Inverter / system questions

[Fatbloke]

Hi All

I am still trying to decide on 16 x 240w REC poly panels or 16 x 245w Bisol mono panels but currently leaning towards the Bisol panels - any advice / comments???

The other questions are, I was going to use a single SMA 4000TL inverter for the 16 panels to connect to but would it be better with 2 x SMA 2000 inverters or if I just use the single 4000 (dont know what cost of 2 x 2000 would be), should several strings be used and if so how should this be configured?

Cheers

Dave

[Naptown]

16 modules may be a tough number to get to configure into strings 16 is probably too high a voltage and 8 is too low.
Run the string sizing calculator from SMA. Yes you can use 2 inverters.

[vinniethePVtech]

I need Vmp and ImP STC conditions of both panels selected. MAX panel rating means nothing for true system requirements.
Secondly I would buy mono crystalline just to reduce surface area and to stay out of wind shear zones.

[vinniethePVtech]

Ok so I looked up the specs myself.
BISOL
ImP 8.15
VmP 30.2
Module efficiency 16.8%
Load max @ 16 modules 3938 watts


REC SOLAR
ImP 7.9
VmP 30.4
module efficiency 14.2%
load Max @ 3842 watts

It would probably be best to go with the BISOl vs. REC.
BISOL has the higher efficiency rate so long term production will always be better.
All I install are SMA US models which convert dc/ac comfortably with anything above 200v.
So you can easily split into 2 strings of 8 with the BISOL. If run is long you may want to consider 1 string of 16 due to voltage drop.

[Mike90250]

I'd suggest using the inverter's Mfg array sizer caculator, at their website.

[vinniethePVtech]

I'd suggest using the inverter's Mfg array sizer caculator, at their website.

Calculator is no longer offered at their website. However you can download sunny design 2.0 for pv users.

[vinniethePVtech]

The SMA 4000TL requirements:
MMP voltage range 188v~440v
ImP 17 per string

2 BISOL strings of 8 panels work comfortably for the 4000TL inverter. Infact this is better than the specifications of the 4000US which would require a MMP voltage range of 250v~500v
AMPs per string ImP 8.15 X 1.35 = 11.0025amps
Overcurrent protection maxes at 17 per string so 2 strings for the sunny boy 4000TL are perfect!!

[Fatbloke]

Inverter strings

Hi All

Thanks for the replies - it is much appreciated.

I downloaded the SMA Sunny Design 2.0 software and it looks like 2 strings of 8 panels wil be fine.

I will hopefully be ordering the kit (probably Bisol panels) and getting it installed soon.

Cheers

Dave

[KRenn]

Ok so I looked up the specs myself.
BISOL
ImP 8.15
VmP 30.2
Module efficiency 16.8%
Load max @ 16 modules 3938 watts


REC SOLAR
ImP 7.9
VmP 30.4
module efficiency 14.2%
load Max @ 3842 watts

It would probably be best to go with the BISOl vs. REC.
BISOL has the higher efficiency rate so long term production will always be better.
All I install are SMA US models which convert dc/ac comfortably with anything above 200v.
So you can easily split into 2 strings of 8 with the BISOL. If run is long you may want to consider 1 string of 16 due to voltage drop.

What does efficiency have to do with production?

[vinniethePVtech]

What does efficiency have to do with production?

EVERYTHING.
Tell me the difference between a PV panel at 16.8% VS 14.2%.
Add deteriorating defecit factors for the next 20+ years and tell me what panel are you still going to want for producing power? in 15 years alone you can notice upto a 8% AVG. drop in power. You always want PV with higher efficiency to outlast production.

When people look at MAX PV power out put they assume that is 100%. That is false. MAX power is a percentage based on conversion efficiency. That conversion percentage is what offsets the ratio in deficit losses through out the next 20+ years. If all panels were equall to each other at 100% then conversion efficiency wouldn't matter.

Back to Back comparison:
SUNPOWER E18 230 PV panel (18% efficient) VS a suntech 230-20/WD PV panel (13.9% efficient). In 20 years the sunpower module will consistently make more power than the suntech. The closer conversion effeciency gets to 0% that PV gets a 0 return on power. The suntech power has greater probability of reaching 0% before the sunpower PV will reach 0%. Are you understanding conversion efficiency to deficit losses?

Then production begins to drop from deficits, utility bills will start to go back up. Higher percentage in efficiency the less the drop in power will be through out a longer duration of time, avoiding less probability of utility bills going up.

[Naptown]

EVERYTHING.
Tell me the difference between a PV panel at 16.8% VS 14.2%.
Add deteriorating defecit factors for the next 20+ years and tell me what panel are you still going to want for producing power? in 15 years alone you can notice upto a 8% AVG. drop in power. You always want PV with higher efficiency to outlast production.

When people look at MAX PV power out put they assume that is 100%. That is false. MAX power is a percentage based on conversion efficiency. That conversion percentage is what offsets the ratio in deficit losses through out the next 20+ years. If all panels were equall to each other at 100% then conversion efficiency wouldn't matter.

Back to Back comparison:
SUNPOWER E18 230 PV panel (18% efficient) VS a suntech 230-20/WD PV panel (13.9% efficient). In 20 years the sunpower module will consistently make more power than the suntech. The closer conversion effeciency gets to 0% that PV gets a 0 return on power. The suntech power has greater probability of reaching 0% before the sunpower PV will reach 0%. Are you understanding conversion efficiency to deficit losses?

Then production begins to drop from deficits, utility bills will start to go back up. Higher percentage in efficiency the less the drop in power will be through out a longer duration of time, avoiding less probability of utility bills going up.

Disagree with the above.
If a module is rated at 250 watts and loses 10% over the first 10 years it is then a 225 Watt module.
Module efficiency only has to do with conversion rate and physical size of the module. If a Sunpower loses the same % and is the same power it is still a 225 watt module the only difference is it is still smaller.

Production drops are based on nameplate ratings not conversion efficiency.

[vinniethePVtech]

Disagree with the above.


Production drops are based on nameplate ratings not conversion efficiency.

How do you explain AR coating? Its an INCREASE in efficiency. Increases the conversion process. Can EXTEND the conversion process.
When applied to a module that has lost diminishing percentage AR coating replenishes 3.2%.

[Naptown]

It adds to the overall production but does not effect the degradation. The specs are based on decrease of nameplate, not a decrease of efficiency and even if it were the drop would be the same or a higher rate.
2% of 20% efficiency is more than 2% of 15%

[vinniethePVtech]

It adds to the overall production but does not effect the degradation. The specs are based on decrease of nameplate, not a decrease of efficiency and even if it were the drop would be the same or a higher rate.
2% of 20% efficiency is more than 2% of 15%

This is exactly my point though. Lets say STC of 2 PV modules are 230W. That does not mean that applying AR with a 3.2% gain in conversion to surface coverage will equal the same MAX power when that coating is applied. Its a consistent equal percentage in PV CONVERSION, applied over different surface areas to equal a different end result in MAX power.

If you get a 1% loss over 2 years that's a 1% loss of 18% or 13.9% not 100%, every one is assuming 100%. That makes conversion 17% efficient hypothetically for a sunpower, and a 12.9% efficient hypothetical for a suntech.

17% from a 230W would now equal 217W (hypothetical for sunpower)
12.9% from a 230W would now equal 213.45W (hypothetical for suntech)

AR coating alone proves that in conversion at the same percentage will not equal the same MAX power on 2 different surface area modules.
Please read honeywells PDF on AR coating.

https://www51.honeywell.com/sm/em/common/documents/SOLARC_anti-reflective_coating.pdf

[Naptown]

This is exactly my point though. Lets say STC of 2 PV modules are 230W. That does not mean that applying AR with a 3.2% gain in conversion to surface coverage will equal the same MAX power when that coating is applied. Its a consistent equal percentage in PV CONVERSION, applied over different surface areas to equal a different end result in MAX power.

If you get a 1% loss over 2 years that's a 1% loss of 18% or 13.9% not 100%, every one is assuming 100%. That makes conversion 17% efficient hypothetically for a sunpower, and a 12.9% efficient hypothetical for a suntech.

17% from a 230W would now equal 217W (hypothetical for sunpower)
12.9% from a 230W would now equal 213.45W (hypothetical for suntech)

Many module manufacturers use AR glass. Yes this can increase efficiency during times of high angle of incidence. But has nothing to do with the performance drop of the cells themselves. If the losses of the module were based on loss of efficiency and not overall performance the losses would be higher on the high efffeccy module
10% of 18 =1.8
10% of 13.9 =1.39