Solar Losses Guide

PV loss assumptions translate sunlight into usable grid output. Underestimating losses can make a project look better than it is.

Shading loss

Trees, parapets, nearby buildings, chimneys, roof equipment, and terrain can shade modules. Even partial shading can affect string output. For serious projects, shading should be checked with site measurements or 3D modeling.

Soiling loss

Dust, pollen, pollution, bird droppings, and snow can reduce production. Soiling depends on rainfall, cleaning frequency, tilt, local dust, and site access. Dry climates can need a higher soiling assumption.

Thermal loss

PV modules produce less power at higher cell temperature. Roof-mounted systems with poor ventilation can have higher thermal losses than open-rack systems.

Electrical and inverter loss

Mismatch, wiring resistance, inverter conversion, and transformer losses reduce output between the module and grid meter. Inverter clipping can occur when DC array power exceeds inverter output capacity during strong irradiance.

Availability

Availability loss represents downtime from grid outages, equipment faults, communication issues, or maintenance. Small systems often ignore this, but larger systems should include it.

Loss assumptions should be explicit. If a proposal only shows final annual kWh without loss breakdown, ask for the bridge from irradiation to grid output.