Space, access, cable routes, inverter and battery location, and the survey report

By now you know the roof type, its direction, tilt and shading. The last part of the survey turns that into a buildable plan: how many modules fit, how people will reach them, where every cable runs and where the equipment sits. Then you write it all down in a report that someone else could install from without calling you.

Usable area and module count

Start from the clear roof, then subtract:

• Setbacks of about 0.6 m from parapet edges, for safety and access (more on windy coasts, where edge zones see higher wind suction).
• Shade zones of tanks, mumties and parapets (lesson 4).
• Walkways to every row and to tanks, drains and the door.
• Areas the owner wants kept free: clothes-drying lines, pooja space, terrace garden.

Rule of thumb for planning: an elevated, tilted array in rows needs roughly 7.5–10 m² per kWp including gaps; flush-mounted modules on a shed need about 5–6 m² per kWp. Always confirm with a drawn layout.

Worked example: a Pune bungalow

A Pune bungalow has a 12 m × 9 m RCC terrace with a 3 m × 3 m staircase room (mumty) in the north-east corner. The customer needs about 5 kWp.

• Inside a 0.6 m setback the usable rectangle is 10.8 m × 7.8 m.
• Portrait modules (1.134 m wide, 20 mm clamp gap) along the 10.8 m east–west length: 10.8 ÷ 1.154 = 9 modules per row.
• At 15° tilt, each row is 2.20 m deep, with a 0.70 m gap in Pune (lesson 4), so the row pitch is 2.90 m. Two rows need 2.20 + 2.90 = 5.10 m of the 7.8 m depth.
• The back row is kept short to leave a clear path past the mumty door and the inverter cable route: about 6 modules.
• Maximum: 15 modules = 8.25 kWp. The customer needs 9 modules (4.95 kWp), so use the front row only and leave the rest of the terrace free. Note the spare capacity in the report for a future EV.

Access and walkways

• Every module must be reachable for cleaning without stepping on another module. Keep 0.6 m walkways between rows and along at least one side.
• Keep the path from the door to the array, the water tank and the rainwater outlets clear.
• Plan a water point on the roof for cleaning, or a hose route from the tank.
• On sheds, plan walkway planks or fixed walkways along purlins. Sheet roofs are not walkable everywhere.

Cable routes

DC cables run from the array to the DCDB and inverter. Keep them short, tidy and protected:

• Run them in UV-stabilised conduit or covered GI trays, never loose on the slab where people walk.
• Avoid crossing walkways; where unavoidable, use a cable cover.
• Follow walls and parapets; enter the building through a sleeve, sealed against water.
• Keep positive and negative of a string together to avoid large loops (lightning induces voltage in loops).

AC cables run from the inverter to the ACDB and on to the meter, often three or four floors down. Use the existing electrical shaft or a neat external conduit on the staircase wall.

Measure every run on site and add about 20% for slack, bends and terminations. In the example: DC run 14 m measured → 17 m per pole; AC run 18 m measured → about 22 m.

Choosing the inverter location

Battery location (hybrid systems)

• Indoors, in a dry, ventilated room, away from direct sun and water.
• LFP batteries are typically rated to charge at about 0–45 °C; check the datasheet. Rooftop cabins in Rajasthan summers get hotter than that.
• Not in a bedroom, kitchen or escape route. Keep clear space for service.
• Check floor strength for heavy lead-acid banks.
• Keep the battery-to-inverter cable short; it carries high current.

Earthing pits and the meter

• Find soil for earth pits: usually separate electrodes for DC, AC and the lightning arrester (PM Surya Ghar insists on three pits only for 10 kW and above), spaced about twice the rod length apart where space allows and bonded into one earthing system (module m06). Paved compounds may need a pit through the paving.
• Locate the DISCOM meter and check space for the net meter, its isolator and the incoming solar cable. Photograph the meter, its number and the main distribution board.

The survey report

Use the same template every time. It should include:

1. Customer: name, address, phone, consumer number, DISCOM, tariff category, sanctioned load, phase.
2. Consumption: 12 months of units, future loads, outage hours, backup needs.
3. Roof: type, slab thickness, condition, leaks, waterproofing, drains, terrace use.
4. Sketch: dimensions, north arrow, obstacles with heights, setbacks, proposed layout.
5. Electrical: supply voltage, phase loads, main DB, meter location, earthing.
6. Routes and locations: DC and AC cable lengths, inverter, battery, earth pits.
7. Photos: roof from four corners, obstacles, meter, DB, inverter wall, pit locations.
8. Risks and notes: sanctioned load, structural concerns, society NOC, access limits.
9. Customer confirmation: signature or WhatsApp confirmation of key points.

Key points

• Subtract setbacks, shade zones, walkways and owner-reserved space before counting modules.
• Plan roughly 7.5–10 m² per kWp for tilted rows and 5–6 m² per kWp for flush mounting, then confirm with a layout.
• Keep DC runs short and protected, measure every run on site, and add about 20% slack.
• Place inverters in shade with ventilation, and batteries indoors, dry and cool.
• Write a complete, standard survey report with a dimensioned sketch and photos.

Check yourself

1. A usable area is 9.6 m east–west. How many portrait modules 1,134 mm wide (20 mm gaps) fit in one row?
2. Why is a west wall usually a poor inverter location in India?
3. Name four things a survey sketch must show.