Energy – how much do weneed 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 (40 000 000 000, or 40 × 109 W).

■ UK population about 60 million (60 000 000, 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

And how do we generate it?

40 GW

Study by energy com

pany 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.

Wat

t pat

ente

d st

eam

eng

ine

Early measurements from ice cores.More recent results, directmeasurements from Hawaii.

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!

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 CO2?

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 of14 × 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 (10...25 m depth) offshore

sites available about 20 000 km2...■ ...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/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 10%

Wave 5%

Tidal 5%

Other 5%

Total 35%

Renewable balance

“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 thoriumin its Advanced Heavy Water Reactors, in these 232Th is converted to fissile 233U.

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.■ 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

CoreProtons

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 KExtract 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:

A2 r

dE.ds

dt

E

FFAG betatron

■ Make solenoid into toroid sono 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.

AC

toroidsL

C

small R

Time (s)

EM

F (V

)

Flux (w

eber)

Time (s)

Rel. energy spread

Energy (eV

)

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 ± 0.001 × Ki.

■ Differences for latter amplified by factor 10 in plot:

■ Accel. to 100 MeV in about 0.05 ms.

B B0.26T t 0.74T .

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?

13~

Summary

■ The challenge we face is to keep the lights on...without raising the sea level!