Frequently asked questions
How can dynamic demand control
Dynamic demand devices have the potential to earn considerable
income from the services they provide. But before dynamic demand
control is widely incorporated, experts from academia, Government,
the regulator and system operators must help create an effective
market mechanism to reward the technology fairly.
What would the profits be
for incorporating dynamic demand control into appliances?
It is difficult to predict accurately at this stage. However, an
early conservative estimate indicates that a typical under-counter
fridge-freezer could "earn" around £30 during its
life. See a short paper, written mainly for appliance manufacturers,
on the potential financial rewards here
Is dynamic demand control
a new idea?
No. The concept was patented in 1979 in the United States by
power systems engineer Fred Schweppe. His patent protection has
now lapsed and we understand that it is therefore available to all.
He proposed a device called a "frequency adaptive, power-energy
re-scheduler" (FAPER), which provides peak load management
using individual electrical loads. However, Schweppe's idea was
not widely adopted because the regulations and operator policies
covering power systems did not (and still don't yet) include a facility
for rewarding such devices for their valuable grid-stabilising services.
Who is working on this technology?
Dynamic Demand is a public interest organisation and does not seek
to promote any particular commercial approach over any other. There
are several organisations working in this area which you can read
about here. Please contact us if
you know of others working on the technology.
How would a dynamic demand
controller actually work?
To paritipate in second-to-second balancing of the grid, the device must be able to measure accurately the power
system's AC frequency
(nominally 50Hz in the UK) which is a good indicator of the instantaneous
balance between supply and demand. Grid frequency is kept within
strict bounds by the grid operators to ensure that the system remains
balanced. See the UK frequency limits
here. See the current system frequency here.
Frequency is currently controlled by paying large
generators to operate in so-called frequency sensitive mode, altering
their output continuously to keep the frequency near 50Hz. This
ancillary service is called "frequency control" or "frequency
response" and costs the National Grid in the order of £80M
A controller needs a cost-effective way to measure
the system frequency, say using a simple microcontroller to count
the number of processor cycles in a full AC cycle.
Alternatively (or additionally) to participate in other types of balancing (such as longer-term load-shifting) a dynamic demand device must be able to respond to signals that ultimately originate from the grid operator. This can be done through an aggregator, a company that receives a dispatch signal from the grid operator and then sends a signal to many devices under its control.
Any device control system needs to be aware of the needs
of the appliance or plant item it is controlling. In the case of a refrigerator, this means simply
measuring the internal air temperature. A relay or other switching
device is then added so the controller can switch the compressor
(in the case of a refrigerator).
The microcontroller is then programmed to switch
the compressor on and off according not only to the internal air
temperature, but also with reference to the current grid frequency or dispatch signal.
Obviously, the controller must ensure that at no point does the
refrigerator stray out of the acceptable temperature range.
How do we know the effects
on the grid?
Once dynamic demand technology becomes more widely accepted and
understood, power systems operators will want to conduct detailed
studies into the exact aggregated effects of many dynamically controlled
appliances. In February 2006, dynamic demand control fridges were tested by Intertek on behalf of the Department for the Environment,
Food and Rural Affairs under its Market
Transformation Programme. And in December 2008, Npower and RLTec announced field trials (see the news page for more details).
An early simulation study has already investigated
the effects of millions of dynamically controlled refrigerators
on the UK grid system.
you know a little about power systems, you may be interested to
see the output of a simulation (right - gif format). It investigates
a power grid that uses only dynamic demand control (i.e. no spinning
reserve) and looks at what happens when 1320MW of generation is
suddenly lost. This is the amount of lost generation that grid operators
currently plan for.
The indications are that such appliances could
make a considerable contribution to frequency control.