Biomedical Engineering Reference
In-Depth Information
temperature process heat for industrial purposes. To harvest the solar energy, the most
common way is to use solar panels.
Solar technologies are broadly characterized as either passive solar or active solar depend-
ing on the way they capture, convert, and distribute solar energy. Active solar techniques
include the use of PV panels and solar thermal collectors to harness the energy. Passive solar
techniques include orienting a building to the Sun, selecting materials with favorable thermal
mass or light dispersing properties, and designing spaces that naturally circulate air.
Earth's land surface, oceans, and atmosphere absorb solar radiation, and this raises their
temperature. Warm air containing evaporated water from the oceans rises, causing atmo-
spheric circulation or convection. When the air reaches a high altitude, where the tempera-
ture is low, water vapor condenses into clouds, which rain onto the Earth's surface,
completing the water cycle. The latent heat of water condensation amplifies convection,
producing atmospheric phenomena such as wind, cyclones, and anti-cyclones. Sunlight
absorbed by the oceans and landmasses keeps the surface at an average temperature of
14
C. By photosynthesis, green plants convert solar energy into chemical energy, which
produces food, wood, and the biomass from which fossil fuels are derived.
The total solar energy absorbed by Earth's atmosphere, oceans, and landmasses is approx-
imately 122 PWor 122,000 TWas one can infer from
Fig. 15.7
. The energy reached the planet
in 1 hour is more than the world used in 1 year in 2010. Photosynthesis captures approxi-
mately 95.1 TW in biomass. The amount of solar energy reaching the surface of the planet
is so vast that in 1 year it is about twice as much as will ever be obtained from all of the Earth's
nonrenewable resources of coal, oil, natural gas, and mined uranium combined.
From
Table 15.6
, it would appear that solar, wind, or biomass would be sufficient to supply
all of our energy needs, however, the increased use of biomass has had a negative effect on
global warming and dramatically increased food prices by diverting forests and crops into
biofuel production. As intermittent resources, solar and wind energy need to be used along
with a more reliable source. The major restriction on complete shifting to solar energy utili-
zation lies on the landscape change. Disturbing biomass growth for solar energy capture can
change the ecosystem to an undesirable state as elimination of plant biomass can have far-
reaching effects on the sustainability than biomass recycle via utilization.
TABLE 15.6
Solar Fluxes and Human Energy Consumption
Flux
TW
Solar
122,000
Wind
71.3
Biomass
95.1
Primary energy use (2008)
16.42 (2.455 kW/capita)
Fossil
13.337
Nuclear
0.946
Hydro
0.352
Electricity (2008)
2.30 (0.344 kW/capita)
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