ENVE203 Environmental Engineering Ecology (Dec 17, 2012)

ENVE203 Environmental Engineering Ecology

(Dec 24, 2012)

Elif Soyer

‘Renewable Energy & Nuclear Power’

Direct Solar Energy

Sun produces a large amount of energy

Only a small portion is radiated to Earth

Solar energy is different from fossil & nuclear fuels

• It is continuously available

• Dispersed over Earth’s entire surface rather than concentrated in highly localized areas

• Must be collected to make it useful

Direct Solar Energy

Solar radiation varies in intensity

Latitude

Season of the year

Time of the day

Cloud cover

Direct Solar Energy


Latitude

Areas at lower latitudes- close to the equator- receive more solar radiation annually than do latitudes closer to the North & South Poles.

Direct Solar Energy


Season of the year

Molar solar radiation is received during summer than during winter because the sun is directly overhead in the summer & lower on the horizon in the winter

Direct Solar Energy


Time of the day

Solar radiation is more intense when the sun is high in the sky (noon) than when it is low in the sky (dawn or dusk)

Direct Solar Energy


Cloud cover

Clouds

• Scatter

• Absorb

some of the sun’s energy, reducing its intensity

Cone-shaped, naturally formed compressed volcanic ash formations

The hardened material of the pillars is an efficient insulator and the cave dwellings remain cool in summer and warm in winter.

Homes in Urfa Turkey. They keep cool in summer and warm in winter

Direct Solar Energy

However, many modern buildings are designed with gas or electric heating & air conditioning, without attention to the potential advantages of direct solar heating (or shading to avoid heat in summer)

Heating Buildings & Water

Air inside a car sitting in the sun with its windows rolled up

Air inside a greenhouse

becomes much hotter than the surrounding air

Visible light from the sun penetrates the glass & warms th surfaces of the objects inside, which in turn give off infrared radiation- invisible waves of heat

Heat does not escape because Infrared Radiation cannot penetrate glass, and the air within the glass grows continuously warmer


Passive solar heating

A system of putting the sun’s energy to use without requiring mechanical devices to distribute the collected heat

Solar energy heats buildings without the need for pumps or fans to distribute the heat Depending on the building’s design & location, passive heating saves as much as 50% of heating costs

Passive solar heating designs

A solar sunspace can be added to the existing homes


Active solar heating

A system of putting the sun’s energy to use in which a series of collectors absorb the solar energy, & pumps or fans distribute the collected heat

Most common collection device: A panel or plate of black material Primarily use for heating water (household use or swimming pool)

Active solar water heating

Solar Thermal Electric Generation

Producing electricity in which the sun’s energy is concentrated by mirrors or lenses to either heat a fluid-filled pipe or drive a Stirling engine

Trough-shaped mirrors, guided by computers, track the sun for optimum efficiency, focus sunlight on oil-filled pipes, and heat the oil to 390 oC Heated oil water storage system water into superheated steam turns turbine to generate electricity


Heat can also be used in a Stirling Engine the air in a cylinder of the engine goes through a cycle of repeated expansion and contraction as it is heated by the air and cooled by the water, moving the engine’s piston up and down

http://en.wikipedia.org/wiki/Stirling_engine

http://upload.wikimedia.org/wikipedia/commons/e/eb/Beta_stirling_animation.gif

The world’s largest solar thermal system Mojave Desert in southern California, US

Solar thermal plants produce electricity at a cost of $0.95 to $0.13 per kWh

Solar thermal plants do not produce air pollution or contribute to acid rain or global climate change


Generating Costs of Electric Power Plants, 2010

Photovoltaics

A method of converting sunlight to electricity using layers of materials that either readily give up or absorb electrons

Sunlight excites electrons, which are ejected from silicon atoms. Useful electricity is generated when the ejected electrons flow out of the PV cell through a wire

Photovoltaics

PVs generate electricity with no pollution & minimal maintenance Used for any scale, from small, portable modules to large, multimegawatt power plants Disadvantage: PV solar cells are ony about 15% to 18% efficient at converting solar energy to electricity

number of solar panels needed for large-scale use would require a great deal of land

Photovoltaics

The cost of manufacturing PV modules is declining over years in 1975 $90 per watt in 2011 $3.38 per watt

The cost of producing electricity from PVs $0.15 – 0.25 per kWh

for natural gas $0.04 – 0.05 per kWh for solar thermal $0.05 – 0.13 per kWh

These photovoltaic panels are cost effective because they serve 2 purposes: They generate electricity & shade a parking lot

The world’s largest PV plant in Portugan It generates electricity to power 8,000 homes A reduction in 30,000 tonnes of greenhouses gas a year

Farm of solar panels in Leipzig, Germany 33,000 solar panels generate up to 5 MW of power to supply 1,800 homes

Photovoltaics

Future technological progress may make PVs economically competetive with electricity produced by conventional energy sources thin films dye-sensitized solar cells nano-scale PV technologies

Incorporating thin films into building materials tiles, window glass, roofing materials

In the past few years: > 120,000 Japanese homes have installed PV solar energy roofing California: committed to 1 million solar roofs by 2018

Indirect Solar Energy

Biomass:

Plant material, including undigested fiber in animal waste, used as fuel

Wind Energy:

Electric or mechanical energy obtained from surface air currents caused by solar warming of air

Hydropower:

A form of renewable energy that relies on flowing or falling water to generate mechanical energy to electricity

Combustion of wood & other organic material Green plants use solar energy for photosynthesis & store the energy in biomass

Windmills or wind turbines Damming of rivers & streams (solar energy derives the hydrologic cycle)

Biomass Energy

• One of the oldest fuels

Fast-growing plant & algal crops Crop wastes Sawdust & wood chips Animal wastes Wood

• Biomass contains chemical energy Sun’s radiant energy photosynthetic organisms

use to form organic molecules

Biomass Energy

• Renewable form of energy when used no faster than it is produced

• Biomass cannot replace fossil fuels

• Biomass fuel (can be a solid, liquid, or gas) is burned to release

its energy

• Biomass, particularly animal wastes can be converted into biogas

BIOGAS

• Biomass, particularly animal wastes can be converted into biogas

• A mixture of gasses (mostly methane) • Can be stored & transported like natural gas • Its combustion produces fewer pollutants than coal or

biomass: a clean fuel

Biomass Energy

LIQUID FUELS

• Biomass can be converted into liquid fuels, especially methanol (methyl alcohol) & ethanol (ethyl alcohol)

• Liquid fuels can be used in internal combustion engines

• Biodiesel is made from plant or animal oils, becoming more popular - Refined oil from waste oil

produced at restaurants - Biodiesel burns much cleaner

than diesel fuel

Biomass Energy http://www.renew-fuel.com/subproject5.php

Advantages of Biomass Use

• Reduces dependence on fossil fuels • Reduces waste-disposal problem (when wastes are used to

produce it) • Low levels of sulfur & ash produced compared with the

levels when bituminous coal is burned • It is possible to offset the CO2 released into atmosphere

from biomass combustion by increasing tree planting If biomass is regenerated to replace the biomass used, no

net CO2 is contributed to the atmosphere

Biomass Energy

Disadvantages of Biomass Use

• Biomass production requires land, water & energy shifting the balance of agricultural land use toward

energy production might decrease food production, contributing to higher food prices

• Burning wood faster than replant trees results severe

damage to the environment soil erosion, deforestation & desertification, air pollution

(especially when burned indoors) & degradation of water supplies

Biomass Energy

Disadvantages of Biomass Use

• Use of crop residues - crop residues prevent erosion by holding the soil in place - decomposition of crop residues enriches soil, decreasing

its future productivity

Biomass Energy

Wind energy capacity worldwide has increased by 20% to 45% in each of the last 10 years Wind is caused by heating of Earth’s surface is an indirect form of solar energy

Wind Energy

Wind Energy

Wind turbines can be huge- 100 m tall- and have long blades designed to harness wind energy efficiently

As turbines have become larger & more efficient, costs for wind power declined rapidly in 1980 $0.40 per kWh in 2010 $0.04 – 0.06 per kWh

Wind Energy

World’s top producers of wind energy: Germany & United States

Tehachapi Pass, Sierra Nevada in California The world’s largest concentration of wind turbines

Concern: Bird & bat kills Not building major bird migration pathway Painted blades Antiperching devices

Wind Energy

Wind produces no waste & is a clean source of energy Produces no emissions of SO2, CO2, or NOx

Wind Energy

Every kWh of electricity generated by wind power rather than fossil fuel prevents 0.5 – 1 kg of the greenhouse gas CO2 from entering the atmosphere

Hydropower

World’s major renewable source of electrical generation, producing about the same amount of electricity as do the world’s nuclear power plants The sun’s energy derives the hydrologic cycle Precipitation Evaporation from land & water Transpiration from plants Drainage & runoff

Hydropower generates ~ 19% of the world’s electricity most widely used form of solar energy

Hydropower

As water flows from higher elevations back to sea level, its energy can be harvested

Hydropower

A controlled flow of water released down the penstock turns a turbine, which generates electricity

The potential energy of water held back by a dam is converted to kinetic energy

Advantages & Disadvantages of Dams

Other Renewable Energy Sources

Geothermal Energy:

The use of energy from Earth’s interior for either space heating or the generation of electricity

Tidal Energy:

A form of renewable energy that relies on the ebb and flow of the tides to generate electricity

Natural heat within Earth - friction where continental plates slide over one another - decay of radioactive elements

Geothermal Energy

Disadvantage: Difficult to extract, geothermal is not likely to compete with wind, hydropower, or solar energy

just 1% of the heat contained in the uppermost 10 km of Earth’s crust

500 times the energy contained in all of the Earth’s oil & natural gas resources

=

Geothermal Energy

• Pressurized hot water pumped from underground generates steam in a heat exchanger.

• Steam turns a turbine & generates electricity.

• After its use, steam is condensed & recirculated.

• The cooler but still pressurized water is reinjected into the ground, reheated, and used again.

Alternate rising & falling of the surface waters of the ocean & seas that generally occur twice each day Result of the gravitational pull ofthe moon & the sun

Tidal Energy

Energy can be captured (with a dam across a bay or a turbine that works much like a wind turbine) and converted into electricity

Tidal power plants France, Russia, China, and Canada Global production is only a few MW Is not expected to increase much in the near future

ENVE203 Environmental Engineering Ecology (Dec 17, 2012)

Documents