Half on the Tin Sheet, Half on a 17 Foot Structure: 20 kW of Solar for a Hotel in Crowded Lajpat Nagar

What made a congested site hard

• Access: Lajpat Nagar lanes are narrow and busy. A truck could not park at the door, so material came in on smaller vehicles at quiet hours and was carried in by hand.
• No crane: steel sections, modules and the inverter went up the outside of the building by rope, lifted by hand under supervision, because there was no room to stand a crane and no lift big enough.
• Shading: the neighbouring buildings stand close and some are taller. Modules at roof level would sit in shadow for part of the day on some sides.
• A working hotel: guests were checking in and out throughout the job, so noisy work was kept to agreed hours and the stairs and terrace were kept clear.
• Not enough clear roof: the tin sheet roof alone could not take 20 kW, and the open terrace next to it had to stay usable.

Two roofs, one plant

The answer was to split the array. The tin sheet roof took the modules that would fit on it, mounted flat on the sheet at its own gentle pitch, which kept that part of the plant low, quick to install and out of the wind. That used the one part of the roof that was free.

The balance of the modules went onto an elevated structure over the terrace, so that the terrace stays in use underneath and the modules above it clear the parapets and the shadows of the surrounding buildings for most of the day. Both parts feed the same inverter, so to the hotel it is one plant with one meter.

Raising the second half 15 to 17 feet

The elevated structure stands 15 feet high at the front and 17 feet at the back. The two foot difference gives those modules a 5 degree tilt for self-cleaning in rain, while keeping wind load low on a structure that is already tall. The modules are arranged in tables of 4 by 6, with the columns placed so the walkways below stay open and the space under the array works as a covered terrace.

Every column, rafter and purlin came up the building by rope. The structure was assembled on the terrace in sections small enough to handle by hand, then raised and bolted in place.

What we installed

• Solar array: 20 kW of 380 Wp mono PERC modules, split between the tin sheet roof and the elevated structure
• Structure: modules mounted flat on the tin sheet roof, plus an elevated galvanised steel structure 15 feet front and 17 feet rear over the terrace
• Inverter: Luminous 20 kW three-phase grid tie string inverter
• DC and AC distribution boxes by Efab Power Control, with Phoenix Type II surge protection and L&T breakers
• Polycab copper DC and AC cables in a cable tray, with earthing and lightning protection
• BSES Rajdhani net meter

Net metered with BSES Rajdhani

A hotel uses most of its power in the daytime: air conditioning, laundry, pumps, kitchen and lighting. Solar covers a good share of that directly. For the hours when generation exceeds the load, the plant is net metered with BSES Rajdhani Power Limited, so surplus power goes to the grid and is credited on the bill. MGetEnergy prepared and submitted the net metering application, drawings, component list and installation certificate, and saw the net meter through to installation in 2021.

Maintained under a five year O&M contract

• Module cleaning, which matters more in a dusty, traffic-heavy colony
• Tin sheet fixings and the elevated structure checked for corrosion and movement
• Inverter fault logs, ventilation and cooling
• Earthing, surge protection and net meter checks

What this means for other hotels and guest houses in Delhi

Lajpat Nagar, Karol Bagh, Paharganj, Greater Kailash and the other busy colonies of Delhi are full of hotels and guest houses with the same problems: no space, no access, shaded roofs and a terrace that is already in use. Splitting the array between the roof that is free and a raised structure over the terrace gets the full capacity onto a building that looked too small for it, and net metering turns a daytime-heavy load into a bill that shrinks every month.

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