Hi Inaki
It’s a very good question, I think there are a couple of different parts to it, I’ll try and break it down.
You have an ongrid solar system, 1. Does it make sense to go offgrid for environmental or financial reasons?
2. Does it make sense to have some storage capacity for environmental or financial reasons?
The first point is to say that if you want to be independent of electrity suppliers (disconnected from the grid), that is a huge difference to wanting to consume your solar power at night. I won’t go into the details here about why, but in short you’d need to have enough storage to cover you in the depths of winter with very little solar generation, so let’s say you would need 5-10x as much storage, plus a backup generator.
The second point is that the grid is a very effective storer and sharer of energy. It is a resource that is already there, and whilst you may not be using all of your solar power that you generate, your neighbours are consuming it, and you consume theirs when you need it. Batteries are not particularly environmentally sound, they are made of heavy metals that need to be dug up, shipped and manufactured into a battery, and then disposed of.
Bearing that in mind, I would rule out disconnecting from the grid as a sound move either financially or environmentally. I wish it weren’t, I totally understand where you’re coming from in terms of not wanting to be reliant on energy retailers. However, there are some decent ones out there.
However, having a small amount of battery storage to use your solar power at night is a very different prospect, and one I would entertain. Your solar array would probably produce at least 12kWh a day on average, which sounds like 50% more than you consume on average. But if you’re consuming mostly at night then you won’t be using it necessarily. So, a small battery giving you about 5kWh may give you the sort of payback you’re talking about, depending on a whole bunch of factors. Honestly, I’m not sure it would make sense environmentally still, but I’ll let others debate that one.
We’ve got a heap of info here on battery options, good place to start. Let us know if you have follow up questions.
Cheers
Marty