Greetings from cloudy Frederick, MD

[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]

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

[websterize]

From SREC aggregator Sol Systems: "

[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.

[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]

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.

[websterize]

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

[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!

[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.

[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]

Bill
let me think about that one
I still think there would be voltage problem with the 14 modules on one string.
how it would react with the other string in parallel I will have to think about more.
With unequal strings there are going to be losses as they are not matched.

[websterize]

Another scenario: stringing 13 panels to the 3800US and a 13 and 14 to the 7000US. Then we're within voltage spec on the 3800, and we can use all 40 panels. Now this seems to make the most sense.

[Naptown]

We're rethinking the inverter swap -- replace mistakenly installed 3000US (500V) inverters with 3000HF-US (600V) model -- for two reasons. The dimensions of the HFs are different enough that affixing them in the same spot might not work. More importantly, we'd have to leave the 40th panel unplugged (3 x 13 panels).

Instead, we're considering two inverters: a 7000-US with 26 panels and a 3800-US with 14. That's one less inverter to replace, and 40 hot panels, for a 10.4 kW system. This seems to make the most sense.

Also confirmed with Solsystems, a local SREC aggregator, that to qualify to produce SRECs in Maryland, our >10 kW array will need a revenue-grade meter. Right again, Rich.

All inverters in the US are limited to input voltage of 600V
So the 3800 will handle the extra wattage of the 14th panel. Problem is the same as the 3000HFUS with 14 of those modules on a string the voltage is over 600V at your lowest record temperature.
The only viable option I found that will work is the Fronius IG10+
Because of the lower start voltage and stepped power levels you could string 10 modules on a string, use all 40 modules and down the road you will have only one inverter to replace. And if you act fairly quickly that can be extended to 20 years for about half the cost it would be normally.

Here is the crux of the problem
Atis Sun is a Schuco dealer. Schuco provides "packages" to the dealers. These are pre engineered package units designed for a dealer with no knowledge of how to engineer solar to enter into the business. Generally in pre determined configurations, with inverters chosen for the application. Not much thought on the dealers part required. Your's has gone outside of the pallet so to speak.
I do not know if the Fronius is available to them through Schuco I believe Schuco is strictly SMA.
The problem is that SMA does not make a product I could find that works for your application. The problems come in when determining voltages for the most part. 10 on a string is not enough voltage and 14 on one is too much.
The problem did not start with the unexpected change from a 255W panel to the 260's you got. The voltage characteristics of both modules are identical.
As far as the meter goes we are a platinum dealer for Sol Systems we know the requirements although they are the same for everyone regardless of aggregator.

[websterize]

We're rethinking the inverter swap -- replace mistakenly installed 3000US (500V) inverters with 3000HF-US (600V) model -- for two reasons. The dimensions of the HFs are different enough that affixing them in the same spot might not work. More importantly, we'd have to leave the 40th panel unplugged (3 x 13 panels).

Instead, we're considering two inverters: a 7000-US with 26 panels and a 3800-US with 14. That's one less inverter to replace, and 40 hot panels, for a 10.4 kW system. This seems to make the most sense.

Also confirmed with Solsystems, a local SREC aggregator, that to qualify to produce SRECs in Maryland, our >10 kW array will need a revenue-grade meter. Right again, Rich.

[Naptown]

Having a commissioned Webster Solar Billboard by April 30 would exceed my expectations.

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.)