Going Solar

The Earthly Problem
With Earth Day coming up Saturday, it's a good time to take a look 93 million miles away at the Sun. What does the Sun have to do with Earth Day? The answer has to do with energy. Our food is full of chemical energy converted from sunlight and stored in the plants and animals we eat. The Sun warms our environment by providing a stable temperature for life to thrive.

There is another important way that the Sun can help Earth—by providing a clean source of energy for our heat, transportation, and electrical power. How can you harness this power?

People have relied heavily on energy sources that create pollution and dangerous environmental problems. We use fossil fuels such as oil and natural gas to heat our homes, power our cars, and generate electricity. When the chemical energy stored in fossil fuels is released by burning, polluting gases are also released and can harm plants, animals, and humans. These gases rise and become concentrated in Earth's atmosphere, and this effect may be causing the global warming of our climate.

Mining and drilling to extract fossil fuels from deep within Earth also destroy the natural habitats for plants and animals both on land and in the oceans. Nuclear energy facilities provide an alternative to fossil fuels but create dangerous waste.

The Solar Solution
How can the Sun help? The Sun contains an inexhaustible supply of energy that can be used instead of traditional fuels. Sunlight is easy to collect without generating dangerous waste, and it can be converted into electricity or heat in many ways:

• photovoltaic solar cells: These special chemical panels convert sunlight directly into electricity. Photovoltaic solar cells are used in the space shuttle, deep space probes, commercial satellites, solar-powered cars, and even roadside construction signs on highways and handheld calculators.

  

• circulated solar heating: A solar-heated building has glass-covered solar panels on the roof to heat water with sunlight. Then, the heated water flows into the building and is used directly as hot water, or for heating.
• passive solar heating: Large glass windows let warming sunlight into a building. Greenhouses use passive heating to stay warm, even in cooler seasons.
• solar ovens: Solar ovens concentrate solar energy in a small space and are used for cooking and drying food. Like the larger greenhouses, solar ovens are designed to let sunlight shine in but keep the heat from flowing out.

Solar Savings
All of these solar collectors can save money that would otherwise be spent on traditional fuels. Figure out how much money a family can save using a solar hot water heater:

• A typical American family of four uses about 80 gallons of heated water daily. An electric hot water heater would require 14 kilowatt-hours of electricity to heat that water. If electricity costs 10 cents per kilowatt-hour, how many dollars a year does it cost to heat the water with electricity?
• A single solar roof panel can generate the same amount of heat as 10 kilowatt-hours of electricity each day. How much money per year would that family be able to save on heating water?
• If the panel costs $450 to buy and install, how long would it take the family to "break even" on the investment?

Build a Solar Energy Collector

The Sun is a massive source of energy, glowing at a toasty 27 million °F (15 million °C) at its center. But, the Sun is 93 million miles away—how does its energy reach us here on Earth? The energy travels through space as radiation. When some of the radiation arrives here eight minutes after leaving the Sun, it changes form again, and we feel the warmth on our skin.

To celebrate Earth Day, students from around the country will design and build their own solar energy collectors during May and June, in a Science-athon event called Catching Sunshine hosted by TERC and Riverdeep Interactive Learning. TERC is an education not-for-profit research and development firm in Cambridge, Massachusetts dedicated to the improvement of mathematics, science, and technology teaching and learning.

Here's how you can build your own solar collector and even use it to cook your own food. It's easy!

• How solar collection works: Sunlight is visible radiation of energy from the Sun. When the light shines on any object, some of the energy gets absorbed and raises the energy of the object. For the solar collector to work well, it must:
  
  
  • Absorb energy from the sunlight
  • Keep heat from escaping by providing some kind of enclosure
    
    
• How to build your collector: Finding the best materials for your oven is critical. What materials are good at absorbing heat from sunlight? Foil? Paper? Wood? Plastic? What colors work best? Light? Dark? The way to find out is to try different materials, and measure the results in your own solar collector.
  
  
  • Find a container. You might use a shoebox, plastic bucket or jar, paper bag, milk carton, yogurt tub, or cereal box. Avoid anything made of glass!
    
    
  • Choose a transparent material that will allow sunlight to shine into your collector. Remember all of the Sun’s rays needs to shine through the material.
    
    
  • Figure out how to measure the air temperature inside the collector. You need to be able either to take the thermometer out of the collector and replace it without tearing a hole or to locate the thermometer in a place where you can read it easily. (Cellophane tape can be used to plug holes around a thermometer opening.)
    
    
  • Line the inside surfaces of the collector. The sides of the collector should absorb as much sunlight as possible.
    
    
  • Make sure you hold the heat inside the collector. Cold air can enter the collector through holes, and warm air can escape through outside surfaces.
    
    
  • Point your collector so that it catches the Sun’s rays. Try to catch as much sunshine as you can.
    
    
• How to measure your results: The goal of your solar collector is to collect energy and raise the air temperature inside the collector as much as possible. You can print out this page and write your measurements in the table below.
  • First, put your collector in a shady spot. Let it sit for10minutes so the temperature stabilizes. Measure the temperature inside your collector with a thermometer, and record the shade temperature.
  • Next, put your collector in direct sunlight. Let it sit for 10 minutes before measuring the inside temperature with the thermometer. Write down the direct sunlight temperature.
  • Calculate the temperature increase. The temperature increase is the direct sunlight temperature minus the shade temperature. All of the participants in Catching Sunshine have agreed to compare their temperature increases using °C. If you measured your increase in °F, use the formula to convert Fahrenheit to Celsius:

    (°F - 32) x 5/9 = °C

    	°F	°C
    Shade Temperature
    Direct Sunlight Temperature
    Temperature Increase

    
    

• How to compare collectors: Which absorbing material works best? What are the best times and locations to catch sunlight? The Catching Sunshine project will help you answer these questions. Every student who builds and tests a solar collector will share his or her results by submitting them online. Then you can compare your own results with everyone else's and determine what makes a solar collector really cook.

Learn More

• Get more information on solar collectors for cooking at the ClearDome Solar Ovens site.
  
  
• Photosynthesis is one of nature's principal ways of capturing and storing solar energy. Check out the relationship between light and photosynthesis in Riverdeep's Biology Gateways activity The Role of Light in Photosynthesis and Biology Explorer activity Light & Photosynthesis.

• Teachers can enroll classes in the Catching Sunshine project.

This article was written by Eric Hilfer and Judy Vesel, both of whom are scientists at TERC.