Solar Energy
The high cost of oil has induced several countries to look for other much cleaner and more affordable options. The dependability on foreign petroleum has created a set of increasingly prices for those countries who buy their oil. Therefore, the idea of solar energy started to be part of the agendas in many energy meetings around the planet.
It seems very easy and simple to start using solar energy. The propaganda about the rebate options and the economic incentives given by local governments is creating a large group of consumers who rely on the arguments of the companies offering the product, the installation and the service. There is, however, the other side of the story about the construction of solar cells that would store the solar energy. Toxic materials are used to produce photovoltaic cells for solar panels and, therefore, the "ghost" of pollution comes again. In any case, the impact in Mother Nature for the production of solar cells is much less damaging than the one obtained with the waste produced with nuclear energy.
Solar energy is currently being used as a solar heating, solar photovoltaic, solar thermal electricity and artificial photosynthesis. Hot water heaters powered by solar energy are very friendly to install and with easy technology, but the common households are not taking advantage of this or there are not incentives to installing solar water heaters. The other reason could be just plain ignorance of the matter.
Our school district has recently installed solar panels in all the schools within their jurisdiction. Therefore, our school, Jefferson High School in Daly City, uses only electricity converted from solar power. It is also well known that there is a possibility of "selling back" the amount of electricity produced from solar power that is not used. Obviously, this will help me to present a case to the school authorities and in general to the population interested in saving energy and, therefore, saving money as well.
This curriculum unit will serve as the ignition of the project to analyze the amount of energy used per hour, per square foot, particularly in the lower gym of our school, and the cost of this consumption. I see a problem that can be corrected if my students and I can show the amount of money that the school could save. The problem that I am presenting here is that the lights of the lower gym are on continuously after school hours and on Saturdays and Sundays. Even now, during summer break, the lights of the gym are on. This means that the lights are on 24-7. Although I have already mentioned this to the school administration, the answer is "there should be a timer," and no action is taken. On my part, the action I am taking is to educate the students in the subject and together find a solution to avoid wasting energy. As an integrated project among other subjects, students will write letters to PG&E and to the Principal to buy a switch or a timer. Either of these items will be paid by saving energy anyway over the time.
Passive and Active Solar Technology
There are two categories for solar technology, passive and active. Passive technology uses the light and the heat directly from the sun by simple exposure. Certain structures are specifically constructed in a way that their orientation can capture as much of the solar energy as possible.
The active solar technology uses the solar photovoltaic (PV) or the solar thermal systems. The PV technology uses the properties of semiconductors to produce electricity. A semiconductor produces an electrical charge when is hit by the sun and this electrical charge can be transferred through a circuit to anything that uses electricity. The solar thermal technology is classified as low, medium or high temperature collectors. Low temperature collectors use plates generally to heat swimming pools. Medium temperature collectors use also plates to capture the heat and are used to heat water in residential or commercial buildings. High temperature collectors use lenses or mirrors and inclusive parabolic shaped devices to concentrate the heat in one point with the purpose of producing electricity.
Solar thermal energy is very different from and much more efficient than photovoltaic energy, which converts direct sun light into electricity. In 2009, the worldwide production of solar thermal power was only 600 megawatts, but projects for concentrated solar thermal to power up to an additional amount of 14,000 megawatts are on their way.
The Eloquence of the Numbers
Approximately, the amount of solar energy in the form of solar irradiation that our planet receives is 5.5 x 10 24 joules per year. 1 Just to have an idea of the amount of energy from the Sun, the solar energy received by the Earth in 2002 was more in one hour than the energy used by the world in one year. 1a Another comparison is that the amount of solar energy received by the planet in one year doubles the amount of energy that will ever be obtained from all the other sources combined, including coal, oil, natural gas and mined uranium. 2 The unit used for energy in these cases is the joule, which is presented in another section with equivalences and conversions.
Photosynthesis
Approximately, the very large amount of 3 x 10 21 joules per year of solar energy is used by plants and other photosynthetic organisms to "fix" the CO 2 in the atmosphere. As it is known, plants receive CO 2 from the air and after receiving water and sun light energy, it transforms it into sugars and O 2. This is one of the reasons that it is suggested to plant trees in urban zones to "oxygenate" the air. What percent of the total solar energy received by the planet is used for photosynthesis? In terms of percent, and numerically expressing the same question, we can write: What percent of 5.5 x 10 24 is 3 x 10 21? This question will be addressed and solved in the lesson plans and activities section.
I never thought that photosynthesis could be as important as it is in the search of a clean option as a source of energy. After reading several articles where energy and photosynthesis are linked, I started researching more about it, finding information that will show once again, that solar energy is a good option.
Scientists Niek van Hulst, professor at the Institute of Photonic Sciences in Barcelona, Spain and Richard Hildner, professor at University of Bayreuth in Germany, have found that the high efficiency transportation of energy in plants is connected to a quantum-mechanical phenomenon. The transportation of energy during photosynthesis is done at a molecular level and it is very fast, for which, capturing this phenomenon has been very difficult. To accomplish their task, they came up with ultrafast spectroscopy (taking pictures) techniques. 3
To capture a very fast sequence of pictures, Niek van Hulst and Richard Hildner sent femtoseconds of light flashes during the photosynthetic process. 4 A femtosecond is the time that the light travels a distance of one hundredth of the diameter of a human hair. This sequence of pictures helped them to understand how solar energy is transported through proteins. The findings of the efficiency in the transportation of energy in plants through photosynthesis, is opening the possibility of creating a new more efficient solar cell.
Solar Panels
There are different types of solar panels, such as rigid thin-film and flexible thin-film modules, where the material used is mainly glass made of cadmium telluride or silicon. However, here I will refer only to the crystalline and the multi-crystalline silicon module types.
Currently, the biggest problems are to minimize the cost of production of solar panels and to make panels with solar cells with high efficiency. A photovoltaic system contains normally a set of several panels, because a single panel can only produce a very limited amount of power. In addition to the panels, the system contains an electrical inverter, a battery and wiring. Each panel has its DC output approximately between a minimum of 100 to a maximum of 320 watts. An electric inverter is a converter that changes direct current (DC) to alternating current (AC).
Electricity is a type of energy where electrons move through a conductor. In the conductor, generally a wire, the movement of electrons can occur only in one direction or both directions through the wire. If it goes only in one direction, it is called direct current (DC). If it goes in both directions, one, and then, the other one, it is called alternating current (AC). The electricity coming from a battery is an example of direct current DC, while the electricity we use at home when we plug in our household appliances is a good example of alternating current AC.
Efficiency of a Solar Panel
Given a same amount of DC output, the efficiency of a panel is inversely proportional to the area of the panel. In other words, if the same DC output is given, the smaller the panel, the larger efficiency we will obtain. For example, a 20% – efficient 200 watt panel has half the area of a 10% – efficient 200 watt panel.
Very much of the incident light on a panel is wasted, because it cannot cover (process) the entire frequency range of the solar light. If the panels were to be illuminated only with mono-chromatic light, the efficiency would increase by 50%. Therefore, there is another idea to construct a photovoltaic panel where the light would be split in different wavelength ranges, directing the splits onto different cells adjusted for each range.
The best up to date efficiency of a commercial solar panel is around 20.1%, which is much lower than the efficiency of isolated individual solar cells. With this number, the most efficient energy value that a solar panel produces is up to 16.22 watt per square foot or 175 watt per square meter.
The position of the panels when installation takes place is as well very important to obtain the maximum efficiency of the solar panels. The inclination of the panels that can be seen on the roofs of certain houses and buildings is done exclusively to try to receive as much as direct sun-light as possible. The perfect situation would be to have the sun rays at a 90 o angle of incidence on the panels all the time, but the reality is that the sun moves and the Earth moves too. Therefore, there is a certain angle that provides the best range of incidence to obtain the maximum amount of sun over the period of time of a day. There will be not a perfect situation on a continuous basis because of the movement of the sun, but the efficiency will have the tendency to be maximized. 5
At a professional level of installation, the zip code determines the angle of inclination. Installers receive from their companies a set-table with the angles of inclination of the panels. At a "do-it-yourself-level," the zip code is used on a map from the Internet to locate the latitude and longitude of the place where the panels are going to be installed.
A general example of the position of the panels is given in figure-2.
The panel tilt angle for our school with zip code 94014 is calculated in the winter by adding 15 o to the latitude and subtracting 15 o in summer. This is a general rule applicable for all cases. There are newer models that use a photo-tracking device that locates the sunlight and directs the solar panel/s towards the light, adjusting the angle automatically.
Photovoltaic Cells
Photovoltaic cells are also called solar cells, although the light being used to make it function does not necessarily have to come from the sun. In any case, these cells are electronic devices that receive the light, process it and convert it into electricity. The current, voltage or resistance varies, depending on the incidence of light.
The term photovoltaic is compound of two roots, "photos," which means light in Greek and "voltaic," that comes from the Italian Alessandro Volta, who invented the electrochemical cell, called now "battery."
Storage of Energy: The Energy Grid
An energy grid is the interconnected power network to transfer energy. Therefore, an electric grid is a network of coordinated power-providers and power-consumers that are connected by transmission and distribution lines and operated by one or more control centers.
Comments: