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What happens when you generate more than the inverters rating?

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Rob Beckers:
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:
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:
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.

synovialbasher:

--- Quote from: thirteen on September 04, 2012, 10:17:08 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.

--- End quote ---

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:
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

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