INTRODUCTION TO RESEARCH:
During the summer of 2012, I conducted an experiment pertaining to mobile solar panels. This experiment was performed in the context of the IB Extended Essay.
The title of the experiment is: An Investigation into the Energy Budget of Moving and Immobile Flat Solar Panels
Please note that this is still a work in progress and, although the experimentation is done, the different sections of the experimental report are not final and are subject to change.
The submitted paper can be found here
The main goal of this experiment is to investigate whether the motorization of a solar panel is useful in terms of energy produced, when compared to the energy produced by a flat, stationary solar panel. If, the motorized panel is more efficient, the experiment will try to determine if there are periods of the year during which it is better to motorize a solar panel.
In order to perform this experiment, a unique algorithm for finding the sun’s position was created and used with a Lego Mindstorm NXT to make the panel move. The robot was constructed as a motorized frame giving support to a small solar panel that captured the light emitted by a regular 60W light bulb.
In order to avoid sources of external light, the robot, panel and light bulb were placed in a sealed box. The algorithm developed calculated the Zenith and Azimuth angles of the sun and the robot would set the panel’s position accordingly.
Voltage and current were measured for the panel and current was measured for the robot. It was assumed that the robot consumed 9.0V as the robot was operated on 6 1.5 V batteries. The pairs of voltage and current were converted into energy. The energy difference due to motorization was determined by calculating the net energy output of the system.
The experiment showed that the viability of a moving solar panel is dependent on the efficiency of the motor and, that there is a correlation between the net energy production of the motorized system and the period of the year during which the motorization is employed. The research shows that, assuming the motorization system is efficient, the panel should be motorized during the summer.
The sun is a powerful source of energy, and it can be harvested through solar panels to create clean and truly renewable energy. The main components of the sun are Hydrogen and Helium. The Hydrogen is transformed into Helium by a fusion reaction, which releases a large amount of energy. This energy release takes the form of Electro-Magnetic Radiation.
As humans, we can only see a particular fraction of the light emanating from the sun: the visible spectrum. The visible spectrum contains Electro-Magnetic Radiation whose wavelength varies from 400 to 700 nm (De Lloyd,1). This radiation emitted by the sun, mostly in the visible spectrum, can be harnessed and converted to heat or electricity by solar panels.
The conversion from visible radiation to electricity is done by photo-voltaic cells. These cells are made of two thin sheets of silicon, or another semiconductor, separated by a small gap. When photons of light hit the semiconductor, it releases an electron which travels to the other sheet, thus creating a flow of electron, therefore creating an electrical current. This is modeled in Figure 1.
Figure 1: shows how a solar panel works. (Knier,1)
Cells are connected in order to create arrays of photo-voltaic cells. The panels on which these arrays of photo-voltaic cells are places are called solar panels. The cells on a solar panel are connected in series and parallel to increase the energy produced by the solar panel. Solar panels are always flat and usually rectangular in shape. Although most solar panels are non-moving, some are motorized in order to reduce the percentage of light reflected off the panel glass due to the exposed sunlight coming at an angle, which increases the amount of photons arriving at the front contact. These motorized panels are also exposed to the sunlight for longer periods of time and thus creating more electricity. The goal of this investigation is to experimentally determine if the motorization of a solar panel is beneficial. This will consider not only the energy produced by the panel but also the energy consumed by the motors. This investigation will also attempt to determine if there is a certain period of the year where it is better for a solar power to be motorized in any location with the latitude of 55.1 degrees, which is roughly the location of Edinburgh in Scotland.
The assumptions made during this experiment are outlined here:
The first assumption is that the orbit of the earth around the sun is a circle. In reality, the orbit of the earth around the sun is an ellipse. This ellipse is so close to being a circle that, for the purposes of simplification, the orbit of the earth in this experiment was taken to be a circle around the sun.
The second assumption is that there is no absorption of light by the atmosphere and thus, the light source is directly in front of the solar panel and the light emanating from the light source only traverses air.
The third assumption made in order to perform this experiment is that, when the solar panel follows the direction of the sun, the power output of the solar panel will be the same as if neither the solar panel nor the sun move.
The fourth assumption made is similar to the third one and says that, when the sun moves and the solar panel is still, the power output of the solar panel will be the same as if the solar panel was moving and the sun was not.
The third and fourth assumptions are made in order to perform the experiment with the limited materials available, notably, that the Lego Mindstorm NXT Brick can only control 3 motors, and, if both the light bulb and the solar panel were to move, then the number of motors would be greater then 3, specifically 4.
Assumptions number 3 and 4 work as, by changing which object moves, the only change perceived is a change in frame of reference. In the case of assumption number 3, a third party viewer, whose frame of reference is his position vis-à-vis the solar panel and sun will see both the solar panel and the sun move. When changing the frame of reference to that of the solar panel, it does not move as it is in the frame of reference. Since the solar panel follows the sun, the solar panel’s frame of reference sees the sun as a still object. Thus, when the solar panel is mobile, both the solar panel and the sun can be seen as non-moving.
The voltage of the robot was not properly measurable and it is therefore assumed that, the voltage of the robot was constant at 9.0 volts as it was powered on 6 1.5 volt batteries attached in series.
In order to perform this experiment, an experimental setup must be built using the Lego Mindstorm NXT kit. The robot is made of several parts, each essential for a particular part of the experiment and should be built in the order in which they are presented in this paper.
The first part to be built for this experiment is a panel holder (see figure 2). In order to build the panel holder, the following pieces must be taken from the Lego Mindstorm NXT Kit:
– 4*13 holed white straight pieces
– 2* 11 holed white straight pieces
– 4 * 5 holed grey straight pieces
– 2 * 5 holed bent (4 in a line) holed grey pieces
– 2 * 7 holed bent (5 in a line) holed grey pieced
– 3 * small grey lego stick
– 6 * hole to stick converter
– 1 * medium sized black stick
– 1 * stick binder
– All connections are done with small black connections
Figure 3 shows the solar panel holder constructed with Lego Mindstorm NXT.
The pieces listed above were assembled into figure 3
After the solar panel mounting device, an articulation was created using two Lego NXT Motors. This was done by taking a small stick and placing it in the first motor followed by a separator. The motor block was completed by attaching the second motor to the stick. The motor block (figure 4) was attached to the panel holder using vertical to horizontal Lego converters. Figure 5 shows the whole robot assembled.
Figure 4 shows the motor block which is essentially two motors stacked onto each other.
Figure 5 shows the robot complete with both motors and the solar panel holder.
The Robot was then placed in the cardboard box in order to block out all the ambient light from the room and only let the light from the Bulb reach the Solar Panel. The Bulb was placed in the center of the cardboard box (figure 6).
Figure 6 shows the robot in the cardboard box.
All calculations for the creation of the algorithm can be found here.
Figures 9 and 10 are the summary tables of the data taken throughout the experiment.
Combined Average Energy Output of Moving Panel
|Day after Winter Solstice||Average Energy (Watts/Hour)||Uncertainty Average Energy (Watts/Hour)|
Figure 9 Shows the Average Energy Output of the Moving Panel.
ROBOT ENERGY CONSUMPTION
|Days after Winter Solstice (Days)||Energy Consumption (Watts/Hour)||Uncertainty in Energy Consumption (Watts/Hour)|
Combined Energy Data for Immobile Panel
|Day||Average Energy Produced (Watts/Hour)||Uncertainty Average Energy Produced (Watts/Hour)|
Figure 11 shows the average energy created by a flat immobile panel relative to the day.
Although the robot used for this experiment consumed too much energy to make the motorization worthwhile, there are several conclusions which can be made for this experiment.
First, the best time period to motorize a solar panel would be approximately around 90 to 240 days after the winter solstice. This is the best period as it is the period of time when the moving panel produces the most energy. This first conclusion is true only for the model panel when assuming that the motorization system consumes 0.15 Watts/Hour of energy or less. Generally, the best period of time to motorize a solar panel is during the summer.
The second conclusion that can be drawn from this research is that, although some generalizations, like the first conclusion, can be made, the time period during which motorization of the apparatus is advantageous is dependent on the energy production of the panel used and on the consumption of the motorization system. The more energy hungry the robot is, the less advantageous the motorization becomes.
Although this experiment did find answers to the two questions it was designed to solve, the experiment did generate some extra research possibilities that may increase the effectiveness of a solar panel. The first question stems from the second assumption that says that the atmosphere does not reflect or absorb any light and thus, that 100% of the sun light arrives on the panel. This assumption is not always true as many factors may reduce the percentage of light coming through the atmosphere. Such factors include weather and pollution. Thus, the question of how much light the atmosphere absorbs may play a very large role in predicting that a panel will have a greater yield in the summer or winter.
The first assumption, saying that the earth orbits around the sun in a perfect circle, was created as a simplification for the self-created model. The earth orbits in a very slightly elliptical orbit. A further investigation could determine how much this variation in orbit affects the energy created by flat solar panels.
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