Energy firming—what does it mean?

Overview of energy firming

Renewables (wind and solar) were announced as the cheapest technology for producing electricity in Australia in July 2022. Cost details can be found in this CSIRO report. Wind and solar power is also known as variable renewable energy (VRE). Much of the uncertainty around moving to a variable renewable energy system is around the process and cost of “energy firming”. Firming for long-term periods of poor wind and sun (known as energy droughts) is a fundamental requirement of a reliable system.

What is energy firming?

Energy firming is how operators maintain the output from variable and intermittent power sources, such as wind or solar, for a committed period of time. Variable renewable energy (VRE) sources need to guarantee supply in the event of energy droughts (poor periods of sun or wind generation). Other energy sources need to be used to maintain a full supply and to store the energy created by VRE sources.

Why is it important?

Australia has committed to reducing greenhouse gas emissions to limit climate change to no more than 2 degrees Celsius. We have an aspiration to limit warming to 1.5 degrees Celsius. Much of the uncertainty around moving to a variable renewable energy system is around the cost of firming.

Solar energy now costs about $45 per mega-watt hour (MWh) (July 2022) while wind costs about the same as coal per MWh at $50. The renewable energy sector is now supplying the National Energy Market (NEM) with 10,000 MWh of power (according to the Energy Council).

Types of energy firming technologies

There are three currently viable forms of non-fossil-fuel firming technologies:

1. pumped-storage hydro (PSH);
2. industrial-scale lithium batteries; and
3. zero-emission open-cycle gas turbines (OCGT).

Pumped-storage hydropower (PSH) is a major option. When there is excess energy produced by solar and wind it is used to pump water to high level storages. The water can then be released through hydroelectric turbines to meet shortfall needs. There is a 70-80% cycle loss in this process. The Snowy Mountains Hydo-electric Scheme can be used in this way.

Using industrial-scale lithium batteries has made short-term firming possible. However, batteries are only suitable for short-term firming of about 4-6 hours. They do not have the capacity for long-term “energy droughts”.

Zero-emission open-cycle gas turbines (OCGTs also known as peakers) can be deployed even with very high fuel costs for green fuels (such as hydrogen or biodiesel).  They will be able to address energy droughts due to the storage limitations of batteries and pumped hydro. These are new, undeveloped technologies and the cost per MWh is estimated at between $150/MWh and $600/MWh. However their use would be infrequent so the cost would be absorbed easily.

Hydrogen electrolysers could potentially underpin a low emission hydrogen fuel industry for export or for Australian domestic use. Studies indicate that substantial cost reductions are expected over the next few decades.

Fossil-fuel firming

Coal-fired power stations are not suitable for firming because of “inertia” — they take a long time to turn on and turn off. However, gas-fired power stations are being proposes as a solution but as they use natural gas (considerably cheaper than green fuels) which is a fossil-fuel, they will contribute to greenhouse gas production.

The nuclear alternative

Nuclear is being considered in Australia as a firming alternative. Apart from the lack of proper processing facilities and technologies for high level waste, nuclear is expensive and will take too long to build to be able to help Australia meet its greenhouse targets. Modular reactors have been touted but these won’t be affordable until 2050.

Madrigal Communications is a member of the Smart Energy Council. Our writers are experienced in sustainability reporting and energy proposals and tenders