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Harnessing direct solar energy – a progress report

We often hear about solar car challenges and solar heating, but will solar energy ever be a major energy source for industrial societies?
Contents

Key text

Box 1. Eliminating the zeroes
Box 2. Driving on a sunbeam
Box 3. Light to electricity
Box 4. The Big Dish
Box 5. Chemical fuels from the sun Activities Activity 1. Photovoltaic cells and solar collectors
Activity 2. Calculating the amount of solar radiation that can be converted to electricity
Activity 3. Aspects of solar energy collection and use
Activity 4. The cost of solar energy
Activity 5. Showing the movement of water as it heats
Activity 6. Making a solar water heater
Further reading
Useful sites
Glossary
Back to basics
You will get more from this topic if you have mastered the basics of energy – this link will take you to an annotated list of sites with helpful background information.

Key text

Can society meet its energy needs without pollution?

Alternative energy sources are far less polluting than traditional fuels, although they may have other drawbacks. One source of alternative energy is the sun. The Earth is bathed in huge amounts of the sun’s energy. We can use this solar energy directly, simply by capturing sunlight.

Solar energy is our oldest energy source

Humans have always used the sun’s energy directly (eg, for drying clothes and foodstuffs), as well as indirectly to power the agriculture that supplies us with food. This century we have started to use solar energy more effectively, and it is likely that we’ll increase its use in the future.

It’s reliable, free and clean, but...

The great feature of solar energy is the fact that it is likely to continue to exist so far into the future that we can think of it as being unending. It is, therefore, a form of renewable energy. This is a big contrast with non-renewable energy sources, most of which are running out as we use them.

In addition, using solar energy doesn’t cause air pollution or involve damaging the Earth’s surface. It requires no difficult and expensive extraction procedures.

But the main problem is what to do when the sun doesn’t shine. The times when we most need energy – when it is dark or cold – are when sunlight is least available. But there are possible ways around this, so read on...

Compared to fossil fuels, sunlight is a weak energy source

Capturing sunlight is not as easy as it sounds. It is a dilute energy source, spread out over time and space. Earth receives 5.6 x 1018 (5,600,000,000,000,000,000) megajoules of solar radiation each year (Box 1: Eliminating the zeroes), but to make it worthwhile we need to collect it over many hours and across many square metres of ground. We then need to concentrate it so as to make available the sort of power that modern society needs. Sunlight is not as ‘energy-dense’ as oil but this is made up for by the fact that it is present over such a large area.

By careful design and positioning of houses we can use sunlight to warm our homes and our domestic water. This passive solar heating can help us reduce fossil fuel use (and save money) but it’s not enough to replace those traditional fuels entirely.

To be most useful, the energy in sunlight must be converted to another form

Solar energy becomes much more useful when we change it to another form. Light can be changed directly to an electric current by photovoltaic cells. The efficiency with which these convert light to electricity is still too low, and their cost too high, to make them useful for many applications. Furthermore, you need to have a large area of photovoltaic cells to power something like a car – although it can be done, as demonstrated by the entrants in the World Solar Challenge car rally (Box 2: Driving on a sunbeam).

Australian research is forging ahead on reducing the cost and improving the efficiency of photovoltaic cells (Box 3: Light to electricity).

Many places where energy is needed are not very sunny

Unfortunately, we can’t yet power our homes entirely on sunlight. Photovoltaic cells for a house are expensive, and anyway most houses are not in the sunniest part of Australia or the world. The solution is to put the sun’s energy into a form which can be stored and moved around, so that we can collect it in those places where most of it falls and move it to where it is needed.

Steam or hydrogen gas are the best future conversion options

Sunlight can be concentrated by solar collectors – best sited in a desert. These focus sunlight from a large area on to a central vessel in which water is heated to become very high temperature steam. The expanding steam can power a turbine and generate electricity on a sufficiently large scale that it can be sent across a power grid. The world’s largest, free-standing, steerable solar concentrating dish is in Canberra, where it forms part of the Australian National University’s solar research program (Box 4: The Big Dish).

The greatest challenge for solar energy is to power modern society’s transport and industrial needs. Transport fuels must be light but packed with energy. They must also operate when it’s dark, so photovoltaic cells are out. The answer for the future probably lies in hydrogen gas, derived from water split apart using solar electricity or the sun’s concentrated heat (Box 5: Chemical fuels from the sun).

Related Nova topics:

Wind power gathers speed

Generating new ideas for meeting future energy needs

Biomass – the growing energy resource

Fuelling the 21st century

Which way ahead for hydrogen cars?

Box 1. Eliminating the zeroes

Very large numbers are cumbersome to write because of all the zeroes. They are hard to compare – a number with 20 zeroes at the end looks about the same as one with 19, yet it is ten times larger. Large numbers are also hard to name. Once you start talking about a thousand million million million, not only is it long-winded, it’s impossible to keep track and to imagine how the number would look when written down. There is another language problem too – in the English-speaking world, one billion can mean either one thousand million, as it does throughout this book, or one million million, as it does in Britain.

The quickest way around all these problems is to use the simple mathematical method of writing very large or very small numbers, a method used by all scientists too. This form of writing numbers essentially relies on counting zeroes and is called using powers of 10 or exponents. Everyone knows what squaring a number means – it is multiplying a number by itself. Thus, 3 squared is 9. The mathematical way of writing this is 32 = 9. The little number 2 above the 3 is called an exponent. 32 can also be spoken of as three to the power of two. The square of 10 is 100; so 102 = 100. You can say this as ‘ten to the power of two’, or just ‘ten to the two’. If the exponent is 3, then the number is multiplied by itself once again. So, 33 = 3 × 3 × 3 = 27, and 103 = 10 × 10 × 10 = 1000. You may have noticed that when dealing in powers of 10, the exponent is the same as the number of zeroes in the number, as this table shows:

101 = 10
102 = 100 (one hundred)
103 = 1000 (one thousand)
104 = 10,000 (ten thousand)
105 = 100,000 (one hundred thousand)
106 = 1,000,000 (one million)
107 = 10,000,000 (ten million)
108 = 100,000,000 (one hundred million)
109 = 1,000,000,000 (one thousand million or one billion in some countries).

Of course, not all large numbers are always full of zeroes. Suppose we have the number 2,720,000 (two million, seven hundred and twenty thousand). You could call this 2.72 million, or just multiply 2.72 by the appropriate power of 10 for one million. As the million has six zeroes, the exponent would be 6, and the number would be expressed as 2.72 × 106.

Rounding numbers up or down

If a number is more precise, such as 2,738,458, we can either express it as it is, express it using an exponential but keeping all the figures (2.738458 × 106), or round it up or down. Whether we round it or not depends on whether the number is describing a precisely quantifiable thing. For example, if the figure is a calculated average (eg, the number of bacteria found on each square metre of rainforest topsoil), then rounding it is valid. We cannot be sure of the number down to the last bacterium, and even as we are estimating it, the bacterial population is changing. In this case, we would approximate the number as 2.74 × 106 or 2.7 × 106, or even just 3 × 106.

Very small numbers

Very small numbers are also conveniently expressed using powers of 10. In this case, a minus sign is written before the exponent. For example, one-thousandth is 10-3, one-millionth is 10-6, which we say as ‘ten to the minus six’. The exponents represent the zeroes that would come after the decimal point, and the one that comes before it. A concept like 0.0000345 millimetre is hard to grasp and not easily compared with 0.00000345 millimetre (who bothers to count the zeroes?), but the difference is more obvious when they are written as 3.45 × 10-5 millimetre and 3.45 × 10-6 millimetre respectively as there is a clear difference between the exponents 5 and 6. The first number is 10 times less small (which means 10 times larger) that the second.

You can practise using power-of-ten notation either with pure numbers or in combination with units. For example, using exponents, express:

  1. 12 kilometres in metres
  2. 1,234,567,890
  3. one hundred thousandth of a gram
  4. 0.00023

Answers

  1. 1.2 × 104 metres
  2. 1.23456789 × 109
  3. 1 × 10-5 gram
  4. 2.3 × 10-4

Box 2. Driving on a sunbeam

Cars can run on sunlight – in fact, they can race on it. The World Solar Challenge car rally has now become a great Australian tradition, with teams from many countries keen to try their skill at building a solar-powered car and racing it the gruelling 3000 kilometres from Darwin to Adelaide.

The rules state that each car’s solar cells can only cover an area of 8 square metres, which is slightly less than the area of a small bathroom. And the cells can’t stretch out from the car like giant wings! But with a lightweight car and an efficient battery for storing extra power when the sun is bright, a solar car can manage a speed of 100 kilometres per hour and can continue – though usually much more slowly – on cloudy days or when the sun is low in the sky.

Of course, the cars in the solar challenge are expensive ‘one-offs’ and are not your average family sedan. Solar-powered motoring is still some way from being accessible to everyone. But it’s a start – in the same way that the great air races from Paris to London in the early part of this century honed the skills of aircraft designers, so that it eventually became possible to send jumbo jets around the world.

Probably the first widely used solar vehicles will be small cars with roof-mounted photovoltaic cells, batteries for electricity storage, and the ability to top up with mains electricity when left in the garage. Designed for commuting short distances in the suburbs, they will be built with the know-how accumulating from events like the World Solar Challenge. And when these vehicles do roll off the production line, we’ll all breathe more easily as a result!

Related sites

Box 3. Light to electricity

The 1999 Australia Prize was awarded to Martin Green and Stuart Wenham for their work in photovoltaics

Martin Green and Stuart Wenham, from the University of New South Wales, have invented or co-invented seven distinct cell technologies over the past 15 years. These solar cells have held the world efficiency record for converting sunlight into electricity for more than a decade and last year achieved an efficiency of 24.5 per cent, the current world record by a large margin.

The awarding of the 1999 Australia Prize in Energy Science and Technology to Martin Green and Stuart Wenham represents only the second time in the 10 year history of the Prize that it’s been won by an all-Australian team – an indication of the pair’s dominance in the world of photovoltaic research.

There is more information about the winners and their research at the ABC's The Lab.

Read on to find out how photovoltaic cells work.

Photovoltaic cells convert light directly into electricity. It has been known for more than 150 years that light can have an effect on the electrical properties of some materials. This is known as the photoelectric effect. In 1921, Einstein received the Nobel prize for his work explaining this. Photovoltaic cells are based on a related phenomenon called the photovoltaic effect, and interest in this has increased greatly during this century.

The generation of electricity from light relies upon the separation of positive and negative electric charges – electrons and positively charged 'holes', both generated by the light – at the junction between two parts of a semiconductor crystal. Silicon is a semiconductor that can be mixed with tiny quantities of impurities (such as phosphorus and boron) in a process called doping. Doping can produce P (for positive) and N (for negative) materials. A photovoltaic cell is simply a wafer of semiconductor in which there is a junction between N and P materials. On exposure to light, a photovoltaic cell produces a voltage of about 1 volt, comparable with that of a torch battery. The silicon, which is expensive to make in pure form, is in the form of a thin wafer, to catch as much light as possible.

The ultimate efficiency of a silicon photovoltaic cell in converting sunlight to electrical energy is less than 30 per cent, and the Photovoltaic Research Centre at the University of New South Wales holds the present world record with a cell efficiency of about 25 per cent. But cells like this, made from single-crystal silicon, are expensive, and large areas of them are needed to produce useful amounts of power. The search is therefore on for much cheaper cells without too much sacrifice in efficiency. In 1997 the National Australia Day Council acknowledged the importance of this work when it named Professor Martin Green, Director of the Photovoltaic Special Research Centre, as an Australian Achiever.

Several promising lines are being pursued by the University of New South Wales and by Pacific Solar, a joint company formed by the University and Pacific Power, the major New South Wales electricity supply authority. Instead of cutting slices from specially grown silicon single crystals, one possibility involves growing thin films of silicon on much cheaper polycrystalline silicon wafers; another involves evaporating thin films of silicon onto glass plates. Initial results for both of these techniques are very encouraging, and the efficiency is already approaching 20 per cent. Another approach is to use amorphous (glassy) silicon (which can be produced fairly cheaply) instead of crystalline material.

While expensive photovoltaic cells can be used in solar car races, and solar photovoltaic modules on the roofs of houses may also become common, the ultimate aim of photovoltaic technology is to produce large amounts of electrical power from cheap photovoltaic cells, connected together to give a high voltage, and to convert this to alternating current to feed into the power grid. This has already been done on an experimental scale in Sydney, and Australia is a leader in the race.

Related sites

Box 4. The Big Dish

Photovoltaic cells aren’t the only way of converting sunlight to electricity. The Big Dish, at the Australian National University’s Energy Research Centre in Canberra, does it another way.

As its name implies, this solar collector is shaped like a satellite receiving dish. It is actually a solar thermal generator because it relies on heat. The huge curved mirror – the dish – focuses sunlight onto a central container where water is super-heated to steam at a temperature of 1500°C. If you’ve seen how steam at 100°C will escape from a kettle, you’ll appreciate how a much higher temperature could cause even a small amount of steam to expand with massive pressure. This can be used to do work – in this case driving a special generator that produces electricity.

The dish is steerable, so it can track the sun across the sky. Because it is always facing towards the sun, it gathers the maximum amount of energy. The dish isn’t just used for experimentation – it pumps 80 kilowatts of electricity into the Australian Capital Territory’s grid.

With the success of the Big Dish, and using the know-how of the project’s director Professor Stephen Kaneff and his team at the Australian National University, plans are underway to set up a working demonstration plant to provide a hefty 2 megawatts of electricity for Tennant Creek, in the Northern Territory.

Related sites

Box 5. Chemical fuels from the sun

Putting the sun’s energy into a light and portable form is the only way to allow all sectors of modern society to run entirely on solar energy.

Solar energy can help to produce energy in a portable form

In Australia, the CSIRO Division of Energy Technology, in collaboration with Pacific Power, has tested the idea of using high temperatures from concentrated solar energy to drive a chemical reaction between carbon dioxide and methane in the presence of a chemical catalyst. The resulting gas (a mixture of hydrogen and carbon monoxide) can then be stored and transported; it releases energy (which can be changed into electricity) when it is allowed to separate back into its two component gases. These can then be recombined with a further energy input from solar power.

Advantages of hydrogen as a fuel

But for many in the field, it’s clear that the ultimate fuel is hydrogen – the lightest substance in the universe. We can produce hydrogen from water, but need energy to do so. Once we have the hydrogen gas, it can be safely stored and transported. Hydrogen is currently only used to power rockets, but with some modifications it could power all our transport and electricity generators. When burnt, hydrogen releases energy and combines with oxygen in the air to form water – a product with no pollution potential! At the same time, the water that was used to produce the hydrogen is regenerated – so the cycle can continue until the sun burns out.

Ways to generate hydrogen

Hydrogen can be generated from water by using an electric current; this is called electrolysis. The electricity can be derived from sunlight. Another possibility would be to simply use very high temperatures from concentrated sunlight, which can literally tear apart the molecules of water into its hydrogen and oxygen atoms. Ideally the gases would then be separated.

But there are much more sophisticated ways of splitting water using sunlight. The secret lies in plants. When exposed to light, green plants continually split water – releasing the oxygen into the air for us to breathe, and combining the hydrogen with carbon dioxide to form sugars. If we could duplicate this process, we would be well on the way to becoming a truly solar society. Research continues.

The future of hydrogen as an energy source

Australia’s Sir Mark Oliphant, the distinguished physicist, is one of several experts who consider that the move to a solar-powered ‘hydrogen’ society will eventually come. If he is right, desert areas could be used for intensive solar collection and the production of liquid fuels would power our world, in much the same way that modern agriculture, with its huge area of wheatfields, continually converts sunlight into solid chemical energy for us to eat. If this comes about, those countries with a large area receiving intense sunlight – such as Australia – could be as rich as today’s oil-exporters.

Related Nova topics:

Activities

  • Science upd8 (UK)
    • Solar car challenge – students learn about energy transfers in solar cars and consider design features to maximise a solar car’s speed.

  • Mobile Inquiry Technology (The Concord Consortium, USA)
    • Solar cell – use a solar cell to investigate changes in the amount of sunlight at ground level.

  • Re-Energy (The Pembina Institute, Canada)
    Students learn about renewable, solar power, wind, water power and biomass energy. Lesson and construction plans for working models of solar power cars, solar ovens, wind power turbines, water wheels and biogas generators are available.
    • The colour sensitivity of a photovoltaic cell – students use coloured light to test the colour sensitivity of one or more kinds of photovoltaic cells. Using digital voltmeters, students measure the voltages and then graph the results.
    • Building and testing a solar oven – students work in small groups to build a solar oven. They test the oven using two baking pans and record the temperature changes. Instructions on how to build the solar oven are available.

  • Queensland Department of Education (Australia)

  • Science NetLinks (American Association for the Advancement of Science)

  • Energy Information Administration Kid's Page (USA)
    Click on ‘Classroom Activities’ and then ‘Teachers and students’ to access a list of activities including:
    • Solar cooking – students build and test a solar hot dog cooker.
    • Energy in the round – students play a game to reinforce learning about forms of energy.
    • Solar collectors – students compare black and white materials as solar collectors.

  • SunWind Solar Lessons (Sunwind Solar Industries Inc., USA)

  • Ergon Energy (Australia)

Activity 1. Photovoltaic cells and solar collectors

Explain the difference between the two solar technologies that currently produce electricity: photovoltaic cells and solar collectors.

Teachers notes

Photovoltaic cells convert light directly into electricity. Most photovoltaic cells are based on silicon. When light strikes the junction in a thin slice of silicon, it causes a movement of electrons. Photovoltaic cells have no moving parts to wear out and produce no polluting waste products.

Solar collectors focus sunlight from a large area on to a central vessel in which water is heated to become very high temperature steam. The expanding steam can power a turbine and generate electricity. This can be done on a large enough scale that it can be sent across a power grid. Alternatively the heat may be used to drive a chemical reaction resulting in a transportable substance that can release its energy later – possibly to be turned into electricity.

Activity 2. Calculating the amount of solar radiation that can be converted to electricity

The following table lists the daily average hours of sunshine for a number of Australian cities, together with their latitudes. Use the information in the table to help you answer the following questions.

CityDaily average
sunshine
(hours)		Geographical
latitude
(degrees south)
Darwin8.412.2
Brisbane7.527.3
Perth7.831.6
Sydney6.733.5
Adelaide7.034.5
Melbourne5.737.5
Canberra7.235.2
Hobart5.642.5

  1. Use the information in the table to plot a graph of daily average sunshine against geographical latitude. What relationship does your graph show? Which cities do not fit the relationship perfectly? Suggest reasons for these variations.

  2. In Australia, an average of 400 joules of energy are received by each square metre of the Earth’s surface each second of daylight.

    Photovoltaic cells convert solar radiation to electricity and are about 25 per cent efficient. What area of photovoltaic cells is needed to generate enough power to run:

    • a desk-top computer using 300 watts
    • an electric frying-pan using 1350 watts
    • a 2-slice toaster using 600 watts?

      (Power is the rate at which energy is transferred and is measured in watts. Bear in mind that 400 joules of energy per second are equivalent to 400 watts.)

    What area of photovoltaic cells is needed to run all of these appliances simultaneously?

  3. Briefly outline the main problems associated with using photovoltaic cells for domestic use.

Teachers notes

Sunshine is not the same as daylight. Calculations in this activity are only very approximate because we are not taking into account the fact that photovoltaic cells can work in daylight without sunshine, albeit at a reduced rate.

  1. Plotting the data given in the table shows an inverse relationship between geographical latitude and daily hours of sunshine – as latitude increases, the average hours of sunshine decrease. Perth and Canberra (and perhaps Adelaide) are the cities that do not fit the relationship as well, because they have fewer cloudy days.

    • a desk-top computer needs 3 square metres of photovoltaic cells
    • an electric frying-pan needs 13.5 square metres
    • a 2-slice toaster needs 6 square metres
    • 22.5 square metres is needed to run all of the appliances simultaneously.

    Note that the precise figures vary according to the elevation of the sun in the sky and local factors such as cloud cover.

  3. The main problems associated with photovoltaic cells for domestic use are:
    • the sun is not available when domestic energy needs are the highest;
    • the energy has to be stored until it is needed and this requires expensive, bulky batteries;
    • a large area of photovoltaic cells is required;
    • the photovoltaic cells need direct exposure to the sun – northerly aspect without shade.

Activity 3. Aspects of solar energy collection and use

The following topics cover a variety of aspects of solar energy collection and use. Select a topic, research it in the library and present the information that you have found to the class:
  • photovoltaic cells;
  • the use of solar collectors in communications;
  • solar thermal electricity;
  • the use of solar energy for hydrogen fuel production;
  • the World Solar Challenge.

Teachers notes

Biomass, wind energy, wave energy and hydroelectricity could also be used as topics. Students should be able to show how these forms of energy originate from the sun.

Activity 4. The cost of solar energy

Although no-one has to pay for sunshine, people often do not use solar energy because they think it is too expensive.
  • Write a short essay discussing the statement: Sunshine is free; solar energy is not.

Teachers notes

Students' answers should cover the costs involved in collecting solar energy, for example:

  • The purchase of photovoltaic cells. They are still costly because of the materials used in them and because they are not manufactured on a large scale.

  • The installation and connection of photovoltaic cells. The installation is often expensive because of the area of cells required (because of the low power density of solar radiation) and the fact that correct orientation is essential.

  • The purchase of storage batteries.

  • Photovoltaic cells produce direct current electricity at low voltage (about 1 volt) like ordinary torch batteries. For many domestic uses this direct current must be converted to alternating current at 240 volts.

  • The price differential between solar and mains electricity. This depends on the price of mains electricity. An important and controversial point is whether mains electricity is fairly priced. Environmentalists claim that its price is unrealistically low and does not take into account the hidden environmental costs. Thus, solar is unable to compete on a level playing field.

Activity 5. Showing the movement of water as it heats

Hot water weighs less than cold water. This is because a substance occupies more volume and is therefore less dense when it is heated. In gases and liquids, a light substance will rise to the top – hot water rises above cold water. This principle is made use of in most water heaters.

Materials (for small group)

wide test tube (about 4 centimetres in diameter)

glass tube about the same width as the test tube (or a second test tube with the bottom cut off)

2 lengths of glass tubing

2 corks (or bungs) with two holes in each

cold water

food colouring

thermometer

Set up the apparatus (as shown in the diagram) and place it in direct sunlight.

Record the temperature of the water in the tube every two minutes until there is no further evidence of the movement of water through the system.

Questions

  1. Do you think the water has now stopped getting hotter?

  2. What can you do to test your opinion?

  3. Describe what happened to bring about the changes in the appearance of the water.

Teachers notes

  1. The temperature of the water will continue to rise until the rate at which heat is gained from the sun equals the rate at which heat is lost from the water to the surrounding air.

  2. Students could test their opinion by continuing to note the temperature for another 5 minutes.

  3. As water heats it will expand, forcing the coloured water in the lower tube up through the pieces of glass tubing. Water movement may not be visible the entire time if the differential between the colour in the bottom tube and top tube is lost due to mixing.

Activity 6. Making a solar water heater

In this activity, we can see how solar water heaters take advantage of the fact that hot water rises.

Materials (for small group)

large cardboard tray, approximately 60 × 30 × 15 × centimetres (made by cutting down a cardboard carton)

sheet of glass, larger than 60 × 30 centimetres

6 metres of plastic tubing or garden hose

2-litre plastic bottle

cardboard carton (big enough to hold the plastic bottle)

thermometer

scissors with pointed ends

plasticine

sticky tape

water

black and white poster paints

sheet of clear plastic, larger than 60 × 30 centimetres

a variety of insulating materials (eg, old clothing, sawdust, plastic foam, crumpled newspapers)

Set up the model solar water heater (as shown in the diagram) and place it in a sunny position.

Fill the bottle and the plastic tubing with water.

Record the temperature of the water after the solar water heater has been in sunlight for 20 minutes.

Test for the effect on the temperature of altering variables (eg, clear plastic versus glass covering the box; various insulating materials around the bottle; the colour of the bottom of the cardboard box; the angle at which the box is tilted).

Questions

  1. Why was it important to have one end of the plastic hose entering at the top of the bottle and the other end entering at the bottom?

  2. Why did the model solar water heater have a long length of the plastic hose positioned in the bottom of the tray.

Teachers notes

  1. One of the holes should be at the top of the bottle and the other at the bottom to ensure that circulation and mixing occurs as the water is heated.

  2. Positioning as much of the tubing as possible across the bottom of the box ensures that the maximum area of tubing is exposed to the sun.

Further reading

ATSE Focus
March/April 2004
Renewables to the rescue? Wind and solar energy in Australia (by Ian Grey)
Looks at the capacity of Australia to meet its energy requirements using wind and solar power.

Australasian Science
September 2006, pages 31-32
Photosynthetic photovoltaics (by Simon Grose)
Profiles solar cell technology that is inspired by photosynthesis.

Cosmos
18 April 2007
Slicing the cost of solar power (by David Kay)
Looks at a novel approach to make low cost photovoltaic cells.

Ecos
No. 131, 2006, pages 12-14
Solar cities generating new approaches (by Hartley Henderson)
Describes the Solar Cities program to trial the latest solar technology in cities across Australia.

No. 130, 2006, page 33
Roof tiles go solar (by Steve Davidson)
Describes a roof tile that is a solar panel that provides both solar power and solar hot water to homes.

No. 129, 2006, page 4
Solar thermal power warms up
Suggests that solar thermal energy is emerging as a cost-competitive source of electrical power.

No. 124, 2005, pages 28-30
A stirling idea (by Wendy Pyper)
A new spin on the age-old technology of the Stirling engine could provide a cheap, portable, low maintenance renewable energy unit.

No. 124, 2005, page 27
Sun-power technology centre underway
Covers the construction of the National Solar Energy Technology Centre at Newcastle, Australia.

No. 121, 2004, page 30
Reconciliation re-invigorates solar development (by Wendy Pyper)
A new project aims to provide energy from renewable sources for the Yolngu people of Dhuruputjpi in Arnhem Land.

No. 117, 2003, pages 8-9
One golden pond (by Wendy Pyper)
Describes a 'solar pond', which uses shallow ponds of saline water to harness solar energy.

No. 116, 2003, pages 10-12
Siphoning the sun (by Graeme O'Neill)
Describes the kilometer-high solar tower project which could power 200,000 homes.

Nature
7 September 2006, pages 19-22
A new day dawning?: Silicon Valley sunrise (by Oliver Morton)
Looks at interest in photovoltaic research in California's Silicon Valley.

New Scientist
A collection of stories on energy and fuels is available.

8 December 2007, pages 32-37
Solar power: The future’s bright (by Bennett Daviss)
Explores the future of power generation from solar energy.

24 November 2007, pages 42-45
Plugging into the sun (by Dan Cho and David Cohen)
Investigates the potential of space solar power.

5 May 2007, page 15
High cost of capturing solar energy is diminishing (by Jim Giles)
Looks at the potential of concentrated solar power as a source of energy.

9 December 2006, page 32
Cut-price solar panels follow the sun (by Duncan Graham-Rowe)
Reports on a new solar panel that is designed to cut the cost of harnessing the sun’s energy.

11 November 2006, pages 30-31
Take a leaf out of nature's book to tap solar power (by Duncan Graham-Rowe)
Looks at mimicking the process of photosynthesis to harness energy from sunlight more efficiently.

14 October 2006, pages 52-55
Hello solar (by Tim Thwaites)
Tells the story of a solar powered ferry.

27 May 2006, pages 44-47
Two for the price of one (by Herb Brody)
Explains how nano solar cells improve the efficiency of energy production from sunlight.

29 October 2005, page 28
Box of tricks takes surgery into the sticks (by Michael Day)
Describes the solar powered 'hospital in a box' used to perform operations in remote locations.

18 December 2004
Pliable solar cells are on a roll (by Fred Pearce)
Describes a light, flexible solar panel that is made in rolls and can be cut to any length.

17 July 2004
Is the green dream doomed to fail? (by Jenny Hogan and Philip Cohen)
Questions the ability of renewable energy sources to replace fossil fuels without subsidies and incentives.

15 May 2004, page 16
Wring more might from your light
A new semiconductor nanocrystal could convert 60 per cent of sunlight into useable power by releasing more electrons per photon.

Scientific American
January 2008, pages 34-35
Sun power gets a boost (by Mark Alpert)
Explores the incorporation of an artificial photosynthesis process in photovoltaic cell design.

December 16 2007, pages 48-57
A solar grand plan (by Ken Zweibel, James Mason and Vasilis Fthenakis)
Presents a grand plan employing solar technology to provide the U.S. with power.

Useful sites

Your Home (Australian Government)
  • Solar hot water
    Provides technical details about domestic solar hot water systems.
    http://www.yourhome.gov.au/technical/fs43.htm

  • Photovoltaic systems
    Provides technical details about domestic photovoltaic systems.
    http://www.yourhome.gov.au/technical/fs47.htm

Concentrating Solar Thermal Systems (Solar Thermal Group, Australian National University)

Provides technical descriptions of some solar thermal collecting systems.
http://engnet.anu.edu.au/DEresearch/solarthermal/high_temp/concentrators/basics.php

Tapping into the sun (National Renewable Energy Laboratory, USA)

An article on photovoltaic cells with case studies.
http://www.nrel.gov/docs/legosti/old/16631.pdf

How Stuff Works, USA

  • How solar cells work
    Examines how solar cells convert the sun's energy into electricity.
    http://www.howstuffworks.com/solar-cell.htm

  • How power grids work
    Looks at the equipment that brings electricity to your home.
    http://science.howstuffworks.com/power.htm/printable

Australian Government Department of the Environment, Water, Heritage and the Arts

  • Solar thermal
    Lists technologies that use energy from the sun to produce electricity or heat.
    http://www.environment.gov.au/settlements/renewable/recp/solar/index.html

  • Renewable energy commercialisation in Australia
    Lists the renewable energy projects that are being commercialised in Australia, including solar thermal and solar photovoltaics projects.
    http://www.environment.gov.au/settlements/renewable/recp/

  • Solar cities: A vision of the future
    Outlines the Government’s Solar Cities project, in which seven Australian cities will participate.
    http://www.environment.gov.au/settlements/solarcities/index.html

Map of operating renewable energy generators in Australia (Geoscience Australia)

Provides maps of proposed and operational renewable energy generators across Australia.
http://www.agso.gov.au/renewable/

Australian Broadcasting Corporation

  • Solar future (Catalyst, 27 July 2006)
    Looks at a number of promising solar technologies being developed.
    http://www.abc.net.au/catalyst/stories/s1698520.htm

  • Dye solar cell (Catalyst,18 November 2004)
    Describes the development of a new type of solar cell that does not use silicon.
    http://www.abc.net.au/catalyst/stories/s1241478.htm

  • Sunrise or sunset? (transcript from Earthbeat, 24 April 2004)
    Discusses the current status in Australia of research into three types of solar energy: photovoltaics, solar thermal energy and solar hot water.
    http://www.abc.net.au/rn/science/earth/stories/s1093111.htm

Revisiting solar power's past (Solarenergy.com)

A 10-page history of attempts to convert solar radiation into mechanical power. (An article by Charles Smith from Massachusetts Institute of Technology's Technology Review, July 1995.)
http://www.solarenergy.com/info_history.html

Glossary

alternative energy sources. Energy sources different from those in widespread use at the moment (which are referred to as conventional). Alternative energy usually includes solar, wind, wave, tidal, hydroelectric and geothermal energy. Although they each have their own drawbacks, none of these energy sources produces significant air pollution, unlike conventional sources.

fossil fuels. Carbon or hydrocarbon fuels, derived from what was living material, and found underground or beneath the sea. The most common forms are coal, oil and natural gas. They take millions of years to form. Their energy is only released upon burning, when the carbon and hydrogen within them combine with the oxygen in air to form carbon dioxide (CO2 ), or carbon monoxide (CO) and water (H2O). Other elements within the fuels (such as sulfur or nitrogen) are also released into the air after combining with oxygen, causing further pollution with SO2 and nitrogen oxide gases. In the case of coal, ash particles are also a problem.

non-renewable energy. Used to describe energy sources that exist in a limited amount on Earth. Thus all available material could eventually be completely used up. Coal, oil and gas (see fossil fuels) are considered as non-renewable energy sources because the rate of their formation is so slow on human timescales that they we are using them without them being replaced. Uranium (used in nuclear power) is also non-renewable, although its reserves are very large compared to its rate of use. Compare renewable energy.

passive solar heating. The use of the sun to heat buildings. Careful design and positioning of buildings can ensure that sunlight in the winter months will warm them by day, with much of the warmth remaining during the night. Summer sunlight is usually kept out. This does not involve the conversion or harnessing of solar energy.

photovoltaic (PV) cells. Also known as solar cells. A photovoltaic cell is made of thin wafers of two slightly different types of silicon. One, doped with tiny quantities of boron, is called P-type (P for positive) and contains positively charged 'holes', which are missing electrons. (Electrons are negatively charged particles that orbit the nuclei of atoms.) The other type of silicon is doped with small amounts of phosphorus and is called N-type (N for negative). It contains extra electrons. Putting these two thin P and N materials together produces a junction which, when exposed to light, will produce a movement of electrons – and that constitutes an electric current. Photovoltaic cells thus convert light energy into electrical energy.

renewable energy. Used to describe energy sources that are replenished by natural processes on a sufficiently rapid time-scale so that they can be used by humans more or less indefinitely, provided the quantity taken per unit of time is not too great. Examples are animal dung, ethanol (derived from plant sugars), wood, wind, falling water and sunlight. Compare non-renewable. For more information see Renewable energy (Australian Greenhouse Office).

solar collectors. Devices for capturing the sun’s energy over a large area and focussing it on a small area, thereby concentrating it. In this way it can be made to provide extremely high temperatures, used to generate steam that will expand, or to carry out a chemical reaction to produce a portable fuel such as hydrogen. Solar collectors may be curved dishes - like satellite receiving dishes – coated with reflective material, or can consist of an array of reflectors, arranged like flower petals, focussing onto a central point. Usually the dish or the individual reflectors can be steered to follow the sun across the sky.

solar energy. Energy derived ultimately from the sun. It can be divided into direct and indirect categories. Most energy sources on Earth are forms of indirect solar energy, although we usually don’t think of them in that way. Coal, oil and natural gas derive from ancient biological material which took its energy from the sun (via plant photosynthesis) millions of years ago. All the energy in wood and foodstuffs also comes from the sun. Movement of the wind (which causes waves at sea), and the evaporation of water to form rainfall which accumulates in rivers and lakes, are also powered by the sun. Therefore, hydroelectric power and wind and wave power are forms of indirect solar energy. Direct solar energy is what we usually mean when we speak of solar power – it is the use of sunlight for heating or generating electricity.

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Posted February 1997.

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