Alternative Energy

Light Waves

Hydrogen

Photovoltaic Cells

• Made from semiconductor materials

• Produce useful current flow when illuminated with light

Solar Modules

• Produces Direct Current Electricity

• Commercially Available

• Rated by Volts and Watts per Module

Advantages

• Silent • Have no moving

parts • Cause no

environmental pollution in operation

• Never run out

Advantages Cont.

• Can generate power where it is needed, without the need for electricity pylons and wires.

• Work in cloudy weather and are more efficient in low temperatures

• Are not unsightly

Method of Operation

• Three main types– Monocrystalline – Polycrystalline

– Amorphous

Monocrystalline

1. single crystal cells o The first generation of solar cells o excellent conversion rate (12 - 16%)

(23% under laboratory conditions)BUT,

o making them is a painstaking, therefore expensive process

o another drawback - it takes a lot of energy to obtain pure crystal

Polycrystalline

Lower production costs, requiring less energy to make

11 - 13% conversion efficiency (18% in the lab

Amorphous o a more recent technology (mid-70's) o lower production costs, but unfortunately

also o lower efficiency (8 - 10%) (13% in the lab)

Light Energy

• Photons are Phrens

• Light as a wave

• Light as a particle– Photons– Work horse of electrical production

How Does It Work?

• Pure silicon four electrons in outer shell

• Very stable at ambient temperature

• Shares electrons with companions a pair at a time

• Engineers intervene with doping– Deliberate contamination– Deliberate motives

N-Type Semiconductor

• N= negative (electrons are negative charged• Extra electrons from arsenic or phosphorus• Counting atoms at the moment

P-Type Semiconductor

• P= Positive (electron holes are not negative)• Deficient electron shells from gallium or boron• Still counting atoms

N-P Junction

• Where the action occurs

Finally Physics

Power to the People

• One square meter of solar panels can produce up to 150 watts of maintenance-free power for up to thirty years

• The voltage produced by PV panels remains roughly the same regardless of the weather, but the current (amps) and the power (watts) will vary

More Power

• A panel's power is expressed in peak watts, the number of watts it will produce in optimal conditions, i.e. at noon in direct sunlight in cold weather

• Maximum sun intensity is 1.000 W/m2

• VOLTS  x  AMPERES  = WATTS

Configurations

A 12-volt PV panel producing 4 amperes of current has 48 watts of power

News and Discoveries

• Thin Film Technologies • Virginia Tech • Ionic Self-Assembled Multilayers (ISAM)

– nanometer-thick layers of materials – using polymers and molecules called

fullerenes

• Organic dyes from berries• Innovation continues