Use this Forum to find information on, or ask a question about, NASA Earth Science data.
Post Reply
Posts: 6
Joined: Tue Nov 02, 2021 2:55 pm America/New_York
Answers: 0


by maxam » Wed Mar 27, 2024 9:42 am America/New_York

How to calculate the hourly solar radiation on a horizontal surface at the optimal angle?
Is it possible to do this using data from NASA POWER?
If not, how can this be done?
For example, for coordinate 70;-149 in May, the optimal inclination angle is 39 degrees, the insolation value is 6.41.
But there is no data for insolation for each hour


ASDC - bmacpher
Subject Matter Expert
Subject Matter Expert
Posts: 15
Joined: Thu Nov 21, 2019 11:32 am America/New_York
Answers: 1


by ASDC - bmacpher » Wed Apr 17, 2024 4:15 pm America/New_York

Based on your question you are looking for the hourly global total irradiance (GTI) on an optimally tilted panel for the month of May. The current version of POWER data provides only the monthly mean GTI.

If you want to know the hourly GTI on the optimally tilted panel for any given month, you need to apply the isotropic model on an hourly basis and input hourly DNI, DHI and surface albedo, in addition to the solar zenith angle and azimuth angle and panel tilt angle and azimuth angle.

Posts: 3
Joined: Thu Apr 18, 2024 6:05 am America/New_York
Answers: 0


by bobbycaldwell » Mon Apr 22, 2024 3:23 am America/New_York

Absolutely! Here’s how you can estimate hourly solar radiation for a surface tilted at an optimal angle, based on daily data:

Start with Daily Averages: Begin with the daily solar radiation figures available from NASA.

Calculate Hourly Estimates: Use a solar position algorithm to determine the sun's position each hour. Adjust these calculations to estimate the hourly radiation using the normal text formula: I_tilted = I_horizontal * (cos(sun zenith angle) / sin(optimal tilt angle)).

Refine with Tools: To get precise details, consider using tools like NREL’s PVWatts or SAM. These are excellent for providing specific adjustments for your location and tilt angle, ensuring detailed and accurate hourly data.

This method will guide you from general daily data to specific hourly insights, ideal for planning your solar setup effectively and sweetly!!!

Post Reply