2 Definitions

In seeking to define high penetration intermittent generation, the IEA Task 14 group notes that “Although up to now, no common definition of ‘high penetration PV scenarios’ exists, there is consensus amongst the parties developing this Task that a high penetration situation exists if additional efforts will be necessary to integrate the dispersed generators in an optimum manner”.

We build on this philosophy, by suggesting that a high penetration intermittent renewable generation (HP-IRG) scenario exists where it is the variability of the intermittent generation rather than the loads within a network segment that is the dominant factor in determining the need for substation, network or control upgrades. This definition can then be expressed mathematically, based on a comparison of the largest net variability as seen in both loads and generation:

HPIGτexists if | PgiPg(i-1) | ≥ | PliPl(i-1) | for i such that | PiP(i-1) | is maximised

where

Pgi is intermittent power generation (kW) at time i

Pli. is load power (kW) at time i

Pi = Pli — Pgi is the net load (kW) at time i

τ is the time interval between time i and i–1

Note that the variability of loads and generation needs to be assessed over a timeframe appropriate for the network characteristics under consideration - as is the case when assessing other network performance characteristics such as voltage and frequency fluctuations. This is for the purpose of assessing the time interval τ.

Further, commonly described scales at which PV is connected are defined below in Table 1.

Table 1 Scales at which PV is connected

Identifier Connection Point
Small-scale 230V/400V (or 240V/415V) Low Voltage Distribution Network
Utility-scale > 230V/400V (240V/415V) Distribution Network
Large-scale ≥ 66kV Transmission and Sub-transmission Network