Global warming is real, so there no point denying this fact. This global average temperature increase was induced by what is called the greenhouse effect. The massive amounts of carbon dioxide emission is the most contributing factor to this greenhouse effect. With the increase of the greenhouse gases, primarily carbon dioxide, in the atmosphere, the heat coming from the sun that enters the earth’s atmosphere will have more difficulty leaving the atmosphere, thus global warming occurs with this extra trapped heat (Gale, 2011).
One of the most major contributing factors of carbon dioxide produced by humans is energy production from fossil fuels. Coal, natural gas, and crude oil are the major fossil fuels that are currently used daily in many aspects of human lives, such as cars for transportation or electricity from power plants (Gale, 2018). These resources are finite, the need to switch from fossil fuels to renewable energy increases by each day. Renewable energy is the potentially infinite energy generated by renewable environmental phenomenon, which include hydropower, wind energy, and the main focus of this paper, solar power (Gale, 2011).
The energy that is captured from the sun and convert to energy of any type is called solar energy. Solar energy already exists in nature in the form of photosynthesis in plants which they transform the energy from the sun into biomass that is either used by the plant, or consumed by animals and humans, or used as fuel as wood or coal (Funk and Wagnalls, 2017). Humans have already adapted the same type of concept of using the solar energy and converted into usable heat for homes or electricity for power.
The earth daily receives 10,000 times more solar energy than humans consume from fossil fuels in a day (Plitnik, 2013), and 40 minutes of this sunlight is enough to match the humans global energy consumption in an entire year (Zweibel, Mason, and Fthenakis, 2008). The shift to solar energy is necessary for future human survival because solar energy is the cleanest and most abundant of renewable energy sources available to us especially in the United States, where it has the richest solar areas across the entire nation (Kuo, 2011). With each passing year, many facilities finally decide to switch to solar energy, thus the solar energy consumption increases in relative to other renewable energy sources as seen in figure 1 (Monthly Energy Review, 2018)
There are three main types of solar energy systems that are widely used: passive, active, and photovoltaic. A passive solar energy system uses direct heat from the sun to heat up homes, an active system uses heat from the sun to heat up air or other fluids to be used up in another system, and lastly, a photovoltaic system uses specialized equipment to directly convert solar energy into electricity (Plitnik, 2013). The equipment used for photovoltaic system are currently not the cheapest way to generate electricity for the general household, but with each passing day, researchers and manufacturers continue to improve efficiencies and reduce prices of these photovoltaic equipment.
We now see photovoltaic systems incorporated into everyday objects such as laptops, phones, or even clothing. With cheaper and smaller photovoltaic equipment, many parts in Asia and Africa are receiving electricity for the first time in areas where other sources of electricity are not available (Boxwell, 2015). Boxwell (2015) claims that since 2013, solar power became the cheapest form of energy available and sights of solar farms are becoming more common in many parts in North America, Europe, China, and India.
How Power is Obtained
Before obtaining power from solar radiation, it has to be captured efficiently and minimize heat loss during storage. Specialized equipment called solar thermal units, or solar collectors, collect and store solar energy for use in a passive or an active system. Photovoltaic system collect solar energy and directly convert into electricity without the need of solar energy storage.
Passive solar energy systems, often called solar heaters, use a south-facing glass windows to collect solar energy store it in an interior mass that is use to regulate temperature changes. There are three common types for a passive heating system. First, a direct system uses sufficiently sized mass to store heat from the windows and transfers it to the heated space. Second, an indirect system uses a thick wall immediately behind the windows to store the heat, and lastly, an attached-gain system uses a greenhouse attached to the heated area. When heat is required, the greenhouse is opened to let the hot air flow in. It is called a passive system because these system do not use electricity. (Plitnik, 2013).
Active solar systems generally use the passive heating method from the previous explanation heat up a working fluid to be used another energy cycle. Solar energy is collected via south-facing black metallic surface and send it to a storage facility to heat up air or water. For a water system, tubes are soldered to the plate that conducts the heat transfer between the surface and the water, and for air systems, the plate consists of small channels that air passes through for heat transfer (Plitnik, 2013). The prime example of this system is a concentrating solar thermal power system which uses concentrated solar power collectors to heat up a fluid stored in a thermal energy storage tanks to very high temperatures with addition of burning fuel sometimes. The stored hot fluid is used up in cycle with turbines to provide power (Cifarelli, 2018).
For photovoltaic power, small specialized devices called photovoltaic cells, or solar cells, directly converts solar radiation into electricity without any external mechanical devices. These cells are created from micrometers slices of crystalline materials such as silicon, gallium arsenide, or other semiconducting materials deposited on a substrate (Funk and Wagnalls, 2017). To generate electricity using photovoltaic effects, two layers of semiconducting are joined with one having a depleted number of electrons.
When sunlight hits these layers, the photons are absorbed by them, thus exciting the electrons and causing them to jump from one layer to the other, generating electrical charge. Silicon is the most common material used for these layers in solar cells. These layers are also joined by conductive material to transfer the electrical current. To achieve greater efficiency, solar cells have to absorb the most amount of photons possible while having the least amount of reflected photons. The more photons absorbed, the greater the current generated.
To make sufficient amounts of electricity, many solar cells are connected together to create a solar panel (Boxwell, 2015). A solar panel usually contain around forty solar cells within it, and a typical household needs somewhere between ten and twenty south facing solar panels to produce enough power for it. Industrial solar panels are much more specialized and contain hundreds more solar cells than a household solar panel (Plitnik, 2013).
Equipment and Cycles
Photovoltaic cells were first created by Charles Fritts way back in the late 1880s by using germanium crystals to develop a solar cell, but it wasn’t until the 1950s when photovoltaic cells started becoming sufficiently efficient and began to be commercialized. Bell Laboratories created the first solar cells that uses silicon layers, but it was very costly at that era. Only NASA used them in that time to power satellites that need lightweight energy sources that require low maintenance, have a long lifetime, and practically have no mechanical components.
This is achieved by how these photovoltaic perform between silicon layers to produce electricity as I explained earlier in this paper. When many of these cells are connected together into large modular arrays, sufficient amounts of electricity can be generated to power satellites, buildings, or even act as power plants connected to the grid (Plitnik, 2013). When a large enough solar power system is connected to the grid, the excess power it produce is directly fed to the grid system. During the day, the system is able to provide electricity for many buildings, but at the night where no sunlight is present, power is taken from the grid to keep the system running, effectively creating a micro power station (Boxwell, 2015).
In active solar systems, thermal processes use solar power heating to effectively act as a boiler for the working fluid in power cycles connected to pumps and turbines. Solar radiation is collected by flat plate collectors that contain flow passages that the working fluid goes through. The fluid is then heated up by the absorber plate and sent to a thermal tank to be used in a power cycle. Efficient flat plates have to be used to make this process possible.
The total energy transferred to the working fluid per second divided by the total solar radiation collected by the flat plate per second is called the instantaneous collector efficiency, in which manufacturers try to aim for it to be between 40 and 80 percent. To achieve this, flat plates usually contain an optical transparent cover that minimizes heat losses from the plate (Funk and Wagnalls, 2017).