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!
