Photovoltaic Solar Energy Building Industry Technology Academy Western High School

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?

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

Sun Power

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

How do we harness all that power?

The Solar Industry Thermal Photovoltaic 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

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

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

Photovoltaic system

Photovoltaic system

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

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

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

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

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

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

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”

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

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?

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?