Dynamic demand (electric power)

Dynamic Demand is the name of a semi-passive technology for adjusting load demands on an electrical power grid. (It is also the name of an independent not-for-profit organisation in the UK supported by a charitable grant from the Esmée Fairbairn Foundation dedicated to developing this technology.)


The concept is that by monitoring the frequency of the power grid, as well as their own control parameters, individual, intermittent loads would switch on or off at optimal moments to smoothen the overall system load, offsetting and reducing spikes in peak-load demand on the grid.

As this switching would only advance or delay the appliance operating cycle by a few seconds, it would be unnoticeable to the end user. This is the foundation of dynamic demand control. In the United States, in 1979, a (now-lapsed) patent for this idea was issued to power systems engineer Fred Schweppe.


Contents
1 The need for spinning reserve
2 Local load control
3 Ancillary services
4 Implementation issues
5 Frequency service and reserve service
6 UK government investigation
7 See also
8 References
9 External links
//

more



The need for spinning reserve
The power utilities are able to predict to a reasonable accuracy (generally to within one or two percent) the demand pattern throughout any particular day. This means that the free market in electricity is able to schedule just enough base load in advance. Any remaining imbalance would then be due either to inaccuracies in the prediction, or unscheduled changes in supply (such as a power station fault) and/or demand. Such imbalances are removed by requesting generators to operate in so called frequency response mode (also called frequency control mode), altering their output continuously to keep the frequency near the required value.


The grid frequency is a system-wide indicator of overall power imbalance. For example, it will drop if there is too much demand because generators will start to slow down slightly. A generator in frequency-response mode will, under nominal conditions, run at reduced output in order to maintain a buffer of spare capacity. It will then continually alter its output on a second-to-second basis according to the needs of the grid.


This spinning reserve is a significant expense to the power utilities as often fuel must be burned or potential power sales lost to maintain it. The kind of generation used for fast response is usually fossil fuel powered which produces emissions of between 0.48 and 1.3 tonnes of CO2 equivalent for every megawatt hour (MWh) generated. Thus a significant environmental burden, in the form of in increased greenhouse gas emissions, is associated with this imbalance.

frequency control