Renewable Energy Resources for Irrigation - Practices of Irrigation and On-farm Water Management - page 513

generate waste and pollution. Some renewable energy systems actually create envi-
ronmental problems. For instance, older wind turbines can be hazardous to flying
birds.
13.11.1.5 Land Area Required
Another environmental issue, particularly with biomass and biofuels, is the large
amount of land required to harvest energy, which otherwise could be used for other
purposes or left as undeveloped land. However, it should be pointed out that these
fuels may reduce the need for harvesting nonrenewable energy sources, such as vast
strip-mined areas and slag mountains for coal, safety zones around nuclear plants,
and hundreds of square miles being strip-mined for oil sands. These responses, how-
ever, do not account for the extremely high biodiversity and endemism of land used
for ethanol crops, particularly sugar cane.
In the United States, crops grown for biofuels are the most land- and water-
intensive of the renewable energy sources. In 2005, about 12% of the nation's corn
crop (covering 11 million acres (45,000 km 2 ) of farmland) was used to produce four
billion gallons of ethanol - which equates to about 2% of annual US gasoline con-
sumption. For biofuels to make a much larger contribution to the energy economy,
the industry will have to accelerate the development of new feedstocks, agricultural
practices, and technologies that are more land and water efficient. Already, the effi-
ciency of biofuels production has increased significantly and there are new methods
to boost biofuel production.
13.11.1.6 Incapability of Generating Large Amount of Energy
In most cases of renewable energies (except hydroelectric system), the system is
not capable of producing large amount of energy. For this reason, it is a problem to
transmit the generated energy, and the cost becomes high.
13.11.1.7 Longevity Issues
Though a source of renewable energy may last for billions of years, renewable
energy infrastructure, like hydroelectric dams, will not last forever, and must be
removed and replaced at some point. Events like the shifting of riverbeds, or chang-
ing weather patterns could potentially alter or even halt the function of hydroelectric
dams; lowering the amount of time they are available to generate electricity.
Although geothermal sites are capable of providing heat for many decades, even-
tually specific locations may cool down. It is likely that in these locations, the system
was designed too large for the site, since there is only so much energy that can be
stored and replenished in a given volume of earth.
13.11.1.8 Sustainability
Renewable energy sources are generally sustainable in the sense that they cannot
“run out” as well as in the sense that their environmental and social impacts are