Examination of Witnesses (Questions 20
- 39)
TUESDAY 6 MAY 2008
Professor AbuBakr Bahaj, Professor Tony Bridgwater
and Dr Simon Watson University and DR
SIMON WATSON,
Loughborough University, examined.
Q20 Lord MacGregor of Pulham Market:
Going back to wind power, given that the turbines only turn when
it is windy, to what extend do wind farms have to be backed up
by regular fossil fuel or nuclear generation? Are there any potential
technical solutions to that particular problem? Could you also
comment in that regard as to the relative merits and costs of
offshore and onshore?
Dr Watson: There is something called
the intermittency of wind power and I think we prefer to call
it the variability rather than the intermittency. In terms of
variability of wind power, if you take it in perspective in terms
of a power system, the way a power system is run conventionally
you have a large number of sources of demand and those sources
of demand are very variable. However, if you aggregate those sources
of demand over a large area then the overall variability goes
down quite significantly. The system is quite capable of coping
with fairly large changes in demand and typically the power system,
certainly in the UK and any other power system, would carry sufficient
online reserve to cope for the outage of a large power station
which typically might be in the UK of the order of about 1,300
megawatts. In terms of variability of wind power you would never
expect that you would lose 1,300 megawatts, say, of wind power
in the period of seconds which you might do in terms of a large
power station. The best way of trying to cope with variability
of wind power is to spread the wind turbines over a fairly large
geographical area. You tend to find that weather systems move
across the UK. The wind will change slowly across the UK so the
aggregated change in the power output of a number of wind farms
is fairly gentle; the rate is quite slow. In terms of variability
the impact on a system, particularly at the levels we are at the
moment, is quite small and is no more different than the variability
in the demand. If we move towards a system where we have, say,
20 per cent of electricity produced from renewables and let us
say about three-quarters of that came from wind power, then we
might reach a situation where we would have to have a little more
generation on the system which was capable of providing fairly
rapid backup for changes in the wind power output. The studies
that have been done and certainly the work I have done, at the
20 per cent level the extra cost of electricity is something in
the order of 0.2 pence per kilowatt hour which is fairly modest
I would say. You were asking me about how to mitigate the effects
of variability. One way, as I said is to try to spread out your
wind farms over a fairly large area to try to mitigate the changes
in the wind that you get. Another way is to make sure your system
is well-interconnected so, for example, the UK is connected to
France. If those interconnections were increased that would allow
greater movement of power between the UK and the European systems
so that if you had an excess of wind power generation you could
export; if you had a shortfall then you could import power from
other countries. So, spreading out the wind farms and greater
interconnection of power systems are ways of managing the variability.
Q21 Chairman:
If there is an anticyclone hovering over the UK and there is no
wind, what happens then?
Dr Watson: You could argue that might
happen, in fact studies are being done to look at how frequently
peak demand correlates with an anticyclone and no wind. In actual
fact, that is a relatively rare event. Again, to put it into perspective,
a power plant may go off instantaneously and you might lose 1,300
megawatts if it is a large power plant, for one of the interconnectors
to France that is 1,000 megawatts and those interconnections do
go down at least once or twice per month so you will lose large
amounts of generation anyway, even for conventional power generation.
The event you are talking about is a relatively rare event.
Q22 Lord MacGregor of Pulham Market:
Insofar as we have any experience, does the variability differ
between offshore and onshore?
Dr Watson: Obviously at the present time
our understanding of that is more theoretical because the amount
of offshore capacity is small at present, however you would expect
that the variability would be less offshore than onshore for a
number of reasons. The offshore environment is much more open—you
do not have buildings around—so that reduces the amount
of variability due to turbulence that you might get with buildings
around. Secondly, the surface is much smoother so the winds you
get are not affected by grass or trees or objects that again can
create variability. In general there is less variability offshore.
If we are moving to a large number of wind turbines built offshore
compared with onshore I think we would expect less variability
in the long run.
Q23 Lord Lawson:
You have limited your figure to 20 per cent whereas in fact in
the Government's Climate Change Bill there is some question in
the air as to whether this is going to be 60 per cent decarbonisation
or 80 per cent decarbonisation, it is likely that the Committee
will recommend 80 per cent, but even if it were 60 per cent 20
per cent is not going to make a great contribution to that, so
we are talking about something more at which point the backup
that Lord Vallance was talking about becomes even more important.
My supplementary is this, given that you are going to have to
have this backup, is it not the case—if it is not then tell
me—that in fact using nuclear as the backup would be hopelessly
uneconomic so in fact you would be bound to be using conventional
power stations as backup?
Dr Watson: It is true to say that nuclear
is a fairly inflexible form of generation so you would not tend
to use nuclear as a form of backup, you would tend to use plant
which is more flexible which includes coal fired power stations,
it includes open cycle gas turbine power stations and pumped storage
so you would not tend to use nuclear as the form of backup in
such cases.
Q24 Lord Lawson:
If your concern is to minimise the carbon dioxide emissions in
the generation of electricity then nuclear is more effective in
doing that than wind power, given that wind power needs the coal
fired power stations or whatever as backup.
Dr Watson: You could turn that on its
head and say that wind is a more variable form of power than nuclear,
but nuclear is quite inflexible. Nuclear is typically run at base
load so you are going to have some form of balancing generation
to manage that.
Q25 Lord Lawson:
We will have to find that out in our inquiries because there are
plenty of people who say that the new generation of nuclear power
stations is much more flexible. I do not know where the truth
lies. They claim the new generation has much greater flexibility
Dr Watson: I cannot comment on the new
generation.
Q26 Lord Best:
At the level of the individual home, particularly in urban areas
rather than out in the countryside, would I be right in thinking
that the amount that can be contributed to electricity supply
from home grown, on the home turbines, is absolutely infinitesimally
small and hardly worth us giving any consideration to at all?
Dr Watson: I think in general I would
agree with that. I have done studies myself looking at the expected
output of a small micro turbine of the order of one kilowatt and
you get a capacity factor of about one or two per cent compared
with 30 per cent for a large wind turbine. For most people in
an urban area it would not be an economic proposition.
Professor Bahaj: I think the issue in
urban areas is the shadow effect of buildings. Wind turbines really
work as a function of the speed of the wind; the power is related
to the cube of the wind speed so any reduction in the wind speed
reduces the power output. I think in buildings because of the
winds between buildings and so forth it is very difficult to actually
have micro generation wind giving you the optimum efficiency of
conversion.
Q27 Lord Best:
At the macro level, leaving aside the economics, what is the technical
potential for the proportion of Britain's electricity that could
be generated by wind power compared with other countries? Am I
right in thinking that we are quite a windy country?
Dr Watson: Certainly if you compare us
with the rest of Europe we have the best wind resource potentially
available. In terms of the amount of electricity that we could
realistically generate from a technical view point (perhaps not
from an economic view point), you could envisage a situation where
you could produce maybe 70 per cent of electricity from wind but
that would obviously require a large number of wind turbines.
Q28 Lord Best:
You say we are windier than the rest of Europe, is this by a large
factor? Is this a significant difference?
Dr Watson: The trouble is of course you
get very large variations from one location to another. The average
wind speed across the UK is probably something of the order of
5.7 metres a second, something like that. That hides very large
variations; there are upland areas where the wind speeds are higher
than that and clearly the offshore areas where the wind speeds
are higher. The average is a difficult measure to use, but if
you look at it in terms of capacity onshore and offshore it is
significantly higher than most of the European countries in terms
of our overall potential if we were to exploit it fully.
Q29 Lord Griffiths of Fforestfach:
Instead of having these large areas of wind farms and so on, is
there any advance in technology to make them micro?
Dr Watson: Do you mean in terms of visibility?
Q30 Lord Griffiths of Fforestfach:
Yes.
Dr Watson: No. The problem is that if
you go to the smaller scale, because of the way the physics works,
the aerodynamics work, they inherently become less efficient.
One of the measures that is used in terms of the efficiency of
a wind turbine rotor is something called the CP co-efficient and
the maximum that can be, if you look at the amount of energy in
the wind and the amount of energy that a wind turbine can extract,
is something in the order of about 59 per cent and some of the
larger wind turbines are approaching that efficiency. If you go
to a smaller wind turbine, say the sort of turbine you would put
on your house, the efficiency drops down to maybe 25 to 30 per
cent. So from an efficiency point of view it is not a sensible
thing to make the turbines smaller.
Professor Bahaj: There is the issue of
civil infrastructure. If you have smaller turbines the cost will
be greater because you have to have foundations, you have to have
other plants and so forth, so that is another issue which relates
to costs.
Q31 Lord Kingsdown:
Could you clarify what is meant by biomass and bio-energy? What
proportion comes from agricultural by-products and waste, and
what proportion comes from crops and forests grown specifically
to generate energy? Are these proportions likely to change in
the future? How is the use of biomass split between electricity
generation, heating and transport? Is this likely to change?
Professor Bridgwater: That is a very
big question. Biomass of course are plants that grow ranging from
trees and forests to the food we all eat. That is biomass; it
is material that grows and in growing it fixes carbon from the
carbon dioxide in the atmosphere and grows itself. It is the only
renewable source of carbon. Carbon is a source of hydrocarbon
in fuels as well as for food. The amount of biomass that is grown
for energy only in the UK is quite small, tens of thousands of
hectares only, mostly for wood for use in co-firing applications,
particularly up in Yorkshire. There is a lot of agricultural residues
like straw; the UK produces one of the largest amount of straw
in Europe and the straw is used to fire three power stations,
for example, in East Anglia. Straw has a use for animal bedding,
it has a use for energy and there are many other sources of agricultural
waste or residue that can be used for energy. So we have waste
residue by-products for energy and we could also grow crops. The
two favourite ones in the UK are willow (which is known as a coppice
crop, so you grow it in three to five years, chop it down and
it grows again) and a grass called miscanthus which is a very
thick grass and grows about two to three metres high. The UK is
land-limited so the amount of land we have is finite. There is
a view that the maximum amount of biomass that can be grown is
100 million tons per year. We can grow woody crops which are interesting
because they are relatively clean, low in contaminates, burn cleanly
and can be processed cleanly. The other main crop considered being
suitable for energy is something called miscanthus, a grassy crop
which is quite well adapted to UK conditions, but you can get
yields of nearly double that you can get from willow. Bearing
in mind that the land is limited in how much there is, the more
crops you can grow per unit area of land, the more interesting
the crops are. That is one of the downsides of first generation
biofuels like rape for rape methyl ester or bio-diesel. You only
get about one ton per hectare per year whereas willow is typically
around ten and miscanthus can be up to 20. In a land-limited environment
like the UK it is very important to use the land as productively
as possible. That has answered one of your questions I hope. The
second one was what forms bio-energy. You can produce electricity
usually by either burning the biomass and a very effective way
of doing this is co-firing in coal fired power stations because
you can use all the capital investment and all the gas cleaning
by adding some biomass and you can contribute significantly at
the lowest possible cost to meeting UK's carbon reduction targets.
Another way is a dedicated biomass fired power station. There
is one at Lockerbie, 45 megawatt; there is one in Staffordshire,
two megawatt. The Lockerbie one uses forest residues and the Staffordshire
one uses purpose grown miscanthus. So you have co-firing for combustion
and you have also got dedicated biomass combustion in dedicated
power stations using only biomass. You then have the more advanced
technologies for processing which offer the potential or the promise
of greater efficiency using gasification or pyrolysis. These will
deliver systems that have a greater potential for increasing the
efficiency of power production over and above what you can get
by combustion either at power stations or dedicated plant. Bio-energy
can be used for power; it can be used for heat; there is a growing
market in wood chip and wood pellets supplied to small companies,
industrial estates and so on so there is a combustion opportunity
for processed wood (chips, pellets and so on). Then you have the
transport fuel sector which is currently of enormous interest.
It is currently being satisfied by what Paul Ekins has been describing
as first generation biofuels. The problem with first generation
biofuels is that they are competing with food. Sugar, for example,
to make alcohol or ethanol—as is produced in Brazil—is
competing with sugar for food. In the USA it is made from corn
or maize: the corn can be used as a food stuff or it can be used
to make alcohol. In the UK there is both a sugar process for making
alcohol and a wheat based process; wheat of course is a food stuff
as well. The concern with first generation food stuffs is that
there is competition with food and secondly the rates of yield
or the productivity of these crops on land is quite low. Rape
for bio-diesel is probably one ton per hectare and sugar and corn
for bio-retinol in the UK and northern Europe is probably two
tons per hectare. If we go to the second generation crops like
ethanol from wood or hydro-carbon transport fuels by using processes
like growing bio-ethanol we can get yields of up to five tons
per hectare. The status of the technology and how advanced it
is is very important in the UK because we are land limited, we
therefore need to use land as effectively as possible to make
as much of our energy needs as possible. The question of the competition
between transport fuels and heat and power is also interesting
because you make heat and power from nuclear, from wind, from
photovoltaics, from wind, from waves and from tidal. Biomass is
the only source of renewable carbon, carbon for hydro-carbons
in gas and in diesel and carbon for the range of chemicals we
use daily. I think it is important to recognise the unique attributes
of biomass and what it can be used for.
Q32 Lord MacGregor of Pulham Market:
How much miscanthus are we growing in this country? Looking at
the economics, are there any benefits currently in growing miscanthus
from the growers' point of view?
Professor Bridgwater: You get much higher
yields than any other crop, up to 20 tons per hectare. The total
amount of the cultivation is of the order of thousands of hectares;
it is relatively limited. There are about a thousand in Staffordshire
to supply the Eccleshall power plant and there are some big plantations
in southwest England, but it is relatively small. One of the problems
is that the support for growing miscanthus was withdrawn last
summer and this has caused a lot of concern. The investment grants
for planting it were significant and made it a viable crop, but
without that there has been, as I understand it, no more new planting.
Q33 Lord Griffiths of Fforestfach:
I should declare an interest which I did not last time, and that
is my association with Goldman Sachs which has a principal interest
in this area as well as its role an advisory and training business.
I have two questions. The first is, what are the pros and cons
of burning biomass together with coal? Secondly, do biomass plants
have to be relatively small because of the costs of moving them
over distance?
Professor Bridgwater: The advantage of
co-firing is that you have a complete infrastructure for handling
solids, for processing solids; you have all the economies of scale
that go with that and you have all the gas treatment, all the
gas processing and emissions control. Adding up to five per cent
biomass is not going to significantly change the performance or
operational costs of the power plant but there is a contribution
of five per cent (five per cent firing on an energy basis). It
is really an economic argument. I believe that virtually all coal
fired power stations in the UK are now licensed to buy biomass
and the costs and modification to handle the biomass is quite
small, roughly £1 million I understand to a power plant that
cost hundreds of millions to build in the first place. So there
are considerable cost benefits and advantages to coal firing.
The problem with small scale, dedicated biomass, the reason they
are limited in size is firstly the availability of biomass, the
concentration within an area that you can collect it over. You
have to transport the biomass from the forest or the field to
a central place usually by road for the Lockerbie power station,
for example, but once you get up to hundreds of megawatts you
have to go much further afield, you have to consider either rail,
sea or river transport to bring the biomass together and the handling
and transport costs get significantly more. The studies that we
have done indicate that transport cost is not a major factor in
the total cost but there are environmental costs of having lots
of trucks going past your house, through villages to deliver to
the site. There is also the cost of new roads that can handle
all the trucks and maybe new rail heads. So there is an environmental
cost of directly and indirectly building large scale plants. I
think my view is that the future is in a diversity of options
and in de-centralising opportunities.
Q34 Lord Paul:
For transport, which forms of bio-energy have the best prospects?
Which crops can be grown in the UK, and which need to be imported?
Professor Bridgwater: The problem is
not, I think, which are the best crops, it is the total quantity
available. If we are going to go up to 20 per cent substitution
by 2020 there is problem of whether we grow enough in the UK and,
if we cannot grow enough, even by importing all our food the view
is that we can get maybe 20 to 30 per cent. We need to produce
some food ourselves so we are going to have to import biomass.
We then become dependent of course on where we source it from
and the source of that biomass is going to want to add as much
value as possible and probably want to process it locally into
as high a value a product as possible to export. Brazil, for example,
would rather export ethanol than wood chips. It does export wood
chips and it does export ethanol but from a national point of
view they would much rather export the highest value product because
of the earnings they will get for the employment prospects and
for the investment. In the UK the two crops that are considered
most widely as energy crops are willow as wood and miscanthus
as a grass. Miscanthus is what is called a C4 crop and it is more
tolerant to drought, less demanding on water and also on nutrients,
so it is an easier crop to grow and you get very high yields.
The other interest is in algae. There are two types of algae,
one is micro algae and there are some quite optimistic claims
of getting yields of up to 90 or 100 dry tons per hectare from
micro algae, but the cost of this is that it has an intensive
reaction process, very high capital costs and high running costs
of providing access to sunlight and all the nutrients and the
liquid handling. Micro-algae comes round every 15 or 20 years;
it has a lot of interest at the moment both because of the yield
and because of the oil products you can derive from it. The other
algae that is interesting, which means we are less land-limited
than we are now—is to go offshore and look at seaweed, which
is called macro-algae. There is a study at the moment included
in the SUPERGEN bio-energy activity looking at the opportunity
and the potential and methods for the handling and harvesting
of seaweed. I think the interesting new crops to be investigated
with most interest currently are and willow and miscanthus.
Q35 Lord Macdonald of Tradeston:
What is the technical potential for the amount of Britain's energy
that could come from biomass and what impact might that have in
terms carbon emissions? Also, just going back if I may to the
withdrawal of support for miscanthus, it sounds very promising
and I wondered if there were arguments against that encouraged
the Government to withdraw the support and what they might be.
What do you think the potential for rural employment might be
in biomass?
Professor Bridgwater: Clearly the farming
community has not had an easy time over the last ten or 15 years
and they are not very happy about growing crops they have to wait
five years to harvest. Something like miscanthus which they can
plant and harvest annually like a normal crop they are much more
in favour of than short rotation wood where they only harvest
every three or five years. It is a major investment, a major risk
and unfortunately some of the experiences in the UK do not support
the risks involved in farms growing woody crops. There is a need
I think to provide some guarantees or some support to farmers
who do grow woody crops that they are not going to have the contract
cancelled or are left with hundreds of hectares of wood which
nobody wants. It is a question, I think, of dealing with the farmers'
concerns of how they deal with the uncertainty of growing bio-energy
crops. I think it is important to know that as biomass and bio-energy
become more established and become more widely traded then the
risks will go down and farmers will be much happier to grow them,
to handle them, to market them and the price also will drop as
time goes by. At the moment it is getting better but there is
still uncertainty over what happens if ...? What happens if the
plant down the road that wants to buy it goes bankrupt—as
happened in one case—and so on? It is a fairly rapidly changing
situation and as the bio-energy industry grows I think we will
see a greater interest in growing the crops, greater interest
in establishing standards for marketing them, using them and trading
them both within the UK and abroad as well. I cannot remember
the first point of your question.
Q36 Lord Macdonald of Tradeston:
I was asking for the technical potential for the amount of Britain's
energy that would come from biomass and what the impact of biomass
might be in terms of carbon emissions.
Professor Bridgwater: The impact of the
amount of biomass has been considered that you could produce in
the UK, forgetting food, is about 100 million tons a year which
I think equates to the order of between 60 to 80 per cent of the
energy. I would need to confirm that, if I may, but it is of that
order. We have the potential to produce a large proportion of
our current energy but that would mean we would have to import
all our food so you get back to the food versus fuel debate—how
much food do you want to produce and how much energy do you want?—because
you cannot produce everything you want. There has to be some give
somewhere in the system. It is a case, I think, of optimising
the combination of food and fuel. The 100 million tons is an estimate
and it does consider the different types of land productivity,
the non-availability of land due to cities, roads, mountains and
so on. I can try to obtain that information and also work out
what it equates to in power and transport fuel supplies.
Q37 Lord Lawson:
What about Lord Macdonald's miscanthus question?
Professor Bridgwater: I am sorry; can
you remind me of it?
Q38 Lord Macdonald of Tradeston:
What are the criticisms of it that encouraged the Government to
withdraw its support?
Professor Bridgwater: I think it was
a European directive, not a national issue. I believe the Commission
required that the incentives for supporting growing miscanthus
and similar crops was in fact withdrawn. As I understand it, it
is not something the Government wanted to do but they did not
have a choice. Again if you would like to know more on that I
can find out.
Q39 Lord Layard:
Could you briefly explain the different technologies and the pros
of cons of the different types of marine energy? How predictable
and how intermittent would the energy supply be from a large scale
deployment of marine energy?
Professor Bahaj: The two technologies
that we will talk about in terms of marine energy are wave as
well as tidal stream. Tidal stream is different from tidal barrage
which is really just a fence using hydropower to generate electricity.
I will talk about tidal stream and wave power. There are three
competing technologies in wave power. There are others as well
but the three competing ones are the oscillating water column
in which a wave comes into a chamber, it compresses air and goes
through a turbine. As the air goes through the turbine it generates
electricity by turning the turbine. As the wave recedes it also
turns the turbine in the same direction. That is an oscillating
water column. The other one is like a sausage where you have articulated
cylinders and between them you have a power take off system where
it compresses air which drives turbines. The last one is what
is called a power point absorber which oscillates in the sea and
either compresses air or drives an electrical generator. These
are the main three different competing technologies for wave power.
In terms of tidal power, the majority of technologies are related
to horizontal axis turbines, except one which is the vertical
axis turbine. Many of the technologies are based on the horizontal
axis turbine based on wind turbines. There is a lot to learn from
that technology. That actually reviews the technology in two minutes.
Wave power is driven by wind so it is intermittent. Tidal power
is driven by the lunar cycle and therefore you can predict within
half an hour the energy you get from any given site. In terms
of large deployment the majority of developers, at the moment,
are at the prototype stage. In wave energy the first developer
is Pelamis Wave Power Limited in Edinburgh and the first array
is going to be launched in Portugal in the next few weeks. Other
devices that are in the sea are the one in Lynmouth which has
been there for about two years, a horizontal axis turbine by IT
Power and now Marine Current Turbines Limited. Lunar Energy also
have a device which is the shrouded turbine. The shroud itself
enhances the velocity that it goes into the turbine and you get
an enhancement of energy production. Large deployment is still
on hold because the majority of the developers are waiting for
investment in order for them to deploy at the prototype stage.
There are four technologies that are being supported by BERR (or
the DTI before them) and that is the horizontal axis turbine,
the shrouded turbine and another two technologies which are a
variant of the two. Those technologies are still not in large
scale in the sea. The resource is between two and seven gigawatt
average annually. That is four to seventeen gigawatt installed
capacity. This is roughly fifteen percent of UK requirement of
electricity.
Dr Watson: One of the other devices that
has been proposed for wave energy is something called a tapered
channel device, a tapchan. It forces the waves into a constricted
channel and the waves then build up and overtop into some sort
of storage chamber. There is a device called a wave dragon which
makes use of that. The chamber builds up a head of water and that
water can then fall through a turbine and generate power. In terms
of a comment on the variability of some of these, it is true to
say that tidal power is very predictable. It is quite variable
in that it can go from full output to zero output in a matter
of six hours.
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