7 Pages
Unlock Document

Computer Science
CAS CS 101
Michael Manove

MEMO To: From: Chris Peters Date: March 28, 2013 Re: Renewables: Best of the Best The rapid evolution of sustainable energy is undeniable. Fueled by a multitude of factors including technology improvements, environmental concerns, rising oil prices, and international unrest, key stakeholders are increasingly interested in a sustainable energy future. This memorandum seeks to explore which sustainable solutions are the best and concludes that there is no one “best of the best” sustainable sources, but rather a blend of solutions. To do that, it is necessary to first define what constitutes superior sustainable energy. Our energy has traditionally come from fossil fuels because they have been abundant, accessible, and cheap. Likewise, a truly viable sustainable energy source will have to satisfy a diverse constituency of stakeholders, not all of whom are mission-driven toward a clean environment. We will therefore be examining each source on its accessibility, cost, and environmental impact. WIND Overview Wind energy is perhaps the simplest form of sustainability to understand: wind-driven turbines convert mechanical energy into electrical energy for the grid via a generator. We can also harness wind for a variety of practical tasks such as charging batteries, pumping water, and grinding grain (U.S. Dept of Energy). To achieve economies of scale and utility-grade energy, large numbers of turbines are typically concentrated in “wind farms” to provide grid power (U.S. Dept of Energy). The wind industry has been growing more quickly than any other sustainable source. During 2011, approximately 40 GW of wind power capacity went online around the globe, which is more than any other renewable source (REN 21, 57). In the United States, 2,900 turbines went up in 2010 andAmerican wind generates enough energy to power over 10 million homes (NRDC). Costs The cost of wind power has been dropped 85% in the last 20 years (NRDC) due to over- capacity among manufacturers, increased competition, increasing scale and greater efficiency (REN 21, 59). In 2010, efficient wind farms had average costs of 7 cents per kilowatt hour (NRDC). According to the U.S. Energy InformationAgency, the estimated average total system levelized cost for wind farms entering service in 2017 will be $96 per megawatthour (Exhibit C). Advantages There are many clear advantages to wind power. It is free, unlimited, and given the abundant United States land mass, there is plenty of space to capture the wind. Arjun Makhijani of the Institute for Energy and Environmental Research calculated the wind energy potential in the top 20 contiguous states in 2005to be 10,470 billion kilowatt hours; in that year U.S. electrical generation was approximately 4,000 billion kilowatt hours. Thus, the potential wind generation that year, excluding offshore sites, was 261 percent what the U.S. generated (31). Additionally, wind plants are quick to build – less than a year for a 50 megawatt wind farm (NRDC) – and the energy “payback time” is also quick, with three to eight months operating to recoup the energy consumed in building and installation (NRDC). Disadvantages Wind is a variable resource that does not blow all the time in the same area. According to the IEA, the capacity factor of wind turbines ranges from 20% to 40%, which is lower than for other technologies. Wind turbines can also be considered “visually intrusive” (IEA), which means they are more desirable in remote areas. However, this can increase the cost of energy transmission. Building offshore sights mitigates some of these problems, but can also increase the costs of installation and connection to the power grid. SOLAR Overview Solar energy uses the sun to generate electricity in two primary ways. The method most people think of is through photovoltaic (PV) cells that convert sunlight into electricity. This occurs through silicon cells which, when hit by sunlight, knock electrons free of their atoms to flow through and become direct current (DC) electricity (NRDC). Nearly 30 GW of new solar PV came online around the world in 2011, a 74% increase (REN 21, 47). The other primary solar method is “concentrating solar power” (CSP), which collects the sun’s heat to generate steam that powers an electric generator (NRDC). More than 450 MW of CSP came online in 2011, an increase of 35% (REN 21, 47). Costs Solar energy prices have fallen over the past 20 years, with CSP from a plant costing 10- 14 cents per kilowatt hour. On the PV side, continued innovation throughout the value chain, process improvements, and development of organic materials is lowering costs by 7-8% each year (REN 21, 50). According to the U.S. Energy InformationAgency, the estimated average total system levelized cost for PV plants entering service in 2017 will be $153 per megawatthour (Exhibit C). Advantages Like with the wind, the sun is a free, unending source of energy. Its capacity is also practically infinite relative to energy use. According to the Makhijani, assuming 20 percent efficiency and using one percent of U.S. land area, solar electricity generated by PV cells would exceed total U.S. energy generation by eight times. While this is hypothetical, the IEAreported in 2011 that by 2060, solar (PV and CSP) may produce the majority of the world’s electricity (Bloomberg). Disadvantages The sun, like the wind, is variable and fluctuates by location, weather, and time of day and year. Another disadvantage is cost, which makes solar “economical today in only some circumstances” (Makhijani 37). This relates to solar power’s low energy density and the need to transport it from the remote areas where it is often collected (Journal of the International EnergyAgency, 12). GEOTHERMAL Overview Geothermal energy involves harnessing heat from the earth’s crust to either generate steam for generators or for direct heating (NRDC). In 2011, geothermal resources provided an estimated 205 TWh, two thirds of which was for direct heat and the remaining for electricity (REN 21, 40). In the United States, geothermal energy produced just over 3,000 MW of energy in 2010, or half of one percent of all electricity used in the country. Costs According to the NRDC, a new geothermal plant would probably charge $.05 per kilowatt-hour or slightly more during high demand periods (NRDC). According to the U.S. Energy InformationAgency, the estimated average total system levelized cost for geothermal plants entering service in 2017 will be $98 per megawatthour (Exhibit C). Advantages Unlike solar and wind, geothermal energy is less variable as the earth shows no signs of cooling down from within. It is also abundant an all regions as, regardless of where you are, if you dig deep enough you will encounter the heat of the earth’s crust. This will be more of a factor as the same technology developed to tap fossil fuel deep within the earth i
More Less

Related notes for CAS CS 101

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.