Solar constant approx 1300w/sqm
That's measured out in space. On the ground, under clear skies, normal to the incident rays, it's under 1000 W/m^2. Many things affect the calculations, which don't all fit neatly on the back of an envelope. For one: you can't ignore latitude and assume it's at the equator. Sambhar Salt Lake is located at about 28N, so you are already down to maybe 700 W/m^2 on horizontal ground at noon on a perfectly clear day. Second, the capture and conversion efficiency of most panels, even with anti-reflective glass, is relatively poor, meaning that you don't get much power at until the incidence angle gets above, say, 15. That will tend to make that cosine integral more like cos^2: more concentrated in the middle of the curve, much less at the tails. Third: I don't know how the weather is at this location, but surely it isn't perfectly clear every day of the year. When the monsoons come rolling through, there may be days or weeks when it is overcast. Last: there's fill-factor. You won't be able to carpet the entire area with wall-to-wall panels - there will be streets and avenues to allow any part of the array to be reached.