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Fun in the Sun: Solar Heating and Time of Day

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Author: Janice VanCleave

What Effect Does the Time of Day Have on Passive Solar Heating

Category: Physics—Energy—Solar

Project Idea by: Connor Fields

Question: What Effect Does the Time of Day Have on Passive Solar Heating?

Solar energy is a form of radiant energy from the Sun. Radiant energy is energy in the form of waves that can travel through space. Solar heating is a process of using solar energy to heat materials. There are two types of solar heating: active and passive. Active solar heating involves using special devices for absorbing and transporting solar energy. For example, some solar collectors are covered with tubes containing water. As sunlight strikes the collector, solar energy is absorbed and the heat is transferred to the water in the tubes. The hot water circulates through pipes to heat a building or to heat air blown into the building.

Passive solar heating does not use any mechanical means of distributing the collected heat; instead, it is direct heating from sunlight. For example, when sunlight comes through a window, it is absorbed by materials in the room, causing them to heat up. Heat is transferred from warm materials to cold materials until the temperature of the materials is the same. Thus, the heat transfer is by natural means. To get the most out of passive solar heating, buildings can be designed so that more sunlight will enter. In the Northern Hemisphere, the path of the Sun is from east to west across the southern sky. So a building with large windows facing the south will receive the greatest amount of sunlight.

Because of the variations in the amount of solar energy received during the day and at a particular location, generally neither active nor passive solar heating is the only heating source for a building. In order to know when solar heating is going to be the most effective, you must know when the greatest amount of solar energy can be collected during the day. A project question might be, "What effect does the time of day have on passive solar heating?"

Clues for Your Investigation

Design a way to measure the amount of solar energy at different times of day. One way is to design a solar cooker and determine how hot a container of water gets in the cooker in a given amount of time. Use a thermometer to measure the change in the temperature of the water. Repeat the procedure at different times during the day.

Independent Variable: Time of day

Dependent Variable: Amount of solar heat measured by water temperature

Controlled Variables: Solar cooker, amount of time the water is cooked, energy source (sunlight), measuring device (thermometer), environmental conditions such as humidity and cloudiness, position of cooker

Control: Median time

Other Questions to Explore

  1. What effect does the color of the solar cooker have on the amount of solar energy absorbed?
  2. How does the placement of the solar cooker in relation to sunlight affect the amount of solar energy absorbed?
  3. What is a greenhouse, and how does the location of a greenhouse affect the amount of solar energy absorbed?
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