What is load shedding and who decides whose power is cut when there’s not enough electricity? – ABC News

Updated December 06, 2019 15:03:30

When the demand for electricity exceeds supply, sometimes people need to be cut off from power to prevent the whole system from collapsing.

This is called load shedding.

Here's how it works.

Load shedding is when power companies reduce electricity consumption by switching off the power supply to groups of customers because the entire system is at risk.

This could be because there is a shortage of electricity supply, or to prevent transmission and distribution lines from becoming overloaded.

A number of factors can result in load shedding, including extreme weather and infrastructure outages.

In January, a perfect storm of events placed the energy system under unusual strain.

While temperatures soared into the 40s in much of Victoria and South Australia, driving demand for air conditioning, three electricity generation units at coal-fired power plants in the Latrobe Valley were out of action, reducing the amount of available power.

To restore the balance, the Australian Energy Market Operator (AEMO) instructed electricity networks to reduce load, which left more than 200,000 customers without power for up to two hours.

It's important to note that such load shedding is different to planned local outages, such as for maintenance, and unplanned ones caused by damage to wires by events such as storms, bushfires or car accidents.

AEMO decides when load shedding is needed in the National Electricity Market (NEM), which includes Queensland, New South Wales, the ACT, Victoria, Tasmania and South Australia.

Before it turns to load shedding, AEMO has other measures it takes to try to overcome a power shortfall, such as importing more power from other states and tapping into emergency energy reserves (such as South Australia's diesel-powered generators which were switched on for the first time last summer).

It can also appeal to consumers to voluntarily reduce their energy consumption for example by postponing their use of dishwashers and washing machines and pay large industrial electricity users such as Alcoa's Portland aluminium smelter in western Victoria to power down for a period of time

But after exhausting these options, if it still needs to reduce demand, AEMO instructs electricity transmission and distribution companies to carry out load shedding.

AEMO tells the companies how much power needs to be saved, and the transmission and distribution companies then work out how to achieve those reductions.

Approaches vary between the states and territories, and each has a plan in most cases developed by the state or territory government in collaboration with the electricity industry for how load shedding is to be carried out in their jurisdiction, including a schedule for the sequence in which particular loads will be shed and restored.

These plans are based on nationally consistent principles and seek to maintain critical services and spread the inconvenience equitably: a limited disruption to many, rather than more significant disruption to a smaller number of customers.

In Victoria, in its special role as the state's transmission system planner, AEMO works with the State Government to determine the priority order of load shedding.

In WA and the NT, which aren't connected to the National Electricity Market, state and territory authorities decide when load shedding is necessary and how it's carried out.

Areas are disconnected from the power supply by distributors switching off the feeder serving that area.

A feeder is a high-voltage line that could supply anywhere from a few hundred to many thousands of customers.

Which feeders get switched off depends on a number of factors, including where the area sits in the state or territory's priority order of load shedding, how much power needs to be saved and which areas are using the most energy.

The penetration of solar energy also plays a part.

Some areas with a lot of solar panels could be feeding more energy into the grid than they are using.

These areas are unlikely to be disconnected, as to do so would make the shortfall worse.

AEMO says it works with the electricity industry to minimise the impact on the community, particularly major health facilities, emergency services and public transport.

But it says such services can still be affected by load shedding and should have backup arrangements in place.

Distributors also say they seek to avoid disconnecting power to other kinds of critical infrastructure, such as sewerage and water pumping stations, and to large shopping centres.

Energy Queensland said it first switches off "controlled load" energy. These customers receive lower prices in exchange for allowing the distributor to switch them off for a few hours each day.

The impact of this is generally less than other options, because these tariffs are typically used for non-essential equipment such as pool pumps.

Energy Queensland also has demand management agreements with a number of large industrial customers, which are offered lower bills throughout the year in exchange for being available to reduce their consumption at peak times.

In general, the first areas to be turned off will be mainly residential.

Victorian distributors CitiPower, Powercor and United Energy say they annually review the types of customers connected to each feeder in their networks, to determine which should be given priority because they serve critical customers.

Distributors try to minimise the impact of load shedding by rotating the disruptions between different areas: for example, disconnecting one area for a period of up to two hours before restoring its power and disconnecting another area.

"Typically, critical customers are last to have power turned off and first to have supply restored," said Andrew Dillon, the chief executive of Energy Networks Australia, which represents electricity transmission and distribution businesses.

Feeders serving hospitals are less likely to be disconnected, but being located near a hospital doesn't necessarily mean you share its feeder.

Living near a big industrial energy user is unlikely to have any bearing on whether you lose power.

Victoria's biggest energy user, Alcoa's Portland smelter, is served by its own dedicated transmission lines.

If load shedding is necessary in your area, you may not get any advance warning.

"Networks are often only given short notice by AEMO that load shedding is required," Mr Dillon said.

"This may be because a generator fails, creating an unexpected and rapid drop in supply."

When load shedding was ordered in Victoria in January, the rapidly moving situation seemed to take even the state's Energy Minister, Lily D'Ambrosio, by surprise.

On the morning of January 25, Ms D'Ambrosio told a media conference she didn't anticipate load shedding being necessary.

Later that morning, AEMO ordered load shedding.

South Australia publishes a list of which feeders are next in line for load shedding, based on which areas were shut off last time.

It is the only jurisdiction to publish its arrangements.

Michael Brear, the director of the Melbourne Energy Institute at the University of Melbourne said if other jurisdictions were as transparent as South Australia about their plans, it might help reassure people that load shedding was being implemented fairly.

"I think it would be a good thing if they did it [published plans] in all states, so that everybody realises that there's no sort of political or other, less legitimate considerations involved," he said.

"Some people might think, 'They'll turn off that seat because it's a safe seat, but not that one because it's a swinging seat,' or something like that. That doesn't come into play."

Professor Brear says the alternative to manual load shedding would be more widespread and longer-lasting interruptions to power supply.

"There are very good reasons as to why we load shed and why we do it in a systematic way. It's to minimise the inconvenience and share this inconvenience across the whole population so that collectively we don't experience much worse.

"The choice is not between manual load shedding and continuing to have your air conditioning on and drinking your cold beer," he said.

"The choice is between coordinated and controlled load shedding and uncoordinated, uncontrolled load shedding, which might lead to greater problems."

AEMO's summer readiness plan, released this week, warned of a risk of blackouts across the national market but particularly in Victoria, New South Wales and South Australia, due to a combination of extreme weather, bushfires and plan outages.

The state most at risk is Victoria.

In August, AEMO warned that more than a million Victorian households were at risk of being without power this summer during extreme heat if two of the state's power plants which are out of action following faults earlier this year are not returned to service in time for peak periods.

AGL said this week its Loy Yang A coal plant in Gippsland would be back online by mid-December, while Origin said its Mortlake gas plant would not be operational again until the end of the year.

The market operator and Victoria secured extra power reserves ahead of summer to reduce the blackout risk, but Ms D'Ambrosio was not giving any guarantees this week.

"I don't think it's a sound position for anyone to give guarantees [about power] when effectively the Victorian Government doesn't own any of these generators," she said.

Professor Brear said since the closure of Victoria's Hazelwood coal-fired power station in 2017, which removed 1,600 megawatts of generation capacity, the state did not generate enough power to meet demand at its peak.

As for whether load shedding will be necessary this summer, he said it would largely depend on the weather, as well as the preparedness of coal and gas-fired generators.

Weather conditions influence demand for electricity as well as how much wind and solar energy is generated, and how reliably the state's remaining coal-fired power plants operate.

Longer term, he said Victoria needed more capacity to generate dispatchable power power that can be turned on when it's needed, even if the wind isn't blowing and the sun has set.

He said this could be delivered with more batteries, gas plants or pumped hydro.

"We could do with a new power station," he said.

Topics:business-economics-and-finance,industry,electricity-energy-and-utilities,melbourne-3000,australia,vic,nsw,qld,tas,act,sa,nt,wa

First posted December 06, 2019 05:48:49

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What is load shedding and who decides whose power is cut when there's not enough electricity? - ABC News