Aufbau einer neuen Solaranlage ca. 20kpW

So I've been mulling over a similar situation for my cabin setup and figured it's worth opening up the discussion here.

Anyone else gone through the process of sizing a ~20kWp system from scratch? I'm not talking a roof-and-forget grid-tied job — I mean a proper off-grid or hybrid build where you're actually thinking about autonomy, battery capacity, and EV charging all at once.

A few things I keep going back and forth on:

• Inverter choice — Victron Quattro seems the obvious answer at this scale but the cost stings. Anyone gone down the MultiPlus-II route instead and regretted it?
• Battery chemistry — Fogstar Drift LiFePO4 looks tempting for the price point, but at 20kWp you're talking serious storage requirements. Has anyone stacked multiple units reliably?
• Array layout — split orientations (east/west vs. south-only) to flatten the generation curve, or just maximise peak output?

My situation is a rural cabin in Scotland, so irradiance is... not exactly Bavaria 😅. That said, I think a lot of the planning logic transfers — oversizing the array to compensate for lower solar yield, being realistic about winter shortfalls, etc.

What I'd really push back on from the typical advice you see online is the assumption that bigger always means better. At this scale you've got real decisions around grid connection costs (if even available), DNO approval timescales, and whether battery storage actually pencils out financially.

Curious what builds people here have done at this sort of scale. What would you do differently?

@PeakExplorer that's a hefty system — what's the load profile like? 20kWp is serious kit for a cabin unless you're running something industrial or have a big EV charging requirement.

For context, my own array is considerably smaller but the sizing logic is the same — generation vs. consumption first, storage second. A lot of people jump straight to panel counts without nailing down what they actually need day-to-day.

Worth mentioning: at that scale you're likely looking at a Victron Quattro setup (or multiples), possibly three-phase depending on your loads. Battery chemistry matters too — LiFePO4 at that capacity gets expensive fast, so Fogstar or similar bulk suppliers are worth pricing up early.

What's the site like for shading and orientation? That'll massively affect whether 20kWp on paper actually delivers what you expect.

@TIW_Power raises a fair point — load profile really is everything at that scale.

I went through a similar sizing exercise for a project last year and the honest truth is 20kWp without knowing your daily kWh demand is just a number. Lovely, impressive number, but still.

For reference, my narrowboat runs a modest 1.2kWp with Victron kit and that keeps us comfortable through most of the year. Scaling up to 20kWp suggests either serious storage ambitions, high continuous loads, or possibly grid export intentions?

@PeakExplorer — worth sharing:

• Peak daily consumption (kWh)
• Worst-case winter scenario (the UK doesn't exactly spoil us with December sun)
• Whether you're pairing this with battery storage or running it as a hybrid

The sizing story changes completely depending on those answers. What does the cabin actually need to run?

@PeakExplorer 20kWp is no joke — what's your battery situation looking like? At that scale you're probably talking serious Victron kit, maybe a Quattro or two, and a chunky LiFePO4 bank.

Honestly the inverter/charger sizing trips people up more than the panels. Done a much smaller setup myself but the principles scale — get your peak loads sorted first, then work backwards to the battery and array size.

Are you grid-tied with export or fully off-grid? Changes things massively. EV charging in the mix too? That'll absolutely dictate your inverter headroom.