Economic and legal principles in renewable energy development policy - Solar, Wind and Land: Conflicts in Renewable Energy Development - page 16

so does the need for laws enabling landowners to protect their solar
energy systems from shading by neighbors.
Urban gardens can also require a degree of direct solar access that
only open city airspace provides. An increasing number of cities
throughout the country are encouraging the cultivation of gardens on
inner city lots as a means of combating blight and improving urbanites'
access to fresh local produce. Of course, the successful growth of many
food plants requires adequate sunlight. This need for unobstructed
sunlight can also potentially constrain the development of airspace
above neighboring parcels.
Even in the context of green building, access to sunlight via open
airspace has taken on added value in recent years. The United States
Green Building Council's 2009 Rating System rewards points toward
LEED (Leadership in Energy and Environmental Design) Certification
for building designs that satisfy specific natural daylight illumination
requirements. Natural lighting through skylights and windows conserves
energy by mitigating the need for electrical light. Unfortunately, shade
from neighboring buildings or trees can reduce the degree of interior
illumination achievable on a given parcel, necessitating greater reliance
on electricity-dependent artificial light sources.
One other potential use for unoccupied urban airspace is to provide
wind access for “small” wind turbines. Wind turbines convert the
kinetic energy in wind into electric power. Small turbines are petite
versions of commercial turbines and usually generate only enough
power to offset a portion of a single landowner's energy consumption.
These devices may not require direct sunlight, but they still need a
substantial amount of open airspace to function effectively. They are
more productive the higher they reach into the sky and can require that
hundreds of feet of open airspace in the upwind direction to ensure
that winds flowing into them are largely undisturbed. Wind access for
small turbines has historically been a low priority in most jurisdictions,
although this could change as these devices become increasingly cost-
effective and demand for them continues to grow.
Mounting pressure to occupy airspace
Despite the myriad uses for open airspace just described, physically
occupying airspace with buildings, trees, or other structures also creates
substantial value in many circumstances. The sustainability movement
is also bolstering demand for this other category of airspace uses.
Filling more urban airspace with buildings has become an increasingly
attractive policy option in the past few decades as the damaging effects
of suburban sprawl have become evident. Sprawling development on
the suburban fringe tends to require more public infrastructure than
dense urban in-fill projects and can also result in comparatively longer