Good day,
I am trying to model a PV panel; in order to accurately predict the absorbed solar energy, it is not enough to calculate the incident solar radiation, but one needs to have the absorbed radiation.
However, I found out that the absorbance of materials is different for direct, diffused and reflected solar rays; furthermore, this absorbance is affected by the incidence angle of solar radiation.
I need to find some correlations and data on the above subject.
Any suggestions?
Thank you,
Patrick
I don't think you should spend a lot of effort trying to predict anything associated with practical PV systems accurately. There are far too many variables, as you suggest, and trying to define them all will result in a figure of 'efficiency' that you would never actually come across in practice. As Evangelos recommends, just take 0.9 as a figure across all cases. Don't forget that the total solar energy reaching a panel varies as the cosine of the angle of difference between the panel normal direction (perpendicular to the surface) and the actual direction of the sun. This will dominate any result in all except 2D tracking systems.
As a first approximation take a typical value of 0.9 for absorbance for all the cases
I don't think you should spend a lot of effort trying to predict anything associated with practical PV systems accurately. There are far too many variables, as you suggest, and trying to define them all will result in a figure of 'efficiency' that you would never actually come across in practice. As Evangelos recommends, just take 0.9 as a figure across all cases. Don't forget that the total solar energy reaching a panel varies as the cosine of the angle of difference between the panel normal direction (perpendicular to the surface) and the actual direction of the sun. This will dominate any result in all except 2D tracking systems.
Most substances reflect sunlight best, and hence absorb it most poorly, when sunlight strikes them perpendicularly; and reflect sunlight most poorly, and hence absorb it best, when sunlight strikes them at a shallow angle.
Evangelos, Tony, and Jack, thank you for your answers; though I am trying to make an accurate prediction, I will consider your recommendations.
I think that one good place to start is in the book "Solar Engineering of Thermal Processes, Duffie and Beckman". In this book you can find really good correlation to calculate what you need. If I recall correctly is in chapter 2 what you need.
frequently in the literature, the solar radiation absorbed by a PV module is calculated by Qab = A * G * * τ_g α_c β *
where A, G, τ_g, α_c, β are the surface of the PV module, the glass transmissivity, the absorptivity of PV cells and the Packing factor, respectively.
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Try the softwares i.e. RETScreen and HOMER. They incorporate myriad of factors with corresponding correlations and data. They are also free. I hope that find these possibly useful.
Dr. Emmanuel Ackom
UNEP DTU Partnership
Denmark
Dear Patrick, please draw a distinction between precision and accuracy. They are not at all the same thing. What you are doing is calculating the behaviour of a panel with a very high degree of precision. All you will be able to say of the result is that a real panel will NEVER behave like you have predicted because your results while precise are not accurate because you can't take into account all the variables nor put in accurate figures for things like the weather. It is really fine for a paper for publication but not very useful when trying to calculate the energy you will get out of the panel over a year.
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