These are really quite outrageously cheap quotes - I’m assuming they are after the Vic rebate as well as STCs. The rebates hide the value of these systems.
Let me try and put down my thoughts as to why you should step back a bit from the upfront cost, and look at a longer term perspective. After all, these systems should last 20+ years on your roof, and the better quality obviously more likely they will last longer.
If you generate 25kWh per day from these systems (as you roughly should), that’s ~ 9000 kWh a year. I need to make big generalisations here because obviously I don’t know your specific details (I’ll be conservative), lets say you use half of your solar yourself (self consumption) and that offsets you buying energy at 30c/kWh, then the other half you export for 10c/kWh, so you have a blended solar rate of 20c/kWh. That means your solar we generate (9000 x $0.20) $1800 per year.
By that reckoning, you would pay back a $1600 system in less than one year, and a $5000 system in less than 3 years (that’s what I mean about these quotes being outrageously cheap). So the payback period is clearly lightening fast on the cheapest system, but it’s also very fast on a more expensive system. Pay back period is one thing, but what about lifetime value?
Lets say the premium system performs 5% better. Now it’s generating 450 kWh a year more. That’s $900 more (at 20c per kWh) over 10 years, which isn’t heaps. But what if there’s also a 10% less chance of something going wrong? If something does go wrong, and the system has down time, that’s your time wasted in calling people to get it fixed (honestly some of the stories about convincing solar companies to come out and fix their system, sound very painful), it’s also lost money from your solar not working. It would be $35 for every week this hypothetical system is down. Then, probably the most likely scenario, what if the premium system lasts an extra 5 years. Assuming you’ll need to buy a new unsubsidised system 5 years earlier, that means you’ll be spending $8k - $10k (lets say $5k if prices keep falling), whilst the premium system keeps on generating $1.8k per year.
I’m hesitant to give any specific advice here because I know little of the details of these quotes (most importantly, the reviews of the solar companies), but I would just say to thoroughly research these companies, and scrutinise the quotes before pulling the trigger. It’s easy to decide to go the cheaper option now, but I bought a shitty vacuum cleaner 12 months ago, and man I wish I just sucked it up (pun intended) at the time and bought a Dyson. Now every time I need to clean the floor I get a little sad. Life’s too short!