Photovoltaic Solar Energy

1. Photovoltaic Solar Energy Building Industry Technology Academy Western High School

2. What is energy? • Energy is often defined as the ability to do work. • We commonly think of gas, electricity, or other fuels • Several different forms of energy, including kinetic, potential, thermal, gravitational, sound energy, light energy, elastic, electromagnetic, chemical, nuclear, and mass have been defined to explain all known natural phenomena. • The first law of “Thermodynamics” is that energy cannot be created; only transferred between systems • Is electricity created?

3. Solar Energy • The Sun gives of two forms of energy for free • Sunlight – solar radiation • This gives us both light and heat • Without it no life could exist on earth • Gravitational Pull • Along with the moon’s gravitational pull is responsible for the ocean tides

4. Sun Power

5. Free Energy • Our Sun releases huge amounts of energy • Our atmosphere, and clouds reflect or absorb about half of what is directed at us • What hits the surface of the earth in one hour, more than equals the total energy requirements for the earth for an entire year! • The sun is responsible for 99.9% of all renewable energy sources on earth • Wind, wave power, hydroelectricity, biomass & solar • Even petroleum products originated from the sun

6. How do we harness all that power?

7. The Solar Industry • Thermal • Using the Sun’s heat to generate electricity • Solar cooking • Solar hot water • Photovoltaic • Using solar radiation to generate electricity • Solar calculators, light meters, & photovoltaic cells

8. Photovoltaic • From the Greek word phos = light & volt = electricity • Solar cells are made from silicon crystals sliced thin and layered • Silicon is a semiconductor, electricity can pass but with high resistance • Solar radiation pushes electrons through

9. Solar Cells • About the size of your hand • Electrical contacts both front and back • Positive one side negative the other • Covered with antireflective glass

10. Photovoltaic system

11. Photovoltaic system

12. Solar panels • Most efficient solar panels available today 30 – 40% • Average solar radiation is 1000 watts per meter2 • Output of that panel would be 300 – 400 watts • Very costly roughly $800 per watt • Usually used in space • Common efficiency rating for panels 16% • Much more affordable cost of $4 - $5 per watt • Installed cost of system $7 - $9 per watt is common

13. Cost benefit analysis • Systems are sold on a per watt of output basis • Far easier to do a cost benefit analysis • First question asked by a salesperson: How much did you pay for electricity last year? • Easy to obtain information on current electric bill • System is sized to cover 70% to 100% of expected use • More is not better! • Utility companies do not pay for extra – credits only

14. Output of panels • Factors change the output of panels • Intensity of light source • Angle of light source • Panel temperature

15. Intensity of Light • Relative strength of solar radiation • Strongest is at the equator • Black dots represent the amount of sunlight needed to replace all of the world energy use • We receive 6000 times the amount of energy used

16. Angle of light • Best output is when light strikes at 90o to surface • Orientation is usually south • Suggested angle for best output is the same as the latitude of location • Summer and winter changes in sun angle • Tracking systems are optimal

17. Temperature • High temperature will reduce the output of solar cells • Cool temperatures are best, hot to the touch, is bad • Elevated installations are suggested, with air circulation under panels • Evens the playing field, northern climes can still have effective PV systems because of cooler temperatures

18. Inverter • Panels generate DC current (like a battery) • Inverter changes DC current to AC current and changes the voltage to 120/240 for home use • Systems are tied into home electric panel • During sunlight, if output is greater then home use, electricity is put into the power grid • Electric meter will spin backwards • At night, electricity will flow into house normally • This system is called a “Grid tie system”

19. Design • Many homes are designed for “net zero” energy use • Grid tie system, still use energy at night • Annual energy use is a net zero as panel output equals total home use. • Energy conservation is key to “net zero” design • Keyword – Sustainability • To live in a manner that is sustainable by the environment

20. Questions • What are the two types of energy we receive from the sun? • What are two general types of commercial solar energy? • What is the most common material used to make solar cells? • For a home application, should the homeowner require the most efficient solar panels available? Why? • Can you think of a way to analyze the cost of a system to see if it is cost effective to install in a building?

21. Questions • What factors should be considered in the cost analysis? • Would Southern California be a suitable location for a solar system? Why? • Use Google Earth or other mapping software off the internet to find out the Longitude and Latitude of this classroom. • When considering roof pitch, orientation and shading, which rooms on campus would make ideal locations for a photovoltaic solar system? • What information would you want to have from a client in order to prepare a bid to install a solar system?