Greetings from cloudy Frederick, MD

[websterize]

Here's the electrician's thinking. He really wants to make all this right:

"The max voltage on the panels are 37.9 volts. The SMA has 555V listed for 13 panels and that has a +12% buffer built in as 13 panels @ 37.9 = 492.7 +12% of the max = 552V. Adding the 14th panel brings it to 594.2 with the extra 12% we are still under the 600 volts."

But his data are assuming a -10 degree C (14F) lowest ambient temperature. That temperature seems off, based on the readings near my 21704 ZIP at http://www.solarabcs.org/about/publi...map/index.html. -14C, -18C in nearby towns.

We're so close to 600V with a 14-module string, might be prudent to only plug in 39 panels.

[Naptown]

VOC on that module is 37.9 @ 25C
So VOC on 14 modules @25C is 530.6
Now correct to the -14C which is cutting it fairly close and above some of the surrounding area and the temp compensation
and the voltage is 605 Voltage does not drop below 600 until we bring the lowest temp up to -11C and that was 599.36V
-11C is 12.2 degrees F. Still too close for comfort IMHO. Typically I design for 4- 5C below the coldest recorded. But that is a personal preference.

This still does not solve the unbalanced strings on the one inverter. If they insist on connecting the 40th module at least connect it to the smaller less expensive of the inverters. there will be less losses and less replacement expense. But you are taking a chance doing so.

Again the best solution is the fronius inverter. There may be other manufacturers but I like Fronius and looked there
You use all the modules, and will get maximum power from your system.
These are available to anyone.
The array will have to be re-strung into 4 strings of 10 modules each. This will be a PITA of epic proportions for your installer as many if not all the modules will need to be removed and reinstalled to facilitate the new string sizes. This is something I would not look forward to doing and may be why the less than optimal solutions are being offered.

Or just plug in the 39 panels. that works too. Safer but you paid for 40 panels not 39.

[big000000]

Since our install this past Thursday, we've had nothing but clouds and rain. Like gloomy wedding weather, I consider this a good omen. Here's to a bountiful 2012 solar harvest -- very amped to join the PV club.

Hello to you too!

[websterize]

[QUOTE=Naptown;44460]Or just plug in the 39 panels. that works too.

[websterize]

At 39 x 260W (10.14 kW), the array might be Level 1, which in Maryland requires no revenue-grade meter or liability insurance -- because it's AC, not DC, that determines size, according to http://webapp.psc.state.md.us/intran...o/home_new.cfm "Solar PV Frequently Asked Questions"

"How do I determine whether my [Solar PhotoVoltaic System] is a level 1 or level 2 system?

Answer: The capacity of each panel times the number of panels equals the Direct Current (DC) capacity of your system. Multiply that capacity by the Design factor (0.80 to 0.83) to determine the Alternating Current (AC) capacity of your system which is used to determine the level. If the AC capacity is less than 10KW it is a level 1 system. If the AC capacity is equal to or greater than 10KW it is a level 2 system."

How do I determine the design factor multiplier? PV Watts says my derate (Baltimore) is 0.77.

[Naptown]

Correct that will determine whether it is a level 1 or 2 in your case you will be a level 1

I believe the meter requirement is one that the aggregators have however I do not actually do the interconnect agreements and SREC contracts for my firm so you may be correct.

As far as derate goes that is one based on system design and takes many factors into account.
Two things you can definitely change on the pvwatts derate are the top line which is power tolerance. change this to a 1
Also change the inverter efficiency to what your inverters are rated at. The other numbers i would need a lot more information to calculate and is beyond what I would do for free on a forum.

[websterize]

Thanks, Rich. I'll check with a couple of aggregators on whether they base array size on DC or AC for a revenue meter. Appreciate your PV wisdom.

[websterize]

From SREC aggregator Sol Systems: "

[Naptown]

[QUOTE=websterize;44749]From SREC aggregator Sol Systems: "

[websterize]

don't count on it
If they had the inverters installed and inspected tomorrow Allegheny will take 3 weeks to install the net meter. If I had to venture a guess I would say late May to early June. (They have no control over the utility Co.)

Right again, Rich. The Potomac Edison tech plugged in the net meter this morning, a little over three weeks since we received the passing electric stickers on May 18. He also confirmed what you said about the solid state meter counting up even when the three LCD indicator bars run backward (right to left).

What a marathon this has been.

[Naptown]

Well at least you are at the finish line.
Now it will rain for the rest of the week

[websterize]

It's odd how information in posts 53 and 54 is missing. Mod edit? (If so, why no explanation of infraction?)

Update: Found additional edits in posts 35 and 38. As I recall, those posts included boilerplate replies from Matt Bartlett at AtisSun saying, to paraphrase, that they stand behind their work and will make whatever is wrong right. In the end, they did.

[russ]

It's odd how information in posts 53 and 54 is missing. Mod edit? (If so, why no explanation of infraction?)

Update: Found additional edits in posts 35 and 38. As I recall, those posts included boilerplate replies from Matt Bartlett at AtisSun saying, to paraphrase, that they stand behind their work and will make whatever is wrong right. In the end, they did.

No edits in 35 or 38. Edits would be noted at the bottom of the post.

53 & 54 - if an ad or such is deleted no explanation is given - there is just an empty place.

[Naptown]

There is certainly missing information. Both his and my posts were edited.
I don't believe anything that was posted was in any way an advertisement.
and again an edit by a Moderator would leave a tag in the post saying it was edited.

[websterize]

No edits in 35 or 38. Edits would be noted at the bottom of the post.

Right.

53 & 54 - if an ad or such is deleted no explanation is given - there is just an empty place.

The aggregator said, per the Maryland PSC, that array size is based on AC size. I included their reply not as endorsement for the company, but confirmation from a second source. If the mod thought it were an ad, why wouldn't he have removed the company's name?

Whatever the case, June was our first full month with a net meter, and it was a terrific harvest. Even with the record heat, we generated nearly 1.5 MW and ended the billing period with a 140 kWh credit. The bill was $5.37, the price to connect to the grid each month, according to Potomac-Edison. It's never lower no matter how high the credit.

You can follow the array's performance by clicking my username above and following the homepage link to the array's Sunny Portal data page. I'd post the link here, but it might be interpreted as an ad for SMA.