Solar System Sizing & Checklist
What vendors must ask before designing a rooftop, commercial, or ground-mounted project.
Bad solar projects usually do not begin with bad panels. They begin with incomplete site information, rushed sizing, and weak customer discovery. The DGT manual is especially useful here because it treats system sizing, bill of materials, site survey, load calculation, and single-line diagrams as connected tasks rather than separate paperwork.
The Pre-Sales Discovery Checklist
Before a vendor proposes system size, these questions should be answered clearly:
✓ What is the consumer trying to achieve: bill savings, backup, maximum self-consumption, diesel reduction, ESG target, or export revenue?
✓ Is the site residential, commercial, industrial, institutional, agricultural, or remote?
✓ Is the project rooftop, ground-mounted, or carport?
✓ What are the last 12 months of electricity bills showing?
✓ What is the daytime load profile, not just monthly energy total?
✓ Does the customer want on-grid, off-grid, or hybrid operation?
✓ Are there frequent outages, critical loads, or battery backup expectations?
✓ Is the roof shaded, old, weak, leaking, or likely to be renovated soon?
✓ Is there clear access for installation and future maintenance?
✓ Are there utility, DISCOM, or net-metering constraints?
DOE's homeowner guidance is also useful even beyond homes: roof age, tree shade, roof slope, and orientation matter early. DOE notes that south-facing roofs with slopes roughly between 15 and 40 degrees often perform well, though other roofs can also work. In India and similar markets, the real point is not perfect south orientation alone. It is whether the site has enough low-shade, structurally sound, serviceable area to support the chosen design.
The Sizing Conversation Flow
A good sizing conversation usually moves in this order:
- Energy need: How many units are consumed, and what portion should solar offset?
- Timing of load: Is most usage during the day, evening, or during outages?
- Site constraints: How much usable area is actually available after setbacks, shade, access paths, and equipment placement?
- System type: On-grid, off-grid, or hybrid?
- Future changes: EV charging, new AC loads, process expansion, or additional floors?
Project-Specific Sizing Emphasis
For rooftop, commercial, and ground-mounted projects, the sizing emphasis changes:
- Residential rooftop: bill offset, roof condition, subsidy pathway, and backup expectations.
- Commercial rooftop: daytime load match, demand profile, roof penetrations, fire access, and business continuity.
- Ground-mounted: land use, cable routing, drainage, fencing, soil or foundation conditions, and O&M access.
Vendors should never jump directly from "monthly bill" to "system size" without checking shading, sanctioned connection details, inverter placement, earthing, and maintenance access. The DGT and MNRE materials both underline that quality begins before installation, during survey and design.
"The best pre-sales promise a vendor can make is not 'lowest price.' It is 'we will size the system around your load, your site, and your operating reality.'"
A strong requirement checklist also protects the customer. It prevents undersizing, overselling batteries, ignoring roof repair needs, or proposing premium equipment that the site cannot actually benefit from.