PV Inverters

physis · Jul 8, 2005

Re: PV Inverters

I've never read 690 before and I've been trying to figure what the photovoltaic disconnect in 690.14(C)(1) is.

I just can't tell if 690.14(C)(1) is talking about a disconnect for the photovoltaic power source (the solar panel) or the inverter output circuits. 690.13 is specific about what it's disconnect is for. The photovoltaic power source. That has a definition and I can find what it means.

As it is, the PV guy (or at least, his letters ) has stated that the only disconnect that he needs is for the conductors that enter the house from the panels (apparently for compliance with 690.13?)

I just don't know. But tell me if you buy this. I'm gonna put everything that has a definition in 690.2 in quotes. And everything that seems like it needs a definition in bold.

690.14(B) Equipment. Equipment such as "photovoltaic source circuit" isolating switches, overcurrent devices, and blocking diodes shall be permitted on the photovoltaic side of the photovoltaic disconnecting means.

You can tell by what's on one side of the photovoltaic disconnecting means that it goes between the "photovoltaic source circuit" and the "photovoltaic output circuit".

The photovoltaic disconnecting means is the same disconnect as in 690.13 that disconnects the "photovoltaic power source". Because the "photovoltaic output circuit" is the connection to the "photovoltaic power source".

690.14(C)(1) Location. The photovoltaic disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the system conductors.
The photovoltaic system disconnecting means shall not be installed in bathrooms.

Now, the photovoltaic disconnecting means is also being called the photovoltaic system disconnecting means and by either name it looks like they disconnect the system conductors.

690.14(C) Requirements for Disconnecting Means. Means shall be provided to disconnect all conductors in a building or other structure from the photovoltaic system conductors.

Now a means to disconnect photovoltaic system conductors.

Either 690.13 and 690.14(C)(1) are pretty much redundant or when 690.14(C)(1) talks about photovoltaic disconnecting means, system conductors and photovoltaic system disconnecting means it's talking about two or more different things.

Can I say this:

The

photovoltaic power source
photovoltaic system
photovoltaic system conductors
photovoltaic source circuit
system conductors

Are disconnected from all the conductors in the building or other structure and are on the

Photovoltaic side

Of the:

photovoltaic system disconnecting means
photovoltaic disconnecting means
disconnecting means

With the definition of "solar photovoltaic system" being everything from the solar panels to the AC at the load center why are there 9 terms for 2 things and 6 of 'em vague or not defined?

It's like trying to solve a rubicks cube to say you need a solar panel switch.

Or do I just have it all wrong and it only looks bad cause I don't gey it?

Well anyway, 690.15 & 17 are the ones that say you'll probably need a disconnect on the inverter outputs. For most configurations.

I'm curious why you would have to run out of the house and back in because of a disconnect. Aren't the inverter outputs going to the service anyway? Or where are they going?

George Stolz · Jul 9, 2005

Re: PV Inverters

Originally posted by physis:
With the definition of "solar photovoltaic system" being everything from the solar panels to the AC at the load center why are there 9 terms for 2 things and 6 of 'em vague or not defined?

It's like trying to solve a rubicks cube to say you need a solar panel switch.

Or do I just have it all wrong and it only looks bad cause I don't gey it?

I'm curious why you would have to run out of the house and back in because of a disconnect. Aren't the inverter outputs going to the service anyway? Or where are they going?

Click to expand...

The solar panels are outside. They run to a disconnect on the house. From the disconnect, the DC current runs to a charge controller in the basement. Charge controller to batteries. Batteries to inverter. The inverter is in the basement. From the inverter, we've run 4/0 SER to a MDP. (According to the installer, it could be MLO due to the disconnect at the inverter, but we didn't like that much either.

[ July 09, 2005, 12:50 AM: Message edited by: georgestolz ]

hurk27 · Jul 9, 2005

Re: PV Inverters

From the inverter, we've run 4/0 SER to a MDP

George are you talking about from inverters 120 volt output? How many kva is this inverter?

I could understand this large wire on the DC input from batterys but not output?

I think I have read PV panels feeds to controler in house get disco, and batteries feeds to inverter get disco. The only two I know of.
My thinking all disco's should be grouped with service disco? so if main is in panel then this is where I think disco's should go. But I'm not sure.

physis · Jul 9, 2005

Re: PV Inverters

I'm having a great time with thread because I know absolutely nothing about these systems.

I spent, really, a day trying to understand 690. It's horribly written. It's like a terminology bizzar. And it isn't because I'm not familiar with the components.

But I've been wanting to get around to learning how these thing are configured.

Sure. But outside?

Well, I figured you have enough information now to make your own guess.

I still want to know what type of system it'll be. Will it sell power into the grid?

You know, these things are nowhere near as complicated as they seem in 690.

George Stolz · Jul 9, 2005

Re: PV Inverters

Originally posted by hurk27:
George are you talking about from inverters 120 volt output? How many kva is this inverter?

Your guess is as good as mine.

I could understand this large wire on the DC input from batterys but not output?

IMO, they should run another disco outside, if only for future expandability. If a utility does become available (or necessary) then options will be open. I have a minority vote in this venture.

OTH, as prudent as the HO is being about energy consumption, the use of redundant inverters, having 4 days of autonomy, and the 15kVA generator he's having installed from word "go", I think my little disconnect is about eighteenth on the priority list.

On top of that, we have to discreetly place the ugly DC disco next to the front door.

Sam wrote:
I spent, really, a day trying to understand 690. It's horribly written. It's like a terminology bizzar. And it isn't because I'm not familiar with the components.

But I've been wanting to get around to learning how these thing are configured.

Click to expand...

It is pretty darned bad. Their intent is clear as mud. Maybe some probing proposals would reduce some of the ambiguity.

Have you looked at the diagrams at the beginning of 690? They're pretty good for figuring out the configuration.

I still want to know what type of system it'll be. Will it sell power into the grid?

Click to expand...

No. Full-on standalone (w/generator backup). This house is 1.5 hours from the shop, 24 miles up a winding dirt mountain road.

Since I have the 4x4 in the company, I'll be the one to trim it when that happens (my guess: December! ).

physis · Jul 9, 2005

Re: PV Inverters

Full-on standalone (w/generator backup).

Whoa, I'm surprised. I expected interactive. So is this thing gonna be able to supply the building full time? I really don't know what kind of capability they have now days.

My opinion of the diagrams is that they're minimally helpful. Or I should say that they have the stuff I already know but not much that I need to know in them. It was particularly irritating that the disconnect sections are all but undecipherable and they're also conspicuously missing from the diagrams. Maybe that's why. The diagram guy couldn't figure it out either.

I still have to pick a subject for a proposal before I run out of time for the next cycle and I was thinking that this might be it.

And the word photovoltaic is used far too often. It's used to describe things that are very specific and also everything in general. That's just not good. 690 needs some help with nouns.

I'm curious if you agree with my deduction that the disconnects in 690.13 and 690.14(C)(1) are the same disconnect.

George Stolz · Jul 9, 2005

Re: PV Inverters

Originally posted by physis:
So is this thing gonna be able to supply the building full time? I really don't know what kind of capability they have now days.

All you need to know is the general amount of sunlight for an area.

A while back, my wife wanted to do something like that (before she realized, oh yeah, we have no money). I started studying up on this stuff. Built properly, you can construct a concrete house that solely

uses the sun for heating
uses the thermal mass of the house to maintain that temperature overnight
makes use of soffit angles for cooling in the summer, by shading the interior of the house from the high summer sun
obtains electricity from the sun and wind.

I got some good info, bought some cheap plans off the net, and then finally convinced her that we just flat couldn't pull it off at this point.

I made a spreadsheet at that point that did a non-official load calc, well, let me take a picture of it...
First half of page
Second half of page
It's big, so I'm just putting the links up.

The first half is just addition, and after the load calc it starts figuring the most cost-effective method of gettin' 'er done. Adding a range was a real eye-opener! (We originally tried to get rid of the propane guy, too.)

And the word photovoltaic is used far too often. It's used to describe things that are very specific and also everything in general. That's just not good. 690 needs some help with nouns.

Click to expand...

Exactly. If I use wind turbines instead of solar panels, I can practically do whatever I want.

My question is: How easy do DC currents from a solar/wind array start a fire? If the answer is "easily", then I'd say you're right. If it's difficult, I'd say that given how similar the wording is to the wording regarding disconnects in 230, I would say that they were intending to treat the inverter as a "utility". and that 14(C) is in regards to the AC SE conductors. But it's too darned muddy to say either way.

[ July 09, 2005, 11:32 PM: Message edited by: georgestolz ]

physis · Jul 9, 2005

Re: PV Inverters

All you need to know is the general amount of sunlight for an area.

I don't agree. Just to throw a wrench into what might be some over simplifications.

What will the current and voltage output of the arrays be in ten years as compared to the installation date? If you haven't considerdired the essentially "unpublicised" derioriation rate of solar panel output production you might be surprised. I think of it as "save the planet, just don't look in the closet where the rest of the story is" mentality. I'm all for the ecology (I'm big on nature and camping and things and every time I go I do at least one thing to undo something uncool that someone else has done). But I see a disproportionate amount of untruth in this "field" nowdays too.

I want to see a disconnect that kills all outlets within a house outside

I agree.

I would say that they were intending to treat the inverter as a "utility".

Check out the definitions for Hybrid System and Interactive System. By inference, they're calling it a power source.

Then look at Electrical Production and Distribution Network. It would seem to exclude the photovoltaic system. Yet the definition would seem to include it.

Again. A little disorganized.

Weeee. Gives me somethin' to do though.

George Stolz · Jul 9, 2005

Re: PV Inverters

Hadn't thought of the degradation of the panels themselves, I always thought about battery maintenance/death as being the major setback. It could wipe out the cost benefit of an otherwise sound system.

Well, get to work on it!

physis · Jul 10, 2005

Re: PV Inverters

I forget the time span but I think it was ten years. And newer technology may have some improvement. But I think it's 50% in ten years!

You know, ouch.

Hey, how come nobody ever told me that?

Edit: Lead acid batteries are one of the most durable assemblies I can think of. They really only become volnerable when discharged for a couple months or more. The sulphur becomes part of the lead plates and over time becomes brittle. If you jar them around pieces of plate might flake off and land in the bottom of the battery bridging plates. That's why lead acid batteries should be stored charged.

[ July 10, 2005, 12:23 AM: Message edited by: physis ]

George Stolz · Jul 10, 2005

Re: PV Inverters

It makes sense.

Unfortunately, the solar folks have their az to grind, too. I guess burying those little morsels of information help further their cause, if at the cost of well-meaning homeowners.

Reminds me of the "Frustrated Environmentalist" bit in MAD magazine, when I was growing up.

It had a picture of the 4000 tons of styrofoam that the panels are shipped in.

physis · Jul 10, 2005

Re: PV Inverters

I like it. A lot of things that people have been told are environmentally responsible in reality only move the problem to a different place so that they don't see it now. And they will not listen to anybody who isn't a trained anchor-liar on the news.

apauling · Jul 10, 2005

Re: PV Inverters

my understanding of this rule is that whatever energizes the house panel needs to follow the same rules for accessible disconnect as the main panel. Some of the PV systems are smart and won't feed into an energized circuit, so some PV installers try to get away with just running into the system by back feeding a breaker in the panel. This is often done in a sub panel and creates a hazard because there is a two location disconnect, both the main power and the subpanel breaker need to be turned off. In other words, the house power cannot be disconnected with a maximum of six motions.

This can probably be argued, but it is my understanding.

paul

hydroelectric · Apr 2, 2006

Re: PV Inverters

physis said:
I'm having a great time with thread because I know absolutely nothing about these systems.

I spent, really, a day trying to understand 690. It's horribly written. It's like a terminology bizzar. And it isn't because I'm not familiar with the components.

But I've been wanting to get around to learning how these thing are configured.

You know, these things are nowhere near as complicated as they seem in 690.

SAM: Hello! My name is Mike and George Stoltz of Fort Collins CO turned me on to your conversation last July. I am a Master electrician here in CO and I specialize in installing both grid-tie and stand alone PV systems. I recently posted my own question on 690.14, but alas, only received various opinions. I finally received a definitive answer from the local AHJ and am moning forward.

After much review and reviewing the 2005 NEC Handbook, I feel like I finally got a handle on what the 2005 NEC is looking for in Article 690. SO>>>>>> shoot me a question if youi have any left!!

Take Care

Mike

lwd3 · May 14, 2006

Providing 240 V from a 120 V inverter.

Providing 240 V from a 120 V inverter.

Use a Xantrex (formaly Trace) T240 Auto transformer. Approximate cost $350.00.

mikeames · May 15, 2006

If the two are in sync ("There isnt a clock like digital, although I dont doubt it ") its more RC time constants then they will both have the same zero reference voltage. If one goes negative the other goes positive this will in effect double the voltage. If they are on independent references that they will act like the battery example above and will not sum to 240.

PV Inverters

physis

Senior Member

George Stolz

Moderator

hurk27

Senior Member

physis

Senior Member

George Stolz

Moderator

physis

Senior Member

George Stolz

Moderator

physis

Senior Member

George Stolz

Moderator

physis

Senior Member

George Stolz

Moderator

physis

Senior Member

apauling

Senior Member

hydroelectric

Member

lwd3

New member

mikeames

Senior Member