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An hour’s worth of sunshine could power the world for a year. If only we could bottle it. Discover the quest to make this a reality in ‘The Solar Revolution’.

The Solar Revolution

The Solar Revolution: Why bottled sunshine is the fuel of the future
Steve McKevitt & Tony Ryan

£1.99/$2.99

The sunshine that hits the Earth in a single hour could meet the world’s food and energy demands for an entire year. If only we could make use of it that is. Solar power is not just about turning sunlight into electricity – we also need a way of capturing and storing it, of moving it around to where it’s needed. Of providing power during the night. In short, we need a way of bottling sunshine so that we can have as much of it as we want, wherever and whenever we like. Solve this, and we will welcome the solar revolution.

Our current coal, oil and gas energy supplies rely on sunshine captured long ago by plants and animals long since fossilised. Harnessing the sun directly would open the way to a future free from the side effects of burning carbon. But that’s not the only reason to look to the sun. By 2050, the world’s population is predicted to rise to some 10 billion individuals. Our energy requirements will nearly double over the same period. Today we are burning through 20 million years of fossil record every year. We use this energy to stock our supermarkets, light our homes and run our businesses. In the long run, we’re going to need to find a new way of powering our lifestyles.

In ‘The Solar Revolution’, Steve McKevitt and Tony Ryan explore this energy problem and the solutions on offer. From nuclear to wind, fossil fuels to sunshine, they look at where our energy comes from and what the issues are with producing it this way or that. They delve into the science that underpins it all as well, explaining exactly how the sun’s rays might be turned into a new liquid fuel to power the world.

Guardian Short cover image from a photograph by Jonathan Kershaw, CC BY 2.0.

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The Solar RevolutionThis Guardian Short is a companion to a longer work by the authors, The Solar Revolution: One world. One solution. Providing the energy and food for 10 billion people., published by Icon Books. Expanding on some of the issues and science covered in the Guardian Short and delving into new areas, it is available in paperback from the Guardian Bookshop.

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About the Authors

Steve McKevitt is an expert in communications and consumerism. Over a 25-year career his clients have included Nike, Coca-Cola, Deutsche Bank, Sony PlayStation, Harvey Nichols, Motorola, Universal, Virgin, BT and Atari. Steve is chairman of Golden, an ideas agency with clients in the UK, Europe and the USA, and also works as an advisor to national and regional UK government on employment, skills, business innovation and international trade.

Professor Tony Ryan OBE is a polymer chemist at the University of Sheffield. He delivered the 2002 Royal Institution Christmas Lectures and regularly appears on Radio 4′s Infinite Monkey Cage with Brian Cox and Robin Ince, and has been on In Our Time with Melvyn Bragg.

Extract

This extract is edited from Chapters 6 and 7 of The Solar Revolution

Capturing just one hour of the sunshine that hits our planet would enable us to meet the world’s food and energy needs for an entire year – and each year, the sun radiates more energy onto the Earth than has been used in the whole of human history. Both these statements will still be true in 100 or even 500 years’ time, because sunshine will effectively never run out nor weaken. The potential of solar to provide us with energy can be regarded as limitless.

Turning this sunshine into electricity can most readily be achieved by making use of the photoelectric and the photovoltaic effects, two closely related but fundamentally different processes.

Some materials, known as photodetectors, are sensitive to light and other forms of electromagnetic energy. Light itself is composed of tiny packets of energy called photons. When certain photodetectors – various forms of silicon or compounds such as cadmium telluride, for example – are exposed to light, they cast off an electron, which can be captured by an electrode to create a voltage or electric current. This is the photoelectric effect.

In the photovoltaic effect, when photons strike the material in a photovoltaic (PV) cell, some are reflected, some pass right through, but some are absorbed. It’s these absorbed photons that produce electricity. They transfer their energy to the negatively charged electrons orbiting the nucleus of the atoms of the semiconductor found within the panel. This allows the electrons to escape from their natural position, leaving a ‘hole’ behind them, which behaves like a positively charged particle. The photovoltaic effect differs from the photoelectric effect because light isn’t causing electrons to be cast adrift from the material it is striking, but rather to be transferred between different quantum bands in the material. These escaping electrons form an electric current, which can in turn be used to create a build-up of voltage between two electrodes and then be driven through an external load. Devices using the photovoltaic effect are usually called solar cells.

At the moment, the most common way of gathering the sun’s power is to use solar cells and the photovoltaic effect. Individual solar cells produce a very low voltage, so several cells are wired in series inside a weatherproof container to make a PV module, or what we call a solar panel. Panels are often found on the roofs of houses and offices, and although the electricity they produce is currently expensive – $280 per MWh compared with just $40 per MWh for coal – constant developments around PV cells have allowed for production on an industrial scale.

To harvest the sun’s energy at this level requires a solar farm – essentially a vast array of PV panels that can generate electricity on the same commercial scale as a regular power station. Unlike regular power stations, however, location matters a great deal. During cloudless days on the equator, where the Earth’s surface presents a plane that is perpendicular to the sun, the rays beat down at a maximum strength of 2,400 kW/m² of solar radiation per day. In more temperate climes the sun shines with much less ferocity this drops dramatically to between 700 and 1,000 kW/m². Completed in 2008 and covering an area of 110 hectares (1,100 square meters), Waldpolenz Solar Park just outside Leipzig in Germany was the world’s largest photovoltaic power system when it was constructed. It generated 52,000 MWh of electricity in 2011. The solar park in Topaz, south California is due for completion in 2015. It will cover 260 hectares (2,600 square metres and will generate 1,100 GWh of renewable energy annually. This huge variation is due entirely to climate and location. In Germany each megawatt of capacity produces approximately 0.6 GWh in a year, while in California output is more than double at 1.4 GWh per MW, per year.

Now, let us consider scaling up. Currently, assuming an average daily amount of five hours usable sunshine it is reasonable to expect that a typical solar array located in the northern hemisphere to produce between 0.75 and 1 kWh/m² per day. By way of comparison, imagine moving the same system to the Sahara desert. The Sahara covers more than 9 million square kilometres (3.5 million square miles). It’s a barren wilderness with scarce indigenous fauna and flora, inhospitable to human life and of little practical use. With almost no cloud cover and a more favourable solar angle, we would obtain around 8.3 kWh/m² per day. Provided we could keep the sand off the panels, covering just 1 per cent of the Sahara (90,600 km² – an area slightly smaller than Portugal) in solar panels would provide as much electricity as all of the world’s power stations in 2012 combined.

But we don’t need to venture into the desert to find the future of solar power. In cities, where solar farms are not an option, scientists are turning instead to solar trees. As the name implies, they are artificial solar arrays that mimic the look of their real-life counterparts. Solar trees provide shade during the day and at night can even function as streetlights.

What is beyond doubt is that there is more than enough sunlight to allow us to generate all of our electricity, but at present only a tiny fraction of the world’s total electrical output (0.02 per cent in 2008) uses solar radiation as a fuel. As a means of generating electricity, solar energy is, theoretically, nearly perfect. But the practical drawbacks that prevent it from being a truly holistic fuel are considerable. And even if we overcome these problems, scaling up solar power using photovoltaics will be hugely challenging, the reason being that PV cells produce electricity directly, and there is currently no viable, cost-effective way to store that. Also, like all renewables, sunlight is intermittent, while our energy needs are continuous. The sun doesn’t shine anywhere for 24 hours a day, nor does it shine much during the long winter months when our energy demand is greatest.

Yet despite all these drawbacks there remains plenty of untapped potential in solar, particularly if we stop thinking of it merely as a means of generating electricity. It can be so much more than that and one day it will be the source of all the energy we consume. In order to move to that exclusively solar economy we must first address the issues of intermittency, transmission and portability. Finding efficient and cost-effective ways of storing and transporting all the sunshine we capture – ideally as a liquid fuel – is the final piece of the jigsaw.

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