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Are renewables and batteries part of the power generation & storage solution?

By Geoff Carmody - posted Thursday, 9 November 2017


What is a battery? They're everywhere!

We all know what a battery is, right? There are little cylindrical, rectangular, and pill-shaped ones. We put them in torches, remotes, mobile phones, tablets, laptop computers, etc. There are bigger ones we use in cars. There are still bigger ones we use for off-grid homes, and, increasingly, homes on the grid. There are industrial-scale ones used to support electricity grids (just ask taxpayers in SA).

These are modern versions of the 'voltaic pile', invented by Alessandro Volta and others around 1800. Demand for them is taking off.

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Humans have developed other batteries. Some water heaters are effectively batteries, in part. Rainfall stored at a higher level (potential energy) can drive generators as it flows to lower levels (hydro kinetic energy). We can even recycle water between higher and lower dams to achieve a form of renewable energy (pumped hydro). The Commonwealth Government seems keen on this quite old concept (eg, 'Snowy 2.0'). We can use the sun to melt salt and use that as a store of energy to make steam to drive generators. The SA government is keen on this 'thermal solar'.

But Volta and co were latecomers. We've long enjoyed natural battery power. Be careful about contacting an electric eel. It could be shocking.

Over millions and billions of years, nature has produced huge batteries spread all around the world.

Photosynthesis plus decay plus geological storage manufactured massive batteries available to be discharged. We call them fossil fuels, increasingly with a pejorative tone. Exploding stars over the eons disgorged heavy radioactive elements, producing terrestrial nuclear fuel batteries. These have a mixed reception globally. We're happy to use nuclear fusion (when called solar power), provided it's sourced nearly 150 million kilometres away in the sun. Wind power depends partly on solar-induced temperature differences.

Some batteries are discharged fully with one use. Others can be used more than once.

Wood's a battery, when burned. So's food, when consumed. Both are renewable.

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In the most general sense, batteries are means for storing energy for use later. They're ubiquitous.

Life literally couldn't exist without them.

Extracting energy: energy density realities

How efficient are different types of batteries/energy sources? A key metric is 'energy density'.

Broadly, energy density is a measure of how much energy/power you can stuff into how small a weight/volume/area. This can be used to rank alternative sources of energy.

Converting matter into energy is best, as Einstein worked out (E=mc2 and all that). Anti-matter is top of the pops because, combined with matter, all of both are converted to energy. But anti-matter is a bit like 'unobtainium' in the movie Avatar. We can't get it or use it, at least at scale.

For currently-obtainable terrestrial sources, nuclear energy is by far the most energy-dense source available. It converts a very small amount of matter into huge amounts of energy, as per Einstein. We're trying to develop cold fusion. But fission-based power currently is best (for peaceful purposes anyway). Depending on the metric used, this can be thousands of times (plus) more energy-dense than hydrogen and fossil fuels like oil and gas, coal, charcoal and wood.

Depending on the metric used, fossil fuels can be 40 to 50 times (plus) more energy-dense than man-made batteries. They use chemical reactions, usually oxidisation, to generate heat and other chemicals.

Man-made batteries are much less energy-dense than fossil fuels. Battery technology is improving, so lithium-based batteries can be more energy-dense than the old lead-acid batteries. They use chemical reactions to generate electrons, heat and other chemicals.

What about renewables like solar, wind and hydro?

These are the least energy-dense sources. Solar, wind and even hydro power energy sources are very diffuse, not concentrated. They require very large areas (solar and wind) and/or large volumes (hydro) for collection. (They are also intermittent, reducing their average energy density as well.) Measuring these differences involves a blizzard of different metrics. I'll let properly-qualified scientists pontificate on these.

But, to illustrate, I've read startling statements like the following:

  • Gasoline is one billion times more energy dense than wind and water power, and ten quadrillion times more than solar radiation.
  • To store the energy contained in 1 gallon of gasoline requires over 55,000 gallons of water to be pumped up 726 feet (assuming 90% recycling process efficiency).

Energy density 'bang for your buck' is maximised using nuclear power. Fossil fuels come a distant second, but still far ahead of renewables.

These very different energy densities have huge implications for practical energy policy (see below).

First, a little more on man-made batteries.

One-shot batteries tend to be more efficient than rechargeable batteries. Recharging itself degrades battery efficiency.

One-shot nuclear batteries can last for a very long time while having small volumes and modest weight (eg, those powering the still-going 1977 Voyager and the 1997-2017 Cassini space probes). Fossil fuel batteries can deliver a fair amount of energy from relatively modest volumes over a short period, but, once used, they're mainly expended.

Rechargeable batteries have different cycle tolerances that limit usability and battery life. Lead-acid batteries can't be discharged much before the process greatly reduces their effective life. Lithium-based batteries are much better at cycling from low remaining charge to full charge on a regular basis (as we know from our mobile phones, etc.). All rechargeable batteries require another source of energy to recharge them.

Our decades-old, one-sided energy debate

For decades, we've debated energy and greenhouse gas emissions, energy and local pollution, energy and land and water appropriation and/or degradation, energy waste disposal and storage, and the like. The political pressure behind all this has been to move away from energy-dense power/energy to the opposite. Taxpayers have been forced to subsidise this shift, and still are.

Yet we have not discussed energy density much, if at all. And we haven't discussed the potentially huge equipment investment capacity requirements and costs, and land-use demands, that renewables entail.

The Commonwealth Government asserts it's offered a 'game changer': shifting emphasis away from emissions reduction towards more concern about reliability and affordability. Its National Energy 'Guarantee' (NE'G') may have given that appearance to some. But the NE'G' is just an 'announceable'. It's eight pages of imprecise, open-ended, words. COAG hasn't agreed to adopt it yet, anyway, and the signs look 'iffy'. Energy density is not mentioned at all.

Emissions reduction – via lower energy density – still dominates the media. But there are signs the wallets of voters are screaming affordability.

What now?

Renewable energy generation sources, and man-made battery storage, have very low energy densities compared with fossil fuels. Compared with even currently-available nuclear fuels, they're even less energy-dense.

Relatively huge investments in equipment capacity and costs, and in land areas, volumes and/or weight allocated to renewables generation, plus battery storage, are needed to deliver equivalent base load plus peaking electricity, compared with fossil fuels and nuclear power.

We already see the large areas involved even in existing industrial-scale wind and solar farms. We can't see the sizeable equipment costs but relatively puny intermittent energy outputs these actually deliver compared with fossil fuels and nuclear power.

This opinion piece is not about renewables intermittency and the multiplied generation/storage capacity needed to offset that. I dealt with that in my 22 August 2017 opinion piece entitled: Does Australian renewable energy save the earth – or just cost it?

The very low energy density of renewables and man-made batteries is an additional, even larger, capacity multiplication problem. If renewables and man-made batteries are much less energy-dense than nuclear and fossil fuel power sources, then we need to compensate for this energy density disadvantage as well as intermittency, if we want to use them. This means investing in even more generation and storage equipment:

  • The capacity, and space, required for a reliability-equivalent investment in renewables generation plus storage is many multiples of that required in nuclear or fossil fuel electricity generation.
  • Huge dollar investments in at-scale generation and battery storage will be needed. These multiply as renewables penetration increases.

For example, could an equivalent-power, totally renewables-based, electricity generation/storage plant be developed, whatever its cost, within the geographical footprint of the current 2,000 mW (plate-rated) Liddell coal-fired power station?

With current technology, I don't think so. There are lots of other examples suggesting huge tracts of land (or ocean) will be needed to switch from more energy-dense fossil fuel and nuclear energy sources to very diffuse energy sources (and batteries) to do the same job. (I'll assess the land-use economics of renewables in my next piece on 'poles and wires'.)

Energy density issues, and the trade-offs between their implications and other considerations, should explicitly be recognised and dealt with.

A policy perspective

Recently, the conservation argument against energy-dense fossil fuels was that supplies would run out ('peak oil', etc). We're still waiting for 'peak oil'; still longer for 'peak gas' and 'peak coal'.

Now it's claimed we can't use existing deposits of such fuels because they'll increase global warming, local atmospheric pollution, etc. They won't run out at all. Those remaining must be left in the ground.

Fossil fuel prices are rising as emissions standards increase costs. Renewable energy costs are falling. However, the multiplied capacity and storage requirements of reliable renewables will increase total costs and/or slow cost declines.

Even so, many – including the Commonwealth Government – now assert renewables don't need any subsidies.

If so, Australia's small global emissions (1.4% of global anthropogenic emissions and falling), and pusillanimous total overseas efforts to reduce emissions, raise the obvious question.

Why do we need Renewable Energy Targets (RETs) at all? These add to system-wide costs and kill affordability.

Let's abandon RET-type measures, and let technology, energy density, and their costs, sort out the energy mix we use.

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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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