Worked examples: 2, 3, 5 and 10 kW homes and a small shop

This lesson puts modules m02 and m03 together. Each example follows the same seven steps, so you can use it as a template on your next job:

1. Annual units from 12 months of bills
2. Specific yield for the city
3. Raw size = units ÷ yield
4. Round to whole modules (550 Wp here) with a reason
5. Check limits: sanctioned load, phase, roof, state rules
6. Pick the inverter
7. Generation, cost, subsidy and net cost

Costs use the Sunlectric installed-price benchmarks for October 2026 (about ₹60,000 per kW at 3 kW, ₹57,000 at 5 kW and ₹54,000 at 10 kW, before subsidy). They are illustrative; use your own current price list. Subsidy figures follow the PM Surya Ghar 2024 guidelines; check the current notification.

Example 1: a 2 kW-class home in Indore

Inputs: 270 units a month (3,240 a year), single phase, sanctioned load 3 kW, RCC roof with plenty of space.

• Yield: 1,526 kWh/kWp/yr
• Raw size: 3,240 ÷ 1,526 = 2.12 kWp
• Modules: 4 × 550 Wp = 2.2 kWp (3 modules would cover only 78%)
• Limits: 2.2 kW is within the 3 kW sanctioned load; single phase is fine
• Inverter: 2 kW single-phase (DC/AC ratio 1.1)
• Generation: 2.2 × 1,526 = 3,357 units (104% of use)
• Cost: small systems cost more per kW; assume ₹62,000 per kW = ₹1,36,400
• CFA: ₹60,000 + 0.2 × ₹18,000 = ₹63,600
• Net cost ≈ ₹72,800

Note: Madhya Pradesh credits surplus at about the APPC rate (around ₹2.14, as a bill credit, not cash), so a few percent over is fine but no more.

Example 2: a 3 kW home in Pune

Inputs: 380 units a month (4,560 a year), single phase, sanctioned load 5 kW, elevated RCC structure.

• Yield: 1,513
• Raw size: 4,560 ÷ 1,513 = 3.01 kWp
• Modules: 6 × 550 Wp = 3.3 kWp. Five modules (2.75 kWp) would cover 91%; with Maharashtra's upper-slab units costing ₹14–19 each against a ₹2.82 surplus credit, the sixth module pays for itself.
• Inverter: 3 kW single-phase (DC/AC 1.1)
• Generation: 3.3 × 1,513 = 4,993 units (109%)
• Cost: 3.3 × ₹60,000 = ₹1,98,000
• CFA: ₹78,000 (maximum, reached at 3 kW)
• Net cost ≈ ₹1,20,000

Example 3: a 5 kW home in Jaipur

Inputs: 620 units a month (7,440 a year), three phase, sanctioned load 6 kW.

• Yield: 1,546
• Raw size: 7,440 ÷ 1,546 = 4.81 kWp
• Modules: 9 × 550 Wp = 4.95 kWp
• Inverter: 5 kW three-phase (DC/AC 0.99). A single-phase 5 kW unit would also be allowed by many DISCOMs, but three-phase spreads the export across phases.
• Generation: 4.95 × 1,546 = 7,653 units (103%)
• Cost: 4.95 × ₹57,000 = ₹2,82,150
• CFA: ₹78,000
• Net cost ≈ ₹2,04,150

Rajasthan lets domestic consumers choose between net metering and net billing (indicative surplus rates ₹3.26 and ₹3.65, October 2026). For a system sized close to annual use the choice makes little difference; for an oversized one, compare both. Check whether the family is in the state's free-units scheme, which changes the savings but not the size.

Example 4: a 10 kW home in Lucknow

Inputs: a large house using 1,150 units a month (13,800 a year), three phase, sanctioned load 12 kW, terrace about 100 m² usable.

• Yield: 1,390
• Raw size: 13,800 ÷ 1,390 = 9.93 kWp
• Modules: 18 × 550 Wp = 9.9 kWp, in two strings of 9 (string design in m06)
• Roof: at about 9 m² per kWp, needs about 89 m²: fits
• Limits: within sanctioned load; at 9.9 kW the system stays at or below 10 kW, so under the 2024 amendment no technical feasibility study is needed (check state adoption)
• Inverter: 10 kW three-phase
• Generation: 9.9 × 1,390 = 13,761 units (99.7%)
• Cost: 9.9 × ₹54,000 = ₹5,34,600
• CFA: ₹78,000 (capped). UP state top-up: ₹15,000 per kW up to ₹30,000, if the scheme is still open
• Net cost ≈ ₹4,26,600 with the top-up, ₹4,56,600 without

Lucknow's winter haze cuts December–January output to about 60% of March's. Show the monthly chart.

Example 5: a small shop in Ahmedabad

Inputs: a garment shop on a commercial tariff, open 10 am to 9 pm, using 800 units a month (9,600 a year). About 70% of use is in daylight hours. Three phase, sanctioned load 10 kW. The roof is a flat RCC slab.

Commercial customers do not get PM Surya Ghar CFA, and export rules for commercial consumers differ by state and DISCOM. The safe approach: size for daytime self-consumption, so most solar units replace grid units bought at the full commercial tariff.

• Daytime use: 9,600 × 0.70 = 6,720 units a year
• Yield: 1,616
• Raw size: 6,720 ÷ 1,616 = 4.16 kWp
• Modules: 8 × 550 Wp = 4.4 kWp, generating 4.4 × 1,616 = 7,110 units
• Inverter: 4–5 kW three-phase
• Cost: 4.4 × ₹57,000 ≈ ₹2,50,800, no CFA
• DCR modules are not required without CFA, which can lower cost, but check current ALMM rules for net-metered projects (module m04)

If the DISCOM confirms full net metering for this category, the shop could size up towards 5.9 kWp to cover all 9,600 units. Get it in writing first. The business may also claim depreciation on the system; ask the customer's accountant for the current rate.

Summary table

Key points

• Use the same seven steps every time: units, yield, raw size, round, limits, inverter, cost.
• Round with a reason: low export rates favour sizing close to annual use.
• CFA is capped at ₹78,000 from 3 kW upwards; add state top-ups only if currently open.
• Watch thresholds such as 10 kW before adding "one more module".
• For commercial sites without CFA, size for daytime self-consumption unless net metering is confirmed.

Check yourself

1. A Chennai home uses 4,200 units a year (1,486 kWh/kWp/yr). How many 550 Wp modules would you propose?
2. Why did the Ahmedabad shop get 4.4 kWp rather than 5.9 kWp?
3. What would push the Lucknow system's net cost higher than ₹4,26,600?