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Comparing active & passive solar energy systems in cost and efficiency.

Comparing active & passive solar energy systems in cost and efficiency.

Introduction: (Initial Observation)

Increase in the air pollution caused by fossil fuels such as natural oil and gas is just one of the factors that has encouraged people to look for other sources of energy especially solar energy. Global warming and increase in the oil price in the recent years have accelerated such efforts and now many people in many countries are actually using solar energy to substitute parts of their energy needs.

Solar energy systems are classified in two main types. One type is known as passive solar energy system and the other type is known as active solar energy system.

In this project you will compare active and passive solar energy systems in cost and efficiency.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Learn about solar energy as the main source of energy on the planet Earth. Find out how solar energy converts to other types of energy such as chemical energy (in the form of wood), and fossil fuels in the form of natural gas and petroleum.

Read books, magazines or ask professionals who might know in order to learn about the difference between active and passive solar energy and how they can be compared. Keep track of where you got your information from.

Advantages of solar energy

Solar energy is a renewable resource that is environmentally friendly. Unlike fossil fuels, solar energy is available just about everywhere on earth. And this source of energy is free, immune to rising energy prices. Solar energy can be used in many ways – to provide heat, lighting, mechanical power and electricity.

Passive Solar Energy

Passive solar techniques make use of the steady supply of solar energy by means of building designs that carefully balance their energy requirements with the building’s site and window orientation. The term “passive” indicates that no additional mechanical equipment is used, other than the normal building elements. All solar gains are brought in through windows and minimum use is made of pumps or fans to distribute heat or effect cooling.

All passive techniques use building elements such as walls, windows, floors and roofs, in addition to exterior building elements and landscaping, to control heat generated by solar radiation. Solar heating designs collect and store thermal energy from direct sunlight. Passive cooling minimizes the effects of solar radiation through shading or generating air flows with convection ventilation.

Another solar concept is daylighting design, which optimizes the use of natural daylight and contributes greatly to energy efficiency. The benefits of using passive solar techniques include simplicity, price and the design elegance of fulfilling one’s needs with materials at hand.

Passive solar heating

Passive solar heating of buildings occurs when sunlight passes through a window, hits an object, is absorbed and converted to heat. The most efficient window orientation for heat gain is due south, but any orientation within 30 degrees of due south is acceptable. Once the heat has entered the building, various techniques come into play to keep and distribute it. Even in the Canadian climate, the prevention of overheating in the sun space presents one of the biggest challenges.

To let the sun in, a ratio of roughly eight per cent window to floor area is recommended for south walls. Although this number may seem small, it is important to remember it comes from the floor area, which is much larger than the wall area. Again, the control of overheating is a significant issue.

Once the heat is in, a well insulated and air-tight building envelope helps prevent heat loss and allows the solar heat to provide more of the heating needed.


Underground buildings and condensed apartment complexes do not have sufficient windows where sunlight can enter directly. That is where an active solar heating system may be used.

Active Solar Energy

In active solar systems, black absorbers known as solar collectors convert the sunlight to heat and transfer the heat to a liquid such as water that is passing through the solar collector. The heated liquid is then transferred to another location for immediate heating or for storage for use later. Applications for active solar energy include heating swimming pools, domestic hot water use, and hot water for commercial facilities such as laundries, car washes and fitness centers.


In active solar energy systems electrical pumps and fans are used to distribute the heated liquid or to transfer the heat from radiators to the air. Heat transfer liquid used in such systems is usually an anti-freeze. There are also some systems that do not use any liquid and just transfer the hot air.

See more…

Question/ Purpose:

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 compare active and passive solar energy systems for cost and efficiency.

Identify Variables:

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.

Independent variable (also known as manipulated variable) is the method of using solar energy to heat up a model home. Possible values are passive heating and active heating. In the passive system sunlight directly enters the house through windows. In active system sunlight will heat up the air in a solar collector and then the hot air will be pulled into the house using a fan.

Dependent variable is the temperature increase in the house.

Controlled variables are the environmental conditions such as wind, cloud and the air temperature. To ensure all experiments will be under the same conditions, we run the experiments at the same time and the same place.

Constants are the size of the model homes, the construction material, the area of window or heat collector and the general design and structure.


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:

A passive solar heating system is more effective than an active solar heating system. I adopted this hypothesis because in an active solar energy system – parts of heat energy may get lost during transferring from the collector to the house.

Please note that in an active solar energy system you may heat up water and store it in an insulated tank and use it to warm up the house at night. In a passive heating system, you will try to keep the house warm by proper insulation so the heated air in the house will stay warm as long as possible.

Experiment Design:

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.”

Experiment 1: Comparing solar heating systems

Introduction: In this project we will construct two same size model homes (cabins). We will use passive solar energy in one model by installing a large window. The other cabin will have no window; however, it will have a solar collector and an electric fan that pulls the heated air from the collector to the house. Efficiency will be determined by measuring and comparing the increase in the air temperature in both houses.

Material: The house or cabin may be constructed from wood, Styrofoam boards or foam boards. Use nails, pins and wood glue to connect the peaces together. You may also use masking tape in addition to other material on the seams. For window, use clear Plexiglas (Clear acrylic or polycarbonate plastics). For heat collector use thick aluminum foil.


Make two identical cabins with a slanted side for window or for solar collector. This surface is slanted so the sun rays will hit that in a right angle. The recommended size for the cabin is about 30 centimeters (one foot) tall and 30 centimeters (one foot) long; however, any other size will work as well. Just make sure that both cabins have the same shape and size from inside. Keep track of all costs.

Paint the inside of both cabins with black paint (so it will absorb more heat from inside).

Paint the outside of both cabins with white paint, so the walls will not absorb heat.

Passive Solar Energy System

To prepare one house for passive solar energy, mount a glass or Plexiglas on its slanted surface to form a window. It is not easy to cut a glass or Plexiglas. You may need to order them be cut to size. Secure the window using nails, pins, masking tape, wood glue, silicon glue or a combination of these.

Insert a thermometer on the side of the house. Your model house using passive energy system (through large window facing sun) is ready. Keep it in the shade or in a cold room until you are ready to do your measurements in a sunny hour of the day.

Active Solar Energy System


To prepare one house for active solar energy, cover the slanted opening with the same material as all other walls. This will be a cabin or house with no windows.

Now you must install or construct a solar collector over this surface.

First cover this surface with aluminum foil. Make two holes on two corners of this surface. Over one hole mount a small electric fan blowing inside. Small electric fans known as CPU fan are used in most computers and may be purchased at a few dollars. These fans need a 12-volt DC current that may be supplied by a small transformer or by two 6 volt batteries linked in series. Make the necessary wiring* and make sure that the fan is working.


* Get help from parents/skilled adults in making the connections.


Use the same material that you have used to construct the house and make a 5 centimeters (2 inches) tall wall wall around this surface. Connect the wall and secure it using pins, nails and glue.


Place another sheet of thick aluminum foil over the walls so there will be a gap between this layer and the previous layer. These two layers together will form a chamber known as collector. The air inside the collector will get warm and then will be drawn into the house by the fan.


In order for the collector to absorb the most solar energy, paint its surface with black paint. Acrylic paints work fine for this experiment.

You may think that your solar collector is ready at this time; however, since the black surface is exposed the air currents, parts of its collected heat will be wasted by heating up outside air.


To avoid this problem, you must make a protective layer above this surface. To do that, make a second wall over the first wall and then mount a sheet of glass or Plexiglas over the second wall.


The purpose of this glass is protect the solar collector from loosing its heat by the air current.

Having this layer of glass will make your results more trustable because all solar collectors have such a protective layer. Without that small air currents are also able to cool off the surface of solar collector and reduce its effectiveness.


    1. In a sunny day at 11 o’clock in the morning place both models on a flat area about one meter (3 feet) apart. Make sure that they will not get shade from each other or from the trees or buildings near you.
    2. Record the temperatures in the beginning.
    3. Turn on the fan on the active solar energy model.
    4. Visit the models every 15 minutes and record the temperature until 1 o’clock p.m.

Record your observations/ measurements in your results table like this:

Minutes under the sun Temperature in
Passive system home
Temperature in
Active system home
0 (Initial Temperature)

Make a graph:

Charts and graphs allow you to present or communicate your results visually. Make a chart containing two line graphs over the same grid. One line graph will show the changes of temperature in relation to the sun exposure time in passive system. The other graph shows the changes of temperature in relation to the sun exposure time in the active system. Use a different color for each graph. Somewhere in an empty area of the chart make a legend indicating which of the colors represent the passive system and which of the colors indicate the active system.

If you have access to a spread sheet program such as Excel, you can enter your results table, select your table (by dragging mouse) and then click on the chart button. This will bring up the chart wizard and creates a chart for you.

Which system provided the most heat to your model home?

Which system cost more?

Calculate the Efficiency of the active solar energy system

To calculate the efficiency of the active solar energy system you must calculate the temperature increase in both models. Then you divide the temperature increase in active system by the temperature increase in passive system.

A= Temperature increase in active solar energy system.

P= Temperature increase in passive solar energy system.

Efficiency = A/P

Experiment 2: Solar Cooker Experiment

Solar energy can be used to heat our homes, heat water, cook our food, and power our lights. So what exactly is solar energy? Solar energy is a renewable resource that is environmentally friendly and free. Solar energy can be used in many ways, and it is simply a collection of our sun’s heat.

There are two different kinds of solar energy systems. One type is called an active solar energy system and the other is called a passive solar energy system. An active solar energy system collects heat from the sun and circulates it through a hot water or heating system. They use solar collectors and additional electricity to power pumps or fans to distribute the sun’s energy. Active solar energy systems are generally more complex than passive solar energy systems, and contain more moving parts. A passive solar energy system is one that relies on natural methods of collecting and distributing heat from the sun. Passive energy is more sustainable than active energy systems because passive systems use far fewer natural resources to build and maintain.

You can build your own solar energy system.

In this experiment, you will construct a model of a parabolic solar collector that will cook a hot dog.

A solar hot dog cooker is a passive Energy System.


    • 14- inch sheet of aluminum foil
    • 11 x 14- inch piece of poster board
    • 1 unpainted wire coat hanger
    • Cellophane tape or masking tape
    • 2 boxes (one for the collector and one for a stand)
    • 2 nuts
    • 2 bolts

RESOURCES: You can find poster board at art supply stores and nuts and bolts at a hardware store.



1. Make the ends of the parabolic out of the cardboard using the pattern shown below.

2. Tape the aluminum foil to the piece of poster board.

3. Curve the poster board and tape it to the two curved ends.

4. Attach the trough to the box frame using nuts and bolts. Make sure the trough can move up and down but will stay in one place.

5. Put holes at either end of the trough focal point.

6. Straighten the wire coat hanger and bend one end to make a handle.

7. Push the coat hanger through the hole on one side. Put the hot dog on the coat hanger, and push the coat hanger through the hole on the other side.


      1.  Place the solar cooker so the mirrored trough faces the sun.
      2. Adjust the trough up and down until the mirrored surface focuses the sun on the hotdog.
      3. Cook the hot dog.


    • How long did it take to cook the hot dog?
    • Did you have to move the cooker to keep the sun focused on the hot dog?

This experiment is very similar to a parabolic collector. Parabolic collectors are made of a trough and a tube running down the center of the trough. The trough is a long rectangular mirror formed in a U-shape. The mirror is tilted toward the sun to focus the sunlight on the tube. The parabolic shape is perfect for focusing the sunlight on the tube. The tube carries the fluid to be heated. A tracking device keeps the mirrors pointed toward the sun as it moves across the sky. Parabolic collectors are used mostly to provide hot water for use in industry and sometimes in homes. They are also used to produce electricity.

Note that using a tracking device to keep the mirrors or collectors toward the sun makes it an active solar energy system.

Materials and Equipment:

Make your final list of materials and use it in this section of your report. Note that in many cases you can substitute the material suggested in this project guide with similar material found in your home. For example in the second experiment you may use a skewer instead of a coat hanger.

What type thermometer do I need and where can I buy the that?

You may use any dial thermometer or glass thermometer for this experiment as long as they cover the range of temperatures in your cabin (32-140ºF or 0-60ºC). Use the following link to see some usable models:

Dial Type Thermometers: TDIAL70CS, TDIAL220FL, THMPR1, TDIAL1IN

Glass Thermometers: GAT20150, GAT20110, VG80403, GS6302, GS6402

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.


If you do any calculation in relation to your project, write your calculations in this section of your report.

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.

Possible Errors:

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.