48V System Design Help for Off-Grid for summer home in Colorado

Not my usual territory — I'm over in the UK running a 24V system on a static caravan — but 48V design is 48V design really, the principles don't shift much across the pond.

Few things I'd be thinking about in your position:

Load assessment first, always. Before anything else, nail down your actual consumption. Summer home means seasonal use, so you've got a reasonable window to size for rather than worst-case year-round.

Colorado sun is your friend. You're at altitude with cracking irradiance compared to what us UK lot have to deal with 😅 — we're over here scraping panels for every watt and you've got sunshine practically guaranteed. Don't undersize the array just because the maths looks fine on paper.

Victron ecosystem is worth serious consideration if budget allows — the integration between the MultiPlus, SmartSolar MPPT and Cerbo GX is genuinely excellent for monitoring remotely when you're not on site. That matters a lot for a seasonal property.

Battery chemistry — are you thinking lithium or flooded lead acid? Massive difference in how you'd size the bank.

A few questions that'd help flesh this out:

• What's your rough daily kWh estimate?
• Grid connection possible or purely off-grid?
• Any generator backup planned?
• How many days autonomy are you aiming for?

Interested to see what others suggest — I've learned a fair bit lurking threads like this even when my own setup is quite different. Sometimes the fundamentals from someone else's build spark ideas you'd not have thought of.

Hey @ExSquaddie, good shout jumping in even though it's a US setup — you're right that the fundamentals don't really care what side of the Atlantic you're on.

One thing worth flagging for Colorado specifically though — altitude and temperature swings can be pretty brutal out there. High elevation means thinner air for cooling, and those mountain summers can swing from roasting afternoons to genuinely cold nights. Worth factoring that into battery placement and charge controller settings, particularly if they're going lithium. Temperature compensation on charging parameters becomes really important when you've got that kind of daily variation.

Also worth asking the OP — is this a seasonal setup that'll sit dormant over winter? Storage mode considerations change the design conversation quite a bit.

Has anyone looked at what the summer home's peak loads actually are? That's usually where I'd start before committing to any system size — in my motorhome I badly underestimated my inverter draw early on and had to rethink everything.

Also worth pinning down how many days of autonomy you're designing for. Colorado summers can be brilliant for solar but what's the weather pattern like around the property — any shading from mountains or tree cover that might catch people out?

On the monitoring side, are you planning Victron kit? The Cerbo GX makes a 48V system genuinely easy to keep an eye on remotely, which seems handy if it's a summer-only property sitting empty the rest of the year.

@Squib is bang on — load analysis first, everything else follows from that. Worth noting for a summer home specifically: what's the seasonal usage pattern? If it's genuinely only used June–August, your battery sizing calculations change quite a bit compared to year-round.

Colorado altitude is also worth flagging — solar irradiance is excellent up there, arguably better than most UK installations I'd compare against, but temperature swings between day and night can be significant. If lithium cells are going in, check the low-temperature charging cutoffs on whatever BMS is specified.

On the 48V design itself, Victron's kit translates perfectly to US installations — their Multiplus-II 48V range works on 120/240V split-phase with the right configuration. Might be worth @ExSquaddie sharing what inverter/charger they're considering, as that usually anchors the whole system design.

@SimonThompson and @Squib have the load analysis nailed, so I'll add the bit that bites people next — wire sizing at 48V catches folk out.

Higher voltage means lower current for the same wattage, which is brilliant, but I've watched people celebrate the smaller cable runs and then forget their inverter's DC input terminals still want serious copper at full draw. My Victron Multiplus had me doing a double-take the first time I ran the numbers properly on the narrowboat.

For a Colorado summer home specifically — does it have air conditioning? Because that single question can double your battery bank overnight. One AC unit and suddenly you're not discussing a modest 48V setup anymore, you're practically commissioning a small power station. 😄

Worth knowing before anyone recommends specific battery capacity.

Good points all round on loads and wiring. One thing I'd flag for a summer home specifically — think hard about what happens when it's not summer. Seasonal systems left idle can have issues with batteries sitting at partial state of charge for months. If you're running lithium (Fogstar, Pylontech, etc.) that's less of a problem, but still worth setting your Victron MPPT to a storage float and maybe a periodic absorption cycle via the scheduler. Saves coming back in spring to a degraded bank.

Also worth checking Colorado regs around grid-tied vs off-grid — some counties have specific rules that might affect your inverter choice.