Chapter 2

Introduction

For most of the twentieth century, electricity followed a familiar pattern. Large power stations burned coal, oil or natural gas to generate electricity, which was then transmitted across long distances before reaching homes, businesses and industry.

This system powered the growth of modern society and proved remarkably effective at delivering electricity at scale. But over time, new technologies began to challenge the assumption that electricity had to come primarily from large fossil-fuelled power stations.

Hydroelectric dams demonstrated that renewable electricity could be generated on a massive scale. Wind turbines became larger, more efficient and more affordable. Solar panels moved from satellites and specialist applications onto rooftops and into vast utility-scale power stations. At the same time, battery storage, digital control systems and modern power electronics began changing what electricity networks were capable of managing.

The result is one of the largest shifts in power generation since national electricity grids were first built. Renewable energy is no longer sitting at the edge of the electricity system. It is becoming one of its central components.

The Fossil-Fuel Electricity System

For much of modern history, electricity systems were built around a relatively small number of large centralised power stations. Coal-fired plants became especially important because they could generate enormous quantities of electricity continuously, while gas-fired power stations later provided a more flexible source of generation that could respond more quickly to changing demand.

The basic structure was straightforward. Fuel was transported to a power station and burned to release heat. That heat was used to produce high-pressure steam or hot combustion gases, which turned turbines connected to electrical generators. The electricity was then stepped up to high voltage and transmitted across the grid before eventually being distributed to consumers.

This model shaped electricity networks for generations. Power flowed primarily in one direction: from large generators, through transmission and distribution networks, towards millions of customers.

The system worked because fossil fuels could be stored and burned whenever electricity was required. Power stations could increase or decrease their output in response to changing demand, making them well suited to a grid where electricity consumption varied throughout the day.

But the same system also embedded fossil-fuel combustion deep within the electricity sector. Every unit of electricity generated from coal or gas involved releasing carbon that had previously been stored underground into the atmosphere.

As the need to reduce greenhouse gas emissions became increasingly clear, attention turned towards technologies capable of generating electricity without continually burning fuel.

Hydropower - Renewable Energy's Early Giant

Although renewable energy is often associated with modern solar panels and wind turbines, large-scale renewable electricity has existed for much longer. One of the earliest major technologies was hydroelectric power.

Hydroelectric systems use the gravitational energy of water. In a typical dam, water is stored in a reservoir at a higher elevation. When released, it flows through turbines, converting gravitational potential energy into mechanical rotation and then into electricity. The underlying principle is simple, but the scale can be enormous.

Large hydroelectric dams have supplied significant amounts of electricity in many countries for generations. Unlike solar and wind, hydroelectric stations can also provide a degree of controllability because operators can often change the flow of water through the turbines in response to demand.

This made hydro especially valuable in electricity systems dominated by large centralised generators. It also demonstrated something important long before modern solar became widespread: renewable energy could operate at the same scale as conventional power stations.

Hydropower does, however, depend heavily on geography. Suitable river systems, elevation differences and reservoir locations are not available everywhere, and large dams can have major environmental and social impacts.

For that reason, hydro could never be the complete answer on its own. But it was the first clear demonstration that large-scale electricity did not have to depend entirely on fossil fuels.

The Rise of Wind

The next major transformation came from wind. Humans have used wind energy for centuries to propel ships, pump water and grind grain. Modern wind turbines apply the same basic principle on a much larger and more sophisticated scale.

Instead of directly driving mechanical equipment, the rotating blades of a wind turbine turn a generator that produces electricity.

Early commercial wind turbines were relatively small and expensive. Over time, however, decades of engineering development transformed the technology. Turbines became taller, blades became longer, control systems became more advanced and manufacturing became increasingly efficient.

Increasing turbine size is especially important because larger rotors sweep a greater area and can capture more energy from the wind. Taller towers can also access stronger and more consistent wind speeds. This evolution has enabled wind farms to produce electricity at increasingly large scales.

Onshore wind farms are built on land, often in open rural areas where wind conditions are favourable. Offshore windfarms are built at sea, where wind speeds are often stronger and more consistent and where enormous turbines can be installed away from densely populated areas. Modern offshore turbines are among the largest rotating machines ever built, with individual units capable of generating many megawatts of power.

At the same time, improvements in manufacturing, installation, blade design, materials and operations have helped drive down the cost of wind-generated electricity. Wind moved from being a specialist technology to a major source of electricity in many regions.

Solar Steps Into the Spotlight

Few energy technologies have changed as dramatically as solar photovoltaics. For decades, solar cells were associated primarily with satellites, remote equipment and small specialist applications. They worked well, but they were too expensive to compete with conventional electricity generation on a large scale.

That changed gradually, then rapidly.

Manufacturing expanded. Production processes improved. Silicon wafers became thinner. Solar cells became more efficient. Modules became larger and more powerful. Supply chains matured, competition increased and factories began producing solar panels on an enormous scale.

As the technology improved, the cost of solar electricity fell. This created one of solar's greatest advantages: modularity. A solar cell produces only a small amount of power. Connect many cells together and they form a module. Connect multiple modules together and they form an array. Continue adding arrays and the same fundamental technology can scale from a few watts to hundreds of megawatts or even gigawatts.

This means solar can be deployed in places where traditional power stations cannot. A small panel can power a remote sensor. A rooftop system can supply a home. A commercial installation can cover a warehouse. A utility-scale solar farm can supply electricity to an entire region. The underlying photovoltaic effect remains the same. Only the scale changes.

This flexibility has allowed solar to spread rapidly across very different electricity markets. It can be installed by individual households, businesses, utilities and governments. Projects can range from a handful of panels to millions.

Solar also benefits from having no moving parts during normal operation, relatively low maintenance requirements and no fuel cost once installed. As panel efficiency improved and manufacturing volumes increased, solar moved from an expensive niche technology into one of the defining technologies of the global energy transition.

Why Renewables Became Competitive

The rise of renewable energy was not caused by a single breakthrough. Instead, it came from a reinforcing cycle of engineering improvement, manufacturing scale and investment. When a technology is produced in larger quantities, manufacturers gain experience. Factories become more efficient, supply chains improve and production costs can fall. Lower costs make the technology attractive to more customers, which increases deployment even further.

That additional deployment creates more opportunities for innovation, competition and investment. The cycle begins again. 

For solar, this can be thought of as:

Better technology → larger manufacturing scale → lower costs → more deployment → more innovation

Wind followed a similar path. As turbines became larger and more efficient, the amount of electricity produced by each machine increased. Larger projects encouraged investment in specialised vessels, factories, supply chains and maintenance systems, which helped the industry mature further.

This process links directly to the economics explored in Part 7.

A renewable technology does not need to be environmentally beneficial alone to expand rapidly. It becomes far more powerful when it also makes financial sense.

As the cost of generating electricity from wind and solar declined, developers, utilities, businesses and households increasingly began choosing them because they could provide competitive electricity as well as reduce emissions.

Unlike fossil-fuel power stations, solar and wind also require no continuous purchase of fuel. Most of the cost is concentrated upfront in construction, while the energy source itself, sunlight or wind, is free.

This changes the economics of electricity generation. It also means that improvements in financing, manufacturing and project design can have a major effect on the final cost of renewable electricity. The transition therefore became driven by more than environmental policy. Technology and economics began reinforcing each other.

 A Global Energy Transition

The growth of renewable energy is now taking place across the world. Different countries are moving at different speeds and for different reasons, but the underlying drivers are increasingly similar.

Climate targets encourage governments and companies to reduce greenhouse gas emissions. Falling technology costs make renewable projects more economically attractive. Energy security encourages countries to reduce dependence on imported fuels. Growing electricity demand creates the need for new generation capacity.

Solar and wind can contribute to all four. 

In some countries, utility-scale solar farms are supplying rapidly growing cities. In others, offshore wind projects are generating electricity far from the coastline. Rooftop solar is allowing households and businesses to become electricity producers as well as consumers, while hydropower continues providing large amounts of renewable electricity in regions with suitable geography.

The result is not simply a collection of individual renewable projects. It is a transformation in the structure of the electricity system itself. For more than a century, the grid was designed around a small number of large, controllable power stations. Now, electricity increasingly comes from thousands or even millions of different sources. Some are enormous. Some sit on individual rooftops. Some produce electricity whenever the sun shines or the wind blows rather than whenever operators choose.

This creates a new engineering challenge. Generating enormous quantities of renewable electricity is only the first step. That electricity still has to be transmitted, balanced, stored and delivered reliably at exactly the moment people need it.  The transition therefore does not end with building more solar panels and wind turbines. The electricity grid itself has to evolve.

Looking Ahead

Renewable energy is transforming where electricity comes from, but it is also changing how electricity systems must operate.

Solar generation rises and falls with daylight. Wind generation changes with weather conditions. Millions of rooftop systems can both consume electricity and export it back into the network.

At the same time, electricity supply and demand must remain balanced every second of every day.

In the next chapter, we'll explore how a renewable electricity system is built, from transmission networks and smart grids to battery storage, demand response and the technologies that allow millions of different energy resources to work together as one reliable system.