OCPD for a Xantrx GT inverter-protect from utilty backfeed

Earthandsol · August 2009

Greetings fellow sun worshippers( or just fans)'
I am new to posting here, but have been lurking for several years. I have installed one grid-tie system and several off-grid systems so I feel just experienced enough to be more dangerous and effective than ever.
Finally, the ? In my area ( SE Tenn) our electrical overlord TVA ( all bow ) has set a new stone tablet decreeing how we shall connect to the sacred power lines. This new requirement (administered and re- interpreted thru our local Electric co-op) requires all Grid-tie systems to backfeed their measly current ( 1.9 kw or 7.9 amps @ 240 volts for this system I reference) directly to the utility transformer( rather than backfeeding a double -pole breaker thru the customers existing service as is typical in many places and once ( prior t0 7/1/09) was the law here.
So now there are typically no OCPDs ( overcurrent protections- fuses or breakers) located between the very large utility transformer and my GT 2.8 inverter and then my 10 Evergreen Spruce 190 watt panels - there will be a Square D 30 amp lockable disconnect ( I typically have used unfused models as less $ and easier to find) to protect the lineman and utility from a rogue inverter. Xantrex specs are a 0 amp Max. utility backfeed current so is trusting the inverter to stop any utility backfeed a good idea or am I just being a cheap squid -
Chris

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Cariboocoot · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

You have a great sense of humour.

But I can't be reading this right: NO circuit protection between the inverter and the power transformer?

mike95490 · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

Maybe it's the first step to allowing the "transformerless" inverters, which rely on the step-up/down transformer to do their work. Less "junk" in the path give them better performance.

Do you get to back feed the meter to get credit for your contributions ?

niel · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

i think you need to talk to tva about it as your local coop might be misinterpreting something. you have a right to protect yourself with a fuse or breaker imho.

Solar Guppy · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

Sounds more like they dont do net-metering .. they require a seperate meter for the Solar and you get paid by what that meter shows for generation.

The GT inverter has an internal fuse, so its protected, but it is a requirement for the wiring to have over-current as you can't have 4 AUT running into the Xantrex GT, so at the dedicated meter, it needs to have a properly sized overcurrent device for the wiring ( I believe the GT specs 15-25 amp depending on the model )

Earthandsol · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

Thanks for the replies. They do not do net metering - they pay for everything you produce at a nice 12cent per kwh premium and sell you everything you use. This doesn't really make up for the expensive method of hooking up though. They retain rights to any carbon credits.etc. and then " sell" your green power to other TVA customers.
They require #4 copper ( plenty big for my 7.9 amps)so wire size is sufficient for any inverter loads or overloads - I was wondering if anyone had any suggestions for inexpensive fusing or breakers - I have even considered an HVAC fusible pull disconnect -but they strike me a cheap and cheesy- Square D makes great stuff but if you step off the sidewalk ( in terms of something not commonly available) it seems rather arcane their retail pricing structure and unfortunately I live far from a good Electrical supply. I could spec the required Square D disconnect as fusble and now as i type - i realize I should probably just pay up and move on. i just get frustrated at having to make these systems any more complicated and expensive than necessary. Common sense has left the bulding- thanks again
Chris

t00ls · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

Earthandsol wrote: »

.
Finally, the ? In my area ( SE Tenn) our electrical overlord TVA ( all bow ) has set a new stone tablet decreeing how we shall connect to the sacred power lines. This new requirement (administered and re- interpreted thru our local Electric co-op) requires all Grid-tie systems to backfeed their measly current ( 1.9 kw or 7.9 amps @ 240 volts for this system I reference) directly to the utility transformer( rather than backfeeding a double -pole breaker thru the customers existing service as is typical in many places and once ( prior t0 7/1/09) was the law here.

I live in the tva service area and have a xw 4548 grid connected....first,I've seen no mention that you cant put a breaker in-between the inverter and grid power,as that is how I have mine Eg:100 amp 2 pole bi-directional breaker between grid and generation meter and a 60 amp lockable disconnect between generation meter and inverter.........and second

it is a requirement that the utility company net meters ...you can ask tva

the reason for this is you have to be able to net meter on the grid meter ....you cant do that if it goes directly to the tranformer

your utility company is getting you to not put power back through their meter so you pay exactly what is distributed to the house

in fact...you are now paying for what you put into the grid because it will go to your home first before it goes into the transformer

better call tva and explain that your utility company is "bending you over"

t00ls · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

c&p from TVA with applicable highlighted

Below is an overview of how the program works:

* An eligible, renewable generation system is installed by a residential, commercial, or industrial power customer served by a participating local power company of TVA power.
* TVA will purchase 100% of the green energy output at a premium of $0.12 cents per kilowatt-hour (kWh) for solar and $0.03 for all other renewable generation sources above the retail rate plus any fuel cost adjustments. All new participants will qualify for an additional $1000.00 incentive to help offset start-up costs.
* Payment is issued in the form of a credit on the participant’s monthly power bill by the local power company, who will meter both the power use of the home or business as well as the output of the renewable generation system.
* The power company will provide monthly statements showing energy used and any applicable credit due. The power bill will be reconciled monthly with these energy credits. If the system produces more than the home or business consumes, a check will be issued monthly or annually, at the discretion of the local power company.
* All equipment must be in compliance with environmental regulations and national standards, certified by a licensed electrician, and meet all applicable codes.
* The customer is guaranteed payments for 10 years from the start of the agreement with the local power company.

and here

Following are the installation requirements:

Please note that the installation requirements are subject to differ depending on the participating local power company.

* Submit a completed application form for interconnection to local power company prior to purchasing equipment.
* Must comply with all requirements established by the local power company for interconnection to their distribution system including signing the Interconnection Agreement.
* Interconnection and safety equipment must be listed by UL or ETL for continuous interactive operation with an electric distribution system.
* All equipment must include a manual, lockable visible load break disconnect switch easily accessible by local power company.
* Must be manufactured and installed in compliance with the National Electric Code.
* Must be permitted and certified by a licensed electrician, and pass applicable code inspections.

I know that the nec code says specifically that you have to have a breaker installed for the fact that a lockable disconnect will not stop an overload unless it is fused....and you say yours isnt,so you would be in violation of that code

anyone else have a comment on this ...correct me if I'm wrong

Cariboocoot · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

You know, this kind of resistant (pun intended) utility company policy towards grid-tie is only going to encourage a lot of illegal installs.

This one is even worse than the "we get all your excess power for free", but not quite as bad as "you should pay us even though you're not connected to the grid" - both of which have been brought up on this forum elsewhere.

BB. · August 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

Problem is that the cost of electricity (power plant infrastructure and fuel to run it) is less than 1/2 of the utility's cost...

From a pure economics point of view--customers supplying their own power (and even using the "grid" to distribute excess daytime power to neighbors for "free")--just does not make sense.

It only works economically when the amount of power being generated "at home" is a small fraction of the entire grid (round off error on the balance sheet).

And utilities have their own way of "fixing" the problem. Meters that "turn forward" when back powered (charging you for putting power on the grid).

"Reservation charges" (in California current required for commercial electric accounts) based on your highest 15 minute usage in the last one year--which accounts for (very roughly) 1/2 of the total electric bill. For me, the reservation charges (if implemented for residential power) could be based on my peak Solar Output Power (usually, my peak solar output is more than my peak power consumption)...

For the most part, Solar GT would be best to keep under the radar--If it ever becomes a profit and loss on the Utility Ledger (say >10% of their capacity)--It will become obvious that Solar GT does cost utilities to support.

-Bill

Earthandsol · September 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

I am sorry if I wasn't clear - I can install OCPD - protection -the utility doesn't care but wants it only on their terms which are usually expensive and baffling and profitable for wire and equipment providers. ( i.e. #4 copper 1000 'spool on my current job to backfeed a 1.9 kw array to their transformer- in a new trench 2 ft horizontally from the existing underground service with rigid conduit required everywhere exposed

an earlier grid-tie system which under the old TVA contract was a net metered system required a service sized( the size of the customer's elec service ) lockable disconnect in line before the customer's service panel so they can shut off the entire service to protect against the 1.4 kw PV array backfeeding the customer's panel (( I had to convince 2 engineers that a 100 amp disconnect was sufficient as the customer's service was only 100 amps even though all the supplied model diagrams showed 200 amp disconnects))
TVA is moving away from net-metering as they are expected to do TOU rates in the next year or less and my Utility wants to stay out front. I am glad if anyone can do a battery - based Grid tie system like an XW inverter - but my read from the TVA website says nada- if interested read to the bottom of this FAQ
http://www.tva.gov/greenpowerswitch/partners/faq.htm#16
I agree Bill that the economics seem to make little sense from either side of the equation. I am just weary of spending more time , money and materials to make the math even worse all the way around.
Still I am glad to be working outside harnessing the sun.
Chris

niel · September 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

my take on that faq is that they are assuming a straight gt system and made no mention of not being allowed a battery backed gt system. they say it won't be powered because straight gt systems stop feeding the grid due to anti-islanding, but a battery backed system would do the same thing with the grid and has anti-islanding except your batteries are now powering the inverter for ac into the home. at the bottom where it says, in other options for outages, i'll bet they have in mind a generator set to switch on for the outage, but a battery backed pv system is fine too and i see no language there disallowing it.
the disconnects i'm not surprised about.

t00ls · September 2009

Re: OCPD for a Xantrx GT inverter-protect from utilty backfeed

I dont want to sound rude....but however you read that link.....you must have misunderstood or dont understand how a battery based xw works....I wont explain it ....but the way I read it is exactly the way I have mine hooked up......my complete system only cost me $9,500 that isnt a lot ....I have followed the nec code and nothing I have done is baffling.....I'm not even sure why you first started this thread....you dont have a good question......and your not answering a question.................what I do see,is a lot of disinformation about doing grid tie with TVA and TVA themselves

I wont be back to this thread

OCPD for a Xantrx GT inverter-protect from utilty backfeed

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