Has anyone actually mapped their daily load profile before sizing their system?

I've been going through my setup recently and started wondering if I've been doing this all wrong from the start. Most of the advice I see is "add up your watt-hours and multiply by 1.25" or whatever, but that ignores when things are running. My fridge compressor kicks in every 20 minutes or so, my 12V pump is a brief spike when I use the tap, and my lighting is almost entirely in the evenings when the panels are obviously doing nothing.

I spent a weekend logging everything with a Renogy battery monitor and a clamp meter on individual circuits. Turns out my actual peak demand clusters between 6–9pm, which is exactly when my 200Ah LiFePO4 needs to be doing all the heavy lifting. Morning solar is great but it's mostly going into the battery rather than serving live loads. Made me rethink whether I actually need more panel capacity or just more storage.

Has anyone else gone through this kind of exercise properly? I'm curious whether a dedicated energy logger like a Victron Cerbo or even just a Raspberry Pi with some current sensors would be worth setting up permanently, or if my one-off weekend audit is good enough for practical purposes. Would love to know what tools others have used and whether it actually changed how you sized or configured anything.

@Brian1975 mapped mine on a Post-it note in a Tesco car park, turns out "kettle, laptop, occasionally the angle grinder" is not a load profile — it's a cry for help from my Victron BMV-712.

@ExFarmer21 ha, the Tesco car park method is genuinely underrated 😄

I actually did a proper load profile last spring before upgrading my leisure battery bank. Spent a week logging everything in a spreadsheet - not just what I was running but when. Made a massive difference. Discovered my morning routine (kettle twice, laptop charging, phone, water pump) was hammering the system for about 90 minutes right after a cloudy night when the batteries were already low.

The timing matters as much as the total watt-hours. Two systems with identical daily consumption can need completely different solutions depending on whether loads are spread out or clustered. @Brian1975 the "multiply by 1.25" rule is fine as a starting point but it completely ignores peak demand periods and seasonal solar variation. What monitoring kit are you currently running?

@Brian1975 yes, and it genuinely changed how I sized my Victron MPPT and battery bank for the cabin.

The key insight wasn't total watt-hours — it was peak demand clustering. I logged every load against a 24-hour timeline and found I had three distinct "spike windows" where simultaneous loads were pulling hard. The simple watt-hour multiplication method completely missed that, and I'd have been constantly hitting inverter current limits.

What I actually used was a basic spreadsheet with 30-minute time blocks. Column for each appliance, actual measured draw (not nameplate), probability of simultaneous use. From that you can extract both your daily Ah requirement and your realistic peak VA figure — which then drives your inverter sizing more accurately than any rule of thumb.

The Fogstar cells I eventually specced were a direct result of understanding that profile properly rather than just padding a rough estimate.

Spent three days logging everything in the shepherd's hut before I bought a single panel. Kettle at 07:30, laptop running 09:00–13:00, evening lights — turns out my evening spike was the killer, not the daytime draw.

That peak demand window completely changed which Victron MultiPlus I went for. If I'd just done the watt-hour sum @Brian1975 describes, I'd have undersized the inverter by a comfortable margin and wondered why it kept tripping.

The other thing nobody mentions: seasonal shift. My summer profile and December profile look nothing alike. I now keep a simple spreadsheet — nothing fancy — with two columns: average day and worst-case day. Sized the Fogstar Drift battery bank against the worst-case. Haven't been caught out yet.

The maths is easy. It's the honest logging that takes discipline.

Great thread @Brian1975. I did exactly this before expanding my system last year - spent a fortnight with a Shelly plug on every socket logging to a spreadsheet. What surprised me wasn't the big obvious loads, it was the cumulative drain from things I'd forgotten about entirely. My 12v compressor fridge was cycling every 22 minutes overnight when temps dropped, which I'd never have guessed from the spec sheet alone.

The other thing worth mentioning is that a single day's logging isn't enough - seasonal behaviour matters massively. My winter profile looked almost nothing like summer, mostly because of lighting hours and how often I was actually running the woodburner fan.

If anyone wants a starting point, a Shelly EM or similar clamp meter on the main feed gives you the whole picture without plugging and unplugging individual monitors everywhere.