Monocrystalline vs polycrystalline — which is better?

The efficiency gap's honestly become academic for most domestic setups. What matters more is your actual installation constraints and how you're using the array.

I've got mono panels on my garden office and they perform fine even when partially shaded in winter — the cell structure just handles it slightly better. But that's because I spec'd the system around my specific roof pitch and orientation. On a static caravan where you might be repositioning or dealing with variable tilt angles, the mono's slight edge in temperature coefficient becomes more tangible.

Where I'd push back on pure efficiency metrics is that modern polycrystalline panels from decent manufacturers (Renogy, Canadian Solar) are genuinely reliable workhorses. The real variable isn't mono vs poly — it's panel quality, your charge controller (MPPT makes a massive difference here), and whether your battery bank can actually absorb what you're generating.

If you're tight on space and serious about maximising output, go mono. If you've got room and want better value, poly's perfectly adequate. Just don't cheap out on the rest of the system trying to save £200 on panels. That's false economy.

On my narrowboat I've got a mix because I'm a cheapskate who bought panels second-hand over three years — honestly can't tell the difference in real-world output on a cloudy Tuesday in the Midlands, which is most Tuesdays. The real killer is shading and installation angle, not whether your panel's got one crystal or many having an identity crisis.

What @CliveBaker said about installation costs is spot on — spending an extra £300 on mono panels then botching the mounting to save tenner means you've won the battle and lost the war. My Victron monitoring gear shows my hotchpotch setup performs fine because everything else is dialled in properly.

If you're building from scratch and space is genuinely tight (like a shepherd's hut roof), mono wins. Otherwise? Polycrystalline's perfectly adequate and your budget stretches further for decent controllers and batteries, which'll make more difference to your system than obsessing over panel type.

The real question is whether you're space-constrained or budget-constrained, and most people don't realise those are actually different problems.

I've got monocrystalline on my static caravan setup — went that route because roof space is genuinely limited and I'd rather have fewer panels doing the heavy lifting. But that was a deliberate choice knowing I'd pay more upfront.

What @CliveBaker said about installation costs is the bit most people miss. If you're getting someone in to mount them, labour's the same whether it's mono or poly. If you're DIY-ing it like I did, honestly the difference becomes even smaller.

The durability angle's worth a mention too — both are solid these days, but I've seen older poly panels degrade a bit more noticeably than mono. That said, a £400 polycrystalline panel lasting 22 years instead of 25 is still a better ROI than a £600 mono panel if your space allows it.

Go with what fits your roof and your wallet. The difference in real-world output won't keep you awake at night.

Got monocrystalline on the boat and polycrystalline on the shepherd's hut, and genuinely couldn't tell you which performs better because I'm too busy pretending the battery monitor isn't screaming at me in both locations.

@OffGridGeek's got the right idea though — mix and match beats religious adherence to either camp. The real game-changer for me was sorting out shading and panel angle, which made approximately one million times more difference than worrying about the silicon lattice structure.

If you're genuinely space-constrained (like, boat-roof constrained), mono wins. Otherwise the cost-per-watt argument's getting thinner every year anyway. My Victron setup doesn't care which type it's charging from, just that the sun's doing its job.

Mix of both here on the motorhome and it's revealed the uncomfortable truth: I can't actually tell them apart in real-world conditions because clouds, angle, and my dodgy wiring are doing far more damage to output than silicon crystal structure ever will.

The efficiency gap's closing anyway — modern polys punch well above their weight compared to what we were fitting five years back. Space is usually the constraint for us mobile types, so monocrystalline makes sense per square metre, but honestly if you've got a decent MPPT controller (running a Victron here) it's handling the voltage/current variations from either type without breaking a sweat.

Buy what's in stock and doesn't cost a fortune, wire it properly, and you'll spend your time troubleshooting dodgy connections instead of regretting panel choice.

On the van, went mono purely because roof space is about as generous as a Tory budget—one panel had to earn its keep. That said, modern poly's efficiency gap is genuinely negligible now, so unless you're running a solar farm in a cupboard, either'll do the job fine.

The real variable nobody's mentioning is temperature coefficient. Both mono and poly degrade in heat, but monocrystalline typically performs slightly better in cooler conditions—relevant if you're in Scotland like me. That said, for van/boat installations where space is premium, I'd prioritise wattage density over the mono/poly distinction. A quality 400W mono panel beats a dodgy 300W anything.

Temperature coefficient's a good shout @RiverRunner. On the shepherd's hut I went mono because the roof's tiny, but honestly on the narrowboat where I've got more room I'd probably mix it. The cost difference has compressed so much these days that it's more about your specific space and shading patterns than pure efficiency metrics.

@RiverRunner's spot on about temperature coefficient—that's where the real-world difference shows up. I've got a mix on my array and the monos genuinely outperform in summer heat, which matters if you're in the south or on a south-facing roof. The efficiency gap has narrowed though; polycrystalline's come on leaps and bounds. New panels (either type) are vastly better than five-year-old ones.