What a 300 kW Solar Plant Costs and Needs: Roof, Connection, Approvals

A 300 kW rooftop solar plant costs indicatively ₹81–90 lakh turnkey, excluding GST, scaled from our published band of ₹24,000–32,000 per kW. It needs about 30,000 sq.ft of shadow-free roof, or roughly 1.2 acres on the ground, generates about 36,000 units a month, and usually connects to the existing low-voltage bus after DISCOM approval.

Central or string inverters at 300 kW?

This is the first design choice and it shapes the rest. A central inverter is a single large unit, in the region of the plant's full AC capacity, in a plant room. String inverters are several smaller units, typically of 50–60 kW class, mounted near the arrays. A 300 kW plant would use five or six of them.

We usually choose strings at this size, for three reasons. A failed string inverter costs you a fifth of output or less, not all of it. DC cable runs are short because the inverters sit at the roof blocks, which matters when 30,000 sq.ft is spread over several sheds. And replacing one unit is a half-day job. A central inverter earns its place when there is one large unobstructed roof or a ground-mount array with a dedicated inverter room. Ask each bidder for the number of units, the MPPT inputs per unit and the warranty period, because that is where a low per-kW price often hides a different design.

What does the plant need, in numbers?

The table gives working figures for a 300 kW plant. They are scaled from the benchmarks on our size pages, so they are indicative, and the 250 kW and 500 kW pages bracket them.

The tariff is illustrative: use the rate on your own bill for the units solar replaces. Payback depends more on your self-use share than on the module brand. Run your numbers in the solar payback calculator and size the plant first in the solar calculator. For neighbouring sizes see the 100 kW, 250 kW, 500 kW and 1 MW pages.

Roof or ground: which is right?

Roof-mount avoids land and uses space that earns nothing now. It needs a structural check, because modules and structure add load to sheds that were designed for sheets and purlins, and the check is cheaper before the order than after. Ground-mount suits a factory with spare land, a weak roof or a roof that is mostly skylights. It needs about 1.2 acres at 300 kW, a clear boundary against shadow, and a longer cable route. Our plant area calculator shows the working, and the roof load calculator gives a first look at structure.

How does a 300 kW plant connect?

The connection follows your existing supply and the state supply code. A factory on an HT supply with its own transformer usually feeds the plant into its low-voltage bus behind that transformer. A low-tension consumer connects at its main panel. Two checks matter before design: sanctioned load or contract demand against plant size, using the sanctioned-load calculator, and whether the transformer can absorb generation minus minimum load, which our 250 kW page identifies as the stress case on a Sunday afternoon. Neither is a solar-only question, and a quote that skips them is a price for a plant that may not connect.

The CEA connectivity regulations require protection that trips the plant on voltage and frequency excursions and on loss of grid, with reconnection only after the network has been stable for at least sixty seconds, and require that inspections and tests be completed before physical connection. The interface relay settings and the single-line diagram are what the DISCOM reviews.

What is the approvals sequence?

1. Survey the roof, run a shadow study and confirm the structure.
2. Check sanctioned load or contract demand against 300 kW, and the transformer headroom.
3. Apply to the DISCOM. For rooftop solar, the Rights of Consumers Rules as amended in 2024 give fifteen days for the technical feasibility study, with the proposal treated as feasible if the DISCOM does not respond.
4. Obtain Electrical Inspector approval where the installation is in the state's notified scope. This depends on the voltage the plant ties in at, not on its kW alone; in Punjab, for example, the line is every new installation above 650 V.
5. Install, test and submit the installation certificate. The DISCOM then has fifteen days to sign the connection agreement, fit the meter and commission, under the same amendment.

We run the DISCOM and inspector paperwork in parallel with procurement so that approvals are not the critical path. State-by-state notes are on our solar policy page.

What moves the price inside the range, and what sits outside it?

Within the published band, the roof moves the price more than the module brand does. The mounting structure depends on whether the roof is RCC, a metal shed or a pre-engineered building, and its type and gauge are set by the roof. Cable runs matter too: a plant spread over several shed blocks has more DC cable and more combiner work than one clean roof, and a long run from the arrays to the inverters or to the panel adds cost that a flat per-kW quote may not carry.

The band covers modules, inverters, structure, DC and AC cabling, earthing and lightning protection, protection and metering, installation, testing and commissioning, and the DISCOM and net-metering approvals. It excludes roof strengthening or civil works, HT-side works or a transformer or bay addition where the site needs one, battery storage, land for a ground-mount alternative, and statutory fees. When you compare quotes at 300 kW, ask each bidder to confirm in writing which of those it has included, who supplies the meter and the CT where one is needed, and what the monitoring and warranty terms are. A quote that is 10 percent lower with the transformer check left out is not lower.

The GST rate on the plant is separate from all of this and is charged on top of the figures here. Confirm the rate in force on the date of your order with your accountant or on the CBIC site.

How Secured Engineers helps

We design the plant in-house, file the DISCOM net-metering application and the Electrical Inspector submission ourselves, and can deliver MEPF and solar under one contract, so a transformer or panel change is scoped once. We work from offices in Noida (Delhi NCR) and Ludhiana, with 535+ projects across 18+ states and 89.77% repeat clients. The solar EPC service page lists scope and exclusions.

Start with the solar calculator, then send us your last twelve bills and the roof layout. Message us on WhatsApp, call +91 70099 85817, or ask for a free proposal.