MITES Middle School Introduction To Engineering Systems
2 A couple of reminders Today s lecture will be quite brief, (yay!)so please stay as quiet as you can and avoid playing with any of the items on the tables (including your own pencils, sticky notes, and notebooks = only use these for note-taking and questions!) Please DON T SWIVEL IN THE CHAIRS!!! I know it s tempting (even for me), but it s distracting to your peers! Don t forget that you are responsible for creating a poster on a topic we have covered, so please pay attention!
3 Objectives of Today s Lesson Understand solar energy and describe the ways we can use it. Understand the basic structure and function of a Photovoltaic Cell (and how it creates electricity). Understand what a Microgrid is and how we will use it (Dr. Islam).
4 Harnessing Solar Energy to Create Electricity
Solar Energy A Bright Idea! I d put my money on the sun and solar energy. What a source of power! I hope we don t have to wait til oil and coal run out before we tackle that. - Thomas Edison
Bet ya didn t know: People have been harnessing solar energy for a long time! Solar collector for heating water A home in California in 1906
SO, WHERE IN AMERICA DO YOU THINK WE CAN GET THE MOST SOLAR ENERGY?
WHY?
Sun Angles A little review of the sun and the seasons.
10 Now that we have reviewed some facts about the sun, let s focus on how we can use the HUGE amount of energy it makes available to us!
Two Main Categories: Solar Thermal Solar Photovoltaic (PV) Water heating and cooking Electricity production *OUR FOCUS
Solar Thermal Energy Technology Cooking Water Heating
Solar Water Heating
How Does it Work?
Solar Thermal Energy Technology Cooking Water Heating
Solar Cooking
Benefits of Solar Cooking Consumes no fuels/wood Generates no air pollution and no greenhouse gases Produces no smoke Eliminates fire dangers
More Benefits of Solar Cooking Eliminates work No daily search for firewood 2 Billion people rely on wood for cooking fuel! Cooks foods slowly and thoroughly Preserves nutrients Foods will not burn
Solar Cooking How Long Does it Take? Vegetables/Rice /Wheat: 1.5-2 hrs Beans: 2-3 hrs Meats: 1-3 hrs Bread: 1-1.5 hrs
Two Main Categories: Solar Thermal Solar Photovoltaic (PV) Water heating and cooking Electricity production *OUR FOCUS
Solar Electric Systems (Photovoltaic Cells)
Solar Electric Systems Photovoltaic (PV) systems convert light energy directly into electricity. Commonly known as solar cells. The simplest systems power the small calculators we use every day! More complicated systems will provide a large portion of the electricity in the near future.
How Does it Work? Sunlight is composed of photons, or bundles of radiant energy. When photons strike a PV cell, they may be reflected or absorbed (transmitted through the cell). Only the absorbed photons generate electricity. When the photons are absorbed, the energy of the photons is transferred to electrons in the atoms of the solar cell.
How Does it Work? Solar cells are usually made of two thin pieces of silicon, the substance that makes up sand and the second most common substance on earth. One piece of silicon has a small amount of the element boron added to it, which gives it a tendency to attract electrons. It is called the p- layer because of its positive tendency. The other piece of silicon has a small amount of the element phosphorous added to it, giving it an excess of free electrons (and a negative tendency). This is called the n-layer because it has a tendency to give up negatively charged electrons.
How Does it Work? When a photon strikes the PV cell, its energy is used to push one of the extra electrons contained on the n-layer (negative layer) of silicon into the circuit. The pushed electron will travel through the circuit until it reaches a hole in the p-layer (positive layer) of silicon, giving us an electrical current as it travels (*remember, + and charges attract one another).
How Does it Work?
Helpful PV Animations Let s keep it quick and simple!
Some cool pictures 28
29 What is this guy DOING? Why do you think we included this picture? How can this apply to harnessing solar energy?
Solar Concentrators The concentrators use an array of mirrors to focus sunlight onto highefficiency solar cells. Four supports hold the cells in front of the mirrors. The supports also supply cooling water and electrical connections
Concentrators are COOL! 31
What variables can have an effect on the amount of PV Cell Conversion Efficiency? Wavelength of light hitting the PV device Recombination of electrons with holes before ever entering the current Continued 32 Photovoltaic Cell Conversion Efficiency = A fancy way of saying the amount of solar energy that shines on a PV device that is actually converted into electrical energy we can use.
33 Photovoltaic Cell Conversion Efficiency (continued ) Natural Resistance of certain materials to electron flow Temperature (works best under low temp; too hot = not very efficient) Reflection of photons by the materials (=antireflection is super important!) Electrical Resistance (must maintain constant contact with grid for good conduction) Angle of the PV cell (must be at optimum angle to absorb the most photons)
34 PV Panel Installation and Angle Efficiency Let's think about how you would place a photovoltaic (PV) panel on a roof to get the maximum amount of energy output from it: Should the PV panel be installed flat against your roof so that it has the same slope as the roof, or would it be better for it to lie horizontally and point straight up into the sky? Should it stand up on its edge, vertically? Would the direction you oriented it matter?
35 What do you think? From the our review, you learned that the angle at which the sun hits the Earth changes quite often. How could we compensate for this with the installation of our PV panel?
36 PV Cell Angle Efficiency INQUIRY What is the best angle and orientation at which to install the PV panel so you can get the most efficient use of the sun s energy over the course of the year at your specific location? A New Angle on PV Efficiency : Activity 1 ONLY
37 A New Angle on PV Efficiency INQUIRY Each group of 5-6 will need the following materials: Mini PV panel Multimeter and 2 wires with alligator clips 100-watt lamp 2 pieces of cardboard (same size as panel) Protractor Duct tape 1 set of instructions with 1 investigation worksheet per group ONLY
38 A New Angle on PV Efficiency INQUIRY THIS IS CALLED AN INQUIRY FOR A REASON YOU AND YOUR LAB MATES ARE INQUIRING ABOUT THIS TOPIC, SO SOME CONFUSION AT FIRST IS NORMAL AND EXPECTED! PLEASE FOLLOW YOUR DIRECTIONS AND IF YOU ARE HAVING TROUBLE, MAKE SURE YOU CONSULT THOSE BEFORE GIVING UP!
39 A New Angle on PV Efficiency INQUIRY Experimental Set-Up Step 1: Go to your station with your lab mates Step 2: Support your solar panel (using cardboard pieces and tape) See Fig. 1 Step 3: Connect the + and pins to the mulitimeter and to the the PV panel Step 4: Turn multimeter on (make sure it is on DC and measuring in ma) and place the panel 1-2 feet directly under the lamp. Step 5: Point the PV panel directly at the lamp and tape the base to the table to prevent movement.
40 A New Angle on PV Efficiency INQUIRY Experimental Set-Up Step 6: SKIP Step 7: Lay the panel completely flat and record the current for this angle (0º) on your worksheet. Step 8: Make sure your protractor is centered at the front edge of the PV panel EACH TIME YOU MEASURE for accurate data. Step 9: Repeat the procedure in STEP 7 with varying increments by 10º and continue to record data on your worksheet. Graph results!
41 Now, please direct your attention to Dr. Islam who is here to discuss the Microgrid!
42 THE PARKING LOT ANY questions you may have, POST EM HERE!
43 References The KidWind Project http://learn.kidwind.org/teach (Accessed 6.13.2012) A New Angle on PV Efficiency http://www.teachengineering.org/view_activity.ph p?url=collection/cub_/activities/cub_pveff/cub_pv eff_lesson01_activity1.xml (Accessed 6.13.2012) The Solar Panel and Electric Motor http://www.swe.org/regionb/b007/documents/sola rsource.pdf (Accessed 6.13.2012) U.S. Department of Energy (Energy Basics) http://www.eere.energy.gov/basics/renewable_en ergy/pv_cell_conversion_efficiency.html (Accessed 6.18.2012)