P2a (i) Collecting Energy from the Sun www.PhysicsGCSE.co.uk P2a (i) Collecting Energy from the Sun You will learn about: Photocells and how they work Where photocells may be used

Solar Energy www.PhysicsGCSE.co.uk REMEMBER: Some of the Earth’s most beautiful sites are of sunrises and sunsets. Solar energy provides earth with a source of energy – without it life would not exist. Plants depend on light for photosynthesis and animals depend on the heat to keep them warm. Solar Energy A solar cell uses the Sun’s light and changes it into electricity. They are used on houses, streetlamps and also satellites in space. A photocell changes light into electricity. It does not have to come from the Sun. Photocells work better when they have a larger surface area or when the light intensity is high. They are good alternative to power stations when transmitting electricity is difficult like I space. Photocells produce direct current like a battery. This means the current flows in One Direction. Not this kind of One Direction… REMEMBER: Photocells change light into electricity. Solar Cells use Solar energy. Photocells are also called photovoltaic cells. This kind of One Direction!

www.PhysicsGCSE.co.uk Why use a Photocell? Photocells can be seen in more places than ever before. This is because there are so many advantages: Electricity is made from a renewable resource Once built, no pollution is made so there is no contribution made to the greenhouse effect They are robust and well built and need little maintenance No fuel or cables are needed to make them work This image shows how engineers have found another way to make a street lamp work. When a car or lorry passes at high speed the wind caused by the vehicle turns the turbine on the street lamp and generates direct current electricity. However, if the cars do not pass or if it is not windy, or if there is no light for the photocells above, then electricity cannot be generated.

How Photocells Work www.PhysicsGCSE.co.uk e- p-type silicon + - REMEMBER: Photons cause electrons to be knocked out of place. Therefore a hole remains ready to be filled by a new electron. Photocells are made of p-type silicon and n-type silicon. Silicon is a neutrally charged material. If boron is added then there is an absence of free electrons. These absences are known as holes. This is known as p-type (positive) silicon. If phosphorus is added then there are more free electrons increasing the ability to work as a conductor. This is known an n-type (negative) silicon. e- Light is made of packets of energy called quanta or photons. These photons are absorbed by the silicon and cause electrons in the n-type silicon to become knocked loose. They move into the electric field and then flow in a circuit by Direct Current. A voltage has been made. When this happens ‘Positive Holes’ are made in the opposite direction to the electron movement. p-type silicon When p-type and n-type silicon are put together they create an electric field between them. This is called the p-n junction + load - n-type silicon Factors affecting the current, or power, produced by a photocell. Current is directly proportional to: Light intensity (directly proportional) Surface area (directly proportional) Distance from light source (1/d2 proportional)

Questions What is the difference between a photocell and a solar cell? www.PhysicsGCSE.co.uk Questions What is the difference between a photocell and a solar cell? A street lamp has a solar cell connected to it. It is not necessary for the lamp to shine during the day. How does the lamp shine at night if there is no sunlight to make it work? Solar cells are placed on South facing roofs in England. Where would they be placed on an Australian house? What is the charge of a hole in a photocell?

www.PhysicsGCSE.co.uk Questions What is the difference between a photocell and a solar cell? Photocell uses any light. Solar cell uses light from the Sun. A street lamp has a solar cell connected to it. It is not necessary for the lamp to shine during the day. How does the lamp shine at night if there is no sunlight to make it work? During the day a battery, or capacitor, is charged up ready to be used at night. Solar cells are placed on South facing roofs in England. Where would they be placed on an Australian house? North facing. What is the charge of a hole in a photocell? Positive