Short answer
Size your system from your electricity consumption, not your roof area. Take your average monthly units from recent bills, divide by 30 for daily consumption, then divide by the expected generation per kW per day (about 4.2 units in Telangana). That gives your target capacity in kW. Then confirm your shadow-free roof area can hold it at roughly 80 to 100 sq ft per kW.
Step 1: Find your actual consumption in units
Your bill shows consumption in units (kWh). Take an average across several recent bills rather than a single month, because consumption varies seasonally. Air conditioning in summer changes the picture substantially.
If you only have the rupee amount and not the units, divide the energy charge by your tariff per unit. Be aware that most bills also include fixed charges and duties that are not proportional to consumption, so dividing the total bill by the tariff overstates your usage.
Step 2: Convert to a daily figure
Divide your average monthly units by 30. A household consuming 400 units a month is using roughly 13 units a day. This is the number your system needs to generate to offset your consumption on an annual basis.
Step 3: Divide by expected generation per kW
For Telangana, plan against roughly 4.2 units per kW per day as an annual average. Our example household needing 13 units a day would therefore need approximately 3 kW.
This is the point where the calculation becomes an estimate rather than arithmetic. The actual figure for your roof depends on orientation, tilt, shading and the specification of the components used.
Step 4: Check your roof can hold it
At roughly 80 to 100 sq ft per kW, a 3 kW system needs approximately 250 to 300 sq ft of shadow-free area. If your available area is smaller, you have three options: install a smaller system and accept a partial offset, use higher-efficiency modules to fit more capacity into the same area, or use an elevated structure that lets you build over an area you also want to keep using.
Step 5: Sanity-check against your goals and budget
A system sized to fully offset annual consumption is a reasonable default, but it is not the only sensible choice. Some customers deliberately install less because of budget, planning to expand later. Others install more because they expect consumption to grow: an electric vehicle, an additional floor, a new air conditioner.
What matters is that the number is deliberate. A capacity chosen because it was the package on offer, rather than because it matched consumption, is the most common reason customers are disappointed with their results.
Related questions
What size solar system do I need for a 3000 rupee electricity bill?
It depends on your tariff. At around ₹7.5 per unit for a residential connection, a ₹3,000 bill corresponds to roughly 400 units a month, or about 13 units a day. At an annual average of 4.2 units per kW per day, that suggests approximately a 3 kW system. Your own tariff and slab structure will shift this figure, so use your actual units rather than the rupee amount where possible.
Should I install a bigger system than I need?
Usually not by much. Surplus exported to the grid is settled according to your DISCOM's net metering rules, which may not compensate you at the same rate you pay for imported units. Modest headroom for future consumption growth is reasonable. Significantly oversizing on the assumption that export is as valuable as self-consumption generally is not.
Want this applied to your property?
Get an indicative system size for your electricity bill, then talk to us about what it would look like on your roof.