Running a well pump on solar

Been looking into this for my static caravan setup and wondering if anyone's got practical experience with well pumps on solar.

Currently running a basic system — 4kWp of panels, Victron MPPT controller, and a 10kWh battery bank. It's adequate for most things, but I'm thinking about installing a small well for water independence rather than relying on the tank deliveries.

The issue is, most submersible pumps I'm looking at draw 1-2kW when they kick in, which is a decent spike. I've read that some folks use them during peak sun hours only, but that seems impractical if you need water throughout the day. Others mention hybrid setups with a small petrol backup, but that defeats the object somewhat.

Few specific questions:

1. Are there low-power submersible pumps out there? I've seen some 12V/24V variants but they seem to have rubbish flow rates.
2. Does a larger battery bank make this viable, or is it more about matching peak demand? I'm wondering if adding another 5kWh would actually help.
3. Anyone running a pressure tank system? Reckon that's the answer — pump during the day, store it, use gravity pressure when needed?

I'm keen to avoid oversizing the whole system just for the pump, so any real-world setups would be helpful. What wattage are people actually getting away with?

Right, I've been through this with my cabin setup. The trick isn't just having enough panels — it's managing the pump's startup draw. Well pumps can pull 3-4x their rated current when they kick in, which'll trip your system if you're not careful.

I went with a Victron Smartsolar 150/100 paired to a decent battery bank (LiFePO4, about 10kWh usable). That buffer absorbs the inrush spike. Without it, you're fighting voltage sag constantly.

Your 4kWp is decent, but what's your battery capacity? That's really what determines whether this works smoothly. Also consider whether you actually need the pump running year-round — I sized mine to charge the batteries during peak sun hours, then the pump draws from storage as needed.

Have you looked at submersible pumps specifically? Much more solar-friendly than centrifugal setups.

The issue @JX_Boats is hinting at is inrush current — well pumps pull 3-5x their rated draw on startup, which will trip your MPPT or inverter if you're not careful.

4kWp is decent, but you need to consider:

Battery capacity — Submersible pumps run best with a substantial buffer. I've got a 10kWh lithium setup feeding mine and it handles the startup surge without voltage sag. Lead-acid would struggle badly here.

Pump selection — Avoid cheap AC pumps. Look at Lorentz or Shurflo's solar-specific models. They're sized for lower power draw and ramp up more gradually. I switched from a standard 2hp to a Lorentz 4C and the difference was night and day.

Timing — Run pumping during peak solar hours (10am-3pm). Use a timer relay rather than manual switching. Stops you draining batteries unnecessarily.

What's your battery capacity and pump specs? That'll determine whether you need an oversized inverter or a soft-start controller

You're on the right track with 4kWp, but here's what I've learned the hard way with my motorhome setup — it's all about the battery bank and inverter sizing, not just panels.

That inrush current @Titch mentioned is the killer. A typical submersible well pump pulling 3kW rated will spike to 9-15kW for a couple of seconds on startup. Your Victron MPPT won't help you there — you need an inverter that can handle that surge, and a battery bank big enough to supply it without the voltage collapsing.

I'd suggest:

• Size your inverter to at least 2x the pump's rated power (so 6kW minimum for a 3kW pump)
• Consider a soft starter or Variable Frequency Drive (VFD) — sounds fancy but they cut inrush dramatically
• Run the pump during peak solar hours only (hence the caravan setup works well for this)

The 4kWp should happily recharge after pumping, which is the real advantage of solar here. Just don't expect it to run the

@JX_Boats and @Titch have nailed the critical bits — inrush current is absolutely the bottleneck here, not average consumption.

I've got a 3.5kW submersible on my shepherd's hut setup and learned this the expensive way. Your 4kWp sounds decent on paper, but what matters is instantaneous available power when that pump kicks in. If you're relying solely on battery discharge through an inverter, you'll need a seriously beefy battery bank and low-impedance cabling to handle the surge without voltage sag.

My solution was pairing a small dedicated 48V battery (just 10kWh LiFePO4) with a Victron Multiplus for the pump circuit, isolated from my main solar system. Costs more upfront, but eliminates nuisance trips. Alternatively, some folk use soft starters or variable frequency drives — bit pricey but genuinely effective if you're running larger capacity pumps.

What's your battery capacity and chemistry? That'll determine whether you can get away with just optimising your MPPT settings or if you need

The inrush issue is real, but there's a practical workaround most people miss — soft starters. I've got a Shurflo pump on my narrowboat and adding a soft start module (around £80-120) completely transformed it. Basically ramps up the motor gradually instead of hammering it all at once.

Your 4kWp should handle the average load fine, but you'll need to size your battery bank for those startup spikes. I'm running 10kWh of lithium, which gives me enough headroom. With lead-acid you'd want considerably more capacity as a buffer.

The other thing — check your pump's actual specs. Some are already designed for solar use (lower inrush by default). If you're buying new, look for brushless DC pumps rather than standard AC submersibles. Renogy and Lorentz do decent solar-rated options if budget stretches that far.

What battery setup are you working with? That's genuinely the limiting factor more than the panels in your case.

Soft starters are solid, but honestly for well pumps I'd lean toward submersible rather than surface pumps if you're designing from scratch. Mine's a Grundfos 4" submersible on a dedicated circuit with its own battery bank—keeps the inrush spike isolated from the rest of the system.

The real consideration most people overlook is duty cycle. A well pump doesn't run continuously like a fridge; you're looking at maybe 2-3 hours daily depending on usage. That changes your battery sizing dramatically compared to what the average solar calculator spits out.

With your 4kWp you've got decent headroom, but what's your battery capacity at? That's where the bottleneck usually sits. My setup runs a 48V LiFePO₄ bank specifically because the discharge rate needed for pump startup is brutal on lead-acid.

Also worth checking—static caravan on mains water backup, or are you proper off-grid? Makes a difference to how aggressive your pump needs to be. Some folk use a modest pressure tank (20-30L) to smooth out the cycling and reduce start cycles, which is a

Mate, inrush current will absolutely murder your battery voltage — learned that the hard way with a surface pump that kept nuking my Victron's low voltage cutoff at dawn.

Went submersible in the end and never looked back. Couple of quid more upfront but they're forgiving on dodgy power delivery. Worth noting though: you'll want a proper pressure tank in the mix, not just relying on demand-start cycles. Keeps your pump from thrashing itself to bits every time someone turns a tap.

4kWp should handle a decent submersible if you're realistic about duty cycle — don't expect hot showers and livestock watering simultaneously. Think of your well pump like a guest who only visits when they're invited, not one living in your spare room.

If you're wedded to surface pumps, soft starters work but honestly they're just delaying the inevitable battery drama. Better to size your battery bank properly or accept you'll be running generator backup during cloudy spells.

Static caravan or cabin setup?

The inrush current issue is exactly why I switched my cabin setup to a dedicated solar pump instead of trying to run a standard well pump. Worth considering if you're starting fresh.

If you're committed to a conventional pump though, @SmartSolar_Master's soft starter angle is worth exploring — cuts the inrush significantly. That said, I found the real game-changer was sizing my battery bank to handle the spike rather than fighting it. With your 4kWp, you've got decent generation capacity, but you need the battery headroom.

What's your battery setup like at the moment? If you're running smaller capacity, even a soft starter might just be papering over the cracks. A submersible pump also helps — less cavitation drama when you're drawing from depth, and they're generally more forgiving on electrical spikes.

The other option nobody mentions: variable frequency drives. More expensive upfront, but they ramp the motor smoothly. Seen them work brilliantly on Victron setups like yours, though you'd need proper three-phase kit to really benefit.

What depth's your well, and how much water are you looking to

You've got a decent foundation with that 4kWp setup. The inrush current thing @RiverFinn and @WattAndrea flagged is real — I watched my battery voltage dip hard the first time I fired up a surface pump.

What worked for me was adding a variable frequency drive (VFD) rather than swapping the whole pump. Costs less than a new submersible and smooths out the startup draw massively. Victron plays nicely with most of them.

That said, if you're running this regularly, a proper solar pump (centrifugal, low-head design) might just be simpler long-term. No battery drama, runs direct off panels during daylight. I've got a Shurflo on my cabin setup and it's bulletproof for intermittent use.

Static caravan's got space constraints though — what's your battery bank looking like? If it's undersized, the pump upgrade might be worth it just for reliability.

Submersible's your friend here — inrush is less punchy than surface pumps. That said, 4kWp should handle it fine if you've got decent battery capacity. What's your battery bank looking like? Also consider a soft starter or VFD if you're set on a standard pump — Victron's gear plays nicely with either.