Photovoltaic Solar EnergyBuilding 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 fuelsSeveral 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 systemsIs electricity created?

Solar EnergyThe 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 EnergyOur Sun releases huge amounts of energyOur atmosphere, and clouds reflect or absorb

about half of what is directed at usWhat 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 &

solarEven petroleum products originated from the sun

How do we harness all that power?

The Solar IndustryThermal

Using the Sun’s heat to generate electricitySolar cookingSolar hot water

PhotovoltaicUsing solar radiation to generate electricity

Solar calculators, light meters, & photovoltaic cells

PhotovoltaicFrom 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 CellsAbout the size of your handElectrical contacts both front

and backPositive one side negative the

otherCovered with antireflective

glass

Photovoltaic system

Photovoltaic system

Solar panelsMost efficient solar panels available today 30

– 40%Average solar radiation is 1000 watts per

meter2

Output of that panel would be 300 – 400 wattsVery costly roughly $800 per wattUsually used in space

Common efficiency rating for panels 16%Much more affordable cost of $4 - $5 per wattInstalled cost of system $7 - $9 per watt is

common

Cost benefit analysisSystems are sold on a per watt of output

basisFar easier to do a cost benefit analysisFirst question asked by a salesperson:

How much did you pay for electricity last year?Easy to obtain information on current electric

billSystem is sized to cover 70% to 100% of

expected useMore is not better!Utility companies do not pay for extra –

credits only

Output of panelsFactors change the output of panels

Intensity of light sourceAngle of light sourcePanel temperature

Intensity of LightRelative strength of solar radiationStrongest is at the equatorBlack dots represent the amount of sunlight needed to replace all of the world energy useWe receive 6000 times the amount of energy

used

Angle of lightBest output is when light strikes at 90o to

surfaceOrientation is usually southSuggested angle for best output is the same as the latitude of locationSummer and winter changes in sun angle Tracking systems are optimal

TemperatureHigh temperature will reduce the output of

solar cellsCool temperatures are best, hot to the touch,

is badElevated installations are suggested, with air

circulation under panelsEvens the playing field, northern climes can still have effective PV systems because of cooler temperatures

InverterPanels 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 gridElectric meter will spin backwards

At night, electricity will flow into house normally

This system is called a “Grid tie system”

DesignMany homes are designed for “net zero”

energy useGrid tie system, still use energy at nightAnnual energy use is a net zero as panel

output equals total home use.Energy conservation is key to “net zero”

designKeyword – Sustainability

To live in a manner that is sustainable by the environment

Questions1. What are the two types of energy we receive from

the sun?2. What are two general types of commercial solar

energy?3. What is the most common material used to make

solar cells? 4. For a home application, should the homeowner

require the most efficient solar panels available? Why?

5. 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?

Questions6. What factors should be considered in the cost

analysis?7. Would Southern California be a suitable location for a

solar system? Why?8. Use Google Earth or other mapping software off the

internet to find out the Longitude and Latitude of this classroom.

9. When considering roof pitch, orientation and shading, which rooms on campus would make ideal locations for a photovoltaic solar system?

10. What information would you want to have from a client in order to prepare a bid to install a solar system?