Author Topic: What happens when you generate more than the inverters rating?  (Read 29225 times)

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Valalvax

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What happens when you generate more than the inverters rating?
« on: September 01, 2012, 07:40:44 PM »
So, let's say I have a inverter rated at 500w, and I have 750w of panels, now normally I'd only be getting a small portion of that, but on a super sunny day I might actually be generating near the full 750w, what happens to the inverter? Does it just cap out at 500? Or do I let the smoke out?

boB

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Re: What happens when you generate more than the inverters rating?
« Reply #1 on: September 01, 2012, 11:10:38 PM »
Well, first of all, with your larger than necessary PV array, you will have a charge controller of some sort which will keep your
batteries from overcharging.  If you always have more charging energy than you can suck out by your inverter, you will just
always have a fully charged battery.

Any excess energy from the PV array will be wasted unless you have some way of using it.  (dump loads, etc)

A decent inverter will just limit its output power so it doesn't burn up.  If you overload the inverter AC output, it should
turn itself off.

boB

Rob Beckers

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Re: What happens when you generate more than the inverters rating?
« Reply #2 on: September 02, 2012, 08:39:53 AM »
Valalvax, to complete the story for grid-tie inverters (without batteries): All those inverters will limit the input current so that their output power is limited to the maximum they were designed to handle. For example, say your PV array is generating 350 Volt DC and could provide 10A of current at that voltage (making for 10 x 350 = 3.5kW), if it's a 3kW inverter it'll only draw about 8.6A on purpose, instead of "as much as the array will allow" (making for 8.6 * 350 = 3kW). That's the gist of it...

-RoB-

boB

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Re: What happens when you generate more than the inverters rating?
« Reply #3 on: September 02, 2012, 10:45:23 PM »
One more clarification...

If a PV array provides 10 amps at 350 volts, and the grid tie inverter can only use 8.6 amps, the grid tie inverter will (on purpose) operate
that PV array at a voltage higher than 350 volts to reduce the current and power.  The I/V  (current/voltage) curve of the PV array dictates
what current will be drawn at any particular loaded voltage.  Open circuit is of course 0 amps and is the highest voltage that will be seen
by the particular PV array.

0 amps times that high voltage (Voc) = 0 watts.

boB





Valalvax

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Re: What happens when you generate more than the inverters rating?
« Reply #4 on: September 03, 2012, 11:24:21 AM »
Thanks, the reason I was asking is because the inverter is a significant portion of the cost of any system, and if I buy 1kw worth of panels and an inverter today, then later want to increase my output, well, I'm not going to be getting 1kw all the time, so I could just buy more panels for a fraction of the cost of a total system upgrade and still get increased

I kind of figured that any non-Chinese inverters would be smart enough to do something to avoid dying, but figured it'd be smarter to ask first before letting a couple hundred dollars go up in literal smoke

Rob Beckers

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Re: What happens when you generate more than the inverters rating?
« Reply #5 on: September 04, 2012, 08:09:01 AM »
Valalvax, just be careful when "adding panels" later, since this opens up a whole other can-o-worms. Assuming this is grid-tie without batteries, all those inverters have a maximum input voltage. For many (but check for the one you're planning on using) this is 600V DC. That limits the number of panels you can put in series in a string before letting the magic smoke out of the inverter, and that number is based on the coldest temperature you'll (n)ever see in your area (the colder the PV module, the higher its output voltage). For example, in our -35C / -32F climate we can stick no more than 13 panels (the regular 60-cell type) in series before reaching the 600V limit.

Adding panels to an existing string in series means matching the current of the existing panels, adding new strings in parallel means matching the voltage of the existing string for things to work best. In short, allowing for extension at a later date requires a little planning now.

You may want to consider PV inverters that have two independent inputs if extending the system is in the future (and oversize the inverter to begin with). That way you can more easily use strings of differing panels together.

-RoB-

DamonHD

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Re: What happens when you generate more than the inverters rating?
« Reply #6 on: September 04, 2012, 08:32:51 AM »
Because I extended my grid-tie system piecemeal I have four equal strings each with its own inverter, which gives me maximum redundancy (a single failure can only take 25% off line) and copes well with the different aspects (east- and west- facing) and partial shading of some of the strings.

In other words, adding inverters later to support more panels is also possible in most cases.

Rgds

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thirteen

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Re: What happens when you generate more than the inverters rating?
« Reply #7 on: September 04, 2012, 10:17:08 AM »
I am wondering if there is any certain problem to look for when getting new panels and connecting them to much older panels. I was out scouting for a new hunting area. I came across 14 panels but they are at least 16 years old and only half may be working because of the wiring has been melted at some piont. Some of the other (5) panels have been shot by someone. They have been idle for at least 4/5 yrs. The black berries bushes are covering most of them and I'll say they are 80watt as a guess. They are just sitting in the outdoors looking at the sun. I think they were hit by lightening. There was a house there at one time. The place where the (6) batteries are in is toast and the batteries have the blown tops on them and are broken and bulged. So they have been frozen and are broken. They are Trojen batteries.  I am trying to find out who owns the land and maybe I can get them for the cleanup if they produce electricity.  Everything else has been stripped.  They might be worth the effort maybe.
MntMnROY 13

synovialbasher

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Re: What happens when you generate more than the inverters rating?
« Reply #8 on: September 04, 2012, 11:46:34 AM »
I am trying to find out who owns the land and maybe I can get them for the cleanup if they produce electricity.  Everything else has been stripped.  They might be worth the effort maybe.

I don't think there's any problem with using older panels, but I wouldn't rate them on their rated output (obviously). I'd check every panel's voltage and current. Any extremely low voltage, just get rid of it. If the amperage is low, you could probably work with it and wire it in parallel. With panels, one bad panel will limit all the others to whatever that bad one is, so make sure they all work well.

I'd also check for any leaks or water damage (as this can short your entire system).

As far as the batteries, I'd contact the county and try to get someone on that case. Lead is EXTREMELY dangerous to an environment, and I'm sure the city would be on that one in a heartbeat. There are serious fines for not properly getting rid of those things properly. As far as using them, they're crap. If they're all bulged out, the plates are likely warped and have shorted, and all the acid is probably all gone anyways.

thirteen

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Re: What happens when you generate more than the inverters rating?
« Reply #9 on: September 04, 2012, 12:36:55 PM »
It is out in the country so the county would need to deal with it. I'll look more this weekend. I should be able to get permission to look at them up close. I'll have to take my tree nippers up to cut the black berry bushes.  I'll test them right there and if any are good i'll try and get them.
13
MntMnROY 13

Valalvax

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Re: What happens when you generate more than the inverters rating?
« Reply #10 on: September 05, 2012, 11:47:30 AM »
So what your saying is if I have 5 panels in series, and I want to add panels in parallel, I'll need to add 5 in parallel?

DamonHD

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Re: What happens when you generate more than the inverters rating?
« Reply #11 on: September 05, 2012, 01:49:39 PM »
Yes, ideally, if of the same brand/Vmp.

Rgds

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XOKE

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Re: What happens when you generate more than the inverters rating?
« Reply #12 on: September 08, 2012, 05:41:08 PM »
Hi, I have a 4600watts of PV and a GTI XANTREX 3.8 SP,

theres 20 panels of 230watts each, connections 2 strings of 10 in series. I know a guy that have more than 5000watts to same brand GTI.

By the way I have this just for 41 day and I can read on GTI 1070kw.

Regards

Xoke

Johann

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Re: What happens when you generate more than the inverters rating?
« Reply #13 on: February 03, 2016, 05:05:16 PM »
I am trying to find out who owns the land and maybe I can get them for the cleanup if they produce electricity.  Everything else has been stripped.  They might be worth the effort maybe.

I don't think there's any problem with using older panels, but I wouldn't rate them on their rated output (obviously). I'd check every panel's voltage and current. Any extremely low voltage, just get rid of it. If the amperage is low, you could probably work with it and wire it in parallel. With panels, one bad panel will limit all the others to whatever that bad one is, so make sure they all work well.

I'd also check for any leaks or water damage (as this can short your entire system).

As far as the batteries, I'd contact the county and try to get someone on that case. Lead is EXTREMELY dangerous to an environment, and I'm sure the city would be on that one in a heartbeat. There are serious fines for not properly getting rid of those things properly. As far as using them, they're crap. If they're all bulged out, the plates are likely warped and have shorted, and all the acid is probably all gone anyways.
You might be able to use those batteries for a core.

Mary B

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Re: What happens when you generate more than the inverters rating?
« Reply #14 on: February 03, 2016, 08:46:28 PM »
You do realize this is a 4 year old thread...

jasonmanning

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Re: What happens when you generate more than the inverters rating?
« Reply #15 on: March 09, 2018, 04:10:19 AM »
The efficiency of an inverter determines the efficiency of a solar panel because inverters convert DC into AC. If more power is generated it is clipped down. The device will have an inbuilt charge controller which prevents batteries from overcharging. 8)

Ungrounded Lightning Rod

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Re: What happens when you generate more than the inverters rating?
« Reply #16 on: August 10, 2018, 12:36:35 PM »
So what your saying is if I have 5 panels in series, and I want to add panels in parallel, I'll need to add 5 in parallel?

You'll need to add, in parallel with the five-in-series, another five-in-series (or other arrangement that produces the same voltage, or reasonably close to it).  Panels are current sources with a maximum voltage and are quite happy to have their output dragged down to a lower voltage, or even shorted to zero.  (When shorted they dissipate the same amount of heat as if they were unconnected - just more of it is in the conductors rather than distributed through the semiconductor.)

But they don't like being back-fed a higher voltage than they can produce.  When you start paralleling strings of panels, you want to put a protective diode in series with EACH string, to keep all the strings feeding the output rather than pushing current backward through another panel that is a lower-voltage or has a shadow over part of it.  Exceeding the peak reverse voltage of the cells can destroy them.  Adding the diode may cost you a small amount of power due to its voltage drop, but it's a drop in the bucket compared to what you gain by adding another string of panels - or lose if a string of panels is destroyed by reverse-current.

Re:  Big panel farm, small inverter.  Addressed above (it's fine) but consider this:  If the panels are charging a big bank of heavy-duty batteries, the batteries COULD produce tens or hundreds of kilowatts (for a short time) if they were loaded hard enough to do so.  Like any other load on a power system, an inverter pulls enough current from a (somewhat soft) voltage source to do its job.  If it's JUST an inverter, it's fine.  (And you can even connect multiple inverters, for various loads and purposes, to a common battery bank fed by multiple strings of panels that produce far more power than all the inverters combined.  The extra power just charges the batteries for use after the sun goes away.)

But if they're NOT just inverters there may be an issue.  Some inverters also include charge controllers, or have some charge-controlling behavior (like MPPT voltage-conversion, dump load switching, etc.)  These may be designed to assume they're the only such device in the system.  In cases like that you may need to give them their own panel subset that's small enough for them to handle.  Depending on how well their various systems play together (for instance: low-voltage-shutdown is just fine), you may be able to use a big common battery bank and pool the power from all the panel subsets for evening use, or you may need to have separate battery banks as well as separate panel arrays, for each, or some, of the devices.

Re:  Responding to years-old posts.  This one's a "sticky" and always at the top of the list of articles in the overall board index.  New users will be reading it for years into the future.  So if there's something confusing (or wrong) it's still useful to correct it - for their benefit, even if the original poster has long since dealt with the issue and moved on.
« Last Edit: August 10, 2018, 12:50:50 PM by Ungrounded Lightning Rod »

Alice Miller

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Re: What happens when you generate more than the inverters rating?
« Reply #17 on: May 10, 2022, 11:13:07 PM »
When the maximum power is exceeded, it is likely to cause damage to your inverter and even the rectification of the solar system. I suggest you add an inverter more, or replace with a higher power inverter.

camillitech

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Re: What happens when you generate more than the inverters rating?
« Reply #18 on: May 21, 2022, 01:13:53 AM »
When the maximum power is exceeded, it is likely to cause damage to your inverter and even the rectification of the solar system. I suggest you add an inverter more, or replace with a higher power inverter.

Not so, I ran 3kW of PV through a 1200W Sunny Boy inverter for years in my 'AC coupled' off grid system. I had to do this cos I also had a 6kW wind turbine and 1kW hydro turbine 'AC coupled' and my 6kW off grid inverter couldn't cope with all the power back feeding into my batteries. Only recently upgraded my 1200W Sunny Boy to a 3800W Sunny Boy cos I upgraded from a 6kW off grid inverter to a 10kW one. It is quite common to undersize GTI's to maximise production if your export needs to be constrained.

Cheers, Paul

Amy

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Re: What happens when you generate more than the inverters rating?
« Reply #19 on: April 19, 2023, 05:41:45 AM »


If you generate more power than your inverter's rating, it can result in a decrease of efficiency and cause damage to the inverter. Additionally, it could also increase the risk of fire or personal injury due to electrical overload. It is important to make sure you are not overloading the inverter by verifying that the total solar output is less than the inverter rating. If you need to increase your solar output, you will need to upgrade to an inverter with a higher rating before doing so. Ultimately, it is always best practice to match the inverter's rating as closely as possible with the total solar output of your system.


Rob Beckers

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Re: What happens when you generate more than the inverters rating?
« Reply #20 on: May 14, 2023, 08:00:27 AM »


If you generate more power than your inverter's rating, it can result in a decrease of efficiency and cause damage to the inverter. Additionally, it could also increase the risk of fire or personal injury due to electrical overload. It is important to make sure you are not overloading the inverter by verifying that the total solar output is less than the inverter rating. If you need to increase your solar output, you will need to upgrade to an inverter with a higher rating before doing so. Ultimately, it is always best practice to match the inverter's rating as closely as possible with the total solar output of your system.

Amy, that's not actually how inverters work (or what they can handle). It is very common practise to oversize the PV array vs. the inverter rating. I've commonly seen 150% PV rated output vs. inverter rated output, and those systems have been working just fine for many, many years now.

Solar inverters will actively limit their output power to keep it at their rated limit (or maybe slightly above). Solar panels in full sun don't "produce" anything, unless you allow current to flow and Voltage to exist. A panel in the sun with its leads open has zero current, and therefore zero output power. A short-circuited PV module will produce lots of current, at zero Volt, and therefore again zero output power. Inverters make sure to run on the curve between those two extremes, normally in such a way that they produce maximum output power from the available sunlight (that's the MPPT-point, of the Maximum Power Point Tracking that it stands for). But if doing so violates the inverter limits, either the current limit or output power limit, the inverter will pick a point that ensures it's within its limits. No damage done.

You have to limit solar panels to stay within the Voltage limits of the inverter (a 1000 Volt string into a 600 Volt inverter will of course let the magic smoke out). In theory there is the issue that an oversized PV array will run the inverter "harder" but in practise with A-brand inverters we've never seen any issue with that (for one, 50% of the time the inverter is doing nothing!). There is also a theoretical maximum, where the inverter's on-board processor simply can't respond fast enough in regulating down the output power, but that too is more of a theoretical than practical limit (and some inverter designs use hardware to limit-as-a-last-resort, rather than software). Extra fusing may be required when oversizing the PV input, because the short-circuit current of the solar array may exceed the UL/CSA-listed limits of the wiring in inside the inverter, and series fusing makes this safe. But that's about it. Go ahead and oversize the PV array! It'll make for better ROI.

-RoB-

DamonHD

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Re: What happens when you generate more than the inverters rating?
« Reply #21 on: May 14, 2023, 09:18:48 AM »
I agree that oversizing of PV relative to the inverter/controller is common for better overall return, and for more generation throughput when ReallyNeeded(TM) such as in winter.  I'm doing it a bit on my grid-tied system and a lot (~4x) in my off-grid system.  Not all inverters/controllers will accept this safely but many are explicitly specified to, such as mine.

Rgds

Damon
« Last Edit: May 14, 2023, 09:57:30 AM by DamonHD »
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