A national electricity market, network-wide, synchronised monitoring, analysis and data base system is the only way of providing efficient electricity markets and a sensible approach to conserving system strength, writes Phil Kreveld.
No matter the ways new electricity markets develop or what new sources of energy we might wish to avail ourselves of, we cannot get away from the alternating current synchronicity straitjacket. Physically, electrical power ‘pulses’ in synchrony everywhere, from the furthest, humble domestic solar inverter to the most distant power station. We have a huge national asset base comprising of transmission lines and distribution networks, designed to carry alternating current power. It is our common carrier for energy interchanges and energy delivery to consumers and its operation relies on the maintenance of synchronicity at all times. Given the investment in this vast network infrastructure it’s obvious that whatever our energy plans are for the future, synchronicity will continue to rule!
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The physical requirements of the combined transmission and distribution networks, the main ones being voltage and frequency stability, translate into restrictions on the types of sources of electrical energy that can be connected and on the amount of power that can be carried in networks. These requirements also affect energy markets, which have to work around a commodity that essentially cannot be stored, save for very short periods, and with the prevalence of renewable generation, now have to deal with marked, short-term fluctuations in power. Attempts to integrate the variability of power flows into market designs increasingly point to having to incorporate a networks-wide, synchronous analysis and data platform.
The Australian Energy Market Operator (AEMO) ensures that all wholesale market participants operate on a strict four-second cycle to facilitate settlements but does not include generation within distribution networks, being classed as retail. In the days when power flowed one way—from generators to consumers, metering was comparatively simple. Now, with domestic solar power approaching the collective power of baseload generation, a metering system to fit various market schemes and affording commercial flexibility is necessary.
What we need is a change in mindset—to consider domestic, industrial and commercial electricity generation as a contiguous, synchronous part of the electricity generation, transmission and distribution system. That would imply the use of a universal time-base, for example, precision time protocol (PTP) everywhere in the networks as the basis for metering. Employment of a universal, synchronised timing system would enable granular consumption and generation markets to operate efficiently.
Although not discussed in terms of congestion, its equivalent, namely voltage regulation is the chief distribution network problem listed in an AEMO survey of April, 2020. Congestion caused by the number and increased rating of solar systems is having distribution networks reduce power output of inverters or switching them off at times. Congestion can be controlled by giving synchronised, timed access to distributed energy resources (DER) to limit congestion. The same process can be used to test feeder impedance as a measure of heat build-up. Thus, granular access to distribution networks can be basically made available to ‘prosumers’.
Of course, there are complications, chief ones being the absence of battery-based systems to store energy when access to the network is denied, the basically uncontrolled connection access of single-phase solar systems and the bulk of earlier-installed inverters that essentially cannot be controlled other than by switch-off via demand response enabling devices (DRED). No doubt, these are major problems for distribution networks but having access to instantaneous, synchronized power measurement would provide the essential building block to fairer access for prosumers.
It might appear that the case for synchronicity is not clear from the above network problem descriptions. However, consider a uniform, synchronised timing system with low latency, for example GPS-satellite based, with a multiplicity of analytical metering and monitoring equipment deployed in transmission as well as distribution networks. The data base collecting the information from the synchronised devices would be able to provide snapshots of distribution feeder power and voltages throughout the networks as well as power quality information. Most importantly, an analytically sound basis for DER control would be provided. It would also provide synchronous snapshots of power flow and voltage data, etc. in sub-transmission and point of common coupling (PCC) transmission links. The information thus acquired could be integrated with automatic generator control (AGC). For example, allowing more access to energy export by DERs could cause substation inflowing power to drop below allowable lower limits for frequency and voltage stability, thus invoking curtailment within a distribution network.
The question will arise as to what manner of control is required, in particular for the allocation for ‘prosumer’ access. In truth the control protocols may well turn out to differ markedly between distribution networks and might even result in differences in trading schemes but because of the synchronicity aspect, whatever the particular schemes, all would be accurately relatable to delivery access nodes of the national electricity market (NEM) and therefore would not impede settlement procedures. A synchronous monitoring and data system will also assist in sifting through the ever more complicated marketing schemes that are being proposed to the Australian Energy Market Commission (AEMC), many of which might look interesting on paper, but might founder for lack of a contiguous, synchronised analysis system and data base.
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The presence of the synchronous monitoring system as proposed, would provide for the first time, a data driven process for the enablement of prosumer markets and alleviate the Energy Security Board’s (ESB) principal concern with maintaining system strength, by AEMO keeping a NEM-wide contiguous, second-by-second watch over power flows. The chain of snapshots of the entire grid, generators, and distribution networks would feed into a national data base with control algorithms operating in conjunction with AEMO’s dispatch engine. In that manner we would be achieving the best economic value from the growing prosumer base, have a fairer system of curtailment of small and very large renewable energy (VRE) sources and have a sound basis to guarantee system strength.