Explainer: What does it actually mean to “firm” renewables?

Large power grids are among the most complicated machines humans have ever devised. Different generators produce power at various times and at various costs. A generator might fail and another fills the gap. Demand soars in the evenings and on hot days. In Australia, eastern and southern states trade power across borders. Meanwhile, Western Australia has two grids and the Northern Territory has several.

But these complicated machines are undergoing major change, as we shift from large fossil fuel plants to cleaner forms of power. Wind and sun are now the cheapest way to produce electricity. These renewable sources will soon overtake coal and gas – they’re already averaging 40% of power flowing through the national grid.

Solar and wind are often called “variable” renewable energy sources. Variable, here, refers to the fact the sun doesn’t always shine and the wind doesn’t always blow. On sunny, windy days we get lots of cheap power. But on still nights, we might get little.

This is where “firming” comes in. To firm renewables is to convert this cheap but variable source of power into what we really want: a reliable supply of electricity, there when we need it. Big battery projects are one way to do it. But there are others.

How does firming work?

Storage is the best known way to firm renewables. As floods of cheap power come in, you can store it for later use.

Storage can be performed by grid-scale batteries, where the power is stored directly. But it can also be done by pumped hydro, where water is pumped uphill when power is cheap and plentiful and run back downhill, through turbines, when power is harder to source.

Firming can also be done by virtual power plants – aggregated fleets of smaller batteries in homes and electric vehicles.

Gas peaking plants are another way of firming renewables. In the future, gas plants will go from being a mainstay to the equivalent of a backup generator, fired up only when needed.

Generally, energy storage facilities offer either short- or long-term firming. As more renewable power enters Australia’s grids, we will need both. This is because they offer different levels of storage and response times.

Short term can be as short as seconds to a few hours. Batteries are a common way to provide short-term firming, because they can ramp up very quickly to tackle sudden fluctuations in supply or demand. These fast-response systems help stabilise the grid by smoothing out spikes caused by changing weather.

Long-term firming can be for hours, days or even weeks. This includes large-scale battery storage or back-up generators such as gas plants. Long-term options are crucial to maintain power supply during extended periods of low renewable generation, such as still, cold days and nights in winter.

How are we tracking with firming renewables?

In recent years, large-scale battery announcements have ramped up. Almost 8 gigawatts of battery capacity is now in progress or anticipated to start construction shortly. But the pipeline of future projects is much larger: 75 gigawatts of firming will be required.

While renewable power is cheap, to make it useful and reliable in addition to storage, we need transmission lines to connect large renewable zones to cities and towns. All this adds extra costs.

As the level of renewables in our power grids inches higher, firming costs increase. This is especially true when a grid goes from 95% to 100% renewables, when there’s a sudden jump in cost.

This is why experts have argued for keeping a few gas peaking plants. While they are not emission-free, they are flexible and can start up much more rapidly than coal. They will likely play a key role in firming the grid during renewable droughts and extreme demand – an estimated 5% of the year. That sounds small, but they will be essential.

Eventually, gas peaking plants could switch to hydrogen, if the fuel becomes cost effective. This would cut emissions further.

Firming – at home?

Homes with batteries can also help firm the network by joining a virtual power plant. These networks of batteries can be digitally coordinated to function as a single power plant, helping stabilise the grid.

If a home owner signs up to a virtual power plant program, they hand over some control in return for income. Technologies such as this can support grid stability by charging or discharging in response to supply fluctuations.

These networks are a flexible energy resource. They can inject power to the grid instantly if there’s a sudden drop in solar or wind generation. They can also soak up surplus energy.

These aren’t hypothetical. Several are running or in development in Australia, such as the AGL virtual power plant in South Australia, SolarHub in New South Wales and the new ARENA-funded Project Jupiter in Western Australia, which will commence soon.

Is firming helping?

Firming technologies are already helping in high-renewable grids overseas. Big batteries now allow California’s grid to absorb more renewables, by soaking up daytime solar and releasing it at evening peak.

We’re seeing the benefits of firming locally, too.

On January 20 this year, a heatwave in Western Australia triggered a new record for peak electricity demand – 4.4 gigawatts – in the state’s main electricity network, the South West Interconnected System.

In response, recently built battery storage at Kwinana, Collie, and Cunderdin stored excess power and discharged it at peak times.

The next day, dense clouds swept in, slashing solar output and reducing peak demand. In response, gas generators increased output to firm the grid.

Firming technologies are already playing a vital role in keeping our electricity supply stable, reliable and resilient – and it’s just the start.

Peta Ashworth, Professor and Director, Curtin Institute for Energy Transition, Curtin University and Ehsan Pashajavid, Senior Lecturer in Electrical Engineering, Curtin University

This article is republished from The Conversation under a Creative Commons license. Read the original article.