Author Topic: What happens when you generate more than the inverters rating?  (Read 14524 times)

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Valalvax

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What happens when you generate more than the inverters rating?
« on: September 01, 2012, 05:40:44 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, 09:10:38 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, 06:39:53 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, 08:45:23 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, 09:24:21 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, 06:09:01 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, 06:32:51 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

Damon

thirteen

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Re: What happens when you generate more than the inverters rating?
« Reply #7 on: September 04, 2012, 08:17:08 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, 09:46:34 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, 10:36:55 AM »
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, 09:47:30 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, 11:49:39 AM »
Yes, ideally, if of the same brand/Vmp.

Rgds

Damon

XOKE

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Re: What happens when you generate more than the inverters rating?
« Reply #12 on: September 08, 2012, 03:41:08 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, 03:05:16 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, 06:46:28 PM »
You do realize this is a 4 year old thread...