Introduction: (Initial Observation)
Pollutions caused by fossil based fuels (oil, coal, gas) and harmful effects of such pollutions have forced scientists to look for alternative sources of energy, specially what is now known as clean energy or renewable energy. Most renewable energy comes either directly or indirectly from the sun. Solar-cells are devices that can convert sunlight directly to electricity.
Since solar-cell powered homes rely on the sun light to produce electrical energy, they need to be designed, constructed and positioned in order to get the most amount of energy from the sun.
In this project you will study design considerations for a solar-cell powered home.
Find out about what you want to investigate. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.
Well, Now you are an engineer and a consultant. Your client is asking you to design a solar cell powered home. Do you think that such a thing is possible at all? Can you get all the energy that a home needs from the sun? How much energy do we need for heating, lighting and cooking in a typical house? What do you need to know in order to decide if such an idea is feasible?
Obviously you need to know the daily, weekly, monthly and annual consumption of energy for every specific application and for different seasons. This is helpful because you need to know how much energy do you need to store for nights and days that there is no sunlight.
You also need to know about solar-cells or photo voltaic cells. You need to know how much electricity can be produced from each square foot or each square meter of solar panels.
You will finally need the angle of sun rays in the area in different seasons. Solar panels will get more energy when the sun rays hit the panel in a right angle.
Search the Internet for Home Energy Consumption Data. You will find helpful results such as these:
It seems that average households consumes 100 million BTU per year. But what is BTU? how can I convert it to calorie, watt hours or Joule? Once again search the net for BTU calorie conversion. You may find a result like this:
kilowatt-hour (kWh) = 860 kcal = 3600 kJ = 3412 Btu
Information shows that each kilowatt-hour is 3412 BTU.
What is the average household consumption of energy in kWh? (Use the above numbers to calculate)
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to identify design considerations for a solar-cell powered home. Specific questions are:
How much electrical energy can be produced by each square feet (or square meter) of solar cells per hour, per day and par year?
How many square feet (or square meter) of solar cells is required to supply electrical energy for lighting and appliances in a specific house?
If our experiments show that for each square foot of a specific house, we will need many square feet of solar cells, then we conclude that for that specific house, use of solar-cell as an energy source is not feasible.
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The area of the solar cell is an independent variable. The amount of produced electrical energy is a dependent variable. Controlled variables are the type of solar cell, the location of test and test method and procedures.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following is a sample hypothesis:
Solar-cell can be a good source of energy for warm and sunny regions. If the entire roof a building be covered by solar-cells, enough electricity will be produced for heating, lighting and appliances.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Introduction: We need to come up with a method to measure the amount of electrical energy that can be produced by a solar cell each day. We could possibly use a meter similar to those used by electric company, but they are not easy to find and they may not work with low voltage. We can also use the produced energy to do electroplating or water electrolysis. The amount of plated metal or the amount of produced hydrogen can be used to determine the amount of electricity. These methods are good because we can setup our devices and come back after 24 hours to see the result. A simpler and more affordable method is using a volt meter and an ammeter to record the voltage and current while our solar-cell is connected to a load such as a light bulb. The only problem in this method is that we need to do frequent observations and record the data. We can always multiply voltage by current (amps) to get watts which is the rate of production or consumption of energy. This is the method that we will use.
Get a solar-cell and connect it to an ammeter and a volt-meter as shown here.
Place your setup outside, where you would usually install a solar-cell or in an open area away from the shades of trees and buildings.
Make observations every hour for 24 hours. (Skip night hours because they are all the same. Write zero voltage and zero amps for all night hours). Record your observations in a table like this:
|Hour/ Time||V = Voltage||I = Current (Amps)||Watts = V * I|
It is best if you use a digital ammeter and a digital voltmeter. If you use a multimeter, set do DCV for voltage and set it to DCA for current.
If you are using more than one solar-cell, connect them in parallel as shown in the image.
Every solar-cell is also a diode.
See the calculation section below.
Experiment 2: Does the angle of incidence affect the production of electricity in a solar cell?
After you know how many square feet of solar cells is required to produce enough electricity for a house, you need to decide where to install them and what is the best installation angle and direction. The angle in which the sun rays hit the solar-cell is known as the angle of incidence. Does the angle of incidence affect the production of electricity in a solar cell?
Move your setup to the sunlight. Your setup at this time may include one solar cell to produce electricity, one resistor or small light bulb to consume electricity and finally one or two multi-meters to show the voltage and current.
Place the solar cells in different angles. Record the incidence angle as well as the voltage and current in for each angle of incident. Your results table may look like this:
Control Experiment: You may have another identical setup as your control. You do not change the angle of incident in your control; however you do measure the voltage and current in your control setup every time that you measure and record the voltage and current your experimental setup. This will positively show that changes in voltage and current are caused by changes in the angle of incident; not by an unknown environmental factor.
If you are using the control, you can have a separate results table for your control or you may combine two tables in one like this:
Materials and Equipment:
List of material and equipment may vary based on your final experiment design. This is a sample:
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
After recording the voltage and current in 24 consecutive hours, you will calculate the wattage by multiplying voltage by current in each hour. You will then add all the watts to find out the total electricity production in 24 hours (it will be in watt-hours).
The size of your solar cell may be less than one square foot or one square meter. Measure the exact size of your solar cell and then calculate how much electricity can be produced if your solar-cell area is one unit area.
Using the information that you gather find out how many kilowatt-hours of electricity is used in a house each day. (I think about 100 kilowatt-hors per day is a good estimate). Then calculate how many square feet or square meter of solar cell do you need to produce that amount of electricity.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.