Environmental Engineering Reference
In-Depth Information
deployed rapidly. It is an economical option; cost/MWh compares well with
that of conventional coal or hydropower installations. Several small
countries generate 10-20% of their power needs from wind energy. The
present technology can be relied upon to deliver about 2 W/m
2
of wind
farm. It is a fundamentally attractive option with the potential power
proportional to the third power of wind speed. A recent report (Hansen et
al., 2013) finds wind energy to be the leading or renewable energy source
for electricity production until 2035. The main constraint will be availability
of land in windy areas to locate such farms. In regions with adequate wind
resources, the technology holds promise as a supplementary power source.
Offshore wind farms, especially in deep-sea areas, might be more efficient
than land-based facilities.
Apotentialenvironmental problemwithwindfarmsistheirnegativeimpact
on migrating bird populations. A recent estimate suggests the mortality to
be about 0.27 deaths/GWh generated (Marris and Fairless, 2007). Given
that the bird deaths by fossil fuel plants are greater than 5 per GWh and
that for nuclear power plants are 0.42 per GWh (Sovacool, 2012), the cost is
modest compared to energy derived.
1.1.2.2 Solar Energy
All of the Earth's processes are ultimately energized by solar energy
(excluding chemosynthesis in the seabed). Solar energy reaching the Earth's
surface in a single hour is estimated to be more than the annual global
energy demand (US Department of Energy, 2005). Presently, only a paltry
0.01% of the global energy demand (0.1% of the US demand in 2011) is
met by solar energy. The sunlit half of the globe receives a solar flux of
680 W/m
2
of radiation and is for the most part captured by plants that
very inefficiently (typically <2%) convert it into biomass. (Interestingly,
the incandescent lamp also converts only 5-10% of the input energy into
light!) Biomass generated in turn serves as food to herbivores with the food
energy transferred up the complex food chain to the human consumer. The
energy transfer across trophic levels (say, herbivores to predator carnivore)
is particularly inefficient, approximately only 10%. The rest (~90%) of solar
energy captured by plants is dissipated as low-value heat. The efficiency
electricity is at least an order of magnitude higher in efficiency compared to
photosynthesis.
