Ag & Energy - Lesson 5 - Agriculture & Solar Energy

Ag & Energy - Lesson 5 - Agriculture & Solar Energy

Target Grade Level / Age Range:

Grades 9-12

Time:

50 minutes

Purpose:

By the end of this lesson, students will be able to:

  1. Define electrical solar energy and identify its applications.
  2. Define thermal solar energy and identify its applications.
  3. Understand the potential of solar energy in different regions of the U.S. and discuss potential limitations.

Materials:

Suggested Companion Resources

Vocabulary

  • Thermal Solar Energy: The capture and use of solar radiation for heat. Includes passive designs such as radiant space heating and active designs such as circulating water heaters.
  • Electrical Solar Energy: Conversion of sunlight to direct current (DC) electricity using semiconductors (i.e., silicone crystals) to gather free electrons. Commonly called PV (photovoltaic) or simply “solar panels,” they are the most common form of solar technology.

Interest Approach or Motivator

Post two questions on the white board or other large writing surface.

  1. What do you already know about solar power?
  2. How is it being used in your community?

As students enter the room, have them go to the board and write answers to the questions. Once every student has had a chance to contribute review the responses. For accurate statements recognize the good work. For any incorrect statements identify that we will be exploring this topic more to discover the correct answer.

Procedures

Objective 1: Define electrical solar energy and identify its applications.  

Introduce students to photovoltaics with the following video: Photovoltaics explained: https://youtu.be/manp7iEyxCI

Have students capture the following information into their notes.

  1. When sunlight enters the semiconductor material (typically silicone) it “frees” electrons that can be gathered into a DC current with thin wires placed on the crystals.
  2. Concerns of PV Production:
    1. Solar cell manufacturing is an energy-intensive process that produces GHG and contaminants such as heavy metals.
    2. PV panels pose environmental risks if not recycled properly after their useful life of ~25 yrs.
  3. Farm Benefits of Solar Power
    1. Reliable, low-maintenance energy production
    2. Reduces energy bills and provides profit potential
    3. Unlimited and clean domestic fuel source
    4. Remote onsite power production
    5. Independence from fluctuating fuel prices
    6. Increases overall food security for the U.S.
    7. Self-sufficient
  4. On farm uses of Solar electricity
    1. Lighting: For remote lighting, batteries are charged during the day to run efficient LED light bulbs.
    2. Water pumps: Although the flow rate can be less than one gallon per minute, a DC solar well pump can still provide over 350 gal. of water per day from all but the deepest wells.
    3. Irrigation: Specialized pivot irrigation systems can be powered by deep cycle batteries charged by solar panels, 24v control circuitry, and 90v DC motors. Solar drip irrigation is extremely efficient at delivering water (and fertilizer) directly to the roots of plants for small farms.
    4. Electrical fences: A single solar panel can run an electric fence with no moving parts to break or wear out.  An attached battery will allow it to go days without recharging.
    5. Remote electrical needs: remote electricity supply is often cheaper than having the utility company build new power lines to these locations.
    6. Creative uses: solar powered “scarecrow” uses specific acoustic ranges to deter birds from fields. 
    7. General farm electrical needs
  5. Most affordable option for many applications:
    1. Can significantly reduce on-farm electric costs and provide FREE POWER once system is paid for.
    2. PV cost is currently at a record low of $2/Watt.
    3. Qualifies for generous rebates and tax credits.
    4. Can generate income with net-metering.
Objective 2: Define thermal solar energy and identify its applications.

Prior to class, print out the following information on four different pages (use PowerPoint slides 8-11). Put one type of thermal solar heating set of information in each corner of the room. Instruct students to circulate the room going to each corner collecting notes from each station. Students should be prepared to share one thing they learned from each by the time they return to their seats. Give students 5-7 minutes to complete this task. Once they finish, invite students to share what they learned. 

  • Space heating: Preheat incoming fresh air for farm buildings.
    • Radiant solar: Glazed flat-plate solar collector for heating buildings
    • A black absorber plate, oriented toward the sun, warms the fluid passing through the flow tubes.
  • Water heating: Provide hot water for cleaning, dairy needs, etc.
    • Fluid is circulated through glass tubes within panels and warmed to ~160°F.
    • A heat exchanger pulls the radiant heat from the fluid to warm forced air or water.
    • A thermosiphon solar water heater does not need an electric pump as gravity and thermal convection (hot water rises, while cool water sinks) operate together in the system.
  • Greenhouse heating: Passive solar designs for greenhouses.
    • Water/glycol is warmed by solar thermal panels and circulated through pipes in soil.
    • Heated soil extends the growing season by maintaining nutrients and increasing germination rates.
    • Passive solar heating and cooling takes advantage of natural energy characteristics in materials and building designs with exposure to the sun.
  • Crop and grain drying: Solar thermal convection/air heating.
    • While slower than gas-fired driers, solar thermal grain dryers are extremely efficient and can pay for themselves in just a few years.
Objective 3: Understand the potential of solar energy in different regions of the U.S. and discuss potential limitations.

Navigate to https://maps.nrel.gov/re-atlas/  and display the map on a large screen for students to see. Select only the Solar Photovoltaic layer to be displayed. Discuss with students what they notice about the map.

What states in the U.S. offer the most solar energy potential? (California, Nevada, Arizona, Utah, New Mexico, Texas, Florida)

Why do those states offer the most potential? (Lower latitude equates to longer days year-round, drier climates in the southwest equate to more cloudless days, drier climates equate to less trees that might cast shadows, higher elevations in the mountains could mean more intensity of sunlight)

What states have the least energy potential? (Washington, Minnesota, Wisconsin, Michigan, New York, Vermont, Maine)

Why? (higher latitude equates to shorter days in the winter, more regular cloud cover)

All energy stored in the earth’s reserves of coal, oil, and natural gas is equal to the energy in just 20 days of SUNSHINE!

Producing electricity from solar cells reduces overall air pollutants and greenhouse gasses by approximately 90%, compared to using conventional fossil fuel technologies.

How will farmers finance the installation of these? Will they be worth the investment?

Review:

Use Plickers cards to review and test student knowledge. Prior to class login to the Plickers website and register your account and enter your students on the website https://www.plickers.com/.  Print out the cards and laminate them with non-glossy or matte lamination. Pass out cards to students. Student number should match their name that you entered on the website.

Each card has four sides (A, B, C, D) and will hold up the card facing the teacher with the letter they think is correct at the top of the card. Make sure students hold the card so that they are not covering up any part of the code on the front of the card. Teacher will then use their smartphone or tablet to scan the cards. You can connect your smart device to the project if you want students to see the feedback and responses in real time.

Have the questions and the correct answers preloaded on the website. Questions and choices are below and in slides 14-22. The correct answer is in bold below.

  1. An example of passive thermal solar energy would be:
    1. Water heating
    2. Space heating
    3. Grain drying
    4. Remote electricity needs
  2. Photovoltaics creates what kind of electrical current?
    1. DC (direct current)
    2. AC (alternating current)
    3. EC (electron current)
    4. BC (bi-directional current)
  3. What benefits do photovoltaics offer?
    1. Low maintenance energy production
    2. Remote onsite power production
    3. Reduction in energy bills
    4. All of the above
  4. Which is not an example of on farm photovoltaic solar power use?
    1. Water pumps
    2. Irrigation
    3. Radiant greenhouse heat
    4. Electrical fences
  5. A thermal solar water heater does not need a pump and works on gravity and thermal convection because
    1. A heat exchanger pulls the heat from the fluid
    2. Hot water rises, cool water sinks
    3. The panels tilt to let water flow down
    4. Glass tubes keep the water viscous and flowing
  6. Water/glycol warmed by solar thermal panels and circulated through pipes in the soil provide what benefit?
    1. Provide maximum exposure to the sun
    2. Help water the plants
    3. Help loosen the soil
    4. Heat the soil extending the growing season
  7. Which grain drying system, while slower, is most energy efficient?
    1. Propane gas fired drier
    2. Motor auger grain dryer
    3. Thermal grain dryer
    4. Natural air low temperature drying
  8. Producing electricity from solar cells reduces air pollutants by approximately _____ compared to using fossil fuels.
    1. 90%
    2. 80%
    3. 70%
    4. 60%
  9. What semiconductor is typically used to construct photovoltaic cells?
    1. Arsenic
    2. Selenium
    3. Silicon
    4. Tellurium

Essential Files (maps, charts, pictures, or documents)

Sources/Credits

Author(s)

Will Fett

Organization Affiliation

Iowa Agriculture Literacy Foundation

Agriculture Literacy Outcomes

  • Theme 1: Ag and the Environment
    • Describe resource and conservation management practices used in agricultural systems (e.g., riparian management, rotational grazing, no till farming, crop and variety selection, wildlife management, timber harvesting techniques)
    • Evaluate the various definitions of “sustainable agriculture,” considering population growth, carbon footprint, environmental systems, land and water resources, and economics
  • Theme 4: STEM
    • Describe how agricultural practices have contributed to changes in societies and environments over time
    • Evaluate the benefits and concerns related to the application of technology to agricultural systems (e.g., biotechnology)
  • Theme 5: Culture, Society, Economy & Geography
    • Discuss the relationship between geography (climate and land), politics, and global economies in the distribution of food

Education Content Standards

  • SS.9–12.G.1: Essential Concept and/or Skill: Understand the use of geographic tools to locate and analyze information about people, places, and environments.
  • HS-PS1-5. Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
  • HS-PS3-4. Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics).
  • HS-ESS3-1. Construct an explanation based on evidence for how the availability of natural resources, occurrence of natural hazards, and changes in climate have influenced human activity.

Common Core Connections

  • RST.9–10.2: Determine the central ideas or conclusions of a text; trace the text’s explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.

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