Accordingto Energy UK, over 54% of the UK’s electricity was produced from fossil fuels in2016 – 42% from natural gas, 9% from coal and 3.1% from other sourcesi.However, burning these fossil fuels creates dangerous greenhouse gases, such ascarbon dioxide, which damages the atmosphere and contributes towards globalwarming. This in itself makes fossil fuels an inconvenient source of energy, butwhen coupled with the prediction that fossil fuels will run out by the end ofthe centuryii,it becomes clear why it is vital that we explore alternative energy sources. So,what are our potential options for energy in the future? SolarPanelsOurfuture energy sources would ideally be renewable, meaning they will never runout, unlike fossil fuels which are unrenewable. One of the best renewablesources of energy is the sun, whose energy can be captured and collected usingsolar panels. A solar panel is a large collection of small solar cells.
Theidea of using a solar panel to collect energy is based on the photovoltaiceffect, which was first observed by father and son Antoine-César andAlexandre-Edmond Becquerel in 1839iii.This is the idea that a potential difference can be created between twomaterials when light is incident upon it. This phenomenon was studied heavilythroughout the mid 19th century, which lead to the creation of thefirst solar cell by American inventor Charles Fritts in 1883iv.Fritts’ cell was made from of a layer of selenium covered with a thin film ofgold. Although this was a monumental discovery, it wasn’t deemed a viableenergy source due to its efficiency of <1%.
However,with advances in technology, solar panels are now a much more suitable methodof producing electricity. Green Match now quote their solar panels asdelivering between 15%-22% efficiencyv,which is still lower than the average efficiency of producing electricity fromfossil fuels (around 36%vi),but substantially greater than Fritts’ cell. Modern day solar panels are madeup of many individual photovoltaic cells. Each cell is made from two layers ofsemi-conducting silicon. The top layer is seeded with phosphorus, giving itextra electrons and hence a negative charge.
The bottom layer is seeded withboron, which gives it a positive chargevii.A depletion layer is sandwiched in between these two silicon layers, whichdisallows the flow of electrons between the two silicon layers. This depletionlayer helps each layer to retain its positive/negative charge, or elseelectrons would simply jump from the negative layer to the positive layer tobalance out the charge. When photons from the sun hit the negatively charged silicon,the electrons can gain enough energy to escape the silicon via thephotoelectric effect. Electrical conductors are attached to each layer ofsilicon so that the free electrons can travel through the conductor, around acircuit, and back into the positive layer to complete the circuitviii.
This is how a solar cell can produce an electric current when under sunlight. WindTurbinesAnotherrenewable energy source is wind. Wind turbines can harness the wind to produceelectricity. Humans have used wind energy for thousands of years, such as forpropelling boats, but they’ve only been used for generating electricity since1887 when Prof James Blyth created the world’s first known wind turbine inScotlandix.
Modern day wind turbines still work in a similar way. As air passes through theblades of the turbine, it causes it to rotate. This rotation turns anelectrical generator, inducing an electric current in the traditional way. Thegenerated electricity travels from the generator to a step-up transformer,which then transports the electricity at a high voltage, yet low current, towhere it’s needed. Itis quite simple to calculate the power generated by a wind turbinex.The kinetic energy, KE, of any mass, m, with velocity, v, can be calculated by: Equation (1) Andthe rate of mass flow can be given by: Equation (2) Therate of change of energy, or power, of the wind can be given by: Equation (3) Bysubstituting Equation (2) into Equation (3), it can be found that: Equation (4) However,it is not possible for a wind turbine to capture all of this power from thewind. A power coefficient, Cp,can be factored into the equation: Thevalue of this coefficient varies from turbine to turbine, but it can never beabove 0.
59 due to Betz’s Lawxi.The value of Cp usuallylies around 0.35-0.
45x. NuclearPowerThereare two process in which nuclear power can be produced – fission and fusion.Nuclear fission is already in use in the UK, accounting for 21% of electricity producedin 2016i.Fission involves the splitting of uranium-235 into a variety of smallerdaughter nuclei. This is done by firing a slow-moving neutron at the uraniumnucleus, which causes the nucleus to become so unstable that it splits intodaughter nuclei and some more neutrons. Below is a possible fission equation: Thisuranium nucleus is composed of 92 protons and 143 neutrons.
In terms of atomicmass units, these constituent parts of the nucleus have a total mass of (92 x1.00728) + (143 x 1.00866) = 236.
90814 u (where 1 u = 1.661 x 10-27kg). However, its actual isotopic mass is only 235.04393 uxii.This difference is due to something called binding energy.
When all the protonsand neutrons are separate, they do indeed have a combined mass of 236.90814 u.When these nucleons are brought together to be bound into a nucleus, theybecome more stable, and consequently release energy. The energy released is thebinding energy. According to Einstein’s E=mc2,when the nucleons lose energy, they also lose mass. This is what causes themass of a uranium-235 nucleus to be less than the combined mass of itsconstituent parts. Lookingback at the equation, the total mass of the reactants is 236.
05259 u, whilstthe final mass of the products is 235.85328 u. This means the mass lost duringthis reaction 0.19931 u, which equates to 2.
98 x 10-11 J, or around 186MeV. This is an incredibly large amount of energy considering it’s from justone nucleus. Considering just one gram of pure uranium-235 would contain around2.56 x 1021 nuclei, this gram could produce over 76 GJ of energy. In general, a nuclear reactionwill produce energy if the binding energy per nucleon of the products isgreater than that of the reactants. You can imagine the above equation in twosteps. Energy must be put in to break the uranium nucleus up into itsconstituent nucleons, equal to its total binding energy.
Energy is thenreleased when these nucleons recombine to form the daughter nuclei. Thisprocess does not actually happen, it just makes it easier to consider theenergy changes. There must be the same number of nucleons on each side of theequation, as protons and neutrons can’t just disappear. The binding energy pernucleon of uranium is less than that of tin and molybdenum. Therefore, lessenergy is put in when breaking up the uranium than is released when the Sn andMo nuclei are formed. This explains why, overall, energy is released, and themass decreases.
Asimilar explanation can be applied to nuclear fusion. Contrary to fission, fusioninvolves fusing together two small nuclei to produce a larger nucleus. The mostcommon reaction for nuclear fusion involves reacting deuterium (hydrogen-2) andtritium (hydrogen-3) to produce helium-4 and a neutron. Again, as helium has ahigher binding energy per nucleon than the hydrogen nuclei, energy is releasedduring this process. To look at it quantitatively, this reaction causes a massof 0.01889 to be lost, which is equivalent to 2.
82 x 10-12 J, or17.6 MeV. As one gram of hydrogen (which is 50% deuterium and 50% tritium)would contain around 2.41 x 1023 nuclei, this one gram sample couldtheoretically produce 679 GJ of energy. Whichis the best method?Enoughsolar energy is incident on the Earth every hour to meet the energy needs foran entire yearxiii.Of course, this is assuming the entire world was covered with 100% efficientsolar panels, but it does show the huge potential of using the sun as a sourceof energy.
We only need to capture ~0.01% of the sun’s energy tocontinuously power the entire world. An average onshore wind turbine willproduce around 6 million kWh in a year, which is enough to provide electricityfor 1,500 average EU householdsxiv.Nuclear fission already supplies around a fifth of the UK’s energy, and this isexpected to rise to a third by 2035xv.This shows that all three methods have their merits. Furthermore, none of thesemethods release greenhouse gases, so are much better for the environment thanburning fossil fuels.
However,whereas solar and wind are renewable, sustainable sources of energy, thereactants required for nuclear energy production are limited, but they willstill last for the foreseeable future. Another downfall of nuclear is that itdoes produce radioactive waste products. These can be harmful to theenvironment and wildlife, as well as human life, so has to be stored carefullyfor a long period of time.
Thedrawbacks of solar and wind energy are that they’re not always available. Asolar panel cannot produce electricity when it’s not sunny, and wind turbineswill only work at wind speeds of around 5-25 ms-1xiv