What a 400 kW Solar Plant Costs and Needs: Roof, Connection and Approvals

A 400 kW rooftop solar plant for a factory typically costs about ₹1.04–1.12 crore excluding GST, interpolated between our published 250 kW and 500 kW pages and inside the ₹24,000–32,000 per kW C&I band. It needs roughly 40,000 sq ft of shadow-free roof, generates about 48,000 units a month in north India, and sits just under the 500 kW ceiling that many net-metering rules apply.

What does a 400 kW solar plant cost?

We publish pages for four sizes: 100 kW, 250 kW, 500 kW and 1 MW. There is no 400 kW page, so the row below is arithmetic between the neighbours, not a separate quotation. The per-kW rate falls as capacity rises, because structure, cabling and approvals are spread over more kilowatts.

Four things move a 400 kW quote inside or outside that range: roof type (RCC needs ballast or anchored structure; a PEB sheet roof needs a purlin check), the cable run from the array to the inverter room and then to your incomer, whether the connection is LT or HT, and the module and inverter specification. A quote well below the range usually removes scope, typically structure gauge, protection or approval liability, rather than adding efficiency. Compare BOQs line by line.

When you ask for quotes, give every bidder the same basis: capacity stated as DC kWp and as AC inverter kW, roof drawing, sanctioned load, supply voltage, and whether you want the price with or without the DISCOM fees and the safety approval. Without that, two quotes for "400 kW" can describe plants of quite different size, and the cheaper one is simply the smaller one. Ask each bidder to name the module brand and wattage, the inverter make and warranty term, and the structure's steel grade and coating, because those three lines carry most of the price difference.

How much roof, and how many units?

The working figure is 100 sq ft of shadow-free roof per kW, so 40,000 sq ft for 400 kW. That means usable area, after you subtract lift rooms, water tanks, skylights and parapet shadows, not the building footprint. If the roof cannot carry the array, ground-mounting needs about 1.4 to 2 acres, scaled from the 4-acre-per-MW working figure on our 1 MW page.

At about 120 units per kW per month in north India, 400 kW generates roughly 48,000 units a month, or 5.8 lakh units a year. At the ₹9 per unit avoided-energy assumption used on the size pages, that is an upper bound of about ₹4.3 lakh a month if every unit is consumed on site. Exported units are valued at zero in that arithmetic, and fixed or demand charges are not avoided by solar. The 250 kW and 500 kW pages show simple paybacks of about 2.3 and 2.0 years at full self-use; 400 kW falls between them and lengthens as self-use drops. Run your own tariff and shift pattern in the solar payback calculator.

Which connection route does 400 kW fall under?

The central Electricity (Rights of Consumers) Rules, as amended on 28 June 2021, say that where a state regulation is silent, the commission may allow net metering up to 500 kW or the sanctioned load, whichever is lower, and net billing or net feed-in for other loads. States then set their own limits, and they differ:

• Punjab: the 2021 PSERC regulations, as reproduced by PSPCL, cap net-metered rooftop capacity at 500 kWp and limit a non-domestic plant to 70% of sanctioned load or contract demand. For 400 kW that implies about 570 kW of sanctioned load or contract demand. The regulations have been amended since, so confirm the current text with PSPCL.
• Jammu & Kashmir: the JERC 2023 regulations allow net metering up to 500 kW and limit the plant to sanctioned load or contract demand.
• Maharashtra: the regulator has kept a 1 MW net-metering limit, above the central default.

A practical reading: a 400 kW plant is not a special case anywhere we checked, but it is close enough to the ceiling that a small change matters. If the plant grows to 520 kW after a roof survey finds more usable area, it may move from net metering to net billing in some states, which changes how exported units are valued. Decide the size with the ceiling in mind, not after.

So 400 kW is usually inside the net-metering ceiling, but your sanctioned load can be the binding limit, not the plant size. Check it first with the sanctioned-load calculator. If you want more than the ceiling allows, or have a large night load that rooftop solar will not serve, the next routes are net billing, captive generation or open access.

What interconnection voltage and inverter layout?

The Punjab regulations tie the interconnection voltage to the voltage at which the consumer already receives supply, and require compliance with CEA connectivity standards. In practice a 400 kW plant connects on the LT side of your own transformer or on an HT feeder, depending on your existing supply; the DISCOM's feasibility study confirms transformer and feeder headroom. Where the rule caps capacity by rated AC inverter output, as Punjab's does, the DC array can typically be built somewhat larger than the inverter rating, so state clearly which number your quote and your application use.

At 400 kW, string inverters are typical: several mid-size units, each with multiple MPPT inputs, so shading on one roof section does not drag down the rest, and a failed unit takes out a small slice of generation. Central inverters become more attractive from about the 1 MW range, where one large unit and an MV transformer reduce cost per kW. Whichever you choose, ask for the monitoring scope and the inverter warranty term in writing.

What approvals does a 400 kW plant need, and how long?

1. Load and roof check: sanctioned load, feeder and transformer headroom, roof structure.
2. DISCOM application: filed on the DISCOM portal with the single-line diagram and site details. Jammu & Kashmir's regulations, for example, set 20 days for the technical feasibility study.
3. Design and procurement: structure design, module and inverter orders.
4. Installation and electrical safety: installation, testing, and Electrical Inspector approval or self-certification as your state's notification allows.
5. Agreement, meter and commissioning: the 2024 amendment to the central rules asks the DISCOM to complete this within 15 days of the installation certificate; J&K's regulations set 30 days.

End to end, a clean rooftop job typically takes three to four months, and the DISCOM steps often decide the end date. Incomplete drawings are the most common reason a file sits still.

How Secured Engineers helps

We design the plant in-house and file the DISCOM net-metering application and the Electrical Inspector (CEIG) approval ourselves, so one team owns the file from sanctioned-load check to commissioning. Solar and MEPF can sit under one contract, which matters if the new roof load, the transformer or the fire-safety layout is part of the same project. We work from offices in Noida (Delhi NCR) and Ludhiana, and our record covers 535+ projects across 18+ states, with 89.77% repeat clients.

Start with the solar calculator for a first number on your bill, read the factory solar page for how a project runs, then send us your electricity bill. You can message us on WhatsApp, call +91 70099 85817, or ask for a free proposal with the roof, connection and approval route set out for your site.