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Old 02-16-10, 11:42 AM   #11
Xringer
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Here's the high lights of UL-1741
UL 1741 highlights

Anti-Islanding test is an important part of the testing, but most UL testing includes
fire prevention factors & and anti-electrocution as the main thrust of the testing.
At least it was that way when I was getting FCC & UL testing done for NEC printers and PCs.


The risk of 'electrocuting a lineman' down the road is always going to be a problem.
If it's not part of their training to double check lines (for back-feed) before working on them, it should be.

Anytime you have a storm with lightning, there is a chance that a grid tied inverter might get damaged.
If it's not 100% fail-safe with redundant back-up/continuous self-testing, it just might keep putting killer AC out to the grid...

Touching 'dead' lines after a storm is like flying in a helicopter..
You have to really trust complicated machinery..

~~~
I wonder what happens when you have a few grid-tied systems on the same short street..?.
It seems all it would take is some downed lines, and a single malfunction to keep all the grid-tied systems on-line...
It seems like they would feed each other..
Tricking the systems into thinking the grid was still connected..

Or, maybe some goofball with a 6kw gas gen connected to the grid??
That might keep those Enphase homes making juice..?.


Last edited by Xringer; 02-16-10 at 11:51 AM.. Reason: crazy idea..
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Old 01-29-11, 11:22 AM   #12
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XRINGER: Thanks for the post on the Chinese MPPT inverter!

There is, at least to me, a very good reason for being able to deliberately ISLAND a grid-tie solar array. That reason is disaster preparedness. Tornadoes, Hurricanes, Fires, Earthquakes, Accidents, and Civil Unrest happen. Our power grid is pretty reliable... but it wouldn't take much for areas to have very prolonged outages. A disaster interrupting basic services (water, sewer, electric) of a couple weeks or more would drive most people out of their homes. I'm fortunate enough to have a well, a septic system, and a wood stove - BUT, the well pump requires electricity.


If, by replacing one grid-tie MPPT inverter on my solar array with a true-sine wave off-grid micro-inverter, I can have daytime power, then I have water and can stay in my home through tough times. -- Of course, taking such an action INCLUDES opening the main circuit breaker at the power meter so linemen are protected.

Being able to go "off grid" in this manner has a few challenges because grid sensors look for both frequency and voltage. If the grid goes down, a solar array won't be able to drive all the neighbors' loads, so the voltage will fall below specifications and trigger a shutdown. Furthermore, the array might not be able to drive all the loads in the house - particularly if there's not a lot of sunshine. So... you would have to disconnect the grid AND shutdown all unnecessary loads in the house. UPS systems for critical items like the fridge, freezer, and well pump may be required to provide surge current for start-ups. If you're going to try and trick grid sensors with a tiny 200W inverter... all loads in the house will have to be shutdown until the array is back online. Then...when a couple clouds come by and available power is less than the demand, voltage will fall below spec and the array will shut down again.

Tricking the GTI is only one part of the problem. Dynamic loading is another critical feature. Using something like the Enphase Envoy - or better yet, direct communications with the inverter modules, smart-loads could be implemented that could negotiate for "online" time with other loads based on available power and thus improve emergency system reliability.

Think it through, be prepared, and in doing so, be part of the solution in hard times.
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Old 01-29-11, 12:52 PM   #13
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Here's a guy that tricked some GTIs..

I tried the same trick, with a 1200w GTI & a small 300w sinewave inverter.
And, I wasn't able get a stable output from the sinewave unit. It kept blinking
off for a second and the GTI would drop off-line and have to restart.

But, I was using a battery bank to feed the GTI. Next time, I'm going to try it
using the new 400w PV array. These PowerJack GTIs weren't made for battery operation..
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Old 03-08-11, 10:43 PM   #14
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I have to echo other's concerns about the Enphase M190s... as I have a xx panel array of 235W panels. Power production from each Enphase unit maxes out at 199W - so... allowing for 5% inefficiency in the inverter, the array should be producing 9.3kW vs. the 8.3kW that it currently maxes out at.

I've ordered a 300W 24vdc to 240vac, 60Hz inverter to install (in an emergency situation only - with the grid disconnected) to act as reference for the other xx panels. I'm expecting the array will have to be disconnected from all loads for the 5 min required for the Enphase inverters to come online - then, house loads can be added, so long as they are not sufficient to drop the array produced voltage below the specs.... Bound to be a problematic situation...but so is any emergency.
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Old 03-08-11, 11:27 PM   #15
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Your power-up procedure sounds like it should work.
I would be interesting in hearing how your testing works out.
Is the 300w inverter a Sine Wave model? What's going to provide the 24vdc?

I tested my back-up system today (for about 4 hours).
My 2.5kw MSW inverter was supplying the three sump pumps,
(which have been running for about 2 days now),
A small freezer and my PC loads were also on the the backup.

The 500w tracking array provided all the power, while it kept my 48vdc bank charged up.


Spent some money today. Ordered a 'FCA2-05 Failed Circuit Alarm', in case the grid fails in the middle of the night..
I don't want to be sound asleep while my food spoils or my basement floods.
Need to get up and throw some switches..

Also ordered another pair of 200w PV panels! Too good a deal to pass up..

Cheers,
Rich
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Old 03-09-11, 04:58 AM   #16
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Re: electrocuting the linesman
I was taught to put earthing clamps on the lines being worked on, thus any back feed or some idiot turning the system on would not kill off the workers. Dont know how its done in your country but I cannot see the problem, well not in NZ anyways.
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Old 03-09-11, 06:59 AM   #17
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Quote:
Originally Posted by Solar Mike View Post
Re: electrocuting the linesman
I was taught to put earthing clamps on the lines being worked on, thus any back feed or some idiot turning the system on would not kill off the workers. Dont know how its done in your country but I cannot see the problem, well not in NZ anyways.
Whenever a lot of lines go down in a storm... Maybe less qualified people
get sent out into the field.?. Like managers that should be left in the office,
pushing paper and updating their Windows..
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Old 03-09-11, 04:46 PM   #18
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The idea of being able to deliberately put your array into "island mode" is an emergency use only idea. Trying to bring the array on-line with a reference inverter simply will not work if the grid is not disconnected first - there's no way a little 300W inverter could drive the loads of all the other homes on you line segment, let alone your own house load....so voltage would never get to the line levels required to wake up the other micro-inverters. Again, this is an emergency only concept, the intention of which is to alleviate human suffering and allow someone to stay in their home when they might otherwise have to leave.... more than a few days w/o water & sewer, and you just couldn't stay. For those with solar, a well, and septic, a little power could keep you in your own home rather than making you a refugee.
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Old 03-09-11, 05:14 PM   #19
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IF, the line coming into your house was somehow ripped off the pole, and
IF you did not open your main breakers, that 300w inverter
could make that wire laying in your driveway a bit dangerous..

It would be great if the Ephase 190s synced up with the 300w sinewave!
But, if you left a hot line going out, the whole array would be feeding it..

Worse case, a doper sees the wire laying in your driveway, thinks it's copper
and tries to steal it..
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Old 03-09-11, 05:36 PM   #20
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[QUOTE=Worse case, a doper sees the wire laying in your driveway, thinks it's copper and tries to steal it.. [/QUOTE]

This has happened here, except the cables were live at the time securely mounted atop 30' poles, several kms were stolen. Dairy farmer went out to milk his cows at 5am and discovered milking shed had no power, faults linemen discovered the lines had been stolen during the night.

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