Era-Interim-Surface Solar Radiation Downwards

I study about offshore photovoltaic panel installation. In case of an non-tilted panel which is located on water surface is it necessary to multiply the values of Surface Solar Radiation Downwards (SSRD) with an angle factor or these values are ready to be used in further statistical calculations?

Thank you in advance.

Hi Dimitrios,

According to the document:

"All fluxes, including direct fluxes, at the surface and top-of-atmosphere represent the energy (in J) that has passed through a square-metre of a flat horizontal plane"

In ERA-Interim, this energy is accumulated from the beginning of the forecast, whereas in ERA5 the energy is accumulated in the last hour.