Energy and

Society

Physics 20051 Society Technology and Values 20304

Professor Ani Aprahamian

Renewal Energy Resources almost inexhaustible…

Now we will start talking about Solar/Wind/Hydropower

Solar Power 101 - how does sunlight turn into electricity

http://www.youtube.com/watch?v=DFDn6eTV0jQ

http://www.youtube.com/watch?v=K76r41jaGJg&feature=related

How does the sun gets the energy?

Energy from the Sun comes in the form of …

Travelling at the speed of light c (3x109m/s)…

http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg

Different colors have different energies

c=lf speed of lightEnergy of electromagnetic waves = hf

h is planck’s constant = 6.626 x10-34 Jsf is the frequency of the wave…..f=c/l

Spectrum of the Sun. The Sun emits most of its radiation in a wavelength band between 0.1 and 4.0 micrometers (µm).

Spectrum of the Earth. The Earth emits most of its radiation in a wavelength band between 0.5 and 30.0 micrometers (µm).

Solar Constant = 2 cal/min.cm2

Power= Energy/time

Power/Area= Energy/Area.time =esT4

http://videos.howstuffworks.com/general-electric/609-ges-photovoltaic-technology-helps-grow-vineyard-video.htm

http://videos.howstuffworks.com/hsw/6195-energy-solar-energy-video.htm

http://videos.howstuffworks.com/discovery/41268-powering-the-future-solarvideo.htm

Quantum Physics…Blackbody RadiationStefan Boltzman nconstant…..

frequency and wavelength….PhotoElectic Effect

e Is a property of the surface

Renewal Energy Resources almost inexhaustible…

If we have such inexhaustible solar energy…~6000 Times more than all of humanity’s energy needs….

What is the problem?1. Not all of the Electromagnetic Spectrum is absorbed2. Solar cells have to be sensitive to visible part of EM spectrum3. Efficiency of solar cells4. Storage of Energy 5. Not there when it is cloudy…less there in the winter…6. Not there at night

Solar cells: Improve efficiency and cost!!!!!!!!!!!!!!

Now 10-15% of solar energy is converted into electrical energy

Research cells…up to 30% efficiency..not yet deployed in market

Photovoltaics is the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.

Photovoltaic modules and arrays produce direct-current (dc) electricity. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.

Example………….The roof area of an average home is 150 m2 and that of a car is about 7m2.The average US household energy consumption is 3.5 kW.a. How does this compare with the mid-day solar power incident on a typical house roof?b. How about a 300 horsepower car?c. Is it practical to have totally powered solar cars and homes?

Sun shines at 1 kW/m2 what determines this???

House: 1kW/m2 x 150m2= 150 kW

Car: 1 horsepower = 0.75 kW so…300 horsepower = 300 x 0.75 kW=225 kW Sun shining with 1 kW/m2 x 7 m2 =7 kW

How big is the annual electricity budget for the College of Science?The College of Science uses about 25,283,000 kwh a year, costing about $1,264,000.

What’s the environmental impact of all this electricity?Electricity production for the College of Science produces about 16,400 metric tons of carbon dioxide emissions. That’s like putting over 3,500 cars on the road.

Why does the Challenge only include electricity and not heating and cooling?Steam and chilled water are not monitored accurately enough by our current metering system to be used in a competition.If heating and cooling are not included, why does it help to report thermostat problems?In addition to the steam and chilled water used for heating and cooling, electric fans are used to blow the heated or cooled air into rooms. By ensuring that thermostats work properly and that rooms aren’t being over-conditioned, electricity use for these fans is reduced.

Example…………. (like problem 40 in Chapter 21)

What area of typical photovoltaic cells would be needed to produce 25,283,000 kwh a year of electrical power (amount needed by the College of ScienceAt Notre Dame?

Typical single crystal silicon 10 cmx 10cm photovoltaic cell can give 1.5 W of power under full sunlight of 1 kW/m2

25.283 x 109 Wh/yr x 1yr/8766 hrs= 2.8842 x 106 W

28.842 x 105 W/ 1.5 W per cell = 1.923 x106 cells

Each cell has an area of 100 cm2

1.923 x106 cells x 100 cm2/cell= 1.923x 108 cm2 or 1.923 x 104 m2

Each square meter is about 10.76 square feet….

Or 207,000 square feet

including end zones - 57,600 (160 W X 360 L) area of football stadium…..