Distributed generation vs bulk power transmission

Distributed Generation (DG) is generally considered as an alternative to bulk power transport. The basic idea is that the presence of electricity generation inside the distribution systems leads to a reduction of the local electricity needs, which consequently leads to a reduced need for power transmission capacity and thus a deferral of investments in transmission lines. However, due to the different operational characteristics of the plethora of types of distributed generation, this hypothesis may prove invalid. Controllable distributed generation, defined as local generation of which the power output can be regulated by the system operator (e.g. stand-alone gas-fired combustion units) will certainly have a positive impact on this direction. However, in reality different types of DG technologies could de implemented in the distribution systems, such as partially or stringently controlled micro-combined heat and power (micro-CHP) units operating according to different local control modes (e.g. thermal-led control) or non-controllable (stochastic) DG units, such as wind power plants. The operation of such units may lead to an opposite effect regarding the necessary transmission capacity. In this paper we first define four types of DG regarding their level of controllability. We then look into the effect on the transmission system of both stringently-controlled DG (i.e. micro-CHP) and stochastic DG (i.e. wind turbines). It is shown that micro-CHP systems may have a positive effect to the dimensioning of the transmission system, while the presence of wind power plants may instead lead to increased investment needs in power transport capacity.