NMOT - Why Not

[Cmy]

STC is a nice set of fixed conditions but how many reach those levels in real life? Inverter limits state Watts and Amps but not if they are STC, NMOT, or NOCT values. The newer M10, 44" wide, panels exceed the EG4-18 MBBT 25a limit and the S-A 15 26a dual string limit if the STC value. The newer N type topcon panels have higher Isc amps

https://tinyurl.com/26kpu2dn

but the usual lower NMOT numbers.

SignatureJames says the EG4 is good for up to 1.2 x 25a=30a. Sol-Ark says the -15 self limits above 26a. Older comments suggest STC provides a safety reserve but does the Canadian Solar really need 24% safety greater STC than NMOT for safety. Watt reduction is 32%., maybe that string can be a few panels longer

Has anyone measured coming close to STC values in real life? Why have NMOT and NOCT values other than setting realistic expectations.

 

[zanydroid]

For me STC +25% is what NEC gods say I need as wiring and fusing safety margin in case something weird happens with the weather.

The lower measurement standards IIRC are used by my POCO for some interconnect calculations

You can hit or exceed STC easily on a cold day with correct cloud conditions for improving scattered light hitting your panels. Ncsolarelectric has some graphs from recent days on his HMS2000 cheerleading and education thread

 

[sunshine_eggo]

STC is a nice set of fixed conditions but how many reach those levels in real life? Inverter limits state Watts and Amps but not if they are STC, NMOT, or NOCT values. The newer M10, 44" wide, panels exceed the EG4-18 MBBT 25a limit and the S-A 15 26a dual string limit if the STC value. The newer N type topcon panels have higher Isc amps

https://tinyurl.com/26kpu2dn

but the usual lower NMOT numbers.

SignatureJames says the EG4 is good for up to 1.2 x 25a=30a. Sol-Ark says the -15 self limits above 26a. Older comments suggest STC provides a safety reserve but does the Canadian Solar really need 24% safety greater STC than NMOT for safety. Watt reduction is 32%., maybe that string can be a few panels longer

Has anyone measured coming close to STC values in real life? Why have NMOT and NOCT values other than setting realistic expectations.

I've seen my 2970W rated panels output 3600W. Cold ambient, 6500' elevation (more irradiance than at sea level) and cloud edge effects.

NMOT assumes 800W/m^2, so a sunny day and clear sky will often exceed it.

In full sun during the middle two hours of the day, it's rare for my array to put out less than 90% of its rating as I have exceptionally favorable conditions.

The question becomes if your panels EVER see 1000W/m^2 irradiance, then they will achieve STC current.

So don't over-panel the shit out of your MPPTs

 

[Cmy]

No, not trying to go crazy, just trying to understand realistic limits. I am 800 ft above MSL, north Texas, so there are some bright days. Looking at NMOT watts at 2/3rds of STC watts questioned the number of panels. Good to see the higher output.

Like others, doing the EG4/S-A dance. Like the idea S-A 'self limits' above 26a but string wattage is limited to 3200W times 1.2 or 3360W (there is the extra 20% again). So a max of eight 420w panels in series or seven 460w panels. And 600-700W are coming?

https://tinyurl.com/2yc55k5b

EG4 has higher numbers, I prefer four stings vs. six, costs less, and Signature is two hours away. Hitch up the trailer and fewer concerns about shipping damage or moving a pallet from the end of a driveway. I have seen fewer S-A set up issues on the forum than the EG4.

 

[zanydroid]

Are you using PVwatts to help with modeling? You ought to be. If you use that method it will already compensate for weather and use more realistic output

600-700W just means bigger panels. If there was an efficiency breakthrough enabling 600W on same size panels as today the forum boards would be lit up. Those you linked are 80lb…

If you want to go outside the standard sizes you need to be confident in your math and design skills. The above ones are bigger via higher current output. So I think you will get your self into trouble on MPPT limits. Which are often designed for mainstream panel currents. You may find it harder to max out on capacity

Personally I think those big panels are a noob trap that’s not talked about enough as such.

 

[Cmy]

PVwatts is an old friend that helped convince me (along with forum comments) that an E/W split on a 5 degree slope metal roof lost little on the east side and gained a longer day. Using 14kW of panels for planning comparisons, wife freaks when I get on a roof (too old) so hiring install. Typical technology with better always on the horizon.

Just trying to find the sweet spot between a lot of inexpensive small panels requiring more mounting, wires, and labor vs fewer higher watt panels.

 

[zanydroid]

Above a certain size threshold the rooftop installers would probably refuse to work on the panels. 400-450W is the comfort level of most installers for rooftop. Might also exceed some insurance or workplace safety threshold too.

 

[Cmy]

When the house had its composite shingles replaced they used a ladder, a Harbor Freight winch, and a home made wood frame to haul bundles up the nine ft side. While my metal building has 15 ft sides, the peak is 18 ft so easy to work on once panels are up. Definitely liking the 50 lb panels better than the 60-70 lb panels.

 

[zanydroid]

There are some videos on how to rig that kind of sled. Don’t know if any DIY sleds show lifting a panel. There are sleds for lifting solar panels for huge commercial roof projects, $$$$$