Using enphase M215 with old 72 cell 280W panels STC vs NOCT

[doctorman]

planning a solar install on our home

bought these panels and M215 enphase inverters
MODULE TYPE = HANWHA SF260-36-1P280L (280W) MODULES

http://www.atensolar.com/media/data_sheets/h/s/hso_sf260_poly_ul_datasheet.pdf

used this calculator and the NOCT specs of the panels to see which inverter can do my job

https://enphase.com/en-us/support/module-compatibility

the M215 showed as an option , found them for cheap so I decided to use them

a solar guy saw my plans and said you can not use them with M215 ...

If I use STC specs in the calculator, I can not , I would need M250 or higher
If I use Normal operating conditions NOCT I can use M215

M215 handles 215 to 225W max
my 280W panels will be installed East west on a 18 degree angle roof in NY
according to NOCT I will make 204W max
now that I am not facing south and up in New York (zipcode 11021) I doubt I get more than 800 W/m2 irradiance

am I mistaken?
Can I use the M215?

[doctorman]

Spoke with enphase and was told M215 can handle max 48V and 400W before turning off
if it ever gets there it will turn on after the voltage drops to below 48V

normal running V is 36V
max open circuit they like is around 40V to be safe

the number of cells has nothing to do with the calculation
so enphase cares about the actual real Volt and Watt produced which are closer to the NOCT (normal operation condition test)

[J.P.M.]

Forget NOCT specs. They will only muddy the waters. You can do a lot better.

Do this. It'll give you a much cleaner picture of what's likely to go on over the long haul:

1.) Run PV watts with 10 % system losses.

2.) Download the hourly output spreadsheet.

3.) For each hour where the system output is > the sum of the max. inverter outputs, subtract the sum of the max. inverter outputs from that hour's output.

4.) Sum the column that has that difference.

5.) That sum will be a reasonable dart throw of what to expect for clipping over the long haul.

Add: NOCT == Normal Operating Cell Temperature.

[doctorman]

So in my case a
280W panel * 80 units = 22400
and
215W M215 * 80 units = 17200

I in the PVWatt hourly excel sheet I got the following columns

Month

Day

Hour

Beam Irradiance (W/m^2)

Diffuse Irradiance (W/m^2)

Ambient Temperature (C)

Wind Speed (m/s)

Plane of Array Irradiance (W/m^2)

Cell Temperature (C)

DC Array Output (W)

AC System Output (W)

the "Plane of Array Irradiance (W/m^2)" is the actual light each panel gets per/m2 ?
and the column that I should check is the "AC System Output (W)" and compare that to my 17200 correct?

The largest I got was (April 27th) at 17034W which is below the 17200 still so I am fine using the M215 without clipping ?

Forget NOCT specs. They will only muddy the waters
. You can do a lot better.

Do this. It'll give you a much cleaner picture of what's likely to go on over the long haul:

1.) Run PV watts with 10 % system losses.

2.) Download the hourly output spreadsheet.

3.) For each hour where the system output is > the sum of the max. inverter outputs, subtract the sum of the max. inverter outputs from that hour's output.

4.) Sum the column that has that difference.

5.) That sum will be a reasonable dart throw of what to expect for clipping over the long haul.

Add: NOCT == Normal Operating Cell Temperature.

[J.P.M.]

So in my case a
280W panel * 80 units = 22400
and
215W M215 * 80 units = 17200

I in the PVWatt hourly excel sheet I got the following columns

Month

Day

Hour

Beam Irradiance (W/m^2)

Diffuse Irradiance (W/m^2)

Ambient Temperature (C)

Wind Speed (m/s)

Plane of Array Irradiance (W/m^2)

Cell Temperature (C)

DC Array Output (W)

AC System Output (W)

the "Plane of Array Irradiance (W/m^2)" is the actual light each panel gets per/m2 ?
and the column that I should check is the "AC System Output (W)" and compare that to my 17200 correct?

The largest I got was (April 27th) at 17034W which is below the 17200 still so I am fine using the M215 without clipping ?

Good questions.

Did you read the all PVWatts help/info screens before you ran the model ? Doing so may be enlightening and help get the most from the experience. Do yourself a favor. Do some homework and stop spinning both our sets of wheels.

After that:

- What is your array's azimuth ? The "East - west" you write of is confusing to me. One array or two with one facing east and one facing west ? What is the azimuth of the surface normal to the array(s) (with 180 deg. being true south, east less, west more) ?

- The "Plane of Array Irradiance" is the radiant energy on one square meter of panel received in the plane normal to the plane of the array over the hour listed. It is important and interesting and something most are pretty much clueless about, but of little use for what you're looking for right now.

- Under "Advanced Parameters" reread the info about DC to AC size ratio on the PVWatts help/info screens and then rerun PVWatts with a ratio of something like 280/215 = ~ 1.30 for the M215 and see what you get compared to running the same scenario with a ratio of 280/250 = 1.12 for the M250. The difference will be an approximation of what the model thinks the difference in annual output from one inverter model to another will be.