Back of the Envelope Calculations: Renewable Energy
Throughout an introductory level course highlighting sustainability themes, students do a number of Back of the Envelope Calculations to put the large numbers related to energy into perspective. In this calculation for the feasibility of applying wind energy to a new housing development, students are asked to determine the estimated payback time and assess the value of installing a wind turbine to provide electricity to the development. The students discuss the pros and cons of incorporating renewable energy installations into community planning in the context of previous lessons on fossil fuels and renewables.
Context for Use
Description and Teaching Materials
Students should estimate what an average monthly power bill is based on their experience (answers will vary by region and household).
Follow-up discussion questions (emphasizing environmental, social, economic implications):
1) What are the pros and cons of such a wind installation?
2) Where might be the best place to locate a wind turbine in a housing development?
3) How does the payback period change as the cost of electricity from the "grid" goes up and down?
4) Is your answer surprising? (and why)
5) Would you consider this in your neighborhood? (why/why not?)
Teaching Notes and Tips
This activity takes a minimum of 15 minutes, but it could be expanded to allow students to research average household energy usage and cost of wind turbines in advance, as well as to collect household energy bills to determine their electricity rates.
I always remind students to bring a calculator to class, but many of these calculations can be done without one.
These calculations usually generate good discussion, especially about why there isn't broader adoption of renewables in the US. Be prepared to guide these discussions.
Assessment is usually based on whether students participated in the discussion.
One alternative is to convert the back of the envelope exercises into clicker questions, which could be assessed in more detail.
References and Resources
SERC Back of the envelope page by Tewksbury: http://serc.carleton.edu/quantskills/teaching_methods/boe/index.html
US Energy Information Administration: http://www.eia.gov/
US Department of Energy: http://energy.gov/