Presentation on theme: "Energy – how much do we need and how can we get it? ■ Introduction. ■ How much energy do we and will we need in the UK? ■ How can we generate energy without."— Presentation transcript:
Energy – how much do we need and how can we get it? ■ Introduction. ■ How much energy do we and will we need in the UK? ■ How can we generate energy without the CO2? ■ Summary.
How much energy do we need? ■ Total current UK electrical power consumption about 40 GW ( , or 40 × 10 9 W). ■ UK population about 60 million ( , or 60 × 10 6 ). ■ Electrical power use is about 670 W per person... ■...or about 58 MJ per person per day. ■ Relate to “everyday” units: ♦1 kWh = 3.6 MJ, costs about 10p. ♦1 kWh/d = 42 W. ♦Power per person of 670 W = 16 kWh/d. ■ Current energy supply: 40 GW And how do we generate it?
40 GW Study by energy company EdF. Why do we need to do something new? ■ Projection of electricity capacity using current resources: ■ Large shortfall! ■ There is still lots of coal, so why not burn more of it? ■ Imja glacier, 1950s (top)/2007 (bottom): ■ Retreating 74 m per year.
Watt patented steam engine Early measurements from ice cores. More recent results, direct measurements from Hawaii. Why do we need to do something new? ■ “Manmade” CO 2 is causing potentially catastrophic changes in the climate. ■ Because of global warming, we need electric cars, trains, heating... i.e. more electricity, not less... ■...and we need to generate it without the CO 2 !
How much energy will we need? ■ In the UK, we now use roughly: ♦1.6 kW per person on transport. ♦1.6 kW per person on heating. ♦0.7 kW per person “electricity” – i.e. computers, fridges, TVs... ■ Assume in future use electricity for most transport, more efficient than current systems, so require 0.8 kW/p... ■...and that we insulate buildings better, use heat pumps etc. so heating requirements 0.8 kW/p. ■ Total electricity demand then about 140 GW. ■ (C.f. current figure of 40 GW.) ■ Renewable* energy resources: ♦Solar. ♦Biomass. ♦Wind. ♦Waves. ♦Tides. ♦Hydroelectric. ■ Non-renewable energy: ♦Fusion. ♦“Clean” coal. ♦Fission. *Naturally replenished in a relatively short period of time. How can we get it without the CO 2 ?
Solar power and biomass ■ Solar constant 1.4 kW/m 2. ■ At ground level, equator ~ 1 kW/m 2. ■ Correct for latitude, ~ 600W/m 2 peak... to average ~ 200 W/m 2...and for UK weather ~ 100 W/m 2. ■ Supplying 140 GW with solar cells of efficiency ~10% requires area of 14 × 10 9 m 2. ■ This is 6% of land area of UK... ■...and more than 100 times the photovoltaic generating capacity of the entire world. ■ Feasible for ~ 10% of UK needs? ■ Solar power interesting globally: come back to this later. ■ Efficiency of conversion of solar energy to biomass about 1%... ■...and then still have to convert to electricity.
Wind ■ Average UK wind speed ~ 6 ms -2. ■ ½ mv 2, efficiency, max. packing, give wind power density of about 2 W/m 2. ■ Need 30% of UK (70 × 10 9 m 2, i.e. Scotland) to provide 140 GW. ■ Off shore, wind speed higher, power density ~ 3 W/m 2. ■ Need turbines on ~ 45 × 10 9 m 2. ■ Shallow ( m depth) offshore sites available about km 2... ■...but many competing uses and technical problems. ■ Provide perhaps 10% of UK’s future electricity?
Waves ■ Energy in waves hitting UK ~ 40 GW. ■ Difficult to use efficiently, many competing interests. ■ Perhaps provide about 5% of UK’s future electrical energy? ■ Lots of energy in principle (~250 GW). ■ How can it be used efficiently? ■ Competing interests? ■ Perhaps 5% of UK’s future electricity? Pelamis wave energy collector Tides
Hydroelectric ■ UK power density ~ 0.1 W/m 2, so cannot make large contribution. ■ Largest hydro-electric power station is Three Gorges Damn on Yangtse, projected output 20 GW. ■ Displaced ~ 1.2 × 10 6 people, caused, and will cause, ecological problems. ■ Tally for UK so far: ■ We are still missing the lion’s share... ■...and the UK is particularly well off for wind, wave and tidal power! ■ What about “clean” coal, nuclear fission and nuclear fusion? Energy sourceProp. of electricity Solar10% Wind10% Wave5% Tidal5% Other5% Total35% Renewable balance
“Clean” coal ■ Burn coal, capture ~ 90% of CO 2, permanently store in e.g. depleted oil reservoirs. ■ Efficiency of electrical power production decreases from ~ 40% to ~ 30%. ■ UK coal reserves ~ 250 years at current rate of consumption. ■ Globally very important (China building one new power station every week). ■ Use technology for cement factories...
Nuclear fission and fusion ■ Fission currently provides ~ 20% of UK electrical energy. ■ But many (perceived) problems: ■ Safety: ♦Chernobyl. ♦Three Mile Island. ■ Waste: ♦Actinides with half lives of many thousands of years. ■ Proliferation. ■ Uranium reserves uncertain. (Extract from oceans? Use fast breeder reactors?). ■ New approaches needed: ADSR and thorium? ■ Fusion under investigation by ITER. ■ Construction until 2019, first deuterium-tritium plasma 2025?
Nuclear fission ■ Each fission: ♦Caused by absorption of 1 neutron. ♦Produces ~ 2.5 neutrons. ♦Some neutrons lost, k left to cause new reactions. ■ Conventional reactor: ♦Need k = 1. ♦If k < 1 stops working. ♦If k > 1 explodes.
Conventional fission reactor
Fast Breeder Reactor ■ Generally uses 239 Pu as fissile material. ■ Produced by fast neutrons bombarding 238 U jacket surrounding reactor core. ■ 239 Pu fission sustained by fast neutrons, so cannot use water as coolant (works as moderator). ■ Liquid metals (or heavy water) used instead. ■ India has plans to use thorium in its Advanced Heavy Water Reactors, in these 232 Th is converted to fissile 233 U.
Energy Amplifier or ADSR ■ Accelerator Driven Subcritical Reactor is intrinsically safe. ■ Principal: ■ Run with k < 1 and use accelerator plus spallation target to supply extra neutrons. ■ Switch off accelerator and reaction stops. ■ Need ~ 10% of power for accelerator. ■ Can use thorium as fuel. ■ 232 Th + n 233 U. ■ Proliferation “resistant”: ■ No 235 U equivalent. ■ Fissile 233 U contaminated by “too hot to handle” 232 U. ■ There is lots of thorium (enough for several hundred years)… ■ …and it is not all concentrated in one country! Accelerator Spallation Target Core Protons
Energy Amplifier or ADSR
Waste from ADSR ■ Actinides produced in fission reactions are “burnt up” in the reactor. ■ Remaining waste has half life of a few hundred rather than many thousands of years. ■ Can use ADSR to burn existing high activity waste so reducing problems associated with storage of waste from conventional fission reactors. ■ So why haven’t these devices already been built?
Accelerator ■ Challenge for ADSRs is accelerator. ■ Required proton energy ~ 1 GeV. ■ For 1 GW thermal power need current of 5 mA, power of 5 MW. ■ Need high reliability as spallation target runs hot. ■ If beam stops, target cools, stresses and cracks: max. few trips per year of longer than few seconds(?). ■ Compare with current accelerators: ♦PSI cyclotron: 590 MeV, 2 mA, 1 MW. ♦ISIS synchrotron: 800 MeV, 0.2 mA, 0.1 MW. ♦Many trips per day! ■ Cyclotron, fixed B field, radius increases: energy needed too high! ■ Synchrotron, constant radius, B field ramped: current too high! ■ Linac: perfect, but too costly?
Fixed Field Alternating Gradient Accelerator ■ FFAG, radius of orbit increases slightly with energy: protons move from low field to high field region. ■ Simplicity of operation hopefully ensures the necessary reliability. ■ nsFFAG at Daresbury (EMMA): ■ First experiments underway! Inject at low K Extract at high K
FFAG and acceleration ■ RF cavities conventionally used to accelerate charged particles. ■ A problem with FFAG is synchronisation of RF with particle orbits over large energy range. ■ Alternative: inductive acceleration? ■ Use Faraday’s Law:
FFAG betatron ■ Make solenoid into toroid so no problems with stray fields. ■ Use lots of small toroids in parallel rather than one big one: ■ Perhaps use one set of toroids for two or three FFAGs? ■ Make toroids part of LCR circuit. ■ Choose capacitance so resonance at required frequency. ■ E.g. here: ♦f B = 10 kHz. ♦T B = 0.1 ms. AC toroids L C small R
Time (s) EMF (V) Flux (weber) Time (s) Rel. energy spread Energy (eV) FFAG Betatron ■ Field in 50 toroids B = 2 T. ■ Toroid radius r T = 0.25 m. ■ Inject protons with K i = 5 MeV. ■ Integrate over ■ Look at acceleration of particle with central energy and of particles with energy K i ± × K i. ■ Differences for latter amplified by factor 10 in plot: ■ Accel. to 100 MeV in about 0.05 ms.
International solar power ■ More than 90% of world’s population live less than 3000 km from a desert. ■ Could be supplied with solar power. ■ Use solar thermal collectors to heat oil, produce steam, generate electricity, or with Stirling engines: ■ HVDC lines to efficiently transfer to coast (electrolysis to produce H 2 ) and to centres of population. ■ Less than 10% of desert area needed to supply world’s energy needs. ■ Proposal for Europe: Desertec- Eumena.
Summary ■ Producing enough electricity without causing climate change is a challenge. ■ Renewables can provide of UK future needs. ■ Global solar power solution has potential to provide world’s energy needs. ■ Essential for UK and world that all feasible technologies are investigated (solar, wind, wave, tide, fission, fusion, clean coal) – some may not work for technical or political reasons! ■ New approaches to power generation through nuclear fission worth considering. ■ Accelerator Driven Subcritical Reactor interesting: ♦Safe. ♦Produces waste with short half-life. ♦Can use thorium. ■ Major challenge is 5 MW, 5 mA, 1 GeV, extremely reliable proton accelerator. ■ Fixed Field Alternating Gradient accelerators operate with constant magnetic fields, hence reliable and allow very rapid acceleration. ■ Problem synchronising RF? ■ Circumvent by using electromagnetic induction to drive acceleration?
Summary ■ The challenge we face is to keep the lights on...without raising the sea level!