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| Solar arrays at NREL. |
The widely held belief of solar systems is that once the initial cost is paid off, the rest is gravy.
Or more specifically, that the power harvested from the sun is free for those who own their systems. And that's true.
However, there's an important detail to consider, especially if the cost of materials and labor are financed over a long period.
"Numerous studies have shown that degradation rates for silicon modules are typically less than 1 percent per year," says analysis from the National Renewable Energy Laboratory in Golden, Colo.
That means power output diminishes minutely each year and could be significantly less for a system once the up-front costs are paid off after financing. That could mean a photovoltaic solar array produces 40 percent less power than the day it was installed once a 40-year loan is paid. A highly technical NREL study says declines could actually be less, ranging from .5 percent to .7 percent.
