To be fair, Solar power plants never claim that they can...

To be fair, Solar power plants never claim that they can generate power 24 hours a day - I think even Donald Trump would be able to understand that solar panels don't generate power at night

Equally, coal and gas-fired power stations claim their rated capacity as peak generation output, not accounting for downtime. In reality, especially for older power stations, failures are not uncommon, especially for coal burners during hot weather when power demand is high:

Energy prices jump since Morrison coup, as “fair dinkum” coal trips again, and again

NSW grid struggles as coal goes missing after bad trips

Pas-de-deux: Two big coal units trip at same time in Victoria

Liddell, the coal plant that “predates colour TV”, trips again

Coal unit trips in heatwave as Tesla big battery cashes in

Tesla big battery outsmarts lumbering coal units after Loy Yang trips

Of course solar and wind farms fail also - "when the sun doesn't shine and the wind doesn't blow" - but in these cases the failures are predictable from weather forecasts and AEMO can plan accordingly. And in other cases, failures occur as the result of external events such as extreme weather:

Coal and hydro generators struggle after lightning strikes twice on network

Agreed. There's no doubt however that Genex have a business case. Without it, no-one (including NAIF) would lend them money. You can, however, get a general idea of the opportunity for price arbitrage by looking at public sources for power price variation by time of day (especially the morning and evening peaks when Kidston pumped hydro will be planning to operate).

AEMO Data Dashboard

You're welcome!