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Are You in Hot Water? Use the Sun's Energy to Heat Your Own Water

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Isn't it nice to take a nice, hot shower or bath after a long day of playing outside? But have you really thought about how the hot water in your shower or bath gets hot? Sure, the water heater in your house gets it hot, but what makes the water heater work? Water heaters are powered by natural gas or electricity. But are there any other ways to heat water? What about using the Sun? In this science fair project, you'll give it a try by capturing energy from the Sun to heat water.


Areas of Science
Time Required
Short (2-5 days)
Material Availability
Readily available
Average ($40 - $80)
Adult supervision is recommended when using scissors.

Michelle Maranowski, PhD, Science Buddies

  • StyrofoamTM is a registered trademark of The Dow Chemical Company.
  • Scotch® is a registered trademark of 3M.
This project is based on an activity found at the following website:


In this science fair project, you will build what are called batch solar collectors, using different colors of plastic bags, to see which color heats water the best.


Have you ever been camping out in the wilderness, where there aren't even any bathrooms? Well, after a few days of that, a nice hot bath or shower sure would feel good! But warming water takes energy. When you're camping, that might mean using energy from a cooking stove or a campfire to heat up the water. But just think of all the firewood you'd have to gather! And when you're at home, it probably means a natural gas or an electric-powered water heater heats your water. What if you could warm up water without burning wood, or another fuel, or even without using electricity? Turns out, you can, with something called a batch solar collector. Solar means anything relating to the Sun. Using the Sun to heat water is called solar heating. So can you guess what a batch solar collector does? It's is a piece of equipment that "collects" energy from the Sun to heat water. A batch solar collector is a storage tank that sits inside an insulated box (which means that it holds in heat or cold) that faces the Sun. Water flows into the tank and is heated by the Sun. When you need hot water, simply empty the storage tank. As the tank is emptied, more cold water flows in and continues to be heated by the Sun. Batch solar collectors work best during the summer months, because the Sun is out longer during the day and it doesn't get too cold.

The Sun's energy is both free and renewable, meaning it can be used over and over again and it never runs out. Think of it like a movie your parents have rented for you to watch, or a book you've borrowed from the library. When it's time to take it back, sometimes you can renew it, meaning you can keep using it (but unlike the Sun's energy, you can't keep using it forever!). Other water-heating methods, like the ones mentioned before (electricity or natural gas), often use non-renewable energy sources, like coal. However, non-renewable energy sources cost money, and someday they'll run out, because there is a limited amount of them on Earth. Some of them also cause air pollution, and that isn't good for our health or our environment.

In this energy science fair project, you will test different batch solar collectors. You will make batch solar collectors using different-colored plastic bags and StyrofoamTM. Do batch solar collectors really work? Does the color of the bag affect how hot the water gets? Do this quick science fair project and find out!

A high-resolution photo taken of the Sun

Figure 1. The Sun. (NASA, 1999.)

Terms and Concepts



For help creating graphs, try this website:

  • National Center for Education Statistics. (n.d.). Create a Graph. Retrieved May 7, 2009.

Materials and Equipment

Experimental Procedure

Note: Make sure you pick a sunny day on which to try this science fair project and run the trials in the hottest part of the day with the most direct sunlight. If the project takes you multiple days, try to run the tests at the same time of day in the same spot every time.

  1. Take the Styrofoam panel and cover one of the large sides with aluminum foil. Tape the aluminum foil to the Styrofoam with Scotch tape so that the foil is securely attached to it.
  2. Take three plastic bags, one of each color that you are using, and clip a small hole at the bottom of the bag with your scissors. The hole should be just big enough so that a thermometer can fit through it.
  3. Carefully fit a thermometer through the holes in each of the bags. Push the thermometer through, about halfway up the thermometer (there should be a mark on your partial immersion thermometer showing how far it should be inserted into a liquid). Use Scotch tape to tape the bag securely around the thermometer. It should be tight enough that water will not leak out of the hole. See Figure 2.

A thermometer is inserted into an inflated black plastic bag

Figure 2. This image shows an example of a black bag batch solar collector sitting on top of a foil-covered Styrofoam panel.

  1. Now fill the 2-L container with water. Empty the water into one of the bags. Carefully squeeze the air out of the bag and tie it closed. Have an adult help you with this step. Trim off the extra plastic from the top, using the scissors.
  2. Repeat step 4 with one each of the other colored plastic bags. You should now have three different-colored batch solar collectors.
  3. Place the foil-covered panel in full sunlight. Place the three colored batch solar collectors on top of the foil-covered panel, next to each other. The collectors should all be in the Sun, and none of them in shade. Check the temperature of the water in each bag. Read each of the thermometers and record the readings in your lab notebook in a data table, like the one shown below. These readings are the starting temperatures of the water in the batch solar collectors.
    1. The temperature readings should be in Celsius (°C) if possible. Celsius is the standard unit for temperature in most fields of science.
Batch Solar Collector Color Trial Temperature of Water Over Time (°C)
Starting After 15 Minutes After 30 Minutes After 45 Minutes After 60 Minutes
Black 1          
White 1          
Orange 1          
  1. Let the three collectors sit in the sunlight for 15 minutes. Use the stopwatch to time 15 minutes. After 15 minutes, look at the thermometers and record the water temperature for each batch solar collector in your lab notebook.
  2. Let the batch solar collectors sit in the sunlight for another 15 minutes and record the temperature for each bag in your lab notebook. Continue to take readings every 15 minutes for a total of 60 minutes. You should have 5 total temperatures recorded for each bag: starting temperature, 15 minutes, 30 minutes, 45 minutes, and 60 minutes.
  3. Repeat steps 2-8 two more times, with the other plastic bags, to make sure that your results are repeatable and accurate. Always record all of your observations in your lab notebook.
  4. Make a plot of your data, using graph paper, or a website like Create a Graph. Make a line graph. Label the x-axis Time (min) and the y-axis Temperature (). There should be three lines on this graph, one line for each bag color. Does the final temperature of the water depend on the color of the bag? Did one color always heat the water the most? Which color kept the water coolest?
icon scientific method

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.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.
This project explores topics key to Affordable and Clean Energy: Ensure access to affordable, reliable, sustainable and modern energy.


  • Put out your solar batch collectors at different times during the day. Does the time of day affect the temperature of the water in the solar batch collectors?
  • Try making batch solar collectors from bags of many different colors. For example, try a yellow bag or a pink bag and compare the temperatures with the temperature of the white bag.
  • Calculate the rate at which the water heats up, with degrees per minute. Graph this data versus color.


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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Are You in Hot Water? Use the Sun's Energy to Heat Your Own Water." Science Buddies, 8 July 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Energy_p033/energy-power/use-solar-energy-to-heat-water?from=Blog. Accessed 22 Feb. 2024.

APA Style

Science Buddies Staff. (2020, July 8). Are You in Hot Water? Use the Sun's Energy to Heat Your Own Water. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Energy_p033/energy-power/use-solar-energy-to-heat-water?from=Blog

Last edit date: 2020-07-08
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