By Phil Kreveld
When the leader of the Nationals states that we should have nuclear power—and that would make electrical energy more affordable (Insiders, ABC, Sunday 8 November) we are treated to fiction.
Senator Canavan is an economist, used to dealing with facts. As to why he chose to raise this fiction remained unanswered for the audience of the ABC’s program. As to fibs spun by some politicians, the major one is that we have very expensive electrical energy.
The Australian Financial Review weekend edition of 7/8 November carried the following quote: “Grattan Institute energy policy director Alison Reeve says international comparisons of electricity bills are difficult due to differing tax treatments, which are tricky to untangle. Australia’s market is also more transparent than other countries at explaining the cost breakdown of our electricity. With that in mind, we can estimate each country’s cost (including taxes) of using 1KWh of electricity (1000watts in one hour). Based on that, Australia’s costs are still below the average advanced economy. That Australia’s energy bills are slightly cheaper than other countries (even if they have risen significantly) should not be surprising, Reeve says. Australia is rich in natural resources, has world-leading take-up of rooftop solar and the perfect conditions for renewable energy. Wholesale prices offer the easiest apples for-apples comparison for the pure cost of generating electricity. On that measure, Australia’s prices are among the cheapest in the world. However, if we were to add on network costs, Reeve says our prices would move up the rankings. ‘‘We’ve got a small population and a large geography. So we are moving the electricity further and spreading the cost across fewer people,’’ Reeve says.”
Focus on “However, if we were to add on network costs, Reeve says our prices would move up the rankings. ‘‘We’ve got a small population and a large geography. So we are moving the electricity further and spreading the cost across fewer people.”
We have 50,000km of high-voltage transmission lines for a population of 27 million (1.8km/capita). For the USA is 1km/capita, and for Europe under the ENTSOE (European Network of Transmission Systems for Electricity) regime it is 1km/capita. Our spread-out suburbs add to our network costs compared with European high-density apartment living. As to renewable penetration we are roughly equal to ENTSOE but we are likely to have a much higher percentage (80% plus) then Europe as coal-fired generation retires. Europe has significant hydro and nuclear resources.
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Network cost increase is the price for more renewables
Let’s focus on “However, if we were to add on network costs, Reeve says our prices would move up the rankings.”
Our long radial grids are extremely challenged when exposed to inverter-based generation. Most generation in solar and wind is of the phase-locked loop based type. We’ll look at the significance this has on stability and technology investment needs for the transmission grids, and also in medium- and low-voltage distribution.
Let’s commence with what is understood by passive loads. Motors, air conditioners, water heating, lighting are all passive loads; provide the voltage, and they suck up current—and energy. The critical element is the provision of voltage. We’re mainly dealing here with distribution networks, operating at 22kV, 11kV, and 400V, three-phase. Very large commercial loads connect to 66kV and higher transmission line voltages.
Now comes a surprise. The phase-locked inverters, being voltage followers (no voltage—no current output and therefore no power export) aren’t really generators—unlike their stable mates, the voltage formers, sometimes termed, grid formers. The voltage followers are really ‘negative loads’. The passive (‘positive’) loads ‘suck up’ electrical current when you apply voltage to their terminals—current flowing into the ‘load’. The grid following inverters push out current, hence the term of ‘negative loads’. But as already explained, voltage must be available!
So far there are no immediate problems—provided the voltage at the terminals of the inverter is rock solid—and if not rock solid, that it varies only slowly. And what do we mean by variation? There’s the voltage magnitude, for example, a single-phase suburban solar inverter might experience voltages varying from 229-245V. That, by itself, is no hassle—but what is a problem is if phase angles change—and do so rapidly. If alternating current voltages rise and fall and rise, etc. etc. together (i.e. ‘in-phase) we have an ideal situation. But, without rock-solid in-phase voltages, the phase-locked loops can ‘lose the plot’ and switch off inverters. And note; the absence of strong, stable voltage as provided by synchronous generators is a major reason.
What happens then, when those suburban inverters switch off? There is then a rush to provide power from ‘elsewhere’, requiring transmission-connected generators to come to the rescue—pronto! Let’s consider the ‘grand dame’ of renewables—South Australia. It requires the solid voltage from the east, via the interconnecting transmission lines. To beef up the SA networks, there are now four synchronous condensers to prop up voltage—but, and it’s a critical point of differentiation—that’s all they do. If voltage stability cannot be maintained, for example through equipment failure, and inverters go off-line, we’re back to that rush of power from the east.
What if there’s insufficient power available from the east? That’s a nightmare scenario. Frequency drops because this is equivalent to driving a car on a level road and suddenly encountering a hill, but having no additional power to maintain speed. Under-frequency load shedding relays in South Australian distribution networks drop suburban loads, previously wholly or in part supplied from rooftop solar—and blackout ensues.
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Focus on facts
There’s more that flows from the foregoing—voltage and power oscillations, and as reported on a number of occasions, these constitute a truly very challenging grid control scenario for the Australian Energy Market Operator. And that’s where the increase in network costs come in—the very point made at the top of this article where the Grattan Institute commentary is quoted.
The foregoing sketches the engineering constraints of operating a mainly renewable grid. Of course, the solution to replacing conventional synchronous generation, associated with gas and coal-fired power stations, is voltage forming (grid forming) inverters energised by batteries. The ones in employ are used for energy arbitrage—not for grid support! We haven’t had to address that issue because there’s still real synchronous generation in the national electricity market system.
In sum, and reverting to the comments of the Grattan Institute, network costs are continuing to increase because of the engineering requirements for strong voltage and constant frequency support—that is a fact. Our electrical energy costs under high percentage renewables will decrease and resulting network costs will increase—another fact. The fibs regarding the lowering of costs for Australian consumers should cease. The only way to bring energy costs down is to use less—in other words, more insulation, double-glazed windows, smaller volume homes. As to the ‘silver bullet’ solutions, including nuclear ones, being peddled—they’re fictions—because we would achieve the same result being politically promoted were we to use tax payer money to revamp ageing coal-fired generation fleets. That way there’d be a sound, strong voltage network to keep the ‘grid followers’ happy.
It’s high time to wake up to realities.
