By Phil Kreveld
Electrical energy is essential. Everyone agrees. The disagreements are about how it is generated, and how it is transported to consumption centres.
Contemporaneously there is discord on anthropomorphically induced climate change. Are we making the world warmer? Ignoring that question, does it matter how we generate and transport electricity, as long as it’s low cost?
There are those to whom wind and solar-generated electricity are only defensible if we are making the world warmer by burning coal and gas to generate electricity. This is the essence of the climate wars—if we contribute a percent or two to world emissions, why bother with wind, solar, and batteries?
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There is a practical side to the political dissension; wind and solar are less expensive in dollars per megawatt hour than coal and gas-generated electricity. However, the additional cost of transmission and voltage stabilisation need be added as well as costs to investors of curtailment/spillage as that requires rewards for capacity.
Also, the capital cost of new grid controls must be taken into account. To the extent that these are additional costs over and above those for coal, gas and hydro, they must be added to the renewables ‘charge sheet’. When that is done, the costs of the renewables rise toward those associated with traditional sources of electrical energy and differences become less dramatic.
The climate wars also revolve around whether the technologies and costs of renewables are either much lower than traditional generation—or that the reverse is the case. The facts are pointing to renewables being increasingly ‘off the shelf’—the traditional energy sources, less so.
These are not arguments to support one or the other. Both can be solutions for Australia. If cost is the deciding factor, then taking all costs into account is essential. The results of the analyses may well be disappointing to both pro- and contra-renewables parties. That leaves speed of installation of new energy sources to meet projected energy demand as the important consideration.
There is another question: can we make an all-renewable grid work reliably? Those arguing against ‘net zero’, say we can’t. The opposite argument is that there no doubt that we can. Neither side has absolutely positive proof. If the blackout of the Iberian Peninsula illustrates anything, it is that both traditional and renewable sources of electricity contributed to the grid collapse.
Purely traditional grids have been subject to massive blackouts, something conveniently not mentioned by anti-renewable forces. It is an unfortunate feature of large networks. Making renewable networks as reliable as those with traditional sources is perhaps setting the bar too low. We should attempt to do better.
Reading through the report of the European Electricity Network Transmission System Operator (ENTSO-e) on the Iberian Peninsula blackout, provides a closer look at the Incident. It indicates points that we can usefully think about regarding the interaction between human-control and automatic control.
Spanish operators properly adhered to established procedures following 28 April midday voltage oscillations in 400kV transmission lines. In doing so they exacerbated problems that might have been avoided, were generator and transmission line operation combined in a centralised, automatic control.
It is a novel concept, but the integration of renewables into electrically large grids would appear to require it. The value of mechanical inertia is that it can provide time windows of five or more seconds, not only to take action on generator control, and in the case of Spain, to also control var compensators.
Although more is likely to come out of the investigations by ENTSO-e, and the Electrical Power Research Institute (USA), a clearer picture is emerging, one that is also useful for us. The oscillations in the Spanish high voltage lines were damped by operators, paralleling more transmission circuits, thus reducing impedance—the classical way of increasing damping.
The problem was that reduced impedance was mainly capacitive because solar and wind were taking care of local energy requirements, i.e. transmission lines carried very light loads. Transmission voltages kept rising as a result, requiring synchronous generators to run in under-excited mode to absorb reactive power—Spain has no synchronous condensers in its mainland grid. Under-excitation is limited for reactive power absorption because of loss of synchronising torque. As voltage rose more generators were switched off for protection reasons, eventually leading to country-wide grid collapse.
Unloaded transmission lines are an emerging problem for Australia, making sufficient reactive power absorption important. Increasing energy independence of distribution networks during daylight hours, reduces transmission power flow to low amounts. This causes large scale solar and wind generators to curtail energy (and any reactive power support). Our solution is to employ synchronous condensers, and they might be operating in under-excited mode, i.e., effectively as inductors. We have no market for reactive support, neither has Spain.
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Using the Spanish experience as a demonstration of the unviability of renewable energy sources is unwise. However, it is useful to point us to reliable grid management schemes. Many long transmission lines in Australia, exhibit Ferranti-effect, capacitive voltage rise when lightly loaded. This requires excitation control schemes for synchronous condensers, taking account of not only sending and receiving bus voltages, but also of interconnecting distant buses, as well as generator states.
A wholistic engineering approach is what is needed. What we do not need is uninformed climate war comments from the sidelines.
