# Comments on Calculation of Solar Insolation

## Primary tabs

### Correction

Corrected the graph on solar insolation so that it is in kWh/m2/day not kW/m2/day

### Solar Insolation

Hi
I newly started to learn intricacies of solar power generation, and I found your site is the best to learn about solar radiation, Insolation and PV cells etc. When I am dealing with “Calculation of Solar Isolation” I encountered with the following in consistency.
As mentioned in “Calculation of Solar Isolation” I downloaded Solar Isolation for 17 deg. Latitude with zero deg. Tilt by pressing “Download Data” for fig2. It gave me 365 das daily solar Isolation for the Latitude 17 deg. (Average for 365 days is 8.80 Kwh/m2/day). When I downloaded the solar radiation for Latitude 17 deg. using RETScreen Average Solar radiation over a period of 365 days is 5.29 Kwh/m2/day . Global Horizontal Radiation from NASA Surface meteorology and Solar Energy: Global Data Sets for Latitude 17 deg. and Longitude 78 deg. (Parameter: Insolation Incident On A Horizontal Surface (kWh/m^2/day) is 5.19 annual average. From this it shows data from RETScreen and NASA are nearly in consistence. But in your case it is a higher value. Will any body clarify why this mismatch.
Thanks

### Stupid about Insolation question; Horizontal or normal surface

I have found the data on this page incredible useful for my current project( building a solar car for world solar challenge 2015). How ever to I'm simply wondering if the data for first graph represents solar isolation for horizontal surface? In ether case I'm quite keen to know because because I intend to use the data to optimize specific features on the new solar car.

### formula

This is very nice. Happy to see this website. If we want to calculate the insolation, how would we use the "sunset" and "sunrise" formulas in the calculation. Looking forward having info.

### Solar Module

When you say module, which one (module) are you referring to.

thanks