Stick to your original plan. Use 12V.
We're going to make two "huge leaps": first, into the AC mains wiring parts bin, and second, into aluminum wire because there is nothing wrong with aluminum in heavy feeder.
I don't agree with the other advice. They are making compromises because they are worried about voltage drop with such a low voltage over that distance if you choose wires conventionally. They think voltage conversion is worthwhile because it'll be cheaper than copper. I'd agree, so we use aluminum instead.
Use enormous wire that is aluminum. It's cheap!
Around here, 10AWG copper wire (30A) is about the same price as 2 AWG aluminum wire (90A for feeder, 100A for service). And since it's used for very common 100A service wiring, it's a commodity and occupies a price "sweet spot".
So do the same thing in your country. Go hit up the home store/house building DIY supplier or electrical supply (i.e. the guy with crates of consumer units and conduit sticks, not the guy with transistors). Ask them what the common/cheap commodity wire is used for 100A house service entrance wiring (i.e. from where the overhead line comes in, to consumer unit/service panel).
Here in the USA that fat aluminum wire is under $1 per metre per conductor. That's not so bad, what were we ever afraid of? :) You need 2 or 3 Depending on what your local authority says about safety earthing in low voltage DC circuits.
Attaching to fat aluminum
Now certainly, aluminum is a little tricky to attach to at high currents. The issue is the differing thermal expansion rate as compared to copper. However, and this has been tested exhaustively by a great national experiment in the US, aluminum safety is a settled matter. Turns out aluminum lugs are the universal donor, playing well with both Al and Cu wires. Copper lugs are the bigot, and the real root of the problem. Et voilà, equipment often used with aluminum wire has zinc plated aluminum lugs. Easily solved, once you know the score. Still, everything should be equipment listed or certified for aluminum wire.
And these are plentiful and cheap in the AC mains wiring parts bin. What we in North America call "Polaris" connectors (aluminum-shell lug connector) are the normal choice for "merely a splice". But remember, you have two other stones to kill: first you need a circuit breaker somewhere in here, and second you need proper enclosures to make these splices. So you can kill several birds with one stone by selecting certain combo products.
For instance, in the US, my go-to is "micro subpanels" made for a 2-pole circuit breaker. Because they provide fat lugs for aluminum wire, and an approved enclosure, and space for a circuit breaker! And they're cheap. And since this is DC, in the North American market I will select Schneider/Square D “QO" models, as their circuit breakers are specifically cross-listed for DC power. And easily found at the local home store. Even if you don't need the breaker, it's worth it for the approved enclosure and lugs. In North America every breaker is rated for aluminum.
Outside North America, you're into DIN rail service panels, and you can use any commodity DIN rail breaker which is DC rated. The lugs on any larger breaker ought to be aluminum rated.
Safety and reliability of AC mains rated equipment
Is beyond reproach, obviously. If you select equipment approved in your local area for AC mains work, and install it according to instructions including screw torques, you can rest assured that the work is solid. You won't have heating and mystery voltage drops across those connections. It won't burn your house down in the middle of the night.
The breakers will work (if they are DC rated), so either select Square D QO, or in the DIN rail world, just any approved DIN rail breaker rated for DC. Beware the ones that care about polarity and are destroyed by reverse polarity, no reason for that to be an issue.
If you were pulling permits for this work and being inspected, everything I advise above would pass inspection. The main issue I can see is that the equipment will need labeling to say it is part of a DC system not connected to the AC mains.