george

Dear André. Can you please say more on how PVsyst 4,5 and 6 will deal with comment lines (lines which are not Azimuth, Height pairs)? Here is an example of a .hor file: Will all versions of PVsyst (versions: 4,5,6) simply ignore the first three lines? Thank you for the reply.

Thank you for the reply André. Does this mean that in PVsyst version 4, the diffuse radiation calculation was also performed on the horizon with the following azimuth directions: -120 to 120? Or in PVsyst version 4, the diffuse radiation calculations were performed with horizon consisted of -180 to 180 azimuth directions?

Dear Mr. Mermoud, Thank you for the reply. I already took a look at your horizon profile help page, and I am not sure I understand the explanation. The PVsyst 4 used pairs of Azimuth, Height values, where Azimuths started from -120 and went to 120 = making it total of 240 Azimuths? PVsyst 5 and PVsyst 6 use pairs of Azimuth, Height values, where Azimuths start from -180 and go to 180, but with incremental step of 3. So that means: -180, -177, -174 ... , 177, 180. Did I understand that correctly?

Hello, I have a PV SOL 6.0 horizon file. I uploaded it in here (your attachment does not allow attaching .hor filetypes). I need to send this file to a person who is using PVsyst (I still haven't asked which version does he have). The problem is there seems to be some tiny difference between PVsyst and PV SOL .hor files. How can I edit my PV SOL .hor file, so that it can be imported into PVsyst? I took a look at your PVsyst v6 help page, and it says that PVsyst 4, in its .hor files used only azimuths from -120 to 120. But with PVsyst 5, the -180 to 180 azimuths are supported, but the number of azimuths has been reduced from 240 in PVsyst to 120 in PVsyst 5. Did I understand this correctly? Can somebody please show me how can I convert my PV SOL .hor file to PVsyst 4 or PVsyst5 >= .hor file? Thank you in advance.

Hello, I want to conduct an analysis on Photovoltaic array. I need a weather file for particular location. It can not be found in the PVsyst Meteo database. But Meteonorm has it. The problem is that this Meteonorm weather file does not contain data about snow depth nor albedos. I was wondering if I could approximate this by somehow defining the albedo to be 0.6 (ground covered with wet snow) in cases when air temperature is bellow some value. Which value would that be? Certainly not 0°C but probably something bellow 0°C. RETscreen advices using 0.7 albedo for -5°C temperatures, and interpolated albedo values from 0.7 to 0.2 for air temperatures between -5°C and 0°C (example: -4°C - 0.6, -3°C - 0.5, -2°C - 0.4, -1°C - 0.3, 0°C - 0.2, 1°C - 0.2...). Do you think this is correct? I can see from tutorials that you recommend defining a 0.8 albedo for just a few months (when snow is expected). I have no problem with using the 0.8 albedo value, but can I use it when air temperature is bellow some value, instead of just defining it for certain months? Thank you for the reply.

Thank you for the reply André. For some reason I have not been informed about this reply by email. I have just seen it now. When you say: by "albedo contribution", you mean: the contribution of albedo to POA ground reflected radiation? Why is it only "(1-cos(tilt))"? Why isn't it "(1-cos(tilt))/2" as given by Sandia formula: Eg = ((GHI x albedo x (1-cos(tilt))/2) ?

Thank you Marvin.

Ok. I was not interested in question number 2. That one is clear. Only in question 1. So did I correctly understand the explanation of your answer to question 1 in the upper post? (just to add that my reason for using 90 and 40 tilt angles was to explain the difference in what "PV array seeing" depending on the tilt angle. Not to show how these angles affect the POA ground reflected radiation).

But that was not the problem. I understand that lower tilt angles (that is: lower roof angles) lower the albedo effect on POA ground reflected radiation. The issue was to explain, what did you mean by "PV array seeing" in context of what area needs to be considered on reflecting the light onto the window, due to estimation of the average albedo. If I understood it correctly. this is what you meant (see attached photo for simplification). So in case of tilt angle = 90 (upper sketch): averageAlbedo = 1/4*0.25 + 1/4*0.75 + 2/4*0.20 = 0.40 While if tilt angle is 40 (bottom sketch): averageAlbedo = 1/3*0.25 + 1/3*0.75 + 1/3*0.20 = 0.35 I apologize in advance for the quality of the sketch. My intention is not to banalize the discussion, just to check whether or not I understood the explanations.

Thank you André, But I am not sure I have understood you. You compared how lower tilt angles lower the albedo effect on POA ground reflected radiation. But how is that related with "looking through" the window comparison of how solar panel "sees" different areas (with different albedos) around it?

Thank you Marvin, I can see Hamon Engineering is in good hands.

Thank you Marvin, "PV array seeing" a particular area around it is basically like if instead of PV array on a roof, there would be a window on the same place. What a person could see through that window, would be "PV array seeing"? Did I get that right?

Thank you Marvin. What would be the "large body of water"? Not a backyard swimming pool? But a river, lake, sea? Could you specific, which one of these? Also when you say "next to a body of water...", what does "next to" approximately mean? A sea-side cottage up to 100 meters from the coastline? Again I understand that there might not be a precise answer to all of this, but what about an approximate one?

Thank you for the reply Marvin, I am not in a position to measure anything on the site. Let's say that next to the house (from the upper photo) is another house with an aluminium roof (albedo for aluminium = 0.85). On the opposite side of the house there is another house with red tiles roof tiles. Below the roofs, grounds of each of these three backyards are covered with grass (albedo approx. 0.20). Would that mean that this aluminium roof is the largest reflective surface near my roof with PV panels, with the largest value of albedo (0.85)? I did a little testing: nameplate 4 kW azzimuth angle = 180 tilt angle = 45 (Maybe the roof on an upper photo is a bit less, 40, 38 but it does not matter. It's only a test) Location: Dallas Fort Worth, Texas For 1st of July, 12am (noon), with 0.2 albedo I got: Eg = 0.027 kWh/m2 Epoa = 0.85 kWh/m2 Eg = 3.2% of Epoa For the same location and time but with albedo 0.85: Eg = 0.12 kWh/m2 Epoa = 0.95 kWh/m2 Eg = 12.63% of Epoa So just by increase of albedo the Epoa has risen by 10%. PVsyst albedo page, says that PV output can be raised by 5-10% in case of snow on the ground. That's why I want to know more, about which value to chose for albedo in which cases (not talking about snow or water surface areas).

Thank you for the reply Andre. So in this specific upper case, what is the albedo value that should be taken into account when calculating POA ground reflected radiation? If not the albedo of the red roof tiles, then the albedo of the ground surface below the roof?