amps from the bigger array ( of course) but also will do the full mid-day value because it lets the amps through. Of course it might overheat if the amps are too high for too long, so better get a higher amp PWM for that. Say $20 instead of $15 on eBay :)

The whole blurb seems like a lot of salesmen tap dancing for when you end up with a controller too small in amps to do the job. One thing that is useful info is how the AH haul from the shoulder hours is greater than the loss from clipping mid-day.

Also don't forget their other advice about oversizing the array. They warn you are just wasting your money since the controller will just clip the amps. Mena posted about that a while ago from their manual.

Then after all that they slide in that if you are camping in winter with the array tilted up the controller might overheat anyway so don't do that!

You really have to wonder what is going on there. Are there competing parties at the company, each putting out its own blurb?

I'd guess that they just vary the switching on/off time with no extra heating concerns. After all the electronics provides more voltage/amps when the batteries need it and less as they become charged.

This is the first instance that I'm aware of where a mfg has written information on the benefits of a larger array than the stated limit.

Also if you consider a home/industry tracked array (physically following the sun) the controller could easily be at or beyond the maximum array input for many hours per day.

Not a news, really. I believe most (any?) MPPT can be used with oversized array. Benefits are well known: the I/t curve (t=time) becomes flatter with larger array, the tip is clipped but shoulders are wider. Better production in early hours and/or on cloudy days.

Oversizing "might" have a detrimental effect due to more heat in controller operating near max output. Though I have a gut feeling that after you've arrived to clipping point, it doesn't matter how much you exceed it, heat is still the same. Perhaps somebody who understands the clipping better will correct me.

This shows a high cost MPPT would be best to overdrive a bit vs. the PWM where a large controller is generally better.

No regrets having the 60a but the 45a would have been just fine with my 675 watts.

Thanks for the posting.
This is exactly what I do (300 watts solar with 200 watt Sunsaver) for these very reasons. It is nice to see it written out though.

Steve

Very interesting reading. Thanks for posting.

Reck

Moved from technology corner