What is inertia and how does it support the grid? Our electricity network was historically created for baseload power through thermal fossil fuel power plants and therefore works best with the conditions provided by those generators. That is constant output power, frequency, and signal inertia. More recently, the energy generation mix has been diversifying with the rapid uptake of renewable power generation and it brings with it a decreased level of inertia in the grid. Read on to learn more about inertia…Synchronous generators: what are the moving parts? Generating electricity from fossil fuels involves burning non-renewable fuel sources to produce heat. The heat is transferred to a gas, that is, steam in steam turbines and air in gas turbines. The high-pressure, high-temperature gas is used to spin a turbine, which in turn spins an alternator. It is the alternator that actually generates the AC electricity[i]. The term ‘synchronous generator’ comes from the fact that the speed that this generator spins (in revolutions per second) is synchronised with the frequency of the grid (which is necessary to maintain the appropriate AC signal).What is Inertia?Inertia in physics is defined by Newton’s first law of motion, also known as the law of inertia: a body at rest remains at rest, or, if in motion, remains in motion at a constant velocity unless acted on by a net external force[ii]. Inertia, in the case of the electricity grid, is referring to the grid’s ability to ‘push back’ against any disturbances. The spinning turbine of synchronous generators (fossil-fuel fired power stations) provides constant grid inertia; the spinning turbine cannot stop quickly and only very slowly runs down if the pressurised gas slows or stops. Basically, it’s a big heavy piece of machinery that wants to keep spinning at the same speed.What does low inertia result in? A grid that is more susceptible to minor disturbances disrupting the whole system. Another way to think of inertia is as a ‘buffer’. If a disturbance occurs, the turbine will keep spinning and allow some leeway which prevents the minor disturbance from affecting the whole grid. Watt energy has an explanation about FACS here.How is this related to frequency?The frequency in the grid was set historically as the speed of the turbine and alternator of synchronous generators. You can see that the spinning inertia of a synchronous generator will keep the generated power at a consistent frequency. Globally, the frequency in each country is either set at 50 Hz or 60 Hz; the grid in Australia is kept at a constant frequency of 50 Hz, whereas the grid in the USA is set at 60 Hz.What happens when the frequency drops? Grid infrastructure is designed for a certain frequency and MW capacity, if an event occurs that exceeds the designed limits, the system shuts down to protect that infrastructure usually resulting in blackouts – read about the infamous 2016 South Australian Blackout[iii]. However, the Australia Energy Market Operator (AEMO) has processes in place to avoid total system failure; one of these is quick response energy storage. Asynchronous generators Many renewable power generators which are becoming very common on our grid are asynchronous. Wind turbines use rotation to generate electricity, the turbines spin at variable speeds set by the wind and not from constant high-pressure gas which limits the amount of inertia they hold. Solar photovoltaic (PV) cells only produce DC electricity when the sun is shining and have no moving turbines; solar PV has no spinning parts which would contribute to inertia. Both wind and solar are known as intermittent energy sources and have electronic frequency control to match the grid-required 50 Hz.Energy storage & durationTo make up for the decreasing level of built-in inertia on the grid, other buffer systems have been installed – such as batteries. Quick response energy storage can be used to meet frequency variations, stabilise the grid and become that ‘buffer’ or ‘cushion’ to external events. Quick response energy storage is vital for the NEM’s shift to renewable power. However, a full combination of energy storage is needed to meet daily, weekly and seasonal demand while managing intermittent supply generation. Medium and Long Duration Energy storage is also a rapidly expanding market. It refers to the effective length of storage, creating categories within the energy storage market. While batteries are very effective at quick response to electricity output, there are many other forms of energy storage that range from hours to months. Some medium-duration energy storage technologies such as Thermal Energy Storage (TES) can build in a level of inertia to the grid. As we transition to a net-zero energy network, a combination of energy storage technologies is a promising solution to create a stable, and robust grid.MGA Thermal’s technology is medium to long-duration energy storage which is ideal for shifting the supply curve to meet demand on a daily to weekly basis. The TES can repurpose existing thermal power station infrastructure, to create cost-effective, sustainable, robust grid-scale energy storage. Learn more about the MGA Thermal technology here. Published on 10/02/2023 - Arden JarrettA version of this blog was originally published on 18 January 2021.

This is the first article in our informative series on the energy market. We’ll start with some foundations – a basic explanation of the Australian National Electricity Market (NEM) and how it functions. Later articles in the series will build on this topic and discuss the electricity supply curve, negative spot prices, inertia, frequency, and how energy storage can support the NEM.What is the NEM[i]?NEM is short for National Electricity Market. Despite its name, the NEM is not Australia-wide; it includes five states, Queensland, New South Wales, Australian Capital Territory, South Australia, Victoria, and Tasmania. The NEM is both the physical electricity transmission infrastructure (i.e. the network of poles, wires, and other infrastructure) that connect those states, and the energy marketplace, which is operated by the Australian Energy Market Operator (AMEO). The total distance of the NEM is around 5000 km and includes the transmission network that carries power from generators to large industrial users and local energy electricity retailers (companies you buy electricity from for your home).What is the AEMO? AEMO stands for the Australian Energy Market Operator (AEMO) and is the organisation that manages the electricity market, ensuring that supply is matched with demand simultaneously. It’s an extremely important role; without an exact match of electricity, the physics of a power system mean that blackouts and system failures could happen. AEMO manages both the NEM and the Wholesale Electricity Market (WEM) which is the electricity market in Western Australia. AEMO itself does not buy or sell electricity, it manages and facilitates the wholesale market of around 30 retailers and over 100 generation companies. What does the market look like? The NEM is the marketplace is where generators sell electricity and retailers buy it. Retailers then resell electricity to businesses and households. AEMO manages this market in five-minute settlements (5MS), meaning that every 5 minutes AEMO matches a dollar amount that a generator is willing to sell electricity for, to a dollar amount that a retailer is willing to pay for that electricity. The amount which is matched is the market clearing or spot price. AEMO also ensures there’s an adequate reserve on standby in case a generator fails to provide its forecast amount, which ensures system security. States within the NEM have their own price region and don’t bid against each other. What are spot prices[ii]?There are two ways to buy and sell electricity in the NEM wholesale market: through the spot market and the contract market. All electricity in the spot market is bought and sold at the spot price.The spot price is determined by AEMO and it is price where the amount willing to sell and buy is matched in the marketplace. It’s also a mechanism to tell generators how much electricity is needed in the market at any time. As a general principle, if the spot price is low, supply usually outweighs demand, and if the spot price is high, demand usually outweighs supply. You can find the live spot price here. Does the spot price have a fixed cap?The Australian Energy Market Commission (AEMC) sets the market cap and a market minimum, which is adjusted every year in line with the consumer price index as according to the National Electricity Rules (NER). The market price cap for 1 July 2022 to 30 June 2023 is $15,500 / MWh[iii]. The AEMC is essentially the rule maker for Australian electricity and gas markets. They make and amend Australia’s National Electricity Rules, National Gas Rules, and National Energy Retail Rules, as well as provide market development advice to governments[iv].A spot price cap is in place to ensure any extreme spot prices can be moderated. In future articles, we’ll be exploring what situations can cause extreme prices. Energy Generation MixThe NEM began operations in the electricity spot market in late 1998. Since then, the total electricity generation capacity has grown and during the financial year 2021-22 the NEM generation capacity was 53,538 MW[v]. In the last year, between 28.4% and 45.5% of the energy generation in the NEM was from renewable generators. Find the real-time energy mix on AEMO, and compare historical consumption and generation with this tool. How is Electricity Transported?To help visualize the NEM and how electricity travels, we’ve put together a step-by-step, beginning with generation. Bear in mind, this is a simplified visualisation of a very complex system. Generators: Electricity is generated through a range of sources. Historically, a large proportion of power has come from base-load fossil fuel generators. More recently the generation mix has been diversified and renewable power generation has been increasing. Regardless of how the energy is generated; points of generation are often located some distance away from the point of use (industrial or domestic). Prepared for transport: The electricity is put through a transformer to increase its voltage for efficient long-distance transport. Long-distance transport: The high-voltage power is then sent through transmission lines. These are the very big, tower-like lines you see between power stations and cities. Point of Distribution: The transmission lines take high-voltage electricity to a point of distribution. Here, the power is converted to a low voltage through a distribution transformer for local use. Short-distance transport: Transporting the low-voltage electricity from the distribution transformer to the consumer is achieved through distribution lines. These are the power lines you see on suburban streets.Arrival for use; Consumers can be domestic and commercial level (i.e. homes and offices) or industrial (i.e. factories). However, some industrial consumers receive their electricity at high voltage due to power-intensive processes. Advancements in renewable energy in the last few decades have complicated this generator-to-consumer path. Domestic-level rooftop solar photovoltaic cells and batteries can also provide electricity to the grid, creating a bilateral flow of electricity. We will discuss the complexity of adding these points of generation and storage in another upcoming article – it’s different from the traditional system outlined above.AEMO has fantastic educational resources; visit their website here. And view the AEMO Fact Sheet on the NEM.Published 16 January 2022 - Arden JarrettA version of this article was originally published on 2 December 2020.