Solar flux is a given, and isn't modifiable by human activity. But the flux reaching Earth is limited, and in the sense of that which you give up -- opportunity costs -- there's only so much of it available. Stored solar flux -- as biofuels, wind, hydro, or fossil fuels -- represents an exergic potential (value) with an eMergic cost.
Economic prices fail to consider that emergic cost entirely, but in a very real sense it's an account balance being depleted. Environmental sinks also have costs associated with clearing and negative impacts.
Howard and Eugene Odum, ecologists, coined the term emergy and discuss it. There's a fair literature concerning it in ecology, though little or none in economics. I believe economics is in error here.
Again, very much not mainstrem econ. You'll find treatment in ecological, biophysical, and thermoeconomics however: Georgescu-Roegen, Daly, Hall, and Costanza, among others.
http://www.resilience.org/stories/2013-10-06/energy-ecology-...
(By Howard Odum's daughter.)
No, it's not. The ultimate causes for costs are human labor and taxes (including similar concepts like rent or license fees) – everything else derives from that.
You're not paying the Sun for its energy output, but the workers that mine the materials, process them, and build solar panels.