Start with consumption, not with the roof
The most common mistake in residential solar is choosing a capacity because a neighbour installed the same. Your electricity bill is the honest starting point. Look at twelve months of units consumed, not one month, because seasonal air-conditioning and pump loads distort a single reading.
Average monthly units divided by the expected monthly generation per kW gives you an initial capacity indication. In Gujarat, a well-oriented rooftop system commonly generates around 110–125 units per kW per month across the year, though actual output varies with shading, orientation, temperature and cleaning frequency.
Check the shadow-free area you actually have
Roof area on paper is rarely the area available for solar. Water tanks, staircase rooms, parapet shadows, adjacent buildings and trees all reduce usable space. A practical planning figure is roughly 80–100 sq ft of shadow-free area per kW for standard module layouts.
If usable area limits you below your consumption-matched capacity, the design should prioritise the highest-yield section of the roof rather than spreading modules into partly shaded zones.
Respect the sanctioned load
Distribution companies generally link permissible rooftop capacity to your sanctioned load. If your solar capacity requirement exceeds it, a load enhancement may be needed before approval. This is an administrative step that is far easier to handle before installation than after.
The right system is the one that fits
Oversizing produces surplus you may not be compensated for at full value; undersizing leaves you dependent on grid tariffs. The right system sits at the intersection of consumption, usable area, sanctioned load and your investment horizon.
