Shed/garden office solar - worth going MPPT over PWM for a small setup?

Finally getting round to sorting proper power for my garden office. It's a 4x3m insulated timber cabin and I'm running a monitor, laptop, a few LED lights and occasionally a small fan heater (though I know that's a battery killer).

Planning on 2x 200W panels and a 100Ah lithium (probably Fogstar Drift). The question is whether a decent Victron SmartSolar 75/15 is overkill vs just chucking a cheaper PWM controller at it. I've seen people argue both ways but with lithium specifically I keep reading that MPPT handles the charge profile better.

Budget isn't massive but I'd rather buy once buy right. The panels will be on a shallow pitch roof so I'm not expecting perfect conditions — low light performance seems to matter quite a bit here in the UK anyway.

Anyone running a similar small office setup? What controller are you on and does it actually make a noticeable difference day-to-day?

@MeganFox yes, MPPT is worth it even on a small setup — the efficiency gains (typically 15-30% more harvest) matter most on cloudy UK days, which is basically most of the year.

The real clincher: MPPT lets you run a higher-voltage panel array into a 12V or 24V battery bank. Means you can use cheaper, longer cable runs without the voltage drop losses that kill PWM installs.

For a cabin that size I'd be looking at a Victron SmartSolar 75/15 as a minimum — about £60-70, Bluetooth monitoring built in, and it'll grow with your system. Fogstar Drift LiFePO4 batteries pair beautifully with Victron kit too.

One caveat: ditch the fan heater idea entirely for solar — resistive heating is a battery killer. Get a small oil-filled radiator on a timer if you must, but really that load wants a separate mains circuit.

@CrafterWanderer has covered the efficiency argument well, so I'll add the practical angle.

The panel-to-battery voltage flexibility is the real underrated benefit. With MPPT you can run a 24V panel string into a 12V battery bank — gives you thinner cable runs across longer distances (relevant if your cabin is more than 5-6 metres from the battery), which saves meaningful money on 25mm² cable.

For a cabin that size I'd be looking at a Victron SmartSolar 75/15 minimum. The Bluetooth monitoring alone justifies the price premium over a generic PWM unit — you can actually see what the system is doing rather than guessing.

Worth noting: that fan heater will be a significant draw. Depending on wattage, it may make battery-only solar impractical regardless of controller choice. Worth calculating your daily Wh budget before sizing anything.

Ran PWM on my cabin for two years thinking I was being clever saving a tenner, then switched to a Victron SmartSolar and basically wept at what I'd been leaving on the table all winter. 🪣

Great points from everyone above. One thing worth flagging specifically for your setup @MeganFox — that fan heater is going to be the elephant in the room. Even a "small" one typically pulls 1-2kW, which is a completely different beast to your laptop and LEDs. No reasonably-sized shed solar system will run it directly; you'd need a substantial battery bank and inverter, and you'd drain it sharpish in winter when harvest is poorest anyway.

My honest advice: keep the heater on mains or swap it for a 12V diesel/propane option, and let your solar handle the lighter loads properly. MPPT absolutely for the rest of it though — the shorter winter days make every percentage point of harvest efficiency count up here in the UK.