How to oversize the solar panel array so you don't wreck the system?

[Burnrate]

I've read that the charge controllers are much more sensitive to higher voltages than higher amps. Can you just have a lot more amps and the charger will ignore it or will that cause damage as well?

For example if we look at my favorite inverter again (EG4 3000EHV-48) it has 5000W PV Input | 500 VOC Input. For the panel input we can look at the biggest ones that signature solar has right now, the 460 W ones with a 50.8 VOC.

Example one is I have 9 panels in series giving me 457.2 volts with 4140 watts and 9 amps. Well within range of the charge controller on the all in one inverter.

Example two I have two sets of 9 panels in series. The two sets are in parallel so there is 457.2 volts with 8280 watts and 18 amps. Now with this one we are well above the rated input for watts but the maximum amps is 18 and we are still in range with the voltage. Will this damage the charge controller? There are more watts but the amps and volts are within range. How would it handle this? Would it just ignore the extra 3kw?

My goal is to try and understand how to oversize the solar panel array. I would expect a significant loss from heat during the day in summer and would also like to get as much energy as possible in the morning and evening and in winter. Those are my four reasons to oversize the array. Is it possible to do a lot more on one charge controller or do you just need more charge controllers for more panels and there is no sneaky way to get around it?

 

[azoffgrid]

wow your doing just what im doing, only im going with 2 / 8 panel sets. solar tracker mount
i was going to wire 2ea 6500ex 48 v c/i with 8 panels each (blue sun 460 bi facial .)
for 406.4 voc and 3680 watt each. set in series
Im new so ...... thats just my idea What say anyone ???

 

[Scixxor]

I've read that the charge controllers are much more sensitive to higher voltages than higher amps. Can you just have a lot more amps and the charger will ignore it or will that cause damage as well?

For example if we look at my favorite inverter again (EG4 3000EHV-48) it has 5000W PV Input | 500 VOC Input. For the panel input we can look at the biggest ones that signature solar has right now, the 460 W ones with a 50.8 VOC.

Example one is I have 9 panels in series giving me 457.2 volts with 4140 watts and 9 amps. Well within range of the charge controller on the all in one inverter.

Example two I have two sets of 9 panels in series. The two sets are in parallel so there is 457.2 volts with 8280 watts and 18 amps. Now with this one we are well above the rated input for watts but the maximum amps is 18 and we are still in range with the voltage. Will this damage the charge controller? There are more watts but the amps and volts are within range. How would it handle this? Would it just ignore the extra 3kw?

My goal is to try and understand how to oversize the solar panel array. I would expect a significant loss from heat during the day in summer and would also like to get as much energy as possible in the morning and evening and in winter. Those are my four reasons to oversize the array. Is it possible to do a lot more on one charge controller or do you just need more charge controllers for more panels and there is no sneaky way to get around it?

Okay so with the voltage you have to stay under the max VOC, going over it is how you destroy it. For both of your examples, you would be flying too close to the sun with that VOC as the lower the temperature the higher your VOC goes. In your examples, if it ever got to 25 degrees it would exceed the 500 VOC limit. The watt limit is free game so long as you are within the VOC and amp limit you can exceed it. As for the amp limit that's where I'm not so sure, I've heard of people exceeding it just fine but I'm not certain. In a separate thread, @rmaddy said that exceeding the amp limit is just fine and any excess would just be ignored/unused. rmaddy is very experienced and I trust them, they've helped me a lot. Here's a link to that thread, it was an interesting read for me: https://diysolarforum.com/threads/exceeding-voltage-or-amps-on-scc.31208/

 

[chrisski]

The watt limit is free game so long as you are within the VOC and amp limit you can exceed it. As for the amp limit that's where I'm not so sure, I've heard of people exceeding it just fine but I'm not certain.

I would not exceed the amp limit without some certainty. I would much rather get a SCC or two to get the AIO within both amp and volt limits.

I have a 15 amp 24 volt inverter that has pushed 420 watts at a charging voltage of a little over 27 volts. That is the limit of the SCC; volts X amps = Watts and the amp limit is 15. Since my Lion Energy 100 watt panels can slightly exceed their limits, I can hit this 15 amp limit with 4 panels. I have put as many as 9 panels, 900 watts, on the SCC to keep it pushing that 15 amp max as much as possible. This well exceeds the max VOC limit Victron puts on their SCCs.

I have had one over-amperage error. I also set this up so if something went wrong (up in smoke wrong) this would not burn my house down.

With around 500 volts, I'd really recommend staying within all published specs, unless you don't mind your AIO going up in smoke. There's some strategies like different orientation, but I'd not be too comfortable with that.

 

[rmaddy]

As for the amp limit that's where I'm not so sure, I've heard of people exceeding it just fine but I'm not certain. In a separate thread, @rmaddy said that exceeding the amp limit is just fine and any excess would just be ignored/unused.

To be clear, there are two amp limits on a solar charge controller. If you look at the specs for the EG4 3000EHV-48 you will see a "Max Input Current Draw" of 18A and the "Max Charging Current (PV)" of 80A.

The first must not be exceeded. Since the OP is referring to panels with an Isc of 11.5A this means the panels can only be put in series. Putting panels in parallel will exceed the max input current draw.

The latter can technically be exceeded and is referred to as over paneling but the SCC will never provide more than the rated charge current. In this specific case the SCC will max out at a battery charge current of 80A. If the battery charge voltage is 56.8V then this means the SCC can make use of up to 80A x 56.8V = 4544W. To reach the stated 5kW max the battery charge voltage would have to be 62.5V (5kW / 80A) which is certainly much too high for LiFePO₄ batteries. But remember that the 4544W max is what the SCC can take advantage of. You can have more wattage connected to the controller. That over paneling allows you to get closer to the 4544W even when there is less ideal solar conditions. In cases where the panels could produce more than 4544W from the installed panels then no more than 4544W will be used (assuming the 56.8V charge voltage).

Okay so with the voltage you have to stay under the max VOC, going over it is how you destroy it. For both of your examples, you would be flying too close to the sun with that VOC as the lower the temperature the higher your VOC goes. In your examples, if it ever got to 25 degrees it would exceed the 500 VOC limit.

With a Voc of 50.8V and a temperature coefficient Voc of -0.26%/ºC, 9 of the panels will be 457.2V and will exceed 500V at a temperature of about 13ºF/-11ºC. So 9 panels will only be viable if there it never gets colder than that where the panels will be located. One record cold snap could fry the all-in-one if it gets too cold. 8 panels would be the limit if there's risk of temperatures that cold.

Example two I have two sets of 9 panels in series. The two sets are in parallel so there is 457.2 volts with 8280 watts and 18 amps.

You can't since you'll have an Isc of 23.0A, not 18A. Though I would verify with Signature Solar. The stated "Max Input Current Draw" of 18A could mean one of two things. 1) Do not exceed at all or risk killing the all-in-one. or 2) You can go over this a bit but the input current will be clipped to 18A. If option 2 turns out to be the case then two strings in parallel will have an Isc of 23.0A but will be clipped to 18A.

 

[Scixxor]

That certainly clears a lot up for me and It all makes a lot more sense. I didn't realize OP linked the actual panels so I just left the temperature coefficient Voc at 0.33 to be safe but yeah 13ºF is the correct answer. Thank you for being so helpful I aspire to be as knowledgeable as you!

 

[fromport]

I've read that the charge controllers are much more sensitive to higher voltages than higher amps. Can you just have a lot more amps and the charger will ignore it or will that cause damage as well?

For example if we look at my favorite inverter again (EG4 3000EHV-48) it has 5000W PV Input | 500 VOC Input. For the panel input we can look at the biggest ones that signature solar has right now, the 460 W ones with a 50.8 VOC.

Example one is I have 9 panels in series giving me 457.2 volts with 4140 watts and 9 amps. Well within range of the charge controller on the all in one inverter.

Example two I have two sets of 9 panels in series. The two sets are in parallel so there is 457.2 volts with 8280 watts and 18 amps. Now with this one we are well above the rated input for watts but the maximum amps is 18 and we are still in range with the voltage. Will this damage the charge controller? There are more watts but the amps and volts are within range. How would it handle this? Would it just ignore the extra 3kw?

My goal is to try and understand how to oversize the solar panel array. I would expect a significant loss from heat during the day in summer and would also like to get as much energy as possible in the morning and evening and in winter. Those are my four reasons to oversize the array. Is it possible to do a lot more on one charge controller or do you just need more charge controllers for more panels and there is no sneaky way to get around it?

This article (imo) gives a good understanding how to calculate the Voc rise under freezing conditions:

Calculating Max PV Voltage is Not Scary - Sunny. SMA Corporate Blog

In 2008, the National Electrical Code (NEC) added a second paragraph to 690.7(A) stating, “When open-circuit voltage temperature coefficients are...

www.sma-sunny.com

It always surprises me that when it is freezing (& full moon?) how much of a voltage boost is possible that might wreck the input of a charger controller/mppt input.

 

[12VoltInstalls]

As for the amp limit that's where I'm not so sure, I've heard of people exceeding it just fine but I'm not certain. In a separate thread, @rmaddy said that exceeding the amp limit is just fine

To a point. Some equipment just won’t tolerate over-amps.
EDIT rmaddy used less words and a better, more scientific explanation so I delete and defer to his post.

….in my case- last winter, full sun and cold, I got as high as 44A charging on a 50A Epever eith 800W of panels. This winter I plan to split the array and run two 40A Epevers which should keep me well under label limits and permit adding panels to one string - that wouldn’t do well on a single controller.

The point is manipulate the equipment but don’t challenge the engineering

 

[Bvillebob]

A well designed charge controller will monitor its output and operating temperatures and adjust the output amperage to stay within safe limits, regardless of the potential available from the panels. The panels don't "force" anything into the controller, it's up to the controller to take the power from the panels according to the needs of the batteries and its own abilities.

I use Midnite Classic controllers that are rated at 94 amps. Each controller has about 5kw of panels connect to it, which for a 24v system means a maximum current output of nearly 200 amps at 24v. The controllers are connected to a 60 kWh lithium battery system, and they take up to the maximum power from the panels they can safely use, and no more. I actually have their output limited to 85 amps just to provide more headroom and keep them cooler, but it's not necessary.

I do this because I live in western Oregon, where it's dark, cloudy and rainy. In overcast conditions I get twice the output from the panels compared to having a smaller array that would only put out the rated 94 amps, and 8 months of the year it's a huge benefit. If you're in a place where it's sunny most of the time there would be no need.

And note that at the very start I said "well-designed" charge controller, not all are. You need to research the specifics of your device.

 

[Ampster]

The panels don't "force" anything into the controller, it's up to the controller to take the power from the panels according to the needs of the batteries and its own abilities.

That is the important issue. The controller can vary the load that the panels see, thus controlling the output of the panels. However, with respect to the "ability" of the controller, one still needs to be mindful of the voltage and current limits of the charge controller and not exceed those limits.

 

[Burnrate]

Thanks so much everyone. Tons of info! My takeaway is make sure the voltage won't ever go too high but if the charge controller is good you should be able to have more, possibly many more amps and the controller can draw what it wants. For my location (Florida close to the ocean) it is uncommon to see temps drop into the 40's and that is only at night.

The real key is I need to contact the manufacturer to determine what they designed the charge controller to handle in terms of amps.

 

[rmaddy]

For my location (Florida close to the ocean) it is uncommon to see temps drop into the 40's and that is only at night.

It's common for the coldest time of the day to be just at sunrise. Solar panels can jump to full Voc even before the sun breaks the horizon during first light. So plan your panel arrangement and the max Voc for the record coldest temperature where you live.

 

[Burnrate]

It's common for the coldest time of the day to be just at sunrise. Solar panels can jump to full Voc even before the sun breaks the horizon during first light. So plan your panel arrangement and the max Voc for the record coldest temperature where you live.

The coldest days on record were all in the 20's but those all happened in the 1980's or earlier so we won't ever see that again. If I do go with those panels I'll still have room to not hit that 13 degree F that would put me over while using 9.

 

[fromport]

This is from a grid tied inverter (fronius primo 3.8 kW) that is loaded with 2 MPPT inputs.
As can be clearly seen, it flattens out during the middle of the day. More solar input available than it can convert to AC


Same with one of my micro inverters: Enphase M215 maxing out at 221 watts (blue flatline)

As long as there is no over voltage that normally won't damage the inverter.

 

[12VoltInstalls]

those all happened in the 1980's or earlier so we won't ever see that again.

I wouldn’t bet my equipment on that.

Plan for the records; an untimely volcanic eruption can cool the earth unexpectedly.

Human-related climate change- or not- nature is a fickle tester both of human submission and arrogance.

According to a report in Nature, the atmospheric volcanic remnants that caused cooling of the oceans following Krakatoa's eruption lasted nearly a century, enough to counteract a large amount of rising ocean temperature and to a lesser extent a rising sea level that have been going on for centuries.

“We” monitor volcanic activity along known faults because the reality is that we cannot adequately predict eruptions or other tectonic phenomena such as tsunamis and earthquakes.

Never mind that you could simply have a weather event…

 

[chrisski]

I need to contact the manufacturer to determine what they designed the charge controller to handle in terms of amps

I would recommend you are comfortable with what they tell you.

I’ve gotten three word responses to email questions. I’ve also talked to salesman who were not in the tech dept I thought wanted to make a sale and would say anything.

 

[Sirtate]

It seems to me that as long as the voltage doesn't exceed the Max Voc you can't hurt the charge controller.
It's like the difference between a cell-phone charger and a hairdryer at home; both require 120VAC, but one needs more wattage/amps.
The 120VAC is the deciding factor, as long as that number is within spec, the phone charger won't get fried if it is plugged into the outlet immediately after the hairdryer is unplugged.
The phone charger just pulls the amount of current it desires to do its job.

 

[cinoaz]

The phone charger just pulls the amount of current it desires to do its job.

I think the hangup is how inverters do things. In your example, the phone charger is the inverter and someone plugs a hair dryer into it. Now the charger sees a load (OMG) and the charger "tries" to provide it. It's stuck at 120v so it starts raising the amps. If you are on a 15amp circuit and the hair dryer needs 20, the breaker should pop.

However, let's say the charger is plugged into a battery capable of 500amps. The charger will just keep ramping up the amps until something, along the chain, finally gives up the ghost. Most likely the wire which will impersonate a light bulb for a brief moment, maybe the charger is only rated at 2amps but if you put a 20amp load on it, it's going to "try" to get there.....

The unanswered question which is a mostly "I don't know", does the inverter have the smarts to stop itself from trying to eat too much amps on the PV input lines in an attempt to satisfy a load on its AC generation side? Can it self regulate? If the manufacture expects the PV array to be sized correctly, then, you don't need all the parts/expense of the inverter to self regulate because you are controlling how much it eats by sizing the array.

 

[Luxpower_Gilbert]

I believe you can over panel any inverter just don’t over voltage…

 

[12VoltInstalls]

I believe you can over panel any inverter just don’t over voltage…

Some have specified wattage or amp limits called out in the manual- even Victron if I am not mistaken.