PVsyst's forum

Welcome on PVsyst's forum.
It is currently Mon Sep 21, 2020 2:32 pm

All times are UTC+02:00




Post new topic  Reply to topic  [ 5 posts ] 
Author Message
PostPosted: Wed Jan 20, 2016 7:24 am 

Joined: Wed Jan 20, 2016 7:17 am
Posts: 1
I have a very basic question regarding the simulation run by pvsyst.

The temperature data of a location that we feed in pvsyst, is only ambient temperature. Now considering module output reduces with temperature, how does pvsyst determine what exactly is the cell temperature at that location throughout the year>?


Top
   
PostPosted: Wed Jan 20, 2016 1:33 pm 
User avatar

Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1680
The cell's temperature at sun is established using a little energy balance model.
The parameters of this model (U-values, possibly accoding to the wind velocity) are of your responsibility, and defined in the "Detailed Losses".

The model is explained in the help "Project design > Array and System losses > Array thermal losses".


Top
   
PostPosted: Thu Feb 18, 2016 4:57 pm 

Joined: Wed Nov 25, 2015 12:14 am
Posts: 12
Hi André,

as meteo data suppliers provide wind velocity measured at 10m high and wind data inputs for PVSyst standard format meteo file need to be values also at 10m, does the programm recalculate wind velocity for the height of the array (~2m for a free-mounted system, for example) in order to compute array thermal losses? In the help it mentions the Uc value of 29W/m²K has transferred the wind-dependent coefficient assuming average wind velocity of 1.5m/s, but is that value a 10m high measurement? Do I need to recalculate wind velocity if it's not measured at the height of my array?

Thank you in advance for your help.


Top
   
PostPosted: Fri Feb 26, 2016 8:49 pm 
User avatar

Joined: Mon Apr 16, 2012 7:29 pm
Posts: 1680
The effect of the wind on the PV array temperature is expressed as the Uv [W/m2K / m/s] factor, which is a proportionnality factor for the Wind speed.

Now PVsyst cannot provide reliable values for this factor, as we don't have reliable measured references.
Therefore the only way to get this value is to measure it on site (long-term measurement).

Now if you determine this factor with a reference wind velocity measurement at 10 m from the ground, you will get a Uv value.
If you admit a scaling factor for a measurement at another altitude, you will obtain a Uv factor scaled (inversely) by the same amount.

An (old) study of the WMO proposes a scaling facor (Hellmann model) as:
Vh = V10 (0.233 + 0.656 log10 (h+4.75) )
With this expression, the speed at 1.5 m will be 25% less than the speed at 10 m. Therefore the Uv value will be 25% more for a same result.


Top
   
PostPosted: Tue Aug 29, 2017 11:14 pm 

Joined: Tue Aug 29, 2017 10:55 pm
Posts: 1
Regarding the effect of the wind on the PV array temperature, the wind loss factor Uv, is there any special consideration for large installations, for example 100 MW? what value es recommended for such installations?


Top
   
Display posts from previous:  Sort by  
Post new topic  Reply to topic  [ 5 posts ] 

All times are UTC+02:00


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Limited