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24/7 renewables power?

By Geoff Carmody - posted Thursday, 14 July 2022


'Free' sunlight, wind, and rain? Sure. Weather's 'free'. It's also beyond our control. A rational energy policy review would:

Let known technologies drive transparently determined, evidence-based, cost, reliability and emissions outcomes.

Use these outcomes to decide the best cost, reliability and emissions policy 'mix', not the other way around.

Are renewables the cheapest power? Only when available? How about 24/7? What's the evidence?

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We can't plug sun, wind or water into power points. Harvesting these comes first. The cost of that includes renewables generation, storage, transmission, equipment disposal, etc.

The government now draws voters' attention to power transmission ('poles and wires'). This is a big issue indeed. Optimal renewables generation sites often differ from fossil fuel deposits. More, and more specialised, 'poles and wires' are needed, (see AEMO).

'Poles and wires' deliver 24/7 renewables only if enough power can be generated and stored to transport to users in the first place.

Before worrying about 'poles and wires', worry about adequacy of renewables generation,and power storage, and technology.

i. Generation is delivered by PVs (solar), turbines (wind, hydro), and freely-flowing water (hydro).
ii. Storage requires manufactured batteries (tiny to large manufactured batteries for solar and wind, artificial dams for hydro).

Technology is lowering costs and increasing efficiency. That's good. However, intermittency is a big deal for reliable power, 24/7.

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How big? A numerical example, (there are many others), based on past actual South Australian data, shows this for solar and wind.

i. On average over a year, solar generates full power about 15% of every day, and zero for the rest.
ii. On the same basis, wind generates full power a bit over 30% of every day, and zero for the rest.
iii. Solar power varies with the seasons (most in summer), latitudes (most in lower latitudes), cloud cover, etc.
iv. Wind power is geographically and weather-variable. Some places (not least offshore) are more consistently windy.

Suppose solar power is available every day for 15% of the time. For 24/7 power supply, effective generation capacity must be about 6.7 times as much as the equivalent effective fossil fuel generation capacity. Daily power must all be generated when the sun shines.

Suppose wind power is available every day for 30% of the time. For 24/7 power supply, effective generation capacity must be about 3.3 times as much as the equivalent effective fossil fuel generation capacity. Daily power must all be generated when the wind blows.

These 'every day is the same' assumptions are unrealistic. We can face several days, or more, without sun or wind. All the power generation needed for reliable 24/7 power must occur in the day or days before the sunless or windless days. Why? Electricity must be used as soon as generated, or immediately stored in batteries. Otherwise it's lost. Assume power must be generated the day before.

Suppose we have a three day 'drought' of sun or wind. Using our numerical example, solar generation capacity now needs to be 26.7 times the equivalent fossil fuel capacity. All the power for four days must be generated in 15% of the first day. Wind generation capacity needs to be 13.3 times the equivalent fossil fuel capacity. All the power for four days must be generated in 30% of the first day.

Most of the power generated is not used immediately. It's stored in batteries. Storage capacity therefore is a really big deal, too.

If solar power is available every day for 15% of the time, for 24/7 power supply, battery storage capacity must be the equivalent of 5.7 times as much as the equivalent effective fossil fuel generation capacity. For a three day solar 'drought', this generation-equivalent storage increases to 25.7 times the equivalent effective fossil fuel generation capacity.

If wind power is available every day for 30% of the time, for 24/7 power supply, battery storage capacity must be the equivalent of 2.3 times as much as the equivalent effective fossil fuel generation capacity. For a three day wind 'drought', this generation-equivalent storage increases to 12.3 times the equivalent effective fossil fuel generation capacity.

These required generation and storage capacities are additive.

For reliable renewables, therefore, the equipment costs comprise at least three elements that must be added together.

i. Generation equipment needed to harvest enough 'free' solar, wind, or hydro energy.
ii. Plusmanufactured battery equipment sufficient to store most of that for later discharge when needed.
iii. Plusnew and upgraded transmission (FCAS requirements, etc) to transport most power from where generated to where used.

Batteries don't generate power. They store it, more or less inefficiently. Separate energy generation to charge and re-charge them is needed to support them. Electric cars aren't a new source of electricity supply. They are a new source of electricity demand.

Governments usually announce 'big battery' investments (such as Hornsdale in SA) with assertions about how many homes they can power. Typically, these announcements are misleading. For 24/7 power, the relevant questions are: (a) how many homes can be powered 24/7, and (b) for how long? The answers are 'not many' and 'not for long, without re-charging'.

Given the physics – multiplied generation-equivalent capacity requirements across generation, storage, and transmission – what would a 24/7 system, as reliable as we now enjoy, cost? Less than our current system, including costs of now-expensive fossil fuel inputs?

What's the answer? Surely we should know this up-front for a rational policy approach?

A rational energy policy review would start with evidence, not ideology, as follows:

Let known technologies drive transparently determined, evidence-based, cost, reliability and emissions outcomes.

Use these outcomes to decide the best cost, reliability and emissions policy 'mix', not the other way around.

 

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About the Author

Geoff Carmody is Director, Geoff Carmody & Associates, a former co-founder of Access Economics, and before that was a senior officer in the Commonwealth Treasury. He favours a national consumption-based climate policy, preferably using a carbon tax to put a price on carbon. He has prepared papers entitled Effective climate change policy: the seven Cs. Paper #1: Some design principles for evaluating greenhouse gas abatement policies. Paper #2: Implementing design principles for effective climate change policy. Paper #3: ETS or carbon tax?

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