Degradation in the First Year with LID losses

[Tanatip]

I was wondering about the degradation of the first year in aging tool.

If my project using this PV module model as follows:

which define the First-year degradation = 1%, and Annual degradation = 0.4%.

so the LID loss factor we put in the PVsyst shall be 1%.

and then if we going to the aging tool and simulate for the first year, it will suggest 0.2% for the degradation (which come from 0.4%/2).

My question is when we simulate this first year yield, it will include the total losses = 1% + 0.2% = 1.2%

>> which its performance will be lower than the data sheet (98.8% is lower than the 99% that define in the datasheet) in the first year.

So how should I exactly input losses for the LID and first year degradation?

 

Thank you in advance for your kindly support and discussion.

Edited March 5 by Tanatip

[Rafael Santos]

Hi,

 

Normally what I do in this case is to use LID=0,6% (wich is 1% warranted at the end of the first year - 0,4% degradation at the end of the year).

[dtarin]

Lid and annual power degradation are separate degradation modes. They also occur on different timescales. It is common to assume first year annual degradation divided by 2 (as is done in PVsyst).

7 hours ago, Rafael Santos said:

Hi,

 

Normally what I do in this case is to use LID=0,6% (which is 1% warranted at the end of the first year - 0,4% degradation at the end of the year).

This may be conservative, which could be fine, but may not be ideal in other aspects. For example, most PERC modules are Ga-doped and certain suppliers test quite low on LID (~1%). For most PERC modules, first year degradation is 2%, 0.45% annual degradation thereafter. The method above would add 0.775% loss over what would be expected for the first year. For TOPCon modules if your LID is 0.5%, you'd have an additional 0.3% loss in year 1. Might be fine in some cases but not in others, something to keep in mind. 

[Tanatip]

Thank you for your both replies.

5 hours ago, dtarin said:

Lid and annual power degradation are separate degradation modes. They also occur on different timescales. It is common to assume first year annual degradation divided by 2 (as is done in PVsyst).

I'm still confused, what should I input in the PVsyst for LID in the case of datasheet define the First-year degradation = 1%, and Annual degradation = 0.4%.

Thank you.

[Michele Oliosi]

If you follow Daniel's latter examples (1-0.4)/2 = 0.3%? Indeed here you would assume that the loss increases to 0.6% in one year so on average during the first year it is about half of that.

But I am not sure if this assumption is good for all cases of LID. The value is certainly between (1-0.4/2) = 0.8% LID if it occurs during the first few hours, or 0.3% if you interpret the first year degradation value as a linearly increasing function without any further assumption.

I would tendentially use the more conservative estimate of 0.8% LID.

[dtarin]

For clarification I am not suggesting LID divides by 2. LID occurs on shorter timescale compared to annual degradation and should be taken in full. My overall comment is that taking 1st year degradation from the datasheet and subtracting (annual degradation/2) to get LID may be conservative and something to keep in mind. Different modules may test higher or lower in LID and it is recommended to have module-specific data to support LID assumptions. 

Edited Monday at 05:13 PM by dtarin

[Tanatip]

Thank you for your both opinion and clarification, it's very informative.

As i see now, the most reasonable way (also easy to explain) is to calculate LID as follows:

LID = (1st Year Degradation) - (Annual Degradation / 2)

 

Thank you again!