Renewable Energy What parts of nature can we harness to generate renewable energy?

Renewable Energy  Renewable energy, is energy that originates from a replenishable source.  Renewable energy is important because it does NOT require the existence of limited resources, and because it does not lead to significant pollution.

Solar Energy  The sun’s rays can be harnessed for the purposes of heating and electricity.  Both passive and active uses of solar energy occur.

Solar Energy  Passive solar heating refers to using the sun’s energy for direct heating purposes. This allows buildings to avoid expending fossil fuels for the purpose of heating and cooling.  Since the sun’s energy is not constant over time, these buildings need quality insulation to maintain their temperature.

Solar Energy  Buildings that use passive solar heating are designed to take advantage of the sun’s position in the sky.  During summer, the sun takes a high arc in the sky; these buildings have an overhanging roof to help stay cool.  During winter, the sun takes a low arc in the sky; these buildings have large windows to collect added sunlight.

Solar Energy  In the Northern Hemisphere, south-facing windows receive the most sunlight, so these windows will be the largest.  These windows are also double-paned, so they function as additional insulation during nights.

Solar Energy

 Solar energy can also be directly collected and converted to thermal energy. This is active solar heating.  During active solar heating, solar energy is collected with roof-mounted collectors, and used to heat liquid. This liquid is later used to heat the building’s water supply.  8% of all energy spent in the U.S. is used to heat water, so this can help conserve other fuel sources.

Solar Energy  Photovoltaic cells are used to collect solar energy and convert it to electrical energy.  Individual solar cells can only produce a small electrical current. Solar panels are formed by lining up multiple solar cells together, but supplying all the energy for a small city would still require hundreds of acres of solar panels.

Solar Energy  Despite this drawback, research continues to make solar cells more efficient and less expensive.  Solar cells are useful for providing energy throughout the developing world, where energy consumption is low and distribution networks quite limited.

Wind Energy  The sun’s energy heats the Earth’s surface unevenly. This produces air masses in the atmosphere, otherwise known as wind.  We can harness wind to generate electrical energy. Windmills are essentially a mounted turbine and generator; the turbine collects the wind’s kinetic energy and converts it to electrical energy.

Wind Energy  Wind farms are large arrays of wind turbines laid out over a large area.  Wind farms can small, consisting of 20 turbines in small rural areas. They can also be large, and capable of supplying energy to over 500,000 homes.

Wind Energy  The cost of wind energy has fallen as technology has become more efficient. Wind energy is currently the fastest- growing energy source in the world.  The greatest drawback to wind energy is figuring out how to transport wind- generated energy from the turbine to cities where it will be used – in an efficient manner.

Biomass  Any natural material – such as plant material or manure – is considered a biomass fuel.  Biomass fuels are organic and renewable. Contrast with fossil fuels!  Renewable biomass fuels are heavily used for heating and cooking in the developed world.  Wood and dung are common examples.

Biomass  However, biomass fuels produce air pollution, and acquiring these sources can also cause ecological damage.  This is especially true of wood/timber and dung!

Biomass  Methane is one of several byproducts made during the decomposition of organic wastes.  Methane can be burned as a fuel for heating, cooking and electricity.  In China, more than 30 million households use biogas digesters to produce methane.  In the U.S., several landfills use methane from decomposing waste for electricity.

Hydroelectric Energy  Recall the water cycle – precipitation forms streams and rivers that run back to the ocean. The kinetic motion of these waterways can be harnessed to make electrical energy.  Hydroelectric energy is the process of converting this kinetic energy to electricity.

Hydroelectric Energy  20% of the world’s energy comes from hydroelectric generators.  China, Canada, Brazil, the U.S. and Russia are the world’s top countries in using hydroelectric energy.

Hydroelectric Energy  Hydroelectric dams are used to block natural water flow. This creates a reservoir, or large lake for energy use.  The reservoir will be slowly released, converting the reservoir’s potential energy to kinetic energy.  Much like coal and wind power, a turbine is used to collect this kinetic energy, and a generator produces electrical energy.

Hydroelectric Energy

 Hydroelectric dams are expensive, but are also very cheap to maintain. Contrast with nuclear energy.  Hydroelectric dams never release airborne pollutants. They also last longer than a typical fossil fuel power plant.  Dams can also provide other benefits, such as drinking water, irrigation and flood control.

Hydroelectric Energy  Large hydroelectric dams block a river’s natural flow. This can have serious ecological consequences.  Flooding created by the reservoir causes mass displacement of communities.  Decaying plant matter that gets trapped within the reservoirs releases large amounts of methane and other greenhouse gases.

Hydroelectric Energy  Large hydroelectric dams block a river’s natural flow. This can have serious ecological consequences.  The dam blocks further deposition of rich sediment, which makes farmland downriver less productive.  Cutting off different parts of the river can disrupt established food webs and habitats.

Hydroelectric Energy  Micro-hydropower uses a small turbine to collect energy from a stream, WITHOUT having to construct a dam.  This operation is cheaper and less destructive than large-scale hydroelectric energy. It is best suited for providing energy to small isolated areas.

Bell Ringer 1. Identify two benefits and two drawbacks to hydroelectric dams. 2. Describe two ways the home to the left keeps warm in winter.

Geothermal Energy  Some parts of Earth have underground reservoirs of water, reservoirs that are being heated up by energy from the Earth’s mantle.  In geothermal energy, these reservoirs are drawn to provide kinetic energy for a turbine, which allows a generator to convert the kinetic energy to electric.  These reservoirs must be managed, to avoid overuse.

Geothermal Energy  The U.S. is the world’s largest user of geothermal energy, and the world’s largest geothermal plant in the Geysers in California (725,000 households).  The Philippines, Iceland, Japan, Mexico, Italy and New Zealand also make use of geothermal energy.

Geothermal Energy  Geothermal heat pumps are used in over 600,000 households in the U.S. These heat pumps circulate fluid from deep underground to surface level, and back again.

Geothermal Energy  The ground’s temperature is constant throughout the year. As such, it is warmer than the air in winter, and cooler than the air in summer.  Geothermal pumps are useful for moderating household temperatures.

Developing Energy Tech. What energy sources are we looking at for the future?

Alternative Energy  Alternative energy refers to energy sources that are currently in development.  Perhaps the energy source is still in the theoretical stage…  …or perhaps it still needs to be made practical.

Tidal Energy  Tidal energy works very similarly to a hydroelectric dam. Instead of using running water, a tidal power plant traps sea water behind a gate during high tide.  Then, the water is released during low tide. The trapped water returns to the sea. In the process, a turbine is used to collect kinetic energy, and convert it to electrical energy.

Tidal Energy

OTEC  Recall that the sun’s energy only penetrates the ocean to a certain depth. Because of this, surface and deep waters have a significant temperature difference.  Ocean thermal energy conversion (OTEC) seeks to use this difference for the purposes of electricity.

OTEC  First, warm surface water is drawn into a vacuum chamber. Given low pressure, water boils at low temperatures, so the warm water is boiled using very low levels of energy.  The evaporated water becomes steam, which spins a turbine. This converts kinetic energy to electrical energy.

OTEC  Next, cold water from the deep ocean is used to cool the steam, condensing it back to water, so it can be used again.  The cold water heats up in the process, so it is returned to the surface as warm water.  Fresh water is made as a byproduct of this process.

OTEC

 OTEC remains impractical today, as pumping deep water to the surfaces uses about one-third of the energy that would be produced.  Also, the ecological consequences of continually pumping deep water to the surface remains unknown.

Hydrogen Fuels  Hydrogen gas (H 2 ) can be burned as a fuel, much more cleanly than fossil fuels.  While hydrogen is the most abundant element in the universe, H 2 does NOT exist naturally on Earth.  This means we have to extract it from other compounds, such as H 2 O or CH 4.

Hydrogen Fuels  As such, hydrogen fuels require an input of energy at some point before they can be produced.  This energy may come from renewable or non-renewable sources!  Hydrogen fuel cannot be made very efficiently today. Furthermore, it is not very efficient, and so must be compressed before it can be a viable fuel.