Designing a rooftop solar system that maximises energy yield, meets PM Surya Ghar subsidy eligibility criteria, satisfies DISCOM net-metering requirements, and delivers excellent customer experience is a multi-dimensional challenge. For solar installers operating at volume in the government scheme space, having a standardised, technically sound system design protocol is the difference between profitable, repeat-business operations and costly rework, warranty claims, and subsidy rejections.

This technical guide covers every step of rooftop solar system design for PM Surya Ghar installers — from roof assessment and load analysis to panel selection, system sizing, and documentation.

Step 1: Site Assessment and Roof Evaluation

Structural Capacity

Before any system design begins, the roof structure must be assessed for load-bearing capacity. Standard M10 Mono-PERC bifacial modules weigh approximately 22–25 kg per module. A 3 kW system using 540 Wp modules requires 6 modules — approximately 140–150 kg of panel dead load, plus mounting structure. In older residential buildings, a structural assessment may be necessary before installation can proceed.

Shading Analysis

Shade is the single largest yield killer in residential rooftop solar. A shadow covering even 5% of a panel’s area can reduce its output by 30–50% due to current mismatch in series-connected cells. Installers must conduct a shading analysis using a solar pathfinder or digital tools, accounting for shadows from water tanks, parapets, AC units, antennas, and neighbouring buildings at the winter solstice sun angle — when shadows are longest.

Selecting M10 half-cut Mono-PERC modules significantly mitigates shading losses because each module operates as two independent half-strings. A shadow on one half does not proportionally affect the other half’s output — a critical advantage for urban rooftops with partial shading.

Step 2: Load Analysis and System Sizing

Determining Eligible Capacity Under PM Surya Ghar

Under PM Surya Ghar, the maximum subsidised capacity is linked to sanctioned load. The MNRE guidelines recommend system capacity sizing at 1 kW per 150 units (kWh) of monthly consumption, subject to DISCOM approval and available roof space. The maximum subsidised capacity is 3 kW for individual households, though larger systems can be installed with the incremental cost borne by the beneficiary.

Beneficiaries and installers can calculate eligible capacity and subsidy through the official PM Surya Ghar national portal at pmsuryaghar.gov.in.

Panel Count and Array Configuration

System sizing formula: System kW capacity ÷ Module Wp rating = Number of modules. For a 3 kW system using Websol’s 540 Wp M10 Mono-PERC bifacial modules: 3000 ÷ 540 = 5.56 → 6 modules (3,240 Wp installed). The slight over-sizing (3.24 kW vs 3 kW) is standard practice — it compensates for system losses including DC cable resistance, inverter efficiency, and soiling.

Step 3: Inverter Selection and String Configuration

The inverter must be appropriately sized to the array. A general rule: inverter AC output capacity should be 80–100% of array DC capacity. For a 3.24 kW array, a 3 kW or 3.3 kW grid-tie inverter is appropriate. For PM Surya Ghar installations, only grid-tie inverters with anti-islanding protection are permissible — essential for the safety of DISCOM line workers during grid outages.

String configuration must ensure that module Voc (open-circuit voltage) × number of modules in series does not exceed inverter maximum DC input voltage. For standard 540 Wp M10 modules with Voc ≈ 49 V, a 2-string configuration of 3 modules each is typical for 3 kW systems with string inverters.

Step 4: Selecting the Right Solar Module for PM Surya Ghar

Panel selection for PM Surya Ghar must balance four criteria: ALMM compliance, efficiency for available roof area, bifacial suitability for the specific installation type, and supplier reliability.

For a comparison of cell technology options relevant to residential rooftop design, review our guide on MonoPERC vs N-Type vs M10 cell technology selection.

Websol Energy System manufactures M10 Bifacial Mono-PERC cells optimised for Indian rooftop conditions. As a leading solar module manufacturer in India, Websol’s modules offer consistent efficiency, ALMM-eligible manufacturing, and comprehensive product documentation for government scheme installations.

Step 5: Net-Metering Application and DISCOM Coordination

All PM Surya Ghar installations must be connected to the grid through a net-metering arrangement. Installers are responsible for filing the net-metering application with the local DISCOM, along with system drawings, inverter specifications, and module datasheets. Processing times vary by state and DISCOM — plan for 4–12 weeks between installation completion and meter commissioning.

Document checklist for DISCOM and subsidy submission typically includes: module datasheets and ALMM certificate, inverter datasheet and CEC certification, single-line diagram, earthing and lightning protection documentation, installation photographs from multiple angles, and the signed net-metering agreement.

Step 6: Commissioning and Yield Verification

Post-installation, every PM Surya Ghar system should be commissioned with a system performance check: verify string voltages and currents with a DC clamp meter, confirm inverter is grid-connected and exporting, check monitoring portal for real-time generation data, and document the commissioning reading for subsidy claim purposes.

As a best practice, provide every customer with a projected monthly generation chart based on the site’s GPS coordinates and system size — this sets clear expectations and is a powerful tool for generating referrals.