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Free Lunch? Can Solar Energy Systems Pay for Themselves with Utility Bill Savings?

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If you are interested in exploring how renewable energy can improve the environment, this project could be for you. You'll take on a real-life engineering challenge: deciding whether the benefits of a renewable energy technology are worth the cost to implement it. Some sample questions are suggested, but you can also come up with your own question that matches your specific renewable energy interest. Is there such thing as a free lunch?


Areas of Science
Time Required
Long (2-4 weeks)
A mentor who has experience with solar energy systemes (design, hands-on, or both) in the building trades is highly recommended for this project.
Material Availability
Readily available
Very Low (under $20)
No issues

Andrew Olson, Ph.D., Science Buddies


The goal of this project is to investigate the costs and benefits of active and passive solar energy systems. Specific questions that an Investigator might pursue with this project are:


There are lots of reasons for interest in renewable energry sources, for example: the rising cost of crude oil and natural gas, concerns about the limits of the global supply of these commodities, greenhouse gases and global warming, air pollution, dependence on foreign suppliers, to name just a few. This project focuses on one renewable energy source: solar energy.

As you do your background research for this project, you'll find that the term "solar energy" covers a huge range of technologies. There are "passive solar" design techniques to make maximal use of sunshine for heating and lighting needs. There are also "active solar" systems, such as photovoltaic arrays, that directly convert sunlight into electricity and solar thermal electricity systems that use solar heat to generate electricity (and, possibly, hot water for home heating and domestic use). Depending on your interests, you may choose to do a survey-type study comparing the costs and benefits of a number of different technologies. Or, you may want to focus on one particular technology and investigate the costs and benefits under different scenarios.

This project challenges you to answer the kind of question that engineers (and ordinary homeowners) face all the time: How much does a particular technology (or design element) cost, and what is the value of the benefit(s) it provides? This project will require lots of background research.

You can probably come up with hundreds of examples of this type of question, but for your science fair project, you'll just need one good one. Some sample questions are provided in the Objective section, above, and in the Variations section, below. The good thing is that you can tailor this project to your own interests. For the purposes of illustration, we'll use the first question as our example: Is it worthwhile for a homeowner with a 2000 square foot home and a family of four in Sacramento, CA to invest in a home solar thermal electricity energy system for electricity, home heating and hot water?

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:



Materials and Equipment

To do this project you will need the following materials and equipment:

Experimental Procedure

  1. Do your background research on solar energy technologies. Pick a technology that interests you and come up with a well-defined cost-benefit question to answer. For example: Is it worthwhile for a homeowner with a 2000 square foot home and a family of four in Sacramento, CA to invest in a home solar thermal electricity energy system for electricity, home heating and hot water?
  2. Make a list of what you'll need to find out in order to answer your question. Here are some examples to get you started:
    1. How much will the homeowner have to pay for the system components and installation? Get estimates for typical systems from contractors with experience installing these types of systems. You can also ask about expected energy savings. You may want to consider the effect of government-sponsored rebate or tax credit programs.
    2. What are the annual energy costs for a typical household? Research this on the Internet or check with your local utility company for information.
    3. What energy savings will be realized after installation of the system? Will the system replace 70% of the household's energy needs? 85%? 100%? What data is available to support this replacement percentage?
    4. Related questions to consider are: What happens on days when there is little sun? Does the utility company provide a credit on days when the system supplies net energy to the electrical grid?
  3. Do research to gather the needed information.
  4. One of the difficulties you face in answering cost-benefit questions is how to deal with unknowns. For example, when calculating the energy savings, a huge consideration is the future cost of electricity from the utility company. In order to calculate how much the homeowner might save, you have to make some assumptions about how much electricity will cost in the future. One good approach is to try to bracket your estimates with a "best case" and a "worst case" analysis. Here are some additional suggestions to keep in mind when researching unknowns:
    1. Try to gather information from as many different points of view as you can. When you find disagreements, read the arguments and counter-arguments carefully. Is one argument more convincing than another? Why?
    2. Do a "reality check": look for independent verification of the facts and statistics used to support each case.
  5. State your assumptions clearly. Justify your assumptions. Always provide your research sources. If new information later becomes available to you (or your readers), you will be able to go back and see how the new information might change your analysis and conclusions.
  6. Crunch the numbers. Here is where a spreadsheet program can be really helpful. You'll probably want to do your analysis for a matrix of different scenarios. For example: high, medium and low-cost systems (each with a different rate of energy savings); above-average, average and below-average annual family energy usage; best-case, average-case, worst-case analysis for future energy costs.
  7. Compare and present the results. For example, create a graph to show for each scenario how many years it will take for the system to pay for itself in energy savings.
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Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • For a family of four living in an average-sized home in New England, how many years will it take for a home solar thermal electricity system to pay for itself in savings?
  • For new home construction, pick 3–5 passive solar design techniques and analyze design and construction costs and potential energy savings. Compare to a house of the same size built on a similar location without these features.
  • Has your house been remodeled recently? Were any improvements made for energy efficiency (solar systems, better insulation, passive solar heating, better lighting)? Compare your family's energy costs for a similar time period before and after the remodeling (remember that energy usage often varies seasonally). Did the improvements save you money? Analyze the cost of the remodeling work that was specific to energy efficiency (for example, if your house got a new roof, and insulation was added, find out what was the extra cost for the insulation, don't use the entire cost of the roof). Calculate how long it will take for the energy savings to pay for the improvements.
  • How much of a factor would geography play in your analysis? Some possible effects to consider: differences in seasonal temperature swings and patterns of energy use, differences in available sunlight, differences in average home size, differences in construction costs.


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MLA Style

Science Buddies Staff. "Free Lunch? Can Solar Energy Systems Pay for Themselves with Utility Bill Savings?" Science Buddies, 28 Jan. 2022, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Energy_p016/energy-power/solar-power-utility-bill-savings. Accessed 22 Sep. 2023.

APA Style

Science Buddies Staff. (2022, January 28). Free Lunch? Can Solar Energy Systems Pay for Themselves with Utility Bill Savings? Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Energy_p016/energy-power/solar-power-utility-bill-savings

Last edit date: 2022-01-28
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