Solar for a New Factory Under Construction: Roof Design, HT Yard and Approvals Sequencing

Plan solar into a new factory while it is still on paper: design the roof structure for the module load, reserve space in the HT yard and electrical rooms, show the plant on the first single-line diagram, and ask the inspector to approve it with the rest. At design stage this adds little; after the shed is built it means strengthening, new cable routes and a second approval round.

What does a roof designed for solar need that a plain roof does not?

A solar array adds dead load across most of the roof, wind uplift on clamps and rails, and foot traffic for cleaning and repair. A pre-engineered building is normally designed for its roof sheeting, its services and a nominal maintenance load, so unless the designer is told, modules are not in the design basis. Tell the structural designer in the brief, and ask for the following in writing:

• Added dead load in kg per sq m for the mounting type you expect, and the purlin, rafter and column checks against it. Our solar roof load calculator gives a first dead-load figure; it is not a structural check.
• Wind uplift at the roof's edges and ridge, where loads are highest, using the wind loading code for the site.
• Roof geometry that suits modules: pitch, orientation, long unbroken slopes, and ridge ventilators and skylights set out in rows aligned with future module rows, not scattered across them.
• Fixing method agreed with the sheeting supplier, so clamp mounting does not void the roof warranty. Our note on solar on a PEB sheet roof covers this.
• Safe access: anchor points, walkways, ladders and a clear route for cables down to the electrical room.

Keep tall items off the sun side of the roof: stacks, water tanks, exhaust fans and lift overruns cast long shadows. If the array will sit on an RCC roof, decide the parapet height and the waterproofing system before the slab is cast.

Which decisions fall at which stage?

The table follows a typical build from layout to energisation. The right-hand column is the rework that follows if the decision is skipped.

What to reserve in the HT yard and electrical rooms

A solar plant of a few hundred kW to a few MW usually connects on the HT side. Ask the electrical designer to reserve space for the solar incomer or bay, the CT and PT metering and the protection relay panel, and to show the transformer loading with the plant exporting at its peak and the factory at its lowest load. Reverse flow through the transformer, fault level and the coordination of relays with the DG interlock are design items, not afterthoughts. Our notes on connecting at 11 kV and transformer headroom for solar give the checks.

Plan for a larger inverter room than the first phase needs if the roof could carry more later. Expansion is cheap in a room that was drawn for it and costly in one that was not.

How should the approvals be sequenced?

1. Declare solar in the power design. The sanctioned load or contract demand you apply for should support the solar plan, because many states tie plant size to it.
2. New connection and solar application. Whether the utility takes a solar application in the same file as a new connection, or only after the connection is energised, varies. Ask in writing before you plan the programme. For rooftop systems above 10 kW the central rules, as amended in February 2024, set a 15-day feasibility study with deemed approval; HT and state processes may differ.
3. Electrical inspector. Put the solar plant, the DG and the substation on the same drawing set. Inspectorates commonly ask for drawing approval of additions to an approved HT installation too; Tamil Nadu's online services, for example, list drawing approval for new HT installations or additions and alterations to existing ones. Our CEIG approval guide describes the file.
4. Fire. The fire scheme and the roof layout should be drawn together so that firefighter access and DC isolation are shown.
5. Modules. MNRE's office memorandum of 4 August 2026 exempts net-metering projects commissioned by 31 December 2026 from the ALMM cell list (List-II); the module list (List-I) still applies. Private captive plants behind the meter are outside both lists. Check which applies, and the date, against your commissioning programme.

When does it cost more to wait?

Four items are cheap to include in the first design and costly to add: structure sized for modules, a transformer or bay with headroom, cable routes from roof to room, and approvals filed once. The retrofit versions are strengthening a finished roof, a bay addition inside an energised yard, cutting through completed slabs, and a second drawing approval with its inspection. We do not put numbers on that gap here, because the difference depends on the building, but each retrofit item is a line you can ask any contractor to price.

Waiting is sometimes the right choice. If the connection will not be energised for a year, the plant cannot run, and capital is better spent on the building. The point is to design for solar now and build it when the connection and the load are in place. Our guide to new factory MEP planning places solar inside the wider checklist.

How Secured Engineers helps

We design in-house and take MEPF and solar under one contract, so the roof structure, the HT yard, the cable routes and the fire design for a new factory are drawn by one team. Fire NOC, CEIG and DISCOM net-metering applications are filed in-house, and CEIG can be asked to approve solar with the rest of the installation. Our offices are in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients. See industrial solar EPC for the scope.

If your factory is in design or under construction, send the layout, the roof drawings and the single-line diagram, and we will mark what to change now. Our turnkey EPC page describes how the pieces fit. Make a solar enquiry on WhatsApp, call +91 70099 85817, or ask for a free proposal.