At this latitude, the south is the cheap direction.
Everything written about rooftop solar is written for Europe, where the sun stays low in the south and a south-facing obstruction is a catastrophe. Ahmedabad is at 23.03° north. The sun crosses the south at 43.5° even at the winter solstice and gets within a degree of straight overhead in June. What costs you here is the east and the west.
Lost to this obstruction
Put something in the way
The plot is the sky seen from your roof. The centre is straight up, the rim is the horizon, and the three arcs are the sun's track on the June solstice, the equinox and the December solstice. Dark stretches are hours you lose.
The single most common shading object on an Indian roof, and it sits in the worst possible place.
An obstruction due east costs real energy. Due south it costs nothing.
Due north
The sun is never that low in that direction here.
Due east
Lost across the year.
Due south
The sun is never that low in that direction here.
Due west
Lost across the year.
Every one of those four is a 25° tall, 30° wide object — identical except for which way it sits. That is the whole argument for a site survey with a compass rather than a photograph over WhatsApp. It is also why we will happily put panels behind your south parapet and will not go near the east side of a roof with a taller neighbour.
Sun at noon, 21 June
Within half a degree of straight overhead. A flat panel is nearly perfect and a tilted one is not.
Sun at noon, 21 December
Still high. This is why the winter dip here is mild compared with anywhere in Europe.
Ahmedabad
Just inside the Tropic of Cancer, which is the reason for everything on this page.
