Is this too much power for a SB5000US?

System · June 2008

The quoted system is 32 x Mitsu UD185MDF5 panels and an SMA SB5000US.

When I use the CSI-EPBB calculator, I get the warning that "The CEC-AC rating exceeds the rated capacity of the inverter(s)." but the calculator still gives the results as if the limit wasn't exceeded.

When I use the string sizing tool on the SMA website, the maximum wattage moves into the red when the temperature gets down to 59 F. It's already in the yellow at 104 F. What does the yellow mean in the sizing program. There is no documentation anywhere on SMA's website.

I'm thinking I'm going to tell REC solar to go with a the 7000US because it will allow me to, in the future, add a 3rd string of 16 modules.

It also has a higher rated efficiency and the CSI-EPBB calculator adds about another $100 to the CSI rebate with that inverter(95.5 vs 96% efficiency).

mike95490 · June 2008

Re: Is this too much power for a SB5000US?

If your array is not at an optimum angle, you won't achive full output, and wont need the full wattage of the inverter.
If you plan on expansion, then yes, go the next size up. What's the eff. spec of 7000US at 2/3 power ?? More than the SB5000US at 95% Are you locked into SMA
At 59F, does red indicate over voltage, or just over power?

crewzer · June 2008

Re: Is this too much power for a SB5000US?

Sorka,

Based on Merced, CA data from weather.com, I recommend you use 14 F for the low temp spec and 104 F for the high temp spec.

See: http://america.sma.de/glossary.html#coldtemp
and: http://america.sma.de/glossary.html#hightemp

Red numbers in the SMA charts mean that the values exceed specs for the inverter. Green numbers fall within optimal performance specs. Yellow numbers are outside of optimal, but within limits.

Specs: http://download.sma.de/smaprosa/dateien/4752/SB5000US-7000US-101907.pdf

My interpretation of results for strings of 16 modules:

Table 1: Max cold temp corrected Voc = 548 V; Above “Peak Power Tracking Voltage” (250 V – 480 V), but < Max DC voltage (600 V)
Table 2: Max high temp corrected Voc = 406 V
Table 3: Min high temp PPV = 323 V
Table 4: Max high temp inverter power (2 strings) = 4376 W
Table 5: Max low temp inverter power (2 strings) = 5654 W; exceeds Max Output Power spec (5,000 W)
Table 6: Max high temp PV array power (2 strings) = 4582 W

HTH,
Jim / crewzer

System2 · June 2008

Re: Is this too much power for a SB5000US?

Thanks for the responses.

What does "not optimal(yellow)" mean though? Less efficiency? Shorter inverter life? Higher chance of running in derating mode?

crewzer · June 2008

Re: Is this too much power for a SB5000US?

Assuming the SMA calculator incorporates all appropriate NEC 690 factors for voltages, currents, and ambient temperature correction, I don't see any obvious or practical issues with the three yellow numbers above. Perhaps a "yellow" value is one that's within "X%" of the design/operational limits (20%?).

Regards,
Jim / crewzer

BB. · June 2008

Re: Is this too much power for a SB5000US?

Yellow may also mean that the inverter is outside the MPPT function limits of 250 – 480 V.

Or, you are not harvesting the maximum amount of power available (Pmp=Vmp*Imp) from the solar panels if the loaded voltage is outside the 250-480 volt range.

If the 480 volts is only exceeded in cold weather (frosty mornings)--the panels will quickly warm up and should drop below 480 volts--so the losses would be minimal in the grand scheme of things (you will have to check Vmp at the coolest operational temperatures you normally expect).

However, if your array's Vmp drops below 250 volts during the hot summer months--you will loose much more power.

Check to see if the Inverter you are planning on using will simply limit itself to its rated maximum power even if the power supplied by the solar array exceeds the inverter's input power limit--it should. Basically, you might loose some output from a very cold array.

-Bill

Is this too much power for a SB5000US?

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