Introduction: Jaguar Creek

Jaguar Creek Environmental research and education center. 15 buildings occupying 10,000 square feet. Accommodates 50 people for short conferences or long semester stays. “off-the-grid” Own solar electric system. Back-up for rainy periods is gasoline-powered generator. Composting toilets and gray-water leaching fields

Lesson 14.1 Putting Solar Energy to Work

Renewable Energy Use in the United States (6.0% of total US energy)

Principles of Solar Energy Solar constant: 1370 watts per square meter Solar energy reaching Earth as radiant energy and entering the top of the atmosphere. About half of this energy makes it to Earth’s surface. Full sunlight can deliver about 700 watts per square meter.

Diffuse source: Abundant but widely scattered, varying with season, latitude, and atmospheric conditions. This leads to several problems with respect to solar energy…

Hurdles in Using Solar Energy Collection Conversion Storage Cost- effectiveness

Examples of Direct/Indirect Solar Energy Uses Direct Solar space heating Photovoltaic cells Solar-trough collectors Indirect Wind Water Hydrogen

Terms and Definitions: Solar Heating Systems Active: moves water or air with pumps and blowers Passive: moves water or air with natural convection currents or gravity

Flat Plate Collector

Photovoltaic cells

Passive Hot-air Solar heating 75% reduction in energy bills

Solar water heater 1 million residential and 200,000 commercial solar hot- water systems have been installed. So few because of the initial cost (5-10 times more than gas or electric).

Landscaping in Solar heating and cooling Design, positioning, and improved insulation, appropriate landscaping can contribute to heating and cooling efficiency.

Earth-Sheltered Housing Uses Earth as a form of insulation. Orient the building for passive solar heating.

Energy Star In 2001, the EPA extended its program to buildings and began awarding the energy star label to public and corporate buildings that use at least 40% less energy than others in its class and must pass a number of other criteria to qualify.

Solar Production of Electricity The two most feasible sources of solar energy: Photovoltaic cells Solar-trough collectors Converts 22% of incoming sunlight to electrical power at a cost of 8 cents/kwh

How Photovoltaic Cells Work Each cell consists of two thin mylar layers. Lower layer has atoms with single electron in outer orbit – easily lost. Upper layer has atoms lacking one electron in outer orbit – easily accepts electrons. Kinetic energy from sunlight dislodges electrons from lower layer – creates an electric potential between the two layers.

How Photovoltaic Cells Work The potential provides the energy for an electrical current through the rest of the circuit. Electrons from lower layer flow through a device back to upper side. Creates a potential difference. 20% efficiency from solar to electrical energy PV cells do not wear out however,

The Solar-trough Collector

How the Solar-trough Collector Works. The curved reflector focuses sunlight on and heats oil in the pipe. Heated oil used to boil water and generate steam for driving a conventional turbogenerator. 9 facilities in the Mojave Desert of California convert 22% of incoming sunlight to electrical power at a cost of $0.10 per kWh,,barely more than coal-fired facilities.

Pros and cons of Solar: Pros Pollution-free Sustainable electrical power Federal tax credit of up to $2,000 was enacted in the Energy Policy Act of 2005 Eliminates the hidden costs of other sources (air pollution, strip mining, greenhouse gas emissions, nuclear waste disposal… Cons Expense Only works during the day Requires back-up energy sources, e.g., Batteries Some climates not sunny enough

Million Solar Roofs Aims at encouraging the installation of solar energy units on a million residential and commercial rooftops by 2010.

CSP: Use reflecting surfaces to focus concentrated sunlight onto a receiver that transfers the heat to a conventional turbo generator. Solar trough Power tower Only work in areas of abundant sunlight.

Lesson 14.2 Indirect Solar Energy

Hydropower Water under high pressure flows through channels driving turbo generators. Amount of power generated is proportional to the height of the water behind the dam and the volume of the water that flows through. About 6.7% of US electrical energy. 17% worldwide. Most common form of renewable energy. Drawbacks: flooding, displacement of people and other organisms, interfere with migration, habitat distruction downriver from fluctuations in amount of water needed.

Three Georges Dam on the Yangtze River in China, completed Largest ever built. Displaced 1.1 million people to generate 18,000 MW of electricity. Replaced more than a dozen coal-fired plants. Only 2% of US rivers remain undammed.

Wind Power Wind turbine: most practical, wind blows on propeller blade geared directly to a generator. Wind farm: several turbines Pollution free, sustainable Size limitations of wind turbines Largest wind farm is the King Wind Ranch in Upton County, Texas % of global electricity.

Wind Power Pros Pollution free Can still be used for agricultural farming below turbines less than 5 cents per kWh. Amount of wind that can be tapped is immense. Cons Intermittent power Aesthetics Hazard to birds.

Bioconversion- biomass energy Energy derived from present-day photosynthesis Burning firewood Burning wastes Producing methane/alcohol All biomass sources combined give 7% total energy worldwide.

Examples of Bioconversion Burning firewoodBurning wastes Producing methane Producing alcohol

MTBE’s Methyl tertiary butyl ether. Petroleum derivative that has been used as a fuel additive to make the burning of gasoline cleaner. Improve air quality Known carcinogen Showing up in water supplies

Lesson 14.3 Renewable energy for transportation

Renewable sources for transportation Currently two are expanding globally: Ethyl alcohol Biodiesel Corn-based ethanol Reduces greenhouse gases by 13% Reduces reliance on foreign oil.

Fuel Cells: Benefits or Limitations? Device in which hydrogen or some other fuel is chemically recombined with oxygen in a manner that produces an electrical potential rather than initiating burning. Benefits Substitute for fossil fuels Pollution factor Limitations Production technology Portability National distribution system

Hydrogen Conventional internal combustion engines can be run on hydrogen gas in the same manner as they are now on natural gas No CO 2 or hydrocarbon pollutants are produced.

Lesson 14.4 Additional Renewable-Energy Options

Additional Renewable Energy OTEC- ocean thermal energy conversion. Experimental Uses differences in ocean temperature to produce power. Geothermal Using heat in Earth’s interior to heat buildings or drive turbogenerators. Tidal Using the daily rise and falls of the tides to turn turbines

Lesson 14.5 Policy

Aspects of U.S. Energy Policy Mandates to increase fuel efficiency in cars Exploitation of public lands for fossil fuel reserves Subsidies to producers of solar energy technology Research and development on alternative energy technologies

DIRECT SOLAR ENERGY, BIOCONVERSION, AND OTHER SOURCES OF ENERGY Figure 14-27