Raechel Martin

3/1/2012

EGEE101H

Renewable Energy Resources: Solar Energy

As our country grows progressively more disgruntled with the increase in oil prices and

specifically the increase of gasoline prices for individual citizens, we are in need of energy alternatives

now more than ever before. There are other methods to obtain energy by way of fossil fuels other than

petroleum extraction, but they too have their faults whether it is environmental impact or cost. Even

some renewable energy resources, like biomass, prove to be too costly or space consuming to

reasonably generate enough energy to sustain massive populations. The most reasonable renewable

energy source seems to be solar energy. If efficiency of conversion and storage, and cost of the solar

units were improved, the availability of this primary resource would make this renewable energy ideal.

There are two major types of harnessing solar energy, one of which is photovoltaics.

Photovoltaics is the direct conversion of sunlight into electricity at the atomic level; these are the “solar

panels” seen on roofs and such. But how do they work? Electricity is obtained through photovoltaics by

using a material, like silicon, that exhibit the photoelectric effect; this means that when they absorb

photons of light, electrons are released which can then be harnessed as electricity (Knier, 2006).

Multiple cells are connected to form modules, and multiple modules are put together to form arrays,

creating more electricity (Knier, 2006). Even though standard PV cells are made with silicon, tests are

being done to study differences in the efficiencies of other materials. For instance, a Southern California

University team has come up with a plan to use organic PV cells (OPV cells) to convert solar energy into

electricity. According to Alternative Energy (2010), the team has devised a system of graphene/polymer

sheets instead of silicon to convert solar radiation into electricity. The graphene (atom-thick carbon

sheets) paired with polymer sheets with a thermo plastic layer of protection ("Alternative energy,"

Augu), does not prove to be more efficient. Silicon cells are more efficient, with 14 watts of power being

generated from 1000 watts of sunlight, and only 1.3 watts of power being generated from the same

amount of sunlight in a graphene cell ("Alternative energy," Augu). However, graphene costs less and is

more flexible, so it has its advantages ("Alternative energy," Augu).

The other major form of solar energy conversion is solar thermal power or CSP (concentrating

solar thermal power). CSP is the act of using reflectors to concentrate sunlight onto a receiver that then

produces steam which powers turbine-generators to create electricity (Wang, 2011). Basically, this

method of conversion is used in a power plant to disperse electricity like that of a fossil fuel plant, just

less efficiently. The most popular design is a parabolic trough reflector and power-tower receiver; this

includes rows of connected reflectors that direct sunlight onto tubes of synthetic oil that flow to a heat

exchanger, heat the water, and produce high-pressure steam (Wang, 2011). Although many power plant

developers swear by this method, the use of a central tower to collect the directed sunlight and heat

molten salt proves to be useful because it can retain the heat after the sun goes down (Wang, 2011).

Stirling engines, composed of a giant round dick of reflectors that direct sunlight to heat hydrogen gas or

helium, are another common design; the heated gas provides the pressure necessary to drive a piston to

create electricity (Wang, 2011). Regardless of the method used, in order to keep up with the

competition of PV cells, CSP plants must become more efficient and improve storage techniques (Wang,

2011). At sunlight-to-electric peak, the efficiency for a power tower or parabolic trough is about 22-23

percent and 31 percent for a Stirling engine (Wang, 2011). This makes the Stirling the most efficient of

the three at maximum sunlight.

After reading about these different methods, PV cells seem to be the more reasonable choice

for the future. According to Smil (2006), improvements in PV cells could lead to efficiencies of twenty

percent which translates into about 20-40 W/m2, which is higher than both wind and hydropower.

However, the major problems of PV cells include obtaining the resource itself storing it. Indirect

sunlight, through cloud cover or smog, is harder to convert and there are no solid techniques that can be

used to store unused electricity that is generated on a large scale (Smil, 2006). Overall, solar energy

methods will have to be refined in order to make them a prominent method of electricity generation

and overtake fossil fuel use in the future.

Sources

Wang, U. (2011, Jun 06). The rise of concentrating solar thermal power. Retrieved from

http://www.renewableenergyworld.com/rea/news/article/2011/06/the-rise-of-concentrating-solar-

thermal-power

Alternative energy. (Augu). Retrieved from http://www.alternative-energy-news.info/graphene-solar-

cells/

Knier, G. (2006, April 6). Nasa science. Retrieved from http://science.nasa.gov/science-news/science-at-

nasa/2002/solarcells/