- On November 26, 2019, we received an e-mail about miscalculation on the page Calculation of Monthly Average Extraterrestrial Daily Solar Radiation on a Horizontal Surface..
- We confirmed that there are calculation errors as pointed out.
- Thank you very much for pointing out our errors.
- The calculation errors are as follows:

Where

- \(\textrm{Month} = \textrm{April}\quad \textrm{and}\quad \textrm{Day number of year(n)}=105\)
- \(\textrm{Solar Constant},G_{sc}(\textrm{W/m}^2)=1367\)
- \(\textrm{Latitude},\phi(°)=43\)
- \(\textrm{Declination of Sun},\delta(°)=9.64\)
- \(\textrm{Solar Hour Angle at Sunset}, \omega_s(°)=99.1\)

So, \(H_0(\textrm{MJ/m}^2)\) must be

```
t1 <- 24 * 3600 * 1367/pi * (1 + 0.033 * cos(2 * pi * 105/365))
t2 <- cos(43 * pi/180) * cos(9.64 * pi/180) * sin(99.1 * pi/180) + 99.1 * pi/180 * sin(43 * pi/180) * sin(9.64 * pi/180)
t1
t2
t1 * t2 * 10^-6
```

```
[1] 37304279
[1] 0.9094837
[1] 33.92763
```

- But the displayed calculation result is \(26.55746(\textrm{MJ/m}^2)\).
- There are calculation errors in the page.
- Please do not use this page.Thank you for your cooperation.

**Reference**