P2

P2

1. Photocells

   • Advantages
     • Robust, low maintinance
     • No fuel or long power cables needed
     • Does not contribute to global warming- no pollution
     • Renewable energy source
   • Disadvantages
     • Doesn't work when cloudy or bad weather
   • How they work
     • Contain two seperate pieces of silicon joined together to make a p-n junction
       • The p silicon has impurity added to produce an absence of electrons
       • The n silicon has a different impurity added to produce an excess of electrons
     • The suns rays produce photons which are energy packets.
       • They cause free electrons to move producing an electric current.
     • Better when
       • Surface area of photocell is large
       • Sunlight is more concentrated/ intense/ more photons
       • The distance between the light source and photocell is less