# Energy – how much do we need and how can we get it?

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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?
And how do we generate it? Total current UK electrical power consumption about 40 GW ( , or 40 × 109 W). UK population about 60 million ( , or 60 × 106). 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

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. 40 GW Study by energy company EdF.

Why do we need to do something new?
“Manmade” CO2 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 CO2! Watt patented steam engine Early measurements from ice cores. More recent results, direct measurements from Hawaii.

How much energy will we need?
How can we get it without the CO2? 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.

Solar power and biomass
Solar constant 1.4 kW/m2. At ground level, equator ~ 1 kW/m2. Correct for latitude, ~ 600W/m2 peak... to average ~ 200 W/m2...and for UK weather ~ 100 W/m2. Supplying 140 GW with solar cells of efficiency ~10% requires area of 14 × 109 m2. 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 mv2, efficiency, max. packing, give wind power density of about 2 W/m2. Need 30% of UK (70 × 109 m2, i.e. Scotland) to provide 140 GW. Off shore, wind speed higher, power density ~ 3 W/m2. Need turbines on ~ 45 × 109 m2. Shallow ( m depth) offshore sites available about km2... ...but many competing uses and technical problems. Provide perhaps 10% of UK’s future electricity?

Waves Tides 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

Hydroelectric Renewable balance
UK power density ~ 0.1 W/m2, so cannot make large contribution. Largest hydro-electric power station is Three Gorges Damn on Yangtse, projected output 20 GW. Displaced ~ 1.2 × 106 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 source Prop. of electricity Solar 10% Wind Wave 5% Tidal Other Total 35%

“Clean” coal Burn coal, capture ~ 90% of CO2, 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 239Pu as fissile material.
Produced by fast neutrons bombarding 238U jacket surrounding reactor core. 239Pu 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 232Th is converted to fissile 233U.

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. 232Th + n  233U. Proliferation “resistant”: No 235U equivalent. Fissile 233U contaminated by “too hot to handle” 232U. There is lots of thorium (enough for several hundred years)… …and it is not all concentrated in one country! Accelerator Spallation Target Core Protons

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?

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. TB = 0.1 ms. toroids L C AC small R

FFAG Betatron Field in 50 toroids B = 2 T. Toroid radius rT = 0.25 m.
Inject protons with Ki = 5 MeV. Integrate over Look at acceleration of particle with central energy and of particles with energy Ki ± × Ki. Differences for latter amplified by factor 10 in plot: Accel. to 100 MeV in about 0.05 ms. Flux (weber) Energy (eV) Rel. energy spread EMF (V) Time (s) Time (s)

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 H2) 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!

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