Solar Power Plant EPC: How Rooftop and Ground-Mount Projects Are Actually Delivered

Solar proposals tend to arrive as a capacity figure, a generation estimate and a payback
period. All three are outputs of assumptions that are rarely stated — and the gap between a
plant that performs to projection and one that quietly under-delivers is created during design
and execution, not during the sales conversation.

Here is what a solar EPC project actually involves for a captive rooftop or
ground-mount plant in India, and what to interrogate at each stage.

1. Feasibility Is an Engineering Study, Not a Site Photo

A proper feasibility assessment covers the available shadow-free area after accounting for
existing services and future construction; a shadow analysis across the year, including from
adjacent structures; the structural capacity of the roof, including its remaining service life
and waterproofing condition; the site’s solar resource; and the plant’s own load profile, since
a captive plant is only as valuable as the energy it displaces at the time it generates.

2. The Approvals Path Determines the Timeline

Regulatory work runs in parallel with engineering and is the most common cause of delay.
Depending on capacity, connection voltage and state, this can involve the distribution
licensee’s net metering or connectivity approval, approval from the state electrical
inspectorate before energisation, compliance with Central Electricity Authority technical
standards for connectivity, and — for schemes seeking government support — procurement of
modules from the applicable approved list under MNRE policy. Ask any bidder to name the approvals in scope and who owns each
application.

3. Rooftop or Ground-Mount: Different Projects

4. Design Decisions That Show Up in Generation

• String sizing checked against temperature extremes so voltage stays within inverter
  window
• Inverter selection and DC-to-AC ratio matched to the load profile and irradiation
• Tilt, azimuth and row spacing set for the latitude and inter-row shading
• DC and AC cable sizing for loss, not just for current-carrying capacity
• Earthing, lightning protection and surge protection on both DC and AC sides
• Monitoring at string or inverter level, so under-performance is visible early

5. Execution and Commissioning

Execution runs through structure fabrication and installation, module mounting, DC string
wiring, inverter and transformer installation, LT or HT interconnection, earthing and lightning
protection, and the monitoring system. Commissioning should include insulation resistance and
polarity checks on every string, open circuit voltage and short circuit current verification,
earth resistance measurement, inverter parameter setting, protection and anti-islanding checks,
synchronisation with the grid, and a performance check against the design estimate under
measured irradiation.

6. O&M Is Where the Business Case Is Protected

Soiling in Indian conditions can meaningfully reduce output between cleanings, and a single
under-performing string can go unnoticed for months without monitoring. A serious O&M scope
defines cleaning frequency, preventive maintenance schedules, response times, spares,
monitoring and reporting, and a defined performance benchmark rather than a vague uptime
promise.

VTPL executes solar EPC projects — rooftop and ground-mount — alongside its core electrical
EPC business, which means the plant’s interconnection, protection and switchgear are engineered
by people who build substations for a living. With 33+ years of experience across 19+ states
and clients including NTPC, ONGC, GAIL, IOCL and public sector bodies, VTPL delivers detailed
engineering, supply, installation, testing and commissioning on a turnkey basis.

Frequently Asked Questions

What does a solar EPC contractor do?

Takes single-point responsibility for feasibility and detailed engineering, approvals
support, supply of modules, inverters and balance of system, structural and electrical
installation, testing, commissioning and handover — and often subsequent O&M.

What approvals are needed for a captive solar plant in India?

Typically distribution licensee approval for net metering or connectivity, state electrical
inspectorate approval before energisation, and compliance with CEA technical standards — with
additional conditions where government schemes or subsidies apply.

Rooftop or ground-mount — which is better?

Rooftop uses existing area and suits factories and institutions with sufficient shadow-free
roof; ground-mount suits larger captive capacities where land is available. The deciding
factors are available area, roof condition and load profile.

Why do solar plants under-perform their estimate?

Common causes are shading not modelled properly, soiling without adequate cleaning,
undersized cabling and consequent losses, inverter clipping from a poorly matched DC-to-AC
ratio, and faults that go undetected without string-level monitoring.

VTPL delivers solar power
plant EPC projects and grid interconnection works across India. Evaluating a captive solar
plant? Request a project consultation
→