Transcript Energy System Design: A Look at Renewable Energy

Energy System Design:
A Look at Renewable
Energy
Energy System Design Challenge
• Engineering Energy Solutions
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SAFETY!
Harness Renewable Energy
Store the Energy
Transport the Energy
Convert the Energy to light a light bulb
Bragging Rights:
Power Generated x System Efficiency x System Cost Index
System efficiency
Useful Work Output
Energy Input
System Cost Index
Minimum Total Energy System Cost .
Your Team Total Energy System Cost
Let us begin by reviewing the
Engineering Design Loop
Engineering Design Loop
Identify and Define
Engineering Design Loop
Research & Brainstorm
Engineering Design Loop
Select Best Solution
Engineering Design Loop
Communicate
Engineering Design Loop
Prototyping
Engineering Design Loop
Evaluate Solution
Engineering Design Loop
Refining
Engineering Design Loop
Communicate Solution
Since our design project has been
identified and defined, let us start with
some background information on
ENERGY SYSTEMS
Energy is an important commodity in the
modern world. We use it everyday in
many different ways. Here are some
examples:
– Transportation
– Entertainment
– Communication
– Personal Comfort
– Agriculture
– Manufacturing
As societies develop, more and more energy is
needed to sustain and improve the quality of
life. In the last century, worldwide energy use
has increased quickly. To meet these needs,
many different sources of energy have been
used.
With increasing modernization of both
advanced an developing countries, energy
needs are projected to continue rapid growth
To meet these needs, efficient and innovative new
energy systems will have to be developed. An
effective energy system has to harness the energy
and then provide the energy to the consumer in a
useable form on demand. For example, in order to
drive your car, many steps are involved.
Turning on the light in your room is another example of
an energy system with many steps.
Note in this example there is no storage step. Electricity
is difficult to store and must be continuously produced.
Our society has an infrastructure in place to provide
electricity continuously. When the existing
infrastructure can not meet demand, blackouts occur.
Using today’s technology, components of an
energy system may include:
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Methods to harness, collect or extract energy
Energy Conversion
Energy Storage
Transportation of Energy
Engineers develop new energy systems to
make the overall process as efficient as
possible. The technology allows the greatest
end usage from the energy collected.
Currently, fossil fuels (petroleum, coal, natural gas) are
the primary source of energy around the world. In
various forms, fossil fuels are used to power our cars,
heat our homes, light our cities and so much more.
NOTICE: 94% of our current energy consumption comes
from fossil fuels which are limited (non-renewable).
Because of the rapid rise of consumption, these
resources are being quickly depleted.
Our ability to meet the future needs of society lies in
the utilization of renewable sources. These are the
sources of energy which are essentially unlimited.
In hydropower systems, flowing water (which has kinetic
energy) spins a turbine, which runs a generator to
produce electricity.
Although this energy source has been utilized for a long
time, engineers face challenges with location, efficiently
capturing the kinetic energy, environmental concerns, and
conversion efficiency.
The equation shown below describes the
energy that can be collected from flowing water.
Ecollected = ½ • ρwater • v3 • Ac • t • ε
Where
Ecollected – energy collected
ρwater – density of water
v – water velocity
Ac – cross sectional area of the pipe or tubing
t – collection time
ε – efficiency of collection
Windmills can be used to
harness the energy available
from moving air. The rotating
blades of a windmill turn a
generator to produce electricity.
The challenges for engineers in
using wind energy include
location, efficiently capturing the
kinetic energy of the wind,
environmental concerns, and
conversion efficiency. Location
is a significant challenge since
windmills must be placed in a
windy space where there is
enough room for multiple
structures. Public acceptance of
their present is also necessary.
The equation shown below describes the
energy that can be collected from the wind.
Ecollected = ½ • ρair • v3 • Ab • t • ε
Where
Ecollected – energy collected
ρair – density of air
v – air velocity
Ab – area swept by the blade
t – collection time
ε – efficiency of collection
Light and heat are two forms of energy that can be harnessed
from the sun. Solar panels (solar cells) convert sunlight
directly into electrical energy. Other devices know as solar
collectors harness heat from the sun. This heat can be then
converted to other usable forms of energy. The challenges
for engineers in using solar energy include cost, location,
efficient capture of the sun’s energy and the environmental
impact of panel construction. Technological advances in
creating solar cells will make this renewable energy much
more feasible in the future.
The equation shown below describes the light
energy that can be collected from the sun.
Ecollected = I • As • t • ε
Where
Ecollected – energy collected
I – Solar intensity
As – area of the solar panel
t – collection time
ε – efficiency of collection
Energy must be available in a convenient form when and
where it is needed. To meet this need, there are a variety of
ways to convert energy from one form to another. The
conversion allows for easy storage and transportation of
energy.
A solar panel directly converts light into electrical energy
(electricity). In this case, the energy is already in a useable
form. In other words a solar panel acts both as a collection
and conversion device. When energy is in the form of
electricity it is relatively easy to transport across power lines.
However, energy in the form of electricity cannot be easily
stored.
A generator is a commonly used device which converts
kinetic energy to electricity. In the case of hydropower and
wind power, the kinetic energy associated with the movement
of water or air must be converted to a usable form.
Remember: when energy is in the form of electricity it is
relatively easy to transport across power lines. However,
electrical energy can not be easily stored.
A battery is another common conversion device that converts
electricity to stored chemical energy. However, unlike a
generator a battery can also store energy. Because they are
easy to transport, batteries are one of the most commonly
used energy storage devices. After the energy is stored in a
battery, it is converted back to electricity when used.
Batteries have two terminals: one is positive and one is negative.
Electrons collect on the negative terminal of the battery. If you
connect the two terminals with a wire, the electrons will flow from
the negative to the positive terminal, as electricity.
In addition to solar cells, generators, and batteries,
there are many other energy conversion devices.
A few of them include:
Internal combustion
engine:
Converts chemical to
mechanical energy
Fuel Cell:
Converts electrical to
mechanical energy
Electric Motor:
Converts electrical to
mechanical energy
Engineers combine all of the components we’ve talked
about to build efficient systems. The picture below will
remind you of the different possible steps that an
energy system may include.
The overall performance of an energy system is very
important and can be described by the equation below:
Overall System Efficiency = Useful Work Output
Energy Input
No system is ever 100 % efficient since energy will always
be lost to the surroundings. However, increasing system
efficiency is often an engineering design goal.
Remember that an energy system has many possible
components. The overall system efficiency depends on
the efficiency of each step in the process. Each step in the
process will result in an energy loss and therefore, a
decrease in the overall system efficiency.
For example, the chart below shows the efficiency of a
variety of different conversion devices.
Conversion Device/Process
Theoretical
Efficiency
Actual
Efficiency
Remarks
30 kW Steam Turbine
60 - 70%
10 - 15%
Chemical to Thermal to
Mechanical to Electrical
Coal Fired Power Plant
200 MW Steam Turbine
60 - 70%
30 - 35%
Chemical to Thermal to
Mechanical to Electrical
Single Cycle Gas Fired
200 MW Power Plant
60 - 70%
30 - 35%
Chemical to Thermal to
Mechanical to Electrical
5 - 30 kW Fuel Cell
> 80%
35 – 50%
Chemical to Electrical
200 MW Fuel Cell with Combined
Heating/Power
> 95%
45 – 75%
Chemical to Electrical
Chemical to Heat
Solar Cell
30 – 70%
10 – 15%
Light to Electrical
Battery
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60 - 90%
Electrical to Chemical to
Electrical
Internal Combustion Engine
60 - 70%
30 - 35%
Chemical to Thermal to
Electrical
Electrical Motor/Generator
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85 – 90%
Electrical to Mechanical
Incandescent Light Bulb
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5 - 10%
Electrical to Light
Compact Fluorescent Light Bulb
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20 – 25%
Electrical to Light
Wind Turbine
60%?
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Mechanical to Electrical
90%
Electrical to Electrical
Electrical Transmission
The example below shows how the overall system
efficiency decreases with each step of the energy
system. Note for the system below, only 15 % of the
energy collected is ultimately converted to useful work.
Below is another example of an overall system efficiency.
Note for this system, there isn’t a storage step. Power
plants provide electricity ‘on demand’ to customers
because electrical energy is difficult to store. In this
example, only 10 % of the energy collected is converted to
useful work.
Because the supply of fossil fuel is limited, engineers must
develop new methods and improve current technology for
harnessing renewable energy. In addition, it is important to
improve the efficiency of every step of existing energy systems.
Remember how much energy was lost in the previous two
examples. Increasing the overall system efficiency will allow more
of the energy collected to be converted into useful work.
Notice that if the energy system of the future is only 30 % efficient
overall, this system would provide two to three times the amount
of useful work compared to current systems.
In the future our society will be faced with many challenges
in the area of energy efficiency and conservation. Although
engineers of today are already facing these challenges, it
will be up to the engineers of the future to develop
sustainable energy solutions.
• Develop more efficient
energy systems
• Reduce energy
consumption through new
technology
• Reduction in cost, pollution
and energy use in the
manufacture of
photovoltaic cells
• Improve technology for
harnessing renewable
energy
• Improve energy storage
and transport technologies
• Develop new approaches to
conservation
Now that you have a better understanding of the
components of an energy system, let’s take a closer
look at some fundamental principles of engineering
and science related to these topics.
In order to successfully complete your design project, you
will need to be able to define and understand the
relationship between energy, work and power.
There are seven distinct forms of energy:
When you design your energy system, you will likely
have parts that move. So let’s take a closer look at
mechanical energy. In other classes you may have been
introduced to kinetic and potential energy.
Kinetic energy (KE) is the energy possessed by an
object because of its motion.
KE = (½) x (mass) x (velocity^2)
Potential energy (PE) results from an object's height. It
takes energy to lift an object. This energy is stored as
potential energy, which is released when the object falls
back to its starting position.
PE = (mass) x (acceleration due to gravity) x (height)
ENERGY IS THE CAPACITY TO DO WORK!!!
Work and energy have the same units and can be converted
from one to the other.
Work is done when a force acts on an object and causes it
to move. Work can be described by the following equation
Work = (Force) x (distance the object moves)
In an electrical system, this definition of work still holds.
However, in this case an electric field provides the force
which moves charged particles through a medium.
Caution!
Work and energy are not the same
thing. For example, you can
expend energy by pushing on a
door, but expending the energy
doesn’t result in work if the door
doesn’t move.
Power is the rate at which work is done.
It is defined as:
Power = Work / Time
In your design project, you are asked to illuminate a 0.4 W
light bulb for 15 seconds. So you will need to provide at
least 6 Joules of useful work.
To provide 6 Joules of useful work output from your
system, you will need to harness much more than 6 Joules
of energy. How much more will depend on the overall
efficiency of the system you design. Recall that some of
the examples had an overall system efficiency of only 10%.
To determine how much POWER is generated by
the energy system your group designs,
measurement of current and voltage can be used.
Power (Watt) = Voltage (Volts) x Current (Amperes)
Note: Voltage is work per unit charge
(or 1 Volt = Joule/coulomb)
Current is the rate at which
electrical charges move through a
conductor (1 ampere =
coulomb/second). A coulomb is
defined as the quantity of
electricity transported in one
second by a current of one ampere.
It is approximately equivalent to
6.24 x 1018 electrons.
You should have the background to embark
on your energy system design project
• Energy System Design Project
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SAFETY!
Harness Renewable Energy
Store the Energy
Transport the Energy
Convert the Energy to light a light bulb
Your design should
• Maximize Power
• Maximize System Efficiency
• Minimize Cost