By John Kemp
LONDON, July 11 Britain's National Grid has
outlined plans to keep the lights on during the dark winter
evenings of 2014/15 and 2015/16 - when the margin of spare
generating capacity could fall as low as 4 percent and the risk
of some disconnections could be as high as 50 percent.
In the process, it has offered the first look at the grid of
the future. National Grid wants to use a smart approach
to create more flexibility in both electricity generation and
consumption to handle rising demand and the integration of
increasing amounts of uncertain wind power onto the network.
In a consultation that runs until July 26, National Grid is
proposing to create two new mechanisms to curtail demand during
peak periods while providing incentives for generating units
that would otherwise be mothballed or decommissioned to remain
on stand-by in case wind farm output proves insufficient.
Between November and February in 2014/15 and 2015/16, the
projected Demand Side Balancing Reserve (DSBR) would pay
customers who agreed to reduce their consumption by a specified
amount for up to two hours in response to an instruction from
the grid, principally during the peak demand period on week days
between 4 pm and 8 pm.
Any customer with a meter that measures consumption in
half-hour intervals would be able to participate. To encourage a
wide range of customers to take part, instructions will be
issued by smart phone or over the internet, and the contractual
arrangements will be kept simple.
Whenever possible, National Grid will issue warnings in
advance that demand-reduction is likely to be called.
National Grid is also proposing to create a Supplemental
Balancing Reserve (SBR) that would pay operators to keep a
number of generating units that would otherwise have been
mothballed or decommissioned on stand-by between November and
February of 2014/15 and 2015/16.
Some of the SBR may end up being provided by coal-fired and
gas-fired generating plants that would otherwise close. So the
grid proposes to make payments that would cover the cost of
keeping the capacity available, the electricity actually
generated, and having to warm up the power plant before
electricity production begins.
To avoid disrupting the wider market and the government's
objectives for cleaner electricity, the grid would only call on
the SBR as a last resort, after all other options, including
DSBR, have been exhausted.
To ensure that SBR resources are genuinely additional, the
grid will check that the generating units would not otherwise be
participating in the wholesale market, and they will be
forbidden from providing other non-SBR generating and balancing
services in those periods.
National Grid will hold a workshop to discuss the proposals
on July 17 and plans to invite the first offers from consumers
and generators to participate in DSBR and SBR for 2014/15 and
2015/16 in the first quarter of 2014.
National Grid operates Britain's transmission network and is
required to coordinate and direct the flow of electricity in an
"efficient, economic and coordinated manner" under the terms of
It must balance the amount of electricity being put onto the
network by generators and taken off by suppliers on behalf of
their customers, taking into account the grid's finite capacity
to transport electricity from generators at one location to
consumers at another.
It buys a number of different balancing services from both
electricity producers and consumers to help it cope with
potential imbalances over a variety of timescales, ranging from
seconds to hours.
At the shortest timescale, the grid manages second by second
imbalances between supply and demand through its frequency
response programme. Generators are paid to operate slightly
below their full capacity and fast-start generators, for example
gas turbines, are held at a very high state of readiness, so
they can provide an extra surge of power within seconds of an
instruction being given by grid controllers.
At longer timescales, the grid contracts with generators to
provide a Short Term Operating Reserve (STOR). Participating
generators must be able to provide 3 megawatts (MW) or more
within four hours of receiving an instruction, and be able to
sustain this level of output for at least two hours, at least
three times per week. In practice most STOR resources are
available within 20 minutes or less.
National Grid aims to have 1800 MW of STOR available every
day, though depending on system conditions and contract costs
this may be boosted to 2300 MW.
If all else fails, National Grid can resort to "MaxGen,"
instructing generators to run flat out, or request "emergency
assistance" from other system operators in Ireland and France
via the interconnectors.
As a last resort, the grid will issue instructions to the
regional distribution network operators to reduce or disconnect
The full list of balancing services is explained on National
Grid's website and their actual employment is detailed in
monthly reports ().
MIND THE GAP
Britain will still have enough generating capacity to
maintain its target short term operating reserve in the next few
years. But the amount of spare capacity above that to cope with
unexpected contingencies like the unavailability of a major
power station or a burst of very cold weather is set to shrink
to a very low level that is causing concern.
Past experience suggests spare capacity will be narrowest
during early evenings in winter. Over the last 20 years, the
three half-hour periods of maximum power demand each year (known
as "triads") have all occurred between Nov 17 and Feb 8.
The period of highest demand is normally on weekdays, other
than public holidays, between 4 pm and 8 pm. Lights are switched
on, some residential customers return home and begin to prepare
evening meals, but many commercial and industrial users are
still open and operating. The grid can remain under strain for
up to four hours at a time.
DSBR resources are aimed at reducing load during this
critical period, with some support from the supplemental
The disappearance of spare capacity is mostly the result of
policy. Dozens of older coal-fired and gas-fired power plants
are being retired at the end of their economic life and under
the terms of the EU's Large Combustion Plant Directive (LCPD).
They are being replaced by increasing amounts of wind
generation, which is more variable and less reliable.
New fossil-fuel plants to provide a back-up to the wind
farms have not been built because operators are uncertain about
whether they will be able to recover construction costs in the
relatively small number of hours that they are expected to run
In response, the government has proposed introducing a
capacity mechanism that would pay operators to build new
generating units (probably gas-fired plants) to act as a back-up
to the wind farms. An auction would be held for generating
capacity that would be delivered four years ahead, with the
first capacity to be delivered in the winter of 2018/19.
The government is also planning auctions for more
demand-side response (DSR) services, with the first delivery in
the winter of 2016/17.
But that leaves a gap of two winters, 2014/15 and 2015/16,
when the margin of spare capacity is set to become very narrow.
It is this gap that National Grid wants to bridge with the DSBR
However, depending on the results of the capacity mechanism
and DSR auctions, the grid might extend the demand side
balancing reserve and supplemental balancing reserve for the
winter 2016/17 and beyond.
Both DSBR and SBR are stop-gap responses to a problem that
has been caused by the poor sequencing of policy (in particular
the retirement of coal and gas-fired generating units under the
LCPD before a new capacity mechanism is up and running). But
DSBR in particular offers a window into the future.
Smart technology (including half-hourly meters and smart
communications via smart phones and internet-connected devices)
will be employed to curtail demand in line with available
electricity supply, particularly if a period of cold still
weather settles over the country for days at a time, reducing
DSBR is a therefore pilot for Britain's 21st century
electricity system that will have more renewable generation and
require customers to be more flexible in the way they use