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 faç ade 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.
| State | (Cents/kWh) | |
(Cents/kWh) | |
| | 2005 Average Electricity
Rate | 2005 Yearly Cost ($) | 2025 Average
Electricity Rate | 2025 Yearly Cost ($) |
|
Arizona | 8. 9 cents | $1, 170 | 28. 4
cents | $3, 751 |
| California | 12. 5
cents | $1, 652 | 40. 1 cents | $5,
296 |
| Colorado | 9. 0 cents | $1, 996 |
29. 1 cents | $3, 835 |
| Massachusetts | 13.
4 cents | $1, 769 | 43. 0 cents | $5,
673 |
| Maryland | 8. 5 cents | $1, 122 |
27. 3 cents | $3, 598 |
| New Jersey | 11. 7
cents | $1, 544 | 37. 5 cents | $4,
953 |
| New York | 15. 7 cents | $2,
072 | 50. 4 cents | $6, 646 |
| Texas |
10. 9 cents | $1, 439 | 35. 0 cents | $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 faç ade 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
piñ ata and fill it with treats! (Share and Evaluate)
Display your new “ solar designs” around the
school. (Finalize)