By Phil Kreveld
GE Vernova, Siemens Energy, Mitsubishi Power and all other serious suppliers of gas turbines are happy to oblige, given a decade. Is the promotion of gas part of the pile-on directed to ‘renewables’ from climate change sceptics and deniers?
The renewable haters will point out that huge amounts of battery storage are needed but they ignore the gazillion of tons of potential fuel stored in the earth’s crust, which unlike the immediately accessible energy from batteries, need to be dug up, massaged and taken to huge plants for conversion to steam or hot gas, in order to drive a turbine, in order to drive a generator, in order to generate electricity.
The wind blows lots of the time and the sun peeps over the horizon each day, regular as clockwork. The sun’s surface is approx., 5000°K for the moment. This is great for conversion to power (energy/unit time) as we are at about 300°K on the earth’s surface yielding a Carnot cycle efficiency of 94%.
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All that power beaming down over billions of years has helped processes that created vast energy stores of coal, and oil, and gas. We clever Earth dwellers made use of that, releasing stored energy by fire, and using the difference between the temperature of the heat released and suitable cool sinks, for converting the released energy into mechanical work (planes, trains and automobiles) and electrical energy.
Digging up all those below-the-surface stores of potential energy (we got to set fire to them) uses up a lot of energy (requiring capital). And the scarcer and lower in grade, the more money is needed. Utilising the sun (photons) or wind or both costs doodly-dick. Yes, we are bringing the heat death (increasing entropy and evening out temperatures everywhere) of the universe closer, but chances are we won’t be there to witness it.
Leaving fuels in the ground leaves more surface for veggie plots—sure, we need to subtract areas required to put up solar panels, however, sheep may safely graze underneath them.
So, what’s behind the sudden increase in gas popularity as far as electricity generation is concerned?
It’s ‘firming’, a suitably loose concept which emotionally allays fears of sometimes highly variable solar and wind. Firming something that is infirm seems Iike a given but what’s not pointed out is that ‘firming’ is therefore also sporadic. It therefore begs the question as to what else other than infrequent operation, gas-generated electricity will add.
For one, selling energy for very short periods doesn’t sound like much of a business proposition. Selling capacity (the ability to supply energy, whenever needed) is a more realistic business but that is one where battery energy source systems (BESS) can do the job as well. Furthermore, they are available now—not five years or more, out!
In engineering terms, smaller gas turbines, particularly open cycle ones, add much less inertia than coal fired plant. As the Australian Energy Market Operator (AEMO) has indicated, there are inertia deficits in South Australia, Victoria and New South Wales. A shortfall in inertia causes frequency variations when there are changes in power consumption and/or generation. Inertia slows the frequency change sufficiently for the frequency control ancillary services (FCAS) to pump in energy while spinning rotors (coal, gas, hydro) are slowing, because there has been a sudden increase in power demand. BESS in combination with voltage forming inverters do not supply inertia, strictly speaking, but in essence perform the same task as spinning rotor machines.
To understand the value of voltage forming inverters, think of what happens if there is a sudden increase in power demand. A synchronous generator and its turbine slow down a bit. By the time the controls have readjusted steam, gas or water flow, the generator rotor has changed its angular position (a change in voltage angle) in reference to other generators in the grid.
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Voltage forming inverters pick up the change in frequency (delta f) and integrate this as a change required in voltage angle. If frequency has dropped, the voltage angle is increased so as to increase power flow. For small variations, increase in power flow is directly proportional to the change in voltage angle. Admittedly there are some areas that AEMO still has to figure out, one being the total capacity of BESS-voltage forming inverters compared to grid following inverters for wind and solar but it ain’t rocket science! And if you like, we’ll term this useful ‘firming’.
So, do we need gas? Not really! What we do need is for AEMO to be given the means and authority to look at the overall grid requirements as to what ratio of voltage forming to grid following inverters are required, and the overall supervisory and controls schemes. It is a solvable problem. The pollies should really butt out of electrical engineering. All they are achieving, to the extent they are being taken seriously, is to confuse markets and rather than stepping on the gas, they are pulling up the handbrake.
