Assess roof and load constraints, obtain traceable solar resource, compare actual designs and tariff value, then retain commissioning and production evidence.
Collect electricity use by billing period, planned load changes, roof dimensions, orientation, obstructions and roof condition. Obtain the actual structural, access, setback and permitting requirements from the project team. Keep usable array area separate from gross roof area and identify work needed before a PV installation.
Look up monthly NASA POWER horizontal climatology for the coordinates, preview all months and retain the returned location, period and units. Treat it as a regional climate input. Obtain a site-specific AC yield model that includes the actual array plane, shading, module behavior and inverter losses.
Compare actual tilt and azimuth candidates for the same period and roof constraints. Use matching site models or the supported irradiance comparison, then compare inverter proposals with their quoted costs and modeled energy. Keep DC/AC nameplate ratio, annual clipping and backup capability as distinct questions.
Have the design team verify cold/hot module voltage, independent MPPT limits, string currents, approved equipment and the full DC cable path. Resolve service, protection, disconnect, fire-access and utility interconnection requirements through the applicable process before installation or connection.
Use actual self-consumption, export compensation, credit usability and additional charges to calculate the bill benefit. Enter verified incentives only in the year received and add installation scope, roof work, maintenance and replacements to the cash-flow model. Compare the same ownership period across proposals.
Keep the accepted proposal, site model, array layout, tariff version, approvals and commissioning record. Compare measured AC production with a weather- and availability-matched baseline after operation begins. Save revised cases when roof conditions, equipment, consumption or utility rules change.
Record roof observations, bill periods, scope exclusions and professional survey requirements.
Compare an explicit nameplate and daily-energy arithmetic scenario after usable area and module assumptions are established.
Import or enter a documented twelve-month horizontal resource series.
Convert irradiation or integrate actual irradiance intervals on their stated plane.
Check operating-point power or integrate AC intervals without treating them as an annual site forecast. · Integrate measured AC intervals over a consistent reporting period.
Rank feasible tilt candidates from interval resource or comparable modeled yields.
Check the nameplate DC/AC ratio of each proposal.
Compare actual proposal energy value and incremental cost without an assumed topology uplift.
Check the proposed series and parallel configuration against entered voltage and current limits.
Compare actual cable candidates using adjusted ampacity, terminal ratings and full-loop voltage drop.
Separate avoided imports from usable export credits and incremental charges.
Compare annual cash flows, NPV and recovery retained through the chosen horizon.
Compare normalized performance across elapsed periods without attributing every change to aging.
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Monthly climate data has a location, averaging period and physical quantity; preserve these with each lookup.
Array orientation, module behavior and inverter limits belong in an explicit system model.
Review site suitability, proposal terms and the local utility process.
The same horizontal climate series can lead to different AC output for different roof planes, shade and equipment.
Record included roof work, monitoring, warranties and backup functions before interpreting a price difference.