Voc of pv array

[jude kennefick]

Can anyone help. I have measured the Voc of a pv array at the DC isolator. I get 400 V and the array should measure 450. The Voc on the back of each panel says 37.5 but when tested with a volt meter each panel is reading about 33 which x12 would be about 400v. Does anyone know how accurate this measurement and panel specifications should be. The Isc measures correctly for the whole string array. The panels are risen 250.

 

[solarsystems]

all values given on back of panels are for STC. so of coarse there will be differences if your conditions are different! simples

 

[yellowvanman]

In general the Voc will decrease by -0.5% for every C above STC (25C), remember thats the temperature of the panel itself not ambient, but on some module data sheets Voc does vary slightly with irradiance levels, and are unreliable when irradiance is <300W/m2.

For instance on a Sharp panel Voc varies (downwards) by about 10% between STC (1000W/m2) and 300W/m2. Which is about the same level of difference you are experiencing. Was it a cloudy day when you measured this?