Energy System Design: A Look at Renewable Energy

Energy System Design Challenge Engineering Energy Solutions –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: 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. E collected = ½ ρ water v 3 A c t ε Where E collected – energy collected ρ water – density of water v – water velocity A c – 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. E collected = ½ ρ air v 3 A b t ε Where E collected – energy collected ρ air – density of air v – air velocity A b – 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. E collected = I A s t ε Where E collected – energy collected I – Solar intensity A s – 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/ProcessTheoretical Efficiency Actual Efficiency Remarks 30 kW Steam Turbine % %Chemical to Thermal to Mechanical to Electrical Coal Fired Power Plant 200 MW Steam Turbine % %Chemical to Thermal to Mechanical to Electrical Single Cycle Gas Fired 200 MW Power Plant % %Chemical to Thermal to Mechanical to Electrical 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 Cell30 – 70%10 – 15%Light to Electrical Battery? %Electrical to Chemical to Electrical Internal Combustion Engine % %Chemical to Thermal to Electrical Electrical Motor/Generator?85 – 90%Electrical to Mechanical Incandescent Light Bulb?5 - 10%Electrical to Light Compact Fluorescent Light Bulb?20 – 25%Electrical to Light Wind Turbine60%??Mechanical to Electrical Electrical Transmission90%Electrical to Electrical

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 electrons.

You should have the background to embark on your energy system design project Energy System Design Project –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