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# Do We Need Heat for Solar Power?

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### Purpose or Problem

The purpose is to prove that temperature is not a factor in determining if a location is acceptable for solar-energy applications.

### Overview

Making use of energy from the Sun has many important benefits. Solar energy is a clean, renewable, and free source of fuel. It can be used to generate electricity and make hot water for our homes. Solar panels can be mounted on the roof of a home to assist in supplying hot water for the family, thus reducing the home's hot water utility bill.

Do solar panels only work for homes located in warm or hot climates? No. Temperature is not a factor, as this project will prove. If you live in a part of the country where it is cold in the winter, think about sitting at a table next to a bright, sunny window. You can feel heat on your body. Think about getting into a car on a sunny, cool day. The car's interior is warmer than the weather outside. Think about how cold it is in the Arctic, yet it is a very sunny region.

### Hypothesis

Hypothesize that temperature is not a factor in the amount of usable sunlight that can be gathered in an area needed for solar-energy applications.

### Materials' List

• Photovoltaic cell
• DC voltmeters with a millivolt scale
• Thermometer
• A day when the temperature is much colder outdoors than inside
• Daily newspaper or almanac with the times of sunrise and sunset
• Pencil

### Procedure

Connect a DC (direct current) voltmeter with a millivolt scale across the leads (wires) extending from a solar cell. Small solar cells are available at local hobby shops and electronic parts chains. Be aware that the output of the solar cell has a polarity; it has a plus (+) and a minus (–) terminal. Be sure to wrap the bare end of the plus lead of the solar cell to the plus test probe on the voltmeter.

On a cold day, set the solar cell and voltmeter outside in an unobstructed area that is exposed to direct sunlight. Set a thermometer next to it. Wait several minutes for the thermometer to adjust to the temperature. Record the voltage indicated on the voltmeter and the temperature on the thermometer.

Move the solar cell, voltmeter, and thermometer indoors, and place them in a sunny window. Wait a few minutes to allow the thermometer to adjust to the indoor temperature. Record the voltage and thermometer readings. What is the difference in temperature? While there was a big difference in temperature, was there a significant difference in voltage?

Another factor in determining if a location is favorable for the installation of solar panels is the amount of possible daily sunshine. Use the formula:

The "total minutes of actual daylight" can be found in your daily newspaper by finding the time of sunrise and sunset, and then calculating the time difference between them and converting that time to all minutes. The "minutes of the day the Sun could cast a shadow" can be determined by taking a pencil or another object outside just after sunrise and holding it a few inches above the ground. When a clear and discernible shadow can be seen, record the time. Similarly, as sunset approaches, record the time when a shadow is no longer discernible. Subtract the two times to find the minutes of strong sunshine. Then, compute the percent of possible sunshine by dividing shadow time by total daylight time.

### Results

Write down the results of your experiment. Document all observations and data collected.

### Conclusion

Come to a conclusion as to whether or not your hypothesis was correct.

##### Something More
1. If you have a relative who lives a far distance (in another state) from you, ask them if they would do the same experiment as you just did. Compare their results to yours.
2. Does the glass in a window block some frequencies in the spectrum of light? Does it block or pass ultraviolet light? Does it block or pass infrared light?
3. Is the area you live in suitable (economical) for hot-water solar collectors or photovoltaic solar-cell applications? What percentage of days per year does your location experience overcast skies? Gather data from weather sources using the Internet, National Oceanic and Atmospheric Administration (NOAA), or local weather authorities. How would you construct a device that would monitor the amount of cloudiness that occurs during a day?