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The then and now guide to solar energy

How has the use of solar energy changed over time?


How much energy comes from the Sun?

The Sun is a huge sphere of very hot gas and has been producing energy for millions of years.

Solar energy is the radiation from the Sun that reaches Earth. It powers photosynthesis in green plants and is ultimately the source of all food and fuel.

Even though it is about 150 million kilometres away, the Sun is our closest star and sustains all life.

The amount of solar energy that strikes the Earth each day is 10,000 to 15,000 times greater than our daily energy needs.

In fact, the Sun is so powerful, that every minute, enough solar energy reaches Earth to meet our needs for one year!


How do we use solar energy?

Mankind has been using solar energy for thousands of years. The Greeks and the Romans designed and built houses to maximize use of the Sun.

In modern times, there are three main ways of using solar energy:

The Romans also made glass and knew that it could trap solar energy. Sunlight was so important that the Roman legalsystem actually included the right to have access to the Sun!

passive solar heating

solar power stations

solar cells.


Passive solar heating involves any system that can capture the Sun’s energy directly. This can be done using a simple solar collector or by the design of a building.

What is passive solar heating?

For example, the heat of the Sun can be focused on one spot using a curved mirror.

What do you think are the advantages and disadvantagesof passive solar heating?

Solar cookers work on this principle and so require no fuel.

Other examples of passive solar heating include a greenhouse or a south-facing window.


Buildings can be designed to allow in as much light as possible, by incorporating glass walls instead of solid walls. The building is then heated by utilizing the greenhouse effect, which reduces additional energy needs and costs.

How can the Sun heat buildings?

This low energy house not only has a photovoltaic roof but also has been designed so that it requires only a minimum amount of energy for heating and lighting.

maximize access to the Sun.

The house is orientated in an east-west direction and the rear is south-facing to


How does a greenhouse capture solar energy?


Greenhouse effect – ordering activity


Solar power stations use the Sun’s energy to heat water and make steam, which then drives a turbine to produce electricity.

Some solar power stations use a series of mirrors, called heliostats, to reflect light onto a boiler.

© Sandia National Laboratory/NREL

What is a solar power station?

This solar power station in California consists of about 1800 heliostats, with an electrical output of 10 megawatts.


Some solar power stations use curved mirrors, which focus solar energy onto pipes containing water. This heats the water and forms the steam needed to drive a turbine.

More solar power stations


Solar power stations are most effectively located in areas with high light intensity.

Making solar power stations effective

This test design is located in Arizona where the sunlight is intense and the air temperature is high.

The mirrors must track the Sun as it moves across the sky, to be as efficient as possible.

Would this sort of power station be effective in the UK?


Solar cells (or photocells) turn light energy from the Sun directly into direct current electricity.

Solar cells are ideal for use in remote locations where maintenance is difficult and other sources of electricity would be expensive.

Why use solar cells to power satellites?

Manufacturing solar cells is very expensive and requires the use of highly toxic materials. However, once the solar cell is built it produces no pollution and requires little maintenance.

Satellites have been powered using solar cells since the 1950s.


How do solar cells work?


Solar cells suffer from a low efficiency. This is because only light with enough energy causes electrons to be released, which is only about 25% of all sunlight.

The amount of electricity a solar panel can produce depends on two factors: its surface area and the light intensity.

How well do solar cells work?

Producing enough electricity to power a town would require a very large area of solar panels but covering the roof of a house can meet the annual electricity needs of thehousehold.


One obvious problem with solar cells is that they do not produce electricity at night.

What are the problems with solar cells?

Scientists are working to develop improved solar cells, which require less polluting chemicals in their manufacture, cost less to produce and are more efficient than thecurrent technology.

If more electricity is produced during the day than is used, the excess can be used to charge a battery. This can then provide power during the night.


What are solar cells used for?

Solar cells are very useful where the light intensity is highest.

Solar cells are also useful where low amounts of power are needed.

in place of batteries .

These solar panels are in a remote part of Morocco where they are used by a local utility company.

Calculators only require a small amount of electricity, so most calculators now use solar cells


Solar cells can be used very effectively in the right situation.

Where are solar cells used effectively?

The robust nature of solar panels can be exploited in areas where maintenance is difficult.

is clean, quiet and dependable.

The Dangling Rope Marina on Lake Powell in Utah, USA, is only accessible by water. It previously depended on more than 246,000 litres of diesel to fuel its generators.

A photovoltaic energy system has now been installed. It will reduce the cost of providing electricity and


Solar cells are very useful for remote locations where supplying mains electricity would be expensive.

Why use solar cells in remote areas?

This solar-powered street light is in a remote part of mid-Wales with no mains electricity supply close by.

The use of solar power in this way removes the need to lay electricity cables to the light, which is another benefit to the environment.


Pros and cons of solar cells


Solar cells – true or false?


Has the use of biomass fuels changed over time?

The then and now guide to biomass


Biomass, also known as biofuels or bioenergy, is material from living sources. The simplest biomass energy sources are plants, which can be burned to produce steam to turn a turbine.

The carbon dioxide released during burning biomass is absorbed by the replacement plants. Biomass is said to be

‘carbon neutral’ and does not add to global warming.

What is biomass?

Traditionally, wood is burned to give heat but trees grow slowly and require a lot of land. Other materials, such as poultry farm waste, can also be burned.

Biomass fuels are renewable as more plants can be grown, producing yet more biomass.


Methane is a biogas, which can be used a replacement for natural gas. This biofuel can be produced by making use of the natural decomposition of organic waste material.

How can waste create biofuel?

Methane can be produced from concentrations of rotting sewage or manure stored in containers called anaerobic digesters. These can be readily used in remote places, such as this digester on a pig farm.

Another source of methane is the rotting organic waste buried underground in landfill sites. The gas can be drawnup through pipes to generate electricity or provide heat.


Some sources of biomass energy can be processed to produce biofuels that are even more useful.

How else can biofuel be made?

Certain plants can be fermented to form ethanol, a biofuel, which can be used instead of petrol or even aviation fuel, as in this plane!

Sugar cane and beet are the most efficient sources of this ‘bioethanol’ but potatoes, corn, wheat and barley can also be used.

vegetable oils, animal fats or recycled cooking oils. Another biofuel is ‘biodiesel’ which can be made from


What are the pros and cons of biofuels?

Some advantages of using biofuels are:

Some disadvantages of using biofuels are:

energy used in transportation must also be considered.

Biofuels are made from plant materials which makes them completely renewable.

They are biodegradable, so do not cause as much pollution if spilled.

They produce less pollution, when burnt, than fossil fuels.

Vehicles need to be adapted to run on pure biofuel. Large areas of land are needed to grow crops, which

could lead to loss of habitats. Biomass is ‘carbon neutral’ but the environmental impact of

using fertilizers to grow sources of bioenergy and the


Using biofuels – true or false?


Geothermal energy involves harnessing the thermal energy stored within the Earth.

© Joel Renner - DOE/NREL

In some areas, where the hot rocks are near the surface, hot water and steam rise to the surface. This creates features such as steam vents, geysers and hot mid springs.

What is geothermal energy?

This thermal energy comes from the decay of radioactive elements, such as uranium, in rocks under the ground.

The heat released by this radioactive decay warms the surrounding rocks and nearby water.


© David Parsons/NREL

A geothermal power plant can be built to utilize steam and hot water that rise naturally to the Earth’s surface.

How can hot rocks generate electricity?

The steam and hot water provide a way of turning a generator, which then produces electricity.

Sometimes, the hot water is trapped in natural underground reservoirs and does not reach the Earth’s surface. This watercan be reached by drilling to depths of several kilometres.

This is the largest producer of geothermal power in the world. It is in California and has an output of 750 MW of electricity.


In some areas, the geothermal rocks are deep underground where there is no water.

This geothermal power plant in California has 57 wells and produces 52 MW of electricity.

Where this occurs, wells can be drilled down to the hot rocks and cold water is pumped down. The water is heated by the rocks and returns to the surface as steam.

Can deeper hot rocks be used?

Geothermal power plants can only be developed in suitable locations. At the moment, there is only one geothermal power plant working in the UK, in Southampton.


Pros and cons of geothermal energy


biofuel – Biomass that has been processed to produce a more useful fuel, such as ethanol.

biogas – Methane gas that has been produced by rotting biomass waste.

biomass energy – Energy from living matter, which can be used as fuel.

geothermal energy – Heat from radioactive decay in rocks deep below the Earth’s surface.

passive solar heating – A system that can capture the Sun’s energy directly, such as a simple solar collector or the design of a building.

solar cooker – A curved mirror that focuses radiation from the Sun onto one spot to heat food.

solar energy – Energy from the Sun, which is converted into thermal or electrical energy.

Glossary


Anagrams


Solar and thermal renewable energy


Multiple-choice quiz

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