Sizing a system is arithmetic, not guesswork. You need three numbers: how many units you use, how much a kW of solar produces in Kerala, and how much roof you have.
Step 1: bill to units
Divide your monthly bill by your blended tariff (the all-in rupees per unit). As an illustration, a ₹4,500 bill at about ₹7 per unit is roughly 640 units a month. Your own blended rate is on your KSEB bill; the calculator uses an editable tariff table.
Step 2: units to kW
A kW of panels in Kerala typically produces about 3.8–4.2 units per day. Multiply by 30 for a month: roughly 120 units per kW per month. So 640 units ÷ 120 is about 5.3 kW, which we would round to 5.5 kW.
Step 3: kW to roof area
Plan on about 80–100 sq ft of shadow-free roof per kW. A 5.5 kW system needs roughly 450–550 sq ft. If your roof is smaller, the system is capped and the saving becomes partial: the calculator flags this.
What changes the answer?
- An EV adds roughly 150 units a month for 1,000 km of driving.
- Shading from trees or a neighbouring building reduces output.
- Your sanctioned load and transformer headroom can limit the export size: that is what Scout checks.
Use the numbers as a starting point. A site survey confirms roof layout, orientation and shading before design.