### Energy *

```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
(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
Why do we need to do something new?
■ Projection of electricity capacity
using current resources:
40 GW
■ Large shortfall!
■ There is still lots of coal, so why not burn
more of it?
Study by energy company EdF.
■ Imja glacier, 1950s (top)/2007 (bottom):
■ Retreating 74 m per year.
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!
Early measurements from ice cores.
More recent results, direct
measurements from Hawaii.
Watt patented steam engine
Why do we need to do something new?
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.
■ Supplying 140 GW with solar cells of
efficiency ~10% requires area of
■ At ground level, equator ~ 1 kW/m2.
9 m2.
14
×
10
2
■ Correct for latitude, ~ 600W/m peak...
■ This is 6% of land area of UK...
to average ~ 200 W/m2...and for UK
weather ~ 100 W/m2.
■ ...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
■ ...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
Tides
Pelamis wave energy collector
■ 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?
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:
Energy source Prop. of electricity
Solar
10%
Wind
10%
Wave
5%
Tidal
5%
Other
5%
Total
35%
■ 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?
“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)
■ India has plans to use thorium
Reactors, in these 232Th is
converted to fissile 233U.
■ Accelerator Driven Subcritical
Reactor is intrinsically safe.
■ Principal:
Accelerator
Protons
Spallation
Target
Core
■ 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!
■ 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,
increases:
energy
needed too
high!
■ Synchrotron,
constant
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.
■ nsFFAG at Daresbury (EMMA):
Extract at high K
Inject at low K
■ First experiments underway!
■ Simplicity of operation hopefully
ensures the necessary reliability.
FFAG and acceleration
■ RF cavities conventionally used to
accelerate charged particles.
■ Alternative: inductive acceleration?
d
■ Use Faraday’s Law: E   E .d s  
2  rA
■ A problem with FFAG is
synchronisation of RF with particle
orbits over large energy range.
dt
FFAG betatron
■ Make solenoid into toroid so
no problems with stray fields.
■ Use lots of small toroids in
parallel rather than one big
one:
■ Make toroids part of LCR circuit.
toroids
L
C
AC
small R
■ Perhaps use one set of toroids for two
or three FFAGs?
■ Choose capacitance so resonance at
required frequency.
■ E.g. here:
♦ f B = 10 kHz.
♦ TB = 0.1 ms.
FFAG Betatron
■
■
■
■
■ 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:
Field in 50 toroids B = 2 T.
Toroid radius rT = 0.25 m.
Inject protons with Ki = 5 MeV.
Integrate over 0.26 T B  t  0.74 T B .
Energy (eV)
EMF (V)
Flux (weber)
Time (s)
Time (s)
■ 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 H2) and
to centres of population.
■ Less than 10% of desert area needed
to supply world’s energy needs.
■ Proposal for Europe: DesertecEumena.
Summary
■ Producing enough electricity without
causing climate change is a challenge.
■ Renewables can provide ~ 1 3 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.