Future Power Systems 4 - Renewable and Distributed Generation

Renewable Generation replaces fossil fuel burn and consequent emissions. Distributed generation is more efficient at providing electricity near the point of consumption and multi-energy generation systems (heat, cooling, power) can provide that energy more efficiently than conventional methods, although still using fossil fuel. 

The latest Distributed Generation at premises level comprises micro wind, photovoltaic and combined heat and power (sometimes with cooling) installations. Separate large wind generation is accomodated at higher distribution voltages although with careful rules for operation if the system becomes stressed. 

The problem with any renewable generation is predictability and the fact that there is gross variation from day to day. Both irradiance (for PV) and wind speed are difficult to estimate at the lead times relevant to commiting main generation.  

A quick summary of Generation types, 'drivers' and predictability:

Here is an example of wind predictability and the effect on the residual requirement for main generation in Great Britain.  It shows the Day Ahead and 0500 forecasts, then the last forecast and actual trajectory for each time for which forecasts are prepared and actuals are recorded.

And here is an example of 3 days of micro PV outputs superimposed on an 'average' domestic load curve.

In general, CHP and CCHP systems are driven by the heating or cooling requirements of the premises, or the process for which the thermal energy is required. Temperature fluctuates less frequently than other weather variables and plant output is more in tune with demand, which increases with low and high temperatures. 

Also, assuming the CHP runs continuously when the weather is cold, the domestic premises profile might appear as follows:

Note that both the PV and CHP systems may tend to export at times of low premises demand.

Within the current operational framework, it is assumed that more spare and reserve output on conventional generation will need to be carried to meet the increased level of uncertainty introduced by renewable and other distributed generation.