how to convert radiation on horizontal plane to an inclined one

[sensij]

Your link doesn't seem to account for azimuth, it assumes the tilted array is always facing the sun. That is not generally true.

Calculating irradiance on a horizontal plane, and then converting to an inclined plane is more complicated than you need. It would be simpler to directly calculate irradiance on the tilted plane, using solar position and array position to determine the incidence angle.

This link is much more through in the discussion of how to calculate the incidence angle.

cos(incidence angle) * direct radiation = direct radiation incident to the plane of the array.

If you really want to calculate horizontal POA irradiance, and then back to inclined array POA, the next section of the site I linked shows how to do it. Gory math that way.

[dimitrisbronowski]

It sounds like you just need to take the formula you already have (which includes Sun positioning) and set the inclination of the array to 0. Am i still misunderstanding?

I have already the radiation on the horizontal plane. I want to convert it to the inclined plane.
The formula I have can convert the suns radiation from a plane that looks directly at the sun(not from a horizontal plane) to the radiation on an inclined plane.

The formula in the link, which is supposed to transform from horizontal to inclined, doesn't depend on the time of the day. I believe that the angle of the sun as refered to the inclined plane should depend on the time of the day. So I guess I cannot use that formula directly.

[sensij]

It sounds like you just need to take the formula you already have (which includes Sun positioning) and set the inclination of the array to 0. Am i still misunderstanding?

[dimitrisbronowski]

I wasn't clear enough. What I am searching for is the trigonometric formula to convert direct radiation on a horizontal plane to direct radiation on a inclined. I am not interested in diffused radiation models etc. I have the formula that converts the radiation from a plane looking directly to the sun to the radiation on an stationary inclined plane(the one that depends on the inclination of the panel, the time of the day, the day of the year etc). But I don't know how to convert the radiation from the horizontal plane to the plane following the sun so I can have the overall conversion.

Should I just use the formula given at http://pveducation.org/pvcdrom/prope...tilted-surface for Smodule? I am asking because it doesn't seem to take into account the time of the date and I thought that it would be necessary.

[sensij]

There is not a single right answer for how to convert GHI to POA irradiance. You can look at the documentation provided by NREL that supports PVWatts and SAM (System Advisor Model) for some ideas.

Most of the better models will require an estimate of the diffuse fraction. Nrel has spreadsheets to help with this.

[dimitrisbronowski]

Good afternoon everybody!
I have data for the hourly radiation on a horizontal plane and weather conditions for a location for a few years. I need to convert the radiation on the horizontal plane to the radiation on an inclined plane.
Do you know any page that explains well how to do that? Pveducation didn't do it good enough for me to understand.
Even better, does anyone have a matlab script that does it or an excel sheet?

Thank you!