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Frequently asked questions


How can dynamic demand control become reality?
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 (PDF 33kB).

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 per year.

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.

If 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.


What's new?
Latest news on dynamic demand
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Dynamic Demand is an independent not-for-profit organisation
set up by a grant from the Esmée Fairbairn Foundation and supported by charitable donations.