I think that the energy flux is given by:
$$\text{G}=\mathcal{k}\cdot\text{T}^4\cdot\left(\frac{\text{R}}{\text{D}}\right)^2\tag1$$
Where $\mathcal{k}$ is the Boltzmann constant, $\text{T}$ is the surface temprature of the sun, $\text{R}$ is the radius of the sun and $\text{D}$ is the distance from the sun to the earth.
Now, for $\text{D}$ we know that is changes over a year because the earth makes a elliptical orbit around the sun.
Question: Is my formula right?