Understanding your wiring loss
What a typical wiring loss looks like
For a well-designed system with an 80 foot run of 10 AWG wire, wiring loss typically costs around 0.4% of annual output. Industry design standards generally target keeping total wiring loss under 2% to 3%, and a properly sized system should comfortably fall within that range. A DOE federal PV performance study lists wiring resistance among its standard predictable loss assumptions, typically modeled at around 2%.
Why wire gauge has such an outsized effect
Thicker wire has lower electrical resistance per foot, and since power loss scales with the square of current times resistance, even a modest gauge upgrade on a long run can meaningfully cut the resistive loss compared to a thinner, higher-resistance wire. This squared relationship with current is why wiring loss can climb quickly on higher-current systems if the gauge isn't upsized to compensate. Proper conductor sizing is a standard part of a well-designed installation, not an afterthought to fix later, as the Department of Energy's solar system design and O&M resources cover in detail.
Why run length matters more than a simple distance figure
Resistance increases directly with length, and the loss calculation accounts for the full round-trip distance the current travels, not just the one-way distance between the array and the inverter. A longer run on the same gauge wire always means more loss, which is why installers sometimes upsize wire gauge specifically for longer runs to keep total loss in check. See the altitude impact on output calculator for another site-specific factor worth checking. If your array is split across multiple roof sections or planes, run length can add up faster than expected, which the multi-roof plane array splitter tool can help you plan around.
Whether this is something to worry about after the fact
Not usually. A properly designed system accounts for wire gauge and run length during the design phase specifically to keep this loss low, so wiring loss is mainly a design-time consideration rather than something that changes or needs monitoring after installation. Unlike degradation or shading, this loss is fixed once the system is built and doesn't tend to worsen over time.
What to do with this number next
Add this figure into the real world vs nameplate output gap calculator alongside your other loss factors for a complete picture of your system's total expected output. Check the inverter clipping calculator too for another equipment-side factor worth understanding. The annual inspection cost estimator prices the yearly check that catches that problem early.