Find the right kW capacity for your solar installation based on your monthly consumption and city. Includes roof area requirements and cost estimates.
How to Size a Solar System
The right system size balances your consumption, budget, and roof availability. Too small and you still pay a large electricity bill. Too large and you over-invest without proportional benefit (unless you have net metering).
Typical Appliance Consumption
Appliance
Watts
Hours/Day
Units/Month
LED lights (10 bulbs)
100W
6 hrs
18 units
Fan (3 nos.)
225W
10 hrs
67 units
Refrigerator (300L)
150W
24 hrs
108 units
TV (43" LED)
80W
6 hrs
14 units
AC 1.5T (5-star)
1300W
8 hrs
312 units
Washing machine
500W
1 hr/day
15 units
Geyser (15L)
2000W
0.5 hr/day
30 units
Laptop / desktop
80W
8 hrs
19 units
Rule of Thumb
In most Indian cities, 1 kW of solar produces ~120–165 units per month. Divide your monthly consumption by your city's figure to get the system size needed.
Example: Delhi consumption 400 units → 400 ÷ 150 = 2.67 kW → round up to 3 kW.
Roof Area Requirements
Each kW of solar needs approximately 80–100 sq ft of shadow-free south-facing roof area. A 3 kW system needs ~250 sq ft; 5 kW needs ~420 sq ft. Obstacles (water tanks, AC units) reduce available area.
Frequently Asked Questions
Approximately 80–100 sq ft (7.5–9.3 sq metres) of shadow-free roof area is needed per kW. A 3 kW system needs 240–300 sq ft; a 5 kW needs 400–500 sq ft. Bifacial panels can reduce this slightly by capturing reflected light.
To cover 300 units/month in Delhi (avg ~150 units/kW/month), you need approximately 2 kW. In less sunny regions (120 units/kW/month), you need 2.5 kW. Use this calculator for your city-specific recommendation.
Size 10–20% above current consumption to account for future usage growth and panel degradation (~0.5%/year). With net metering, surplus export earns grid credits, so oversizing is not wasteful — you earn from the excess.
PM Surya Ghar scheme subsidises up to 3 kW for residential systems (subsidy: ₹78,000). For systems above 3 kW, you can install without restriction — the subsidy only covers the first 3 kW. Many DISCOMs allow residential systems up to 10 kW or equal to connected load, whichever is lower.