Try to answer all of these questions. Be prepared to share your answers with a partner, and with the rest of the class.

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1 U1YESCO Module 21: Photovoltaic systems - 'Photovoltaic' (or PV for short) means turning light into electricity Solar PV systems provide electricity from sunlight They can provide power for a wide variety of uses Calculators, lights,, ~ fridges, homes and even whole -, villages or towns can use solar electricity as their energy source " 0 00 / I / ~ A solar panel is made up of lots of small cells linked together Each small cell produces a tiny electric current when the Sun shines on it They can do this because they are made of materials called semi-conductors Solar panels can then be linked to form a large solar PY array producing a lot of electricity Solar py systems produce electricity without noise, moving parts to wear out, or pollution One of the advantages of solar electricity is that you do not need to have a power station sending electricity to you along wires Even in the most remote parts of the world, py systems can supply solar electricity for all kind of uses Try to answer all of these questions Be prepared to share your answers with a partner, and with the rest of the class You may have seen a calculator powered by solar cells (You may even have one) Most pocket calculators are powered by batteries What is the advantage of using solar cells to power a calculator? Are there any disadvantages? Where else have you seen solar cells in use? What were they being used for? Can you suggest why they were used for this purpose? What is your main source of electricity? Is it produced from sunlight, or by burning fuels, or by some other means? Think about the word photovoltaic It means 'tuming light into electricity' Which part of the word means 'light'? Which part means' electricity'? Suggest some other words which are related to each of these two parts rage 1

2 U1YESCO Module 21: Photovoltaic systems We can measure the energy of the Sun at the surface of the Earth in units called 'kilowatt-hours' (or kwh for short) 1 kwh is the amount of energy used by a small electric fire in one hour, or the energy that a single hundred-watt light bulb consumes in ten hours In fact, your electricity meter at home or school measures the electricity that you consume in the same units -kwh The Sun's energy that is available for collection depends on the intensity of the light, and on how long the Sun shines Sunny summer days, when the Sun is high in the sky, give more energy than cloudy winter days Close to the Earth's poles, the Sun does not move high in the sky, so the energy supplied by the Sun in the course of a year is greater near the Equator, and less near the Arctic and Antarctic To be able to compare the Sun's energy in different parts of the world, we measure how much energy falls on each square metre of land -we say kilowatt-hours per square metre (or kwh/ m2 for short) Then we add up all the energy that arrives from the Sun in the course of a year Measuring the Sun's energy helps us to find out how much solar energy we can use for our own purposes It can also tell us how big our solar panels need to be to collect enough of the Sun's energy Use the world solar energy map to answer these questions: 5 Compare northern Russia and central Australia Which one receives more solar energy each year? Can you say how much more? 6 Imagine that you are designing an emergency phone for use in remote areas It will be powered by a solar py system Would you need the same size of solar collector in each country (Russia and Australia) to gather equal amounts of energy? Try to explain your answer Page 2 7 List as many reasons as you can why some parts of the Earth receive more energy from the Sun in a year than others

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4 UJYESCO Module 2] : Photovoltaic systems The amount of sunlight arriving varies during the day, and it varies from day to day Here are two ways to monitor the Sun's radiation: Use a home-made sundial Record the position of the end of the shadow every 30 minutes during the day Use a light sensor connected to a datalogger This will record the light level during the day, and you can then print out a graph Alternatively, use a light meter and record readings every 30 minutes Once you have collected some information, you can work out the best places and times for using solar technology to harvest energy from sunlight Safety- Never look directlya t the Sun/ as this can damage your eyesight- Using the results from your sundial experiment, you can fill in a solar log sheet like the one shown here Use a compass to work out the direction of the Sun when it reaches its highest point (when the shadow is shortest) Estimate the angle of the Sun using the length of the stick and the length of the shadow (Hint: you can use your maths trigonometry skills for this, or draw a scale diagram) You could plot a graph to show how the angle of the Sun above the horizon changes during the day Activity 4: Datalogging the Sun's radiation Set up your light sensor ariddiltalogger to record how the light level changes during the course of a day; Things to think about: Where will you position your sensor? In which direction will you point your sensor? How can you test your equipment to check that it is running correctly? When you have a graph to show how the Sun's radiation changed during the course of a day: Try to explain the shape of the graph, and any sudden changes in light level Suggest how the graph would be different at different times of the year Page 3

5 UlYESCO Module 21: Photovoltaic systems In many countries, most of the energy used in homes, factories and schools comes (from burning fossil fuels such as coal, oil and gas This has three main drawbacks Firstly, the process of taking fossil fuels out of the ground can cause damage to the environment This can include damage caused by the extraction machinery and by the pollution that is a by-product of extraction Secondly, fossil fuels give off gases when they are burned Some of these gases can cause environmental problems, such as acid rain Others, such as carbon dioxide (COz> may be causing a change in the global climate -you may have heard the terms "Greenhouse Effect" or "Global Warming" Thirdly, fossil fuels are not free They cost money to bring out of the ground This means that as fossil fuels run out, their price will increase At present, in most countries the cost of electricity from fossil fuels does not include the cost of the damage they cause to the environment This is called the "external" costs If these were included, the price of this type of electricity would be higher The table below compares the costs of electricity from various sources When there is a main electricity grid nearby, electricity from solar PV is still expensive compared to electricity from fossil fuels, and it will take some years before PV is competitive in grid-connected situations However, many technologies that were once expensive are now much cheaper These include things like calculators, digital watches, and personal computers This is the same with solar PV technologies In remote areas of the world it can be cheaper to use a solar elecuic PV system rather than building new pylons and wires In these places, we say that it is more cost-effectiveto use PV Figures are for grid supplies in US cents Figures in Euros are similar at publication date Page 4

6 U/YESCO Nodule 21: Photovoltaic systems Activity 5: Comparing costs i) Find out how much your family (or someone you know) pays for a kilowatt-hour (kwh) of electricity at home or at school ii) How does this compare with the total costs per kwh of electricity in the table? You may have to find out how to convert between currencies iii) If you have a supplier of py systems nearby, find out how much electricity from their technology costs Compare this with the costs shown in the table You may include this data in the "additional information" section of the exchange form if you wish Page 5