Memorandum by the Energy Technology for
Sustainable Development Group, Imperial College London
(a) Are there technical limits to the amount
of renewable energy that the UK can absorb?
Taking this question as "how much intermittent
electricity from wind, tidal, wave (solar) etc. can the UK absorb",
the answer depends critically on:
(a) what other sources of electricity generation
are on the grid,
(b) transmission constraints and
(c) the uses to which the electrical energy can
be put.
Given time to reconfigure the UK as a low-carbon
electricity economy, perhaps 20-30 years, it is quite likely that
a combination of strategies (drawing on a range of insights including
technology design and policy for successful deployment) could
be developed to absorb electricity from such sources equivalent
in energy terms to at least the current electricity output (then
perhaps 25-50% of the much-increased total electricity generation).
Promising options include:
— electric vehicles and electric heating
using heat pumps in addition to "conventional" electricity
use;
— demand side management (eg through
economic incentives such as a dedicated electricity pricing strategy
at individual and business level); and
— prioritised isolation protocols.
(b) How do the costs of generating electricity
from renewables compare to fossil fuel and nuclear generation?
What are the current estimates for the costs of "greener"
fossil fuel generation with carbon capture and storage and how
do these costs compare to renewable generation? What impact do
these various forms of electricity generation have on carbon emissions?
The authors believe that studies showing offshore
wind costs to be roughly comparable to those of fossil fuel with
CCS (e.g in the 2007 Energy White Paper) are broadly correct,
but the question as posed is almost meaningless due to the extensive
qualifications that must be placed on any answers. Some of these
will be listed below. It is also important to consider how the
system costs for different penetrations of renewable deployment
are calculated and translated into cost of electricity impacts.
This is a complex issue that requires consideration of a number
of factors including what other generating sources are assumed
to be included in the network and, hence, how much change is required
to support intermittent generation from many renewable sources
(both in terms of energy back-up and maintaining security/quality
of supply when, potentially rapid, changes in electricity delivered
to the grid occur).
As a guide to practical policy development,
if the question implies that the cheaper source(s) of generation
should preferentially be developed then it is inappropriate. As
things stand we need to explore whether or not CCS can be implemented
as a viable large-scale energy technology option as quickly as
possible, because it does many things that many or all renewables
cannot do (eg tackling CO2 emissions from fossil fuels without
prohibiting fossil fuel use and providing electricity generation
capacity that can be controlled to ensure that real-time supply
matches demand, hence maintaining quality and security of supply).
Similarly, so long as renewable electricity can be produced and
used effectively, a certain amount as a fraction of the energy
mix is desirable. For both renewables and CCS the costs of current
deployment effectively also include the cost of developing options
for further implementation and technological advancement in the
future, until such time as the technologies and the infrastructure
and markets are mature—probably many decades ahead.
Carbon emissions from CCS plants can be any
value, from unabated fossil emission levels down to typically
15% or lower with any viable capture technology operated at full
effectiveness (order 100 kg/MWh for new coal), to very near zero
with some oxyfuel technologies, or negative (potentially to quite
large values) with partial or total heat input to the CCS plant
from biomass. Interim emissions levels (between unabated fossil
emission levels and typical CO2 emissions with "full"
CO2 capture) would be obtained by partial bypass of the capture
system if this was allowed by policy-makers and economically attractive
for plant operators.
Some factors determining the estimated cost
of electricity generation from fossil fuels with CCS are:
— carbon costs (avoided by CCS);
— credit for negative CO2 emissions
associated with biomass use in CCS plants, expected to be co-utilisation
with fossil in many cases;
— payments for ancillary grid services
provided by controllable and flexible fossil CCS plants (which
intermittent renewables require as a complement);
— whether or not the CCS plant is first
of a kind (ie the UK CCS Competition), first generation, second
generation or later; and
— how costs for CCS pipelines are apportioned
between first and subsequent plants.
(c) How do the costs and benefits of renewable
electricity generation compare to renewables in the other key
forms of energy consumption—transport and heating?
This question appears to assume that renewable
electricity cannot be used for transport and heating. Previous
work by some of the authors[69]
suggests that even when starting with biomass, its use in transport
via conversion to renewable electricity, instead of via conversion
to "2nd generation" biofuels, will result in improved
overall biomass utilisation and, if combined with CCS during electricity
generation, negative emissions per km travelled.
For heating, conversion of biomass to electricity
combined with the use of the same electricity in a heat pump also
compares very favourably in terms of conversion efficiency to
direct utilisation. The conversion efficiency in electricity generation
(30-45%, the latter with co-utilisation) is offset by the multiplying
effect of the heat pump (typically three or higher). If the electricity
generation is combined with CCS, negative CO2 emissions per unit
heat used can also be obtained.
Of course, electric vehicles and transport also
allow the use of primary renewable electricity (wind etc.) in
these applications, as well as biomass and products derived from
biomass; it was not clear that the question allowed for this flexibility.
(d) Should British support for renewables
in other countries be allowed to contribute towards meeting the
target for the UK?
Renewables in other countries will not achieve
much in the way of a contribution to UK energy security and may
have little or no effect on global CO2 emission rates, especially
if the other country is covered by an emission cap (since emission
caps tend to get used to their full extent whatever the energy
mix).
(e) What are the costs and benefits of the
present generation of biofuels? Will there be a second generation
of biofuels and, if so, what are the estimated costs? What are,
or are likely to be, the carbon emission impacts of first and
second generation biofuels, and what are the other relevant environmental
effects?
It appears to be inconsistent that electricity
produced from biomass and used as a transport energy source is
not treated in the same way as biofuels, and that this treatment
is not extended to all renewable electricity so used. It is also
arguable that any low-carbon electricity used in transport, which
will achieve comparable climate and energy security benefits to
biofuels (assuming acceptable lifecycle impacts for the latter)
should also be treated in the same way when it comes to incentives
and targets. Indeed, increased use of low-carbon electricity in
transport is arguably a more transformational step than the use
of biofuels, since the latter do nothing to encourage the national
car fleet and transport energy supply infrastructure to change
in ways that will reduce long-term dependence on liquid fossil
fuels.
The authors gratefully acknowledge thought-provoking
conversations with colleagues at Imperial College and elsewhere.
The opinions and interpretations expressed here are, however,
our own.
June 2008
69 Gibbins, J, Beaudet, A, Chalmers, H and Lamperth,
M. Electric vehicles for low-carbon transport Proceedings on the
Institution of Civil Engineers: Energy (2008), in press Back
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