A good survey wins the job and prevents most problems after installation. A rushed one leads to shaded modules, a structure that does not fit, a cable that is 10 m short and a customer who expected backup. The fix is simple: plan the visit, carry the right kit, and ask the right questions.
The five stages
Stage 1: the pre-visit call
Ten minutes on the phone saves an hour on the roof. Ask the customer to send, on WhatsApp or email:
- The latest electricity bill, and ideally 12 months of history. Many DISCOM apps and websites show past bills; MSEDCL, BESCOM, TANGEDCO/TNPDCL and others let the consumer download them.
- Consumer number, sanctioned load (kW) and phase (single or three phase), all printed on the bill.
- Two or three roof photos, taken from a corner, showing tanks, the staircase room and nearby buildings.
- Building details: number of floors, roof type (RCC, tin shed, tiles), age of building, whether it is an independent house or an apartment.
Also confirm who owns the roof. In apartments and housing societies you will need the society's written permission (NOC) to use the common terrace.
Stage 2: the desk check
Before the visit:
- Satellite view. Open the address in a map app. Note roof shape, which way it faces, trees and tall neighbours to the south, east and west.
- City yield. Look up the specific yield for the location (for example Jaipur 1,546 kWh per kWp per year, Pune 1,513, Chennai 1,486).
- First size estimate from the bills (worked example below).
- DISCOM rules. Check the state's net-metering limit (often tied to sanctioned load) and whether the household is eligible for PM Surya Ghar central financial assistance: a residential connection, a suitable roof, and no earlier central subsidy for rooftop solar (check the current guidelines).
Stage 3: the survey kit
| Item | Use |
|---|---|
| 30 m measuring tape and a laser distance meter | Roof size, obstacle positions, parapet heights |
| Magnetic compass and a sun-path or survey app | Roof direction, shading from obstacles |
| Inclinometer (or phone app) | Slope of tin sheds and tiled roofs |
| Clamp meter and multimeter | Check supply voltage and phase loading at the main board |
| Camera or phone with geotagging | Photos of roof, meter, DB, earthing, cable route |
| Torch, chalk or marker, small hammer | Dark ducts, marking, tap-testing plaster and slab |
| Survey form (paper or app) | Same checklist every time |
| Safety shoes, helmet, gloves, harness for sloped roofs | Your safety comes first |
| Optional: drone | Large or unsafe roofs, apartment terraces |
The questions that change the design
About energy use
- What is your monthly bill and roughly how many units? (Confirm on the bill.)
- When do you use most power: daytime (work from home, shop, clinic) or evening?
- Any new loads in the next two years: an EV, more ACs, an induction cooktop, a new floor?
About backup
- How many hours of power cuts do you have, and when?
- Which appliances must run during a cut? This decides on-grid or hybrid (lesson m01-05).
About the roof
- Do you use the terrace for drying clothes, functions, plants or water storage?
- Any plan to build another floor? If yes, the solar structure must allow for it or wait.
- Any history of leakage? Where?
About money
- Rough budget, and whether they want a bank loan. PM Surya Ghar links to concessional loans for small residential systems (check current bank terms).
- Who will decide? If the decision-maker is not at the visit, plan a second meeting.
Write every answer on the survey form. Six months later, nobody will remember who said "no backup needed".
Worked example: first size estimate in Jaipur
A customer in Jaipur sends 12 bills. Monthly units: 280, 260, 300, 420, 560, 620, 520, 430, 380, 340, 300, 270.
- Annual total: 4,680 units. Average 390 a month; the May–June peak comes from ACs.
- Size to cover today's use: 4,680 ÷ 1,546 = 3.03 kWp.
- The customer plans an EV next year, driving about 1,000 km a month at roughly 0.15 kWh/km, adding 150 units a month, or 1,800 a year.
- New annual total: 6,480 units. Size: 6,480 ÷ 1,546 = 4.19 kWp, so about 8 modules of 550 Wp (4.4 kWp).
- The bill shows a sanctioned load of 3 kW. In many states rooftop capacity is linked to sanctioned load, so you may need a load enhancement application before net metering. Note it and tell the customer early.
Always size on the full year, not on one summer bill.
Key points
- Collect bills, sanctioned load, phase and roof photos before the visit.
- Do a desk check: satellite view, city yield, a first size estimate and DISCOM and subsidy rules.
- Carry a standard kit and use the same survey form on every job.
- Ask about future loads, outage hours, terrace use and expansion plans; they change the design.
- Size on 12 months of units, and flag sanctioned-load limits early.
Check yourself
- Why should you collect 12 months of bills instead of only the latest one?
- A customer uses 3,900 units a year in Pune (1,513 kWh/kWp/yr). Roughly what size covers it?
- Name two answers from the customer that would push you towards a hybrid system.
Answers
- Use varies with the season (ACs in summer, geysers in winter). One bill can over- or under-size the system badly.
- 3,900 ÷ 1,513 ≈ 2.6 kWp, for example 5 modules of 550 Wp (2.75 kWp).
- Frequent or long power cuts, and critical loads that must keep running (for example work-from-home computers or medical equipment).