I think to assume BESS has low general maintenance is not fair here. Although it has no moving parts, you need a good number of electrical engineers to monitor the system as well as conduct preventive maintenance checks. Given the size of the battery required if it is going to be store the electricity to phase out coal and gas, it's not a small crew. Hornsdale was built to supply 30,000 homes for 8 hours. SA has some 750,000 homes so the battery was only going to last 20mins. Even with it's current 50% expansion, it is going to last 30mins. You need to cover 12-14 hours at night so that means you need a battery at least 24-28 times it's current size just to cover 1 night. That is an incredibly huge battery and you need a good sized crew to man it.
What if it you want to build redundancy to be able to store 2 night's of electricity? That's 48-56 times it's current size and at what cost? $6.4B - $7.6B? You can buy 20 gas plants at that price tag (or build 4 gas plants and offer the good folks of SA free electricity for 50 years, if nothing it will draw aluminum smelters and heavy industries to SA and revitalize it's economy) and yet a battery that size only covers 2 nights, not to mention it is a battery, not a generator. So no, I don't think the BESS has low general maintenance if it were to scale up to replace a coal or gas plant for baseload purposes.
I am not saying the BESS is useless. It is good if it is to be used for FCAS purposes but it's not going to be economical to replace a coal plant or gas plant as a baseload. Just the cost of offsetting battery degradation eats into the profitability and it's a constant, perennial event (AEMO assumes a 70-80% charge retention for batteries after 10 years and TESLA themselves only provides a guarantee of 70-80% charge retention for 250,000km, so me using a 93% charge retention over 10 year is being optimistic). But ask yourself honestly, will your Li-ion powered iphone still retain 93% of it's charge after you have used it for 10 years?
A gas plant or coal plant once built remains where it is for 30-50 years. You shut it down the turbines one at a time for maintenance 3-5 days a year. Output is minimally lowered and there is zero risk of not being able to supply the grid because it has been cloudy for 2 days in a row or there is a heat wave at night and the winds are still.
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