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 ( %) (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 % 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 W/m 2 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