Wired up a 400W solar array to my garden office last month — here's what I learned

So after months of dithering I finally ran the cables out to the shed. Went with two 200W Renogy panels on a tilt mount, feeding into a Victron SmartSolar 100/20 MPPT, and a single 100Ah Fogstar Drift LiFePO4 as the battery. Total spend landed around £650 all in, which felt reasonable for what it is.

The office runs a monitor, a small desk lamp, and a router — maybe 150–200Wh a day in real use. On decent autumn days I'm seeing 800Wh–1kWh coming in, so the battery barely drops below 90% SOC. Cloudy November days are a different story though — three grey days in a row and I was watching that SOC tick down to 60%, which was fine, but made me think about whether one 100Ah cell is actually enough heading into December and January.

The thing I didn't account for properly was voltage drop over the 12 metre cable run from the panels to the controller. I used 6mm² cable which the calculators said was adequate, but I'm still seeing a small drop I can't fully explain. Anyone else hit this with longer runs?

Wondering whether to add a second Fogstar 100Ah in parallel before winter properly bites, or just accept I'll need to run a short extension lead on the very worst weeks. Curious what others are doing for garden office backup through the dark months.

Nice one @SprinterLife, solid setup. The 100/20 is a great little controller — use the same one on my boat and it's been faultless.

One thing worth keeping an eye on: a single 100Ah battery will hit its limits faster than you'd expect if you're running anything with a decent draw (kettle, monitor, heater etc). The Fogstar Drift is a quality cell but you might find yourself wanting a second one within six months.

Also worth checking your VRM dashboard on the Victron app regularly at first — gives you a really clear picture of where your power's actually going and helps size things properly if you do expand.

How are you finding the tilt mount angle? Fixed or adjustable?

Great setup @SprinterLife! One thing worth keeping an eye on with the Fogstar Drift — it's a lithium battery so make sure your Victron profile is set to LiFePO4 rather than the default AGM setting. Easy to miss if you're just clicking through the initial setup. The Victron app makes it dead simple to adjust via Bluetooth once you know where to look. Also with 400W input into a 100Ah battery you'll likely hit full charge by early afternoon on a decent day, so if you're running anything power-hungry like a monitor or kettle, morning is your friend. What are you actually running in the office? Curious whether the single 100Ah is coping or if you're already eyeing up a second battery! 😄

Really lovely setup @SprinterLife, well done for finally taking the plunge! One thing I'd add from my own experience with a similar arrangement — keep an eye on your cable runs and make sure you've got appropriate fusing close to the battery. It's one of those things that's easy to overlook when you're focused on getting the panels and controller sorted, but it makes a real difference to safety. Also worth logging your actual usage for the first few weeks before adding any high-draw appliances like a kettle or fan heater — 100Ah sounds generous until you realise how quickly those eat into your reserve on a cloudy November day! What are you mainly running out there?

Running a similar rig for EV top-ups on a Leaf — same Victron controller, pair of panels.

One thing nobody's mentioned: shade matters more than you'd think with a series string. Even a chimney shadow clipping one panel tanks output from both. Worth checking your tilt mount angle gives you a clean horizon through winter months — December sun is low and unforgiving in the UK.

Also 100Ah is going to feel tight if you're running a kettle or monitors. Fogstar do a 200Ah Drift for not much more. Might be worth planning the upgrade path now rather than rewiring later.

Good write-up @SprinterLife! One thing worth flagging that nobody's touched on yet — with two 200W panels you're potentially pushing close to the 100/20's input limits depending on your panel specs and how cold it gets. Victron's MPPT controllers can see significantly higher open-circuit voltages on a crisp winter morning than the panel label suggests. Worth plugging your figures into Victron's MPPT sizing calculator if you haven't already, just to confirm you've got adequate headroom. The 100/30 isn't much more money and gives you breathing room if you ever fancy adding a third panel down the line. Probably fine as-is but worth a five-minute check! What's your panels' Voc listed as?