A solar proposal can look precise while resting on weak inputs. Module count, system size, estimated annual production, and payback all depend on conditions that should be verified before a contract is signed. A useful photovoltaic site assessment connects the building’s energy use, roof or ground conditions, electrical infrastructure, utility rules, and commissioning plan into one defensible scope.

For owners, that work reduces surprises. For auditors, designers, and installers, it creates a record of the assumptions behind the system. The objective is not simply to fit the largest array possible; it is to specify a system that the site can support, the utility will approve, and the owner can verify after startup.

Begin with the load, not the module layout

Collect at least 12 consecutive months of electric bills and record kilowatt-hours, billing dates, rate structure, demand charges where applicable, and any estimated readings. Note expected changes such as a heat pump, heat-pump water heater, EV charging, building addition, occupancy change, or efficiency retrofit.

Annual consumption alone does not describe when electricity is used. Monthly profiles help distinguish winter heating, summer cooling, and relatively steady baseloads. Interval data, when available from the utility, can show daytime demand, evening peaks, and seasonal operating schedules. These patterns matter because export compensation and time-varying rates can make the value of a solar kilowatt-hour different from its retail cost.

Complete planned efficiency work before final sizing when practical. Air sealing, HVAC replacement, lighting upgrades, or control corrections can lower the load that the PV system is intended to offset. Our whole-home energy audit baseline guide explains how to organize bills, weather effects, and operational changes before modeling an upgrade.

Confirm roof and site readiness

The U.S. Department of Energy’s Homeowner’s Guide to Solar identifies roof age, size, shape, slope, orientation, and tree cover as important site factors. A field assessment should document:

  • Available roof areas, tilt, azimuth, setbacks, obstructions, and access paths
  • Current shading and likely future shading from trees or nearby construction
  • Roof covering type, age, condition, warranty, and expected replacement date
  • Structural concerns, attachment locations, wind and snow exposure, and drainage
  • Potential ground-mount locations, trench routes, easements, and underground utilities
  • Equipment locations that allow required clearances, service access, and safe routing

A roof near the end of its service life can turn an otherwise sound solar project into an expensive remove-and-reinstall problem. The solar assessment should not substitute for a structural evaluation or roofing inspection when those are warranted. It should clearly identify what must be resolved and by whom.

Shade analysis also needs more than a single photograph. Record the method, observation date, horizon obstructions, and modeled annual effect. Seasonal vegetation and the sun’s changing path can make a roof look better or worse during one site visit than it performs across a year.

Assess the electrical path

Trace the proposed system from modules to the building’s service equipment. Record service voltage, main breaker rating, bus rating, panel manufacturer and condition, available breaker positions, meter location, grounding and bonding conditions, and practical conductor routes. For larger buildings, document transformers, switchgear, distribution panels, service configuration, and ownership boundaries.

Do not promise that a panel upgrade is unnecessary based only on open breaker spaces. The design must address the adopted electrical code, equipment ratings and listings, the proposed point of interconnection, local amendments, utility requirements, and the authority having jurisdiction. Existing defects or obsolete equipment may also affect the scope even when the calculated PV connection is otherwise feasible.

If battery storage may be added later, plan deliberately for its equipment location, operating mode, critical-load panel, controls, and clearances. Solar readiness and storage readiness overlap, but they are not the same design problem. See our battery storage readiness guide for load, architecture, safety, and commissioning considerations.

Make production estimates reproducible

A credible estimate identifies its inputs. At minimum, retain:

  • DC nameplate capacity and module model
  • Inverter model, AC rating, and DC-to-AC ratio
  • Array tilt, azimuth, and layout by roof plane
  • Weather data or typical meteorological-year source
  • Shading, soiling, mismatch, wiring, availability, and other loss assumptions
  • Expected monthly and annual energy, not only a single lifetime total
  • Any degradation assumption and the period modeled

The result is an estimate, not a guaranteed meter reading. Actual production varies with weather, temperature, snow, soiling, equipment availability, shading changes, curtailment, and component performance. Present a reasonable range or sensitivity when an uncertain input materially changes the outcome.

Compare the model with the owner’s historical use and rate structure, but keep energy and financial conclusions separate. A system may produce the modeled kilowatt-hours while delivering different bill savings because rates, export credits, fixed charges, demand charges, or usage patterns changed.

Resolve permits and interconnection before construction

Permitting and utility interconnection are separate approvals. DOE explains that local permitting and inspection generally occur before a rooftop array can interconnect and operate on the grid. Its rooftop solar permitting and inspection guide also notes that requirements and fees differ by jurisdiction.

The project file should identify:

  • Permit application, approved drawings, equipment substitutions, and revision history
  • Structural and electrical documentation required by the local authority
  • Utility application, single-line diagram, equipment data, fees, and study requirements
  • Metering arrangement, export rules, and applicable tariff
  • Inspection results, corrections, and closeout documents
  • Utility permission to operate

Equipment installation does not itself authorize grid-connected operation. DOE’s Solar Energy Guide for Homebuilders describes the interconnection agreement and utility permission-to-operate step. Owners should know who is responsible for each submission, the expected sequence, and how delays or design changes will be handled.

Commission what was installed

Commissioning should compare the finished system with the approved design and establish a baseline for future troubleshooting. The National Renewable Energy Laboratory’s photovoltaic Standard Work Specification calls for required inspection and confirmation that the as-built system matches the specification.

A practical closeout includes:

  • Installed module, inverter, rapid-shutdown, and monitoring equipment model numbers and quantities
  • Array layout, attachment, conductor routing, labeling, grounding, weather sealing, and equipment clearances
  • Required electrical tests and recorded results
  • Inverter startup status, communications, monitoring access, and alarm review
  • Initial production compared with expected conditions at the time of test
  • Approved permits, passed inspections, permission to operate, warranties, manuals, and emergency shutdown instructions
  • Owner orientation and a clear service-contact process

Save screenshots or exports from the monitoring platform after startup, but do not treat an online green indicator as complete commissioning. Establish expected monthly production and an escalation threshold so that a failed string, inverter fault, communications outage, or growing shade problem is noticed rather than discovered in an annual bill review.

Verify incentives as of the application date

Incentive assumptions can materially affect project economics and must be checked before a proposal is accepted. As of October 26, 2026, the IRS states that the federal Residential Clean Energy Credit is not available for expenditures made after December 31, 2025. The current rule is on the IRS Residential Clean Energy Credit page.

State, local, Tribal, and utility programs may still apply. DOE directs consumers to the Database of State Incentives for Renewables and Efficiency, but the project team should confirm the actual program administrator, eligibility date, equipment rules, approved-contractor requirements, application sequence, funding availability, and tax treatment. Never present a rebate, export rate, or tax benefit as guaranteed.

A disciplined site assessment produces more than a solar quote. It creates a traceable chain from load and site conditions through design, approvals, commissioning, and performance review. BPMS can help building professionals organize field observations and supporting records, while engineering, permitting, installation, and utility approvals remain with the qualified parties responsible for the project.