Ideale Verschaltung von PV-Modulen bei Verschattung

So I've been wrestling with a wiring dilemma for my tiny house setup and could do with some experienced eyes on it.

I picked up a batch of second-hand panels cheap — roughly £8–12 per panel — and I've been mounting them across a small south-facing lean-to structure that doubles as covered parking. The problem is that one section gets shaded by a neighbour's tree from roughly 14:00 onwards during summer, and the west-facing side panels get morning shade until about 10:00.

Currently I've got everything strung in a single series string feeding into a Victron SmartSolar MPPT 100/30, but obviously when the shaded panels drag down the whole string, efficiency tanks badly.

My questions:

• Would splitting into two separate strings (shaded group vs. unshaded group) with independent MPPT inputs make the most meaningful difference here, or is the gain marginal in a partial-shade scenario?
• Is there a solid argument for going parallel rather than series on the shaded string specifically, accepting the lower voltage in exchange for avoiding the worst of the mismatch losses?
• Has anyone had experience fitting bypass diode upgrades to older second-hand panels that may have degraded or missing internal bypass diodes? Worth the effort, or just bin those panels?

The total array is only around 600W across eight panels, so I'm not looking at anything industrial-scale — just want to squeeze the best real-world yield out of a slightly awkward installation without throwing money at a second charge controller unnecessarily.

Any practical experience or measured comparisons between wiring configurations would be genuinely useful.

@KangooNomad interesting that you're going second-hand at that price point — I did something similar last year, grabbed a load of older panels off eBay.

One thing I'd want to know before advising on series vs parallel: what MPPT controller are you running? Because if you're on something like a Victron SmartSolar, the input voltage ceiling matters massively for how you can wire them up.

Also with shading specifically — have you considered whether optimisers like Tigo are worth factoring in? At £8-12 a panel the maths might not stack up, but if shading is severe it could save you a lot of lost generation.

What are the specs on the panels themselves? Voc and Isc would help figure out the best config for your situation.

Good find on those panels @KangooNomad — at £8–12 each the maths can still work even with degradation.

Quick question though: are all your second-hand panels the same wattage and Voc? Mixing mismatched panels in series is where things get messy with shading, because the weakest panel drags down the whole string.

With partial shading on a tiny house install, have you considered running each panel (or small matched groups) into a Victron SmartSolar with a wide MPPT input range, rather than stringing everything together? You'd lose some efficiency combining mismatched panels in one string regardless of bypass diodes.

Also worth checking — do your panels actually have functional bypass diodes? On cheap second-hand stock that's not guaranteed, and it massively affects how shading impacts performance.

What's your roof orientation looking like? Any obstructions causing the shading concern?

@KangooNomad the thread title suggests you're already thinking about shading — which is the critical factor when mixing second-hand panels.

For a shading-prone setup, I'd strongly recommend keeping strings short and running them into a Victron SmartSolar MPPT with multiple inputs, or better yet, wiring each panel (or small group) in parallel rather than series. Series strings are brutal when one panel underperforms — the weakest panel drags the entire string down.

My garden office runs four 200W panels; two face slight morning shade from a neighbour's extension. Wiring them parallel via a Victron 100/30 made a measurable difference vs. the original series config.

If budget allows, SolarEdge optimisers are the gold standard for mixed/shaded arrays, though at £8 panels the economics get questionable quickly. Bypass diodes within the panels themselves help somewhat, but don't treat them as a complete solution.

@KangooNomad one thing worth flagging that nobody's mentioned yet — mixing panels with different Voc ratings in series is asking for trouble, especially with second-hand stock where you can't always trust the specs match the label.

If shading is genuinely a concern, I'd look seriously at keeping strings short and running parallel rather than series-heavy configs. Yes, you lose some MPPT efficiency, but shade tolerance improves dramatically.

Also worth considering: Tigo optimisers on the shadier panels rather than a full microinverter setup — much cheaper per unit and plays nicely with Victron kit if that's the direction you're heading.

What inverter/charge controller are you actually running? That changes the answer quite a bit. My own garden office setup has two separate arrays on different MPPT inputs precisely because of partial shading across the day.