Renewable Energy

Introduction

In the time of dire predictions about the effect of global warming, there are many questions that we need to ask about renewable technologies. Which technology can actually shift our carbon based economy to one that does not increase carbon dioxide in the environment? How will we meet our energy demands, and do we actually have the technology to do so?

Renewable energy includes fuels that are not "used up" or those that are naturally replenished. The most common renewable energy sources include solar energy, wind power, hydroelectric, biomass, geothermal and tidal power. Many of us who are concerned about our fossil fuel economy have hopes that renewable energy is a viable solution to our energy and climate problem. Yet, how feasible is it that renewable energies will replace fossil fuels as our primary energy source?

In 2006, renewable energy provided 6.85% of the total energy consumption in the United States [1]. Among the renewables, solar accounts for 0.07%, wind 0.26%, hydroelectric 2.89%, biomass 3.28%, and geothermal 0.35% of total energy use. The remainder was provided by nuclear power (8.2%) and fossil fuels (84.8%: coal and coke 22.6%, natural gas 22.4% and petroleum 39.8%). Since the 1980s, the proportion of total energy consumption provided by renewables has varied from a low of 5.5% in 2001 to a high of 8.9% in 1983. While the total amount of energy produced by renewable sources has increased since 1980, the proportion of renewables is smaller now because of the rise of nuclear power after the 1973 oil embargo [2].

Energy consumption is measured in several different units, in British Thermal Units (BTUs), as well as joules (kilojoules and mega joules), watts (kilowatts, megawatts and terawatts) and calories (kilocalories) [3]. I will use terawatts (TW), as used by Nate Lewis of California in his presentations and publications about global energy use. The world's total demand for energy in 2000 was 13 terawatts (TW), equivalent to 10 ^{1 2} watts. Of this total, the U.S. consumes approximately one-fourth; 3.3 TW in 1998. In 2005, world demand was 16.5 TW, and it is projected that world energy demand will be 28 TW by 2050 [4].

Because coal, oil and natural gas prices remain low compared to renewables, a financial incentive to switch to renewable sources of energy does not exist [5]. However, the incentive to shift to renewable energy sources is the profound evidence of global warming and predictions for future catastrophic changes, among them significant sea-level rise, desertification, and the loss of numerous plant and animal species. It is predicted that the atmospheric CO ₂ concentration, which has historically been 300 parts per million (ppm) or less, will be 750 ppm or more by 2050, according to the "business as usual" model presented by the International Panel on Climate Change (IPCC). To stabilize the carbon dioxide concentration of the atmosphere at 550 ppm, 20 of the 28 TW predicted to be used in 2050 should be produced using renewable energy [4].

What is the potential producing power of the renewable resources? Nuclear power could potentially contribute to the carbon-free energy demand, though it remains controversial because of the large amount of radioactive waste produced. To produce 10 TW of power, 10,000 1-gigawatt (GW) power plants would need to be built, which is more than 200 power plants per year for the next 50 years. Hydropower, while a very clean source of energy, cannot provide energy on a large scale. The power generating potential of every river, lake and stream on the planet is only 4.6 TW. Because most of the large rivers already have power generating dams in place, there is not considerable opportunity to increase the amount of power generated by hydropower, except on a small scale for local power production. Windpower has a potential generating power of 2 TW terrestrially, yet a considerable amount more if wind farms could be located in the oceans. At this time, the technology and efficiency for storing and transporting this energy does not make ocean wind farms a viable option [4].

Solar energy holds the greatest potential for replacing fossil fuels as our primary energy source, according to Nathan Lewis, Chemistry professor at the California Institute of Technology [4]. Enough energy from the sun strikes the Earth in one hour to supply all the energy consumed by humans in an entire year [5]. Based on this prediction, I chose to study a component of solar energy in depth, specifically the solar energy that is stored in plants and converted into the biofuels, ethanol and biodiesel.

My curriculum unit will focus on the biological sources of solar energy including biomass, which is burned (wood) or converted into fuel that can be burned (ethanol, biodiesel). Non-biological sources of solar energy are the rays of solar radiation that can be used passively to heat homes and water, or the rays that are collected by photovoltaic cells and stored to provide electricity. Both types of solar energy are renewable energy resources, and while they are only used in limited capacities currently, they have the potential to replace our fossil fuels in the future. Unfortunately, we have been accustomed to using coal, oil and gasoline for so long that many in our society, including our government, have an inability to envision a successful economy driven by renewable technology.

Biomass, in the form of ethanol and biodiesel, has recently received attention, even though burning of wood is an extremely old practice as is the fermentation of plants into alcoholic beverages. The energy stored in biomass is a result of solar energy, specifically a product of photosynthesis. While biomass is seen as a renewable technology, use of biomass instead of fossil fuels is not always a benefit to the environment. Burning or combustion of these materials does release greenhouse gases, but these effects can be reduced if biomass is used in certain ways.

Which biofuel is the best? Studies have shown that biodiesel has a considerably higher net energy gain than ethanol, though ethanol appears more widely used in the United States [6]. The rationale for usage of one fuel rather than the other appears to be directly related to politics and economics, with tremendous potential impacts on farmers and the food supply.