I need to have a system which can supply circa 15-16MWh/year, manage multiple consecutive 100kWh days, be able to cope with up to 20kW instant power draw across three phases, and deal with extended periods of poor weather where solar PV output is sub-optimal. I have 3 buildings to supply.
Good luck getting much change out of A$40-50k to build a reliable maintenance free system in rural NSW which will stand the test of time.
I'm not averse to doing my own thing. But it has to be compliant with the law and that's pretty tricky in Australia with our standards. Anything I do has to not cause an insurance default for instance.
I built my off-grid backup system with 2.2kW of 2nd hand panels, pre-loved rails, a 4kW AIO inverter and 18kWh of used data centre SLA backup batteries, plus a 3kW generator for redundancy in case solar conditions are poor during an extended outage.
Building my own inverter is beyond my scope though. It's enough to power our essential needs during extended grid outages but is not designed for dealing with the high energy demand of full power supply for our property. I was creative with sourcing stuff and it cost about $3k. Forklift batteries are out of the question. Being disabled (amputee) any DIY stuff I do needs to factor in my capacity to transport, move and house stuff by myself.
The Pareto Principle applies with off-grid:
You can often cover ~80% of the power/energy demand with about 20% of the budget.
The next 20% of power/energy demand requires the other 80% of the budget.
As for worse for the environment, what I'm saying is if you are installing a given amount of PV generation capacity in eastern Australian, then in an off-grid scenario a large chunk of that capacity will go unrealised (batteries full, limited loads and so production will be curtailed), whereas if it were grid tied that excess capacity would be exported and able to offset carbon intensive sources of power on the national grid. It's a better environmental use of that PV generation capacity.
Off grid often requires a different type of property set up, alternative energy sources, different building arrangements and construction, changes to appliances, staggering consumption (tricky when you have more than one dwelling to supply), all designed to reduce both peak power and overall energy demand. Converting existing dwellings to suit an off-grid arrangement is not always simple or cheap. Much budget also needs to be devoted to such strategies.