The History of the Sun (10 minutes - Review)
Begin your lesson with a discussion of how the sun influenced ancient civilizations around the world. First, discuss cave men, our distant antecedents. Move the discussin forward to consider examples of the sun's influence on the more recent cultures of the Middle East, Egypt and Mesopotamia.
Ask students to explore what tools were developed and used to harness the sun as a resource. Talk about how ancient civilizations depended on the sun as a resource for survival and how architecture was influenced in accordance with this resource. If recent social studies lessons have discussed the ancient Egyptians and Mesopotamia, these lessons can help to fuel the class discussion. For example, according to Egyptologists, the true pyramid (i.e. the smooth-sided pyramid) was a solar symbol, its shape signifying the rays of the Sun falling to the earth.
Pyramids were often named in referrence to solar luminescence.
The Sun Today (10 minutes - Investigate)
Relate your discussion to contemporary issues. How do we use the sun today?
- Solar tracking - the sun can be used as a navigation device; we can measure radiance and predict climate and weather patterns from the sun’s movement. It also dictates seasons.
- Passive solar design - Solar passive design is a strategy to harness the sun’s heat energy through unobtrusive architecture.
- Renewable Energy - Photovoltaics (solar Panels) convert the sun’s light energy into electricity.
Investigate what kinds of solar resources you have in your region of the country. This is usually measured in a unit called solar radiance. This is the amount of sunlight that hits a surface. This will change based on where you are and what time of the year. (measured in kW-h/m2) The
National Renewable Energy Lab and sites like
CoolerPlanet will help you calculate the solar radiance in your area.
As a great math activity, obtain a
Solar Pathfinder, if time and resources allow. With the pathfinder you can calculate the solar potential for your school. The pathfinder helps you find information about:
- Time: The Solar pathfinder tells you what time during the day the most sunlight hits the earth.
- Latitude/longitude: These coordinates tell you where you are on the earth.
- Percent of sun: This gives you a percentage of sunlight concentration on a certain area.
Your School, the Sun and Design (10 minutes - Frame/Reframe)
Now focus on your school and its design. How can a consideration of the sun impact your school’s design? How does a design methodology that considers the sun improve our relationship to the earth?
If we design with the sun in mind we can help buildings in terms of:
- Efficiency - lower electricity and heating costs
- Better indoor air quality and lighting
- Reducing climate change footprints
One application is passive solar design, the method of designing a building to use solar energy to provide lighting, heating and cooling.
Buildings consume 50% of all energy produced in the US and 75% of all electricity. Due to this, buildings are one of the nation’s largest consumers of fossil fuels, causing them to be the largest producers of pollution as well as green house gases (which is a direct cause of global warming). By designing with passive solar techniques, a building can save on energy costs which helps to save money as well as cut back on the amount of pollution (and green house gases) produced.
By specifically placing the windows, doors and the roof, carefully choosing the site, materials, and design features, a building can collect, store and distribute the sun’s heat in winter, block the sun’s heat during the summer, and provide natural day lighting. Due to the movement of the earth around the sun and the angle of the tilt of the earth’s axis, in the northern hemisphere having south-facing windows allows for the most amount of solar energy to enter a building.
Another possible application is solar panels. Solar panels can be placed on the façade or roof of the school to collect the sun’s light energy and produce electricity. In most cases and with current technology, you should aim for a 25% offset from solar panel use. Solar will most likely not be able to replace all electricity usage in the school.
Math Connection
Energy is measured in a number of ways depending on what property is being represented.
- Total Energy - Joules and ergs - The total amount of energy in various forms (kinetic, potential, magnetic, thermal, gravitational)
- Power - Watts, Joules/second or ergs/second - the rate at which energy is produced or consumed in time. Power = Energy/Time
- Flux - Watts/meter2, Joules/sec/meter2 or ergs/sec/meter2 - the rate with which energy flows through a given area in given amount of time: Flux=Power/Area
- 1 Joule = 10 million ergs 1 kilowatt = 1,000 watts
- 1 Watt = 1 Joule/1 second 1 megaJoule = 1,000,000 Joules
- 1 hour = 3600 seconds 3 feet = 1.0 meters
Example: A 5-watt flashlight is left on for 1 hour: Convert its energy consumption of 5 watt-hours to Joules.
1 Joule 3,600 sec
5 Watt-hours x ----------------- x --------------- = 18,000 Joules
1 sec 1 watt 1 hour
Problem: How many ergs of energy are collected from a solar panel on a roof, if the sunlight provides a flux of 300 Joules/sec/meter2, the solar panels have an area of 27 square feet, and are operating for 8 hours during the day?
Problem: The common energy unit for electricity is the watt-hour (Wh), which can be written as 1 watt x 1 hour. How many megajoules equal 1 kilowatt-hour (1 kWh)?
Solar Design Lab (20 Minutes - Generate Solutions)
Using the following steps, assist students in the design of the ideal PV for the roof of your school building. The PV system’s goal should be to offset electricity usage by at least 25-50 %.
Step 1: Estimate your electricity needs
To get started, it's good to have a sense of how much electricity your school building uses. You'll have a better point for comparison if you find out how many kilowatt-hours (kWh) the building uses per day, per month and per year. Your school’s utility bill should include this information and can most likely be accessed by contacting the manager of facilities or principal at your school.
The utility bill should also display your costs and many utilities include a graph that displays how your monthly energy use/cost varies throughout the year. That helps you estimate where your highest energy use is and at what time of year.
Step 2: Think about the future
In 2005, average residential electricity rates across the USA ranged from 6 to nearly 16 cents per kilowatt-hour, depending on the geographic location of a home. Average retail and commercial electricity rates have increased by roughly 30% since 1999. This upward trend will likely continue, especially as costs for the coal and hydropower used to generate electricity rise as well.
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State
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(Cents/kWh)
|
|
(Cents/kWh)
|
|
|
|
2005 Average Electricity Rate
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2005 Yearly Cost ($)
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2025 Average Electricity Rate
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2025 Yearly Cost ($)
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Arizona
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8.9 cents
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$1,170
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28.4 cents
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$3,751
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California
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12.5 cents
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$1,652
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40.1 cents
|
$5,296
|
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Colorado
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9.0 cents
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$1,996
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29.1 cents
|
$3,835
|
|
Massachusetts
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13.4 cents
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$1,769
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43.0 cents
|
$5,673
|
|
Maryland
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8.5 cents
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$1,122
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27.3 cents
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$3,598
|
|
New Jersey
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11.7 cents
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$1,544
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37.5 cents
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$4,953
|
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New York
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15.7 cents
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$2,072
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50.4 cents
|
$6,646
|
|
Texas
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10.9 cents
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$1,439
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35.0 cents
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$4,614
|
Math Connection
Using the chart above, ask students to determine the rate of increase for the expected price of electricity in 2025. If your state isn’t listed in the chart, ask students to research projected and real data for your region. How much of an increase will your region see? If this rate of increase continues on a similar path, what is an estimate of the cost of electricity in 2050?
Step 3: How much sun do you get?
A photovoltaic (PV) system's performance is related to the amount of sun available during your region's peak daylight hours. It is also dependant on the efficiency of something called an inverter, which is used to convert solar derived energy from direct current (DC) to alternating current (AC). Most appliances and buildings use AC power sources because they are easier to manage and are less dangerous.
The above image depicts a typical solar panel.
Solar photovoltaic systems work just about anywhere in the US. Even in the Northeast or in "rainy Seattle", a PV system can produce electricity if designed and installed properly. In New York or New Jersey, a one kilowatt system should produce about 1270 kilowatt hours of electricity per year, in Seattle, a one kilowatt system should produce about 1200 kilowatt hours per year. In the Southwest, of course, those ratios will be much greater. You can use something called a solar pathfinder to your regions solar irradiance. Solar Irradiance is the amount of solar energy received on a given surface area in a given time. This measurement varies based on weather and latitude. Solar Irradiance is a constant value, to find your SR value visit:
https://www.nrel.gov/gis/solar.html.
Step 4: Size your system
In general, solar photovoltaic systems sized between 1 to 5 kilowatts (kW) are sufficient to meet the electricity needs of a small home. For a large building or school system, you will need a system that is quite a bit bigger to offset 25-50% of your electricity consumption ranging from 10-20 kW. Most PV systems are grid-tied systems, which means they are connected to the energy grid. This allows you to use solar PV to supplement or offset some of your electricity needs while enabling you to add to the system later if needed.
A general rule of thumb in sizing your system is that one square foot yields 10 watts. So in bright sunlight, a square foot of a conventional photovoltaic panel will produce 10 watts of power. A 1000 watt system, for example, may need 100 - 200 square feet of area, depending on the type of PV module used.
To size your system you will need to do two calculations, which help to determine your system and roof size.
System Size: This is determined by taking your average daily electrical usage,
and dividing that by your solar radiance at 71%. The 71% factor is necessary in order to approximate for the inherit inefficiencies in solar power systems.
1. Determine System Size
a. System Size: (kW) = Daily electrical usage/((Solar Irradiance) x (71%))
Roof Size: Approximate roof size needed to accommodate your solar power system (9-10 watts/sq ft).
2. Determine the size of your roof (that is able to receive sunlight)
a. Roof Size (square feet) = Roof Size/10
After conducting these two calculations you will be able to determine the size of the PV system needed for your school’s energy needs.
Step 5. Determine Cost
To determine your estimated cost use a $9/watt value and multiply this by your system size. Also consider rebates and the costs of insurance, installation and other permitting costs.
Estimated Cost ($) = ($9/watt) x (System Size)
After conducting this study and collecting information, challenge students to redesign their schools using their new knowledge about solar applications and the sun. Some possible re-designs may include:
- Solar Array on the Roof - using the sun for electricity.
- Rooftop learning lab or garden - to use the sun as a way to grow food.
- Solar Passive Design - more windows and better designed façade allows sunlight to come into the school.
Each student should brainstorm, sketch and begin finalizing a design to work with.
After preliminary design and brainstorming, students or design teams will then make models to that illustrate their newly designed schools. (Edit and develop ideas)
Design Fair and Presentation
If possible host a mini-school design fair inviting students and teachers to come see the new designs. To celebrate make a big model of the sun as a piñata and fill it with treats! (Share and Evaluate)
Display your new “solar designs” around the school.(Finalize)