P2a (ii) Collecting Energy from the Sun

You will learn about:Passive Solar Heating

Wind Technology

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Renewable EnergySolar water heaters on roofs are becoming a more common site. The rectangular collectors contain many small tubes that lie on top of black plates. The black plates absorb solar radiation and conduct the heat to the water in the pipes.A convection current is created – warmer water rises to the top of the storage tank and cooler water sinks down to the collector.

www.PhysicsGCSE.co.uk The Sun is a renewable energy resource. This means the energy from the sun will not run out in the foreseeable future.

The warm air from the land rises and moves over the ocean. Here the air is cooled so it sinks. When it returns back to the land it is warmed and so it rises again.This is another example of a convection current.This happens on all beaches. This movement of air is called wind.

The movement of air, or wind, can be used to turn wind turbines. This is another way where electricity can be generated using a renewable energy resource.

Passive Solar HeatingDuring daytime, the floors, walls and fabrics like carpets and curtains absorb the heat.

www.PhysicsGCSE.co.uk In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. It is passive because we are not actively doing anything.

Small North facing windows reduce the amount of light and heat that can escape.

Large South facing windows allow light and heat in. This means that other heating and lighting methods are reduced.

During night this energy is radiated into the house warming it up.This means less heating is needed.

Curved Solar Reflectors reflect light to a focal point. This intense heat can be used to heat liquids like water quickly.

Wind Farms – friend or foe?For:Do not add harmful emissions like carbon dioxide to the atmosphere;They do not contribute to the greenhouse effect.

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Against:Large and cumbersome;Some people say they are ugly;They do not produce that much power;Must be shut down if wind speeds are less than 88km/h.They are very noisy;They could damage bird and ocean life ecosystems;They are very expensive;Wind farms take up a large amount of space.

Wind farming is a very controversial topic. The arguments against are larger in number that the arguments for. But because the greenhouse effect is damaging our Earth so rapidly governments are willing to invest time and money finding alternative ways to generate electricity.

What do you think?

GreenhousesIf you have ever been inside a greenhouse then you know they can get very warm. Greenhouses are generally much warmer inside than outside.The Sun is very hot and it produces short wavelength infra-red radiation. This is able to pass through the glass of the greenhouse. The radiation is absorbed by the plants and soil and warms them. The plants then re-radiate the infra-red radiation. As the plants are not as hot as the Sun, the infra-red radiation they radiate has a much longer wavelength. This plant radiated infra-red radiation cannot pass through the glass. Therefore it stays within the greenhouse and continues to warm it up.

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Homes, sheds, schools and even spaceships can warm up in this way too.For the solar collector to be as efficient as possible computers direct the dish so it faces the Sun throughout the day. You can see that they all point the same way – toward the Sun.

Bjarne Carlsen designed this futuristic concept spaceship. Could it be a reality one day?

Questions

1. Look at the image of the house. It uses Passive Solar Heating to warm it up. How successful do you think it is?

2. What is the best colour for absorbing radiation?3. Lots of people are against the ideas of wind

turbines. Most farmers are not. Why not?4. On a hot Summer’s day a car can get very hot

inside if the windows are closed. Explain why this is.

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Questions

1. Look at the image of the house. It uses Passive Solar Heating to warm it up. How successful do you think it is? It has large South facing windows and smaller side windows to allow as much infra- red radiation (heat) in as possible. This would be absorbed into the walls and floors and radiated out during night. So long as the walls and roof were well insulated the efficiency of Passive Solar Heating would be high.

2. What is the best colour for absorbing radiation? Dull Black.3. Lots of people are against the ideas of wind turbines. Most farmers are not. Why not?

They do not obstruct their day to day work. They are out of the way in an open field so noise pollution is low and mostly out of real sight. Some farmers are paid a subsidiary from the government to allow wind turbines to be used in their fields.

4. On a hot Summer’s day a car can get very hot inside if the windows are closed. Explain why this is. The Sun emits short wavelength infra-red radiation. Glass is transparent to this radiation so it passes through. The seats in the car absorb this radiation and radiate it back out. The seats are not as hot as the Sun so the infra-red radiation has a longer wavelength. The glass is opaque to this radiation so it does not pass through. Therefore it stays inside the car and warms it up. Over time a lot of infra-red radiation builds up in the car so it warms up even more as it cannot escape.

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