Why the Conventional Power System Model is in a State of Transition - The Increasing Penetration of Distributed, Grid-Connected Generation
The traditional power system model for the latter half of the 20th century
was to have relatively large, centralised power stations which generated
electricity for a distributed network. The main elements of the power system comprised the generators, the transmission network and the distribution
The advent of solar and wind power was initially absorbed into this power system model. However, the ongoing penetration of solar and wind power has reached a point where it is causing a transition in the power system model to that of combined distributed and centralised generation.
The distributed generation has a number of characteristics which do not suit the design and operation of the traditional power system model:
· The distributed generation is not located with the centralised generation; it is located in the distribution network
· Being located in the distribution network means it is not controlled by the traditional generation controllers
· Effectively there are two generation systems operating independently, both trying to serve the same load
· The distributed generation has priority over the traditional generation, in that the distributed generation is dispatched immediately it is available
· The traditional generation must be available for peak load and for periods of intermittency, when the distributed generation is not available.
The effect of these characteristics is that the traditional power system model is in a state of transition, with the new model yet to be adequately defined and determined.
The impact of the increase in solar and wind generation is being felt in Germany. The increase in distributed generation has caused the total generation capacity to increase. This has resulted in a continued decrease in the wholesale price of electricity. Conventional power stations are supplying MW; but at a reduced MWHr. The falling wholesale price is impacting the viability of conventional power generation.
Refer: MWs are not MWhs – Monitoring Report Part 2: Energy Transition, the German Energiewende
As the demands on conventional generators have changed, there have been changes in the way this generation is operated. There is an increase in the requirement for peak generation, with a shorter dispatch time. Manufacturers have responded with changes in the technology used for generators. Advances in boiler, turbine and control technology are allowing large coal fired plants to improve their agility. For example, a new lignite-coal-burning power plant built by the German utility RWE Power is now operational at Cologne. Each of the dual 1,100-megawatt steam turbines can ramp generation up or down by 500 MW in less than 15 minutes. This is explained in the IEEE Spectrum article “Quicker Coal Power”
The state of transition of the power system model; and the advent of discussions on the “smart grid”; have changed the concept of the power system. It is moving from a controlled, centralised entity into a combination of a controlled system and a dispersed, uncontrolled and intermittent system operating together.
While the impact on each power system is dependent on the characteristics particular to that system, it is apparent what has happened in Germany. The message for Australia is that a similar impact is likely if similar changes are made to the Australian power systems.
An off-shoot of the power system in transition is that local power generation may be provided as a mini-grid. This is the concept of micro-grids, using a hybrid system of generation from solar, wind, mini-hydro plants, reciprocating engine generators, conventional generators, grid connected batteries, UPS and CHP (combined heat and power) systems.
The micro-grid may serve a large installation e.g. ship, university, hospital, high rise building, mine, critical installation or industrial plant. It may comprise both renewable and conventional distributed generators.
BESST can provide power and control system designs to suit micro-grids, from the feasibility study to the detailed design and commissioning. The designs are customised to suit your application and are based on proven systems. The designs cover micro-grids from off-grid, islanded systems to a grid connected systems via a point of common coupling (PCC).