Engineering Solar: Photovoltaic cells
A brief overview in solar engineering
Engineering in relationship to energy in the 21st century is being highly focused on renewable forms of energy. Renewable and unlimited resources for energy will allow us to ease off our dependency of fossil fuels and help curb pollution. The solar power industry in the US has shown large growth over the last few years, with California being the leading market. As we look to improve the technology within the solar industry, engineers continue to build upon the basic principles to develop better and more efficient processes to capture and utilize the energy. We discussed the basic concept for solar energy in previous blogs, but to understand how the energy is created, we need to look closer to the materials and their structural makeup that are used. Photovoltaic (PV), the method of generating direct current electricity from the photons within sunlight, is the basis on which solar generated energy is derived from.
French physicist Edmund Bequerel had first determined in the late 1800’s that certain materials could create trace amounts of electricity when exposed to sunlight. Know as the photoelectric effect, it would come to be the basis upon which our solar technology would expand. Metal panels provide extremely low efficiency, and are not used in most modern panels. In the early stages of development, photovoltaic panels were utilized primarily in the space programs to power crafts and satellites. The panels used on space vehicles have a much higher efficiency than commercially available panels, but are not available to the mass market. Due to the limited technology and knowledge early on in this field, we are only recently able to really start making use of solar for economical and practical uses.
Commonly, Silicone, one of the most abundant semiconductor materials available, is used in the creation of these solar cells. Thin wafers are constructed and treated in order to establish an electrical field that is positive on one side while negative on the other. One method of treatment used in the construction of these wafers is known as Atomic Layer Deposition (ALD). The majority of ALD is a chemical process which deposits thin-film layers onto a substrate in a conformal manner. These types of thin-film solar cells are known also as third generation solar cells and they tend to produce higher efficiently at more reasonable costs. As the sunlight makes contact with the treated surface of the cell, the electrons become separated from the atoms as they travel through the cell, and by placing conductive leads on either side of the cell, the electricity generated can then be collected and used. While a single PV cell will not produce what would be considered a usable amount of energy for most applications, numerous cells can be combined to create a photovoltaic module or better known as a solar panel. These panels, when placed together in great numbers, have the ability to generate large usable amounts of energy for electricity, direct lighting, heating as well as generating the power needed for vehicles and many other uses.
Engineers look to improve methods
Engineers today are working with different processes and materials to design more efficient surfaces for the cells. For example, engineers at the Department of Materials Science in Singapore have found that by treating poly (3,4-ethylenedioxthiophene) or PEDOT, which is commonly used as a buffer layer within a polymer solar cell, with co-solvents of hydrophilic organic solvents and hydrophobic 1, 2 dichlorobenzene; they have been able to show improvement in the photovoltaic efficiency within the cell. Another setback when it comes to utilizing solar energy is that it is not available at night and during overcast daytime, there are limited amounts of time when the panels will be of optimal use due to the placement of the sun as well as weather. To overcome the problem of maximizing the amount of time during the day in which the panels can collect from the sun, mechanical engineers along with other disciplines have been developing ways to move the panels, or track, to follow the path of the sunlight. The one downside to solar trackers is that the cost of maintenance and energy used to move can offset some of the beneficial savings that come from using solar. Another problem related to the fact that there is no sunlight at night, is that any power generated and not utilized would need to be stored. There are a couple of the ways that solar energy can be stored. On a stand alone type system, energy can be stored by using a series of batteries known as battery banks. By linking a series of batteries together along with a charge controller, the energy can be stored just as you would in a car battery. If the panel system is a grid-tied system, net metering is used to allow you to send power to the grid and roll back your meter. When you pull energy from the grid at night, the meter will roll forward. This allows the grid to be used as a storage device and can obviously handle larger amounts of energy.
Lastly, engineering the proper protection against high winds is difficult. Recent hurricanes are an example of the types of conditions under which solar panels have challenges. When utilities need to be hardened for emergency conditions, solar panels are more difficult to challenge than some others. Please look for our upcoming blog on the impact hurricanes have in regards to the electrical engineering discipline
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