Energy

Energy - SQA Key Definitions : 

• Catalyst - A chemical that speeds up a chemical reaction without being used up or permanently changed in the process.

• Electrolysis - The splitting of water molecules into hydrogen and oxygen using electricity and an electrolyser device.

• Fission - The process of splitting an atomic nucleus into two or more smaller nuclei, releasing energy. 

• Fracking - The hydraulic fracturing of rock using a high-pressure mixture of chemicals, water and sand to release trapped gas. 

• Fuel cell - An electrochemical cell which converts the chemical energy stored within hydrogen directly into electrical energy. 

• Gasification - The process of converting coal into a gas blend of hydrogen, carbon monoxide and carbon dioxide using a thermochemical reaction.

• Hydrogen power - Electricity generation using hydrogen gas, either using specialised fuel cells to generate electricity, or burning in a thermal power station like natural gas.

• Pyrolysis - The process of converting biomass into a gas blend of hydrogen and methane using a thermochemical reaction.

• Shale gas -  Methane gas that is trapped within the impermeable sedimentary rock Shale.

• Steam methane reforming - The reaction of natural gas with steam in the presence of a catalyst to produce hydrogen and carbon.

Energy Resource : Shale Gas 

Energy is vital for every process in the universe to occur and is used by transferring it from one energy store to another. Systems that can store large amounts of energy are known as  'Energy resources'. 

As can be seen from the graph below, even with a global move towards renewable energy, at present, more than 80% of the global energy consumption is based on fossil fuels : 

Even with the transition towards renewable energy, due to increasing energy demand, new fossil fuel reserves continue to be developed globally. As traditional, easy-to-access oil and gas reserves become depleted, extraction companies are now turning to harder-to-extract reserves that had previously not been economically viable. 

One such harder-to-extract reserve is 'Shale Gas', which is extracted through a process known as 'Fracking'. Fracking is a method used to extract methane gas that is trapped within the impermeable sedimentary rock Shale :

Horizontal drilling is used to access the shale, at which point a chemical-water-sand mix is injected into the shale under very high pressure. This fluid causes hydraulic fracturing (origin of the name 'fracking) of the rock. The methane is no longer trapped and flows through the new fractures, enters the wellbore (the drilled hole), and flows up to the surface for collection. The methane is collected and used like any other natural gas; to generate electricity or supplied to homes and businesses. 

Fracking has several benefits, which is why countries are looking to exploit their shale gas reserves. These include :

• Increased Energy Security - Most oil and gas produced globally is by a group of countries referred to as the 'Organisation of the Petroleum Exporting Countries' (OPEC). This works under a 'Cartel' system, controlling price and supply. By allowing countries to access their own reserves, it reduces reliance on energy imports from other countries, promoting stability. 

• Increased Employment - By mining and processing shale gas 'in house', jobs are created in the mining sector, the processing sector and in a range of associated industries. 

• Bridging Fuel - Natural Gas (including shale gas) releases less carbon dioxide than burning coal, so there is some scope to use gas as a bridge, allowing energy generation during the transition to renewable energy sources. 

Fracking does have several challenges and environmental impacts, including : 

• Aquifer/Groundwater Contamination - Chemicals leaking from the wellbore or rising towards the surface through fractured rock could enter the groundwater and contaminate drinking water reserves. 

• Induced Seismic Activity - Earthquakes or tremors can occur when the injection of high-pressure fluid changes the stress balance of the earth's crust, causing pre-existing geological faults to slip. 

• Greenhouse Gas Emissions - Vehicle emissions during excavations, transport emissions and the burning of the shale gas itself all release carbon dioxide into the atmosphere, contributing to climate change. 

• Visual and Noise Pollution - Shale gas is trapped in thin layers across vast areas, which requires a high density of well pads, constant machinery, and heavy transport, all of which create significant visual and noise disturbances.

At present, fracking is under a legislative 'pause' as the UK government moves towards a permanent ban on the practice, due to the concerns raised above : 

Energy Resource : Hydrogen Power

One of the newest energy resources under development presently is 'Hydrogen power'. The element hydrogen can be used in specialised fuel cells to generate electricity, or can be burned like natural gas. This technology is currently not widely used, but is predicted to take a much larger role in energy production. 

In a fuel cell, the hydrogen 'donates' electrons at one electrode and oxygen 'gains' electrons at the other electrode, which causes a voltage to be generated across the cell. In this process, the hydrogen becomes oxidised, forming water, and is released from the cell : 

It is predicted that, by 2100, hydrogen power could make up ~8% of the global energy generation. To put that into perspective, Wind power currently provides ~2% of the global energy generation : 

This hydrogen is not found in its elemental form naturally in the environment in sufficient quantities to be viable, but hydrogen can be extracted from a range of sources : 

Hydrogen power has several benefits, which is why countries are looking to include this technology in their energy production. These include : 

• Abundant fuel source - Hydrogen can be extracted from a range of widely available resources, such as water, fossil fuels or biomass. 

• Reduces carbon dioxide emissions - The 'waste' gas released from a fuel cell is water, and as long as the hydrogen was originally separated using a renewable energy source, overall carbon dioxide emissions will be reduced through its use. 

• Reduced noise and maintenance - A fuel cell has no moving parts, so it runs silently and requires much less maintenance compared to a traditional internal combustion engine. 

• Energy-rich resource - Hydrogen fuel produces more energy per kilogram than either petrol or diesel. 

Hydrogen power does have several challenges and environmental impacts, including : 

• High cost - The materials required to build fuel cells are currently more expensive than those used in traditional energy technology. 

• Storage issues - High-pressure tanks are needed to store the hydrogen in sufficient amounts, which can be dangerous and difficult to handle (hydrogen is explosive). 

• Lack of infrastructure - A commercial fuel station network in Scotland does not currently exist (only 2 in Aberdeen and 1 in the central belt at present), limiting the speed at which fuel cells can be adopted. 

• Increased carbon dioxide emissions - If the hydrogen is produced without the use of renewable energy, the creation of the hydrogen fuel will cause increased carbon dioxide emissions. 

Energy Resource : Nuclear Power

A nuclear power station is a type of thermal power station (same as a coal-fired power station), in which the fuel heats water, which is converted to steam, which drives a turbine, turning a generator, generating Electricity :

Unlike a fossil fuel power station, in which the energy is released from the fuel by burning it, in a nuclear power station, the process is very different.  The source of the energy within the fuel in a nuclear power station is an atomic process known as 'Nuclear Fission'. 

Currently, Nuclear power makes up only ~1.5% of the global energy generation. This production is heavily weighted to 5 key countries: the U.S., China, France, Russia and South Korea, as shown in the graph below (UK included for reference) : 

Nuclear Fission is the process of splitting an atomic nucleus into two smaller nuclei plus a few neutrons, releasing heat energy and gamma radiation. Uranium-235 is used in the fission process in all commercial nuclear power stations as its atoms have relatively large nuclei that are easy to split.

The diagram below shows a nuclear fission process, in which a neutron triggers a Uranium-235 to split into two smaller nuclei (Barium-144 and Krypton-89), releasing three neutrons : 

The neutrons released in nuclear fission then go on hit other uranium nuclei and cause them to split, causing a chain reaction. The chain reaction must be controlled in a nuclear reactor to stop the reaction from running too fast, which risks an explosion. 

The diagram below shows the rapid, exponentially increasing chain reaction of Uranium-235 : 

The above chain reaction releases a very large amount of energy in a very short time, which is effectively a nuclear explosion. 

In order to use this energy safely within a power station, the Energy release must be kept at a constant level. The diagram below shows the core of a Fission Reactor, and can be used to show the control process :

There are four main sections to the core of a Nuclear reactor :-

• Radiation Shielding - The core is contained within a pressure vessel and surrounded by layers of lead and concrete to prevent the release of Radiation. 

• Fuel Rods - Long rods of very pure Uranium-235, the source of the Nuclear Fission.

• Graphite Moderator - Graphite is  used to slow down the Neutrons, increasing the efficiency of the reactor. 

• Control Rods - Made of Boron, the rods absorb Neutrons and by changing the depth of the control rods in the Reactor, the Energy output is controlled. In case of emergency, the rods can be dropped fully into the reactor, stopping the reaction completely. 

Nuclear power has several benefits, which include : 

• Reduces carbon dioxide emissions - As the reaction does not rely on the burning of a carbon-based fuel, overall carbon dioxide emissions will be reduced through its use. 

• Energy-rich resource - Nuclear fuel produces more 2.7 million times more energy per kilogram than Coal. 

• Safety record - Compared to the full supply chain for other energy sources, Nuclear has one of the lowest death rates for energy production : 

Nuclear power does have challenges, however, which include : 

• Non-renewable resource - The uranium required for nuclear fission is a finite resource that will eventually run out (current reserves are projected to last ~250 years). 

• Radioactive waste storage - The waste products from nuclear fission remain radioactive (and therefore extremely hazardous) for tens of thousands of years, making long-term storage both a necessity and a challenge. 

• Nuclear Accidents - Nuclear accidents, such as the Chernobyl disaster, can cause large areas to be unsafe for human habitation, contaminate ground or seawater and cause bioaccumulation of radioactive materials in marine organisms. 

Nuclear Power Case Study : The Fukushima Daiichi Nuclear Incident

The Fukushima Daiichi nuclear accident was a major disaster in N Japan on March 11, 2011, and it remains the most severe nuclear accident since Chernobyl in 1986. Its impacts are still ongoing. 

The Fukushima Daiichi nuclear site is located in a (then) heavily populated region of Japan, approximately 300 km north of Tokyo : 

The Fukushima Daiichi Nuclear plant consisted of 6 nuclear fission reactors, providing electricity to more than 3 million homes across northern Honshu island. 

On March 11, 2011, a magnitude 9 earthquake occurred below the seabed ~180 km away from Fukushima. The reactors automatically and safely shut down, but the earthquake disabled local electricity supplies. The cooling systems for the reactors moved to backup generators at this point, keeping the reactors cool and preventing a 'meltdown'. 

Just under an hour later, a 14m-high tsunami wave triggered by the earthquake reached Fukushima, overtopping the 10m high flood-defence walls and flooding the backup generators, destroying them. Without power, the cooling systems shut down, causing the reactors 3 reactors to undergo 'meltdowns'.  

A meltdown occurs when the fuel rods become so hot that they melt and form a molten mass at the bottom of the reactor. The resulting gases generated can cause explosions and release radioactive material into the environment.  In Fukushima, radiation was released both into the groundwater below the plant and through venting, which prevented further explosions, but released radioactive material into the air. 

More than 300,000 people living in the surrounding areas were evacuated, leaving entire ghost towns behind, with an exclusion zone set up to prevent anyone from returning. The image below shows a town in the exclusion zone, shortly after the evacuation : 

In the years since the earthquake and tsunami, the Japanese government has led efforts to clean up the damage and remove the hazardous material by removing a layer of contaminated topsoil from the entire region, processing and discharging the radioactive cooling water and beginning to remove the melted fuel from the reactors. 

However, this process will take decades, and even now, the exclusion zone still covers an area of 371 km², within which it is deemed too radioactive to stay longer than a few hours safely : 

The Fukushima Daiichi plant's meltdown and release of radioactive material has had a huge impact of nuclear power generation within Japan. In the aftermath, all nuclear reactors were taken offline to investigate how this happened, and put in place further safety measures. It is only recently that Japan has again begun to use nuclear power as a source of energy generation, and is still at a rate well below historical levels : 

The video below shows an overview of the earthquake and tsunami, the resultant meltdowns and evacuation, and the cleanup efforts :