Prioritising Solar Over Shore Power: Setting Up Our Victron System
An electricity bill from the marina prompted a real question: why is Paikea drawing power from shore when there’s a full lithium bank and a growing solar array sitting mostly unused on the roof?
Flipping the default relationship
As standard, the boat’s electrical system worked the opposite way around from what actually made sense — shore power came in as the primary source, with solar and battery only supplementing it when demand spiked. Given the size of the solar array and battery bank already built into this refit, that arrangement had it backwards. The goal became genuinely simple to state and considerably less simple to configure: use shore power only as a backup, and draw from solar and battery as the default.
Credit where it’s due — this discovery came from a conversation with Jason Ellis at a boat show in Amsterdam, who pointed toward a Victron feature that made the whole thing possible. Electrical work isn’t the primary area of expertise here — plenty of genuine trial and error and manual-reading went into actually implementing it, and that’s worth being upfront about rather than pretending otherwise.
The hardware: a Victron MultiPlus 3000
The inverter running all AC power on board is a Victron MultiPlus 3000, connected either through VE Configure or the newer, more user-friendly Victron Connect app — both work, but Victron Connect has become the preferred tool simply for being better laid out. Getting into it requires a VE Bus to USB interface cable connecting the inverter to a laptop, with updated firmware and the Victron Connect software installed before any of the real configuration work can begin.
Two separate settings, easily confused
There are genuinely two different Victron features involved here, and they solve two different problems — worth being precise about which does what.
Prioritise Other Energy Sources, found under the Advanced tab, controls how the boat charges its batteries. Enabled, it sets a “sustain” voltage — 26 volts on this 24-volt system — as a deliberate floor. Below that voltage, shore power kicks in just enough to bring the battery bank back up to that floor, then hands charging duties over entirely to solar (or wind, or hydro, on boats running those inputs) to take the battery the rest of the way to full. It’s not “shore power charges the battery” — it’s “shore power tops up to a safe minimum, then gets out of the way.”
A manual override exists for moments when a full charge from shore power is actually wanted — a button available through the Connect app, a GX device, or the VRM portal, which temporarily undoes the solar priority and lets shore power charge fully instead.
AC Input Control, the second and separate setting, controls something different: whether shore power is even connected to the system at all under normal conditions. Enabled, the inverter defaults into what Victron calls “Island mode” — behaving as a self-contained system that doesn’t draw on shore power unless specific conditions are actually met.
Setting the actual trigger conditions
Configuring AC Input Control on load meant defining exactly when shore power should connect and disconnect. The default threshold sat around 2.5kW, but a lower, more practical trigger got set instead: shore power connects once load exceeds roughly 1000 watts sustained for 10 seconds, and disconnects again once load drops back below approximately 637 watts. That 10-second delay matters — it stops the system flicking shore power on and off for every brief power tool trigger-pull, only engaging for genuinely sustained draw.
A voltage-based backup trigger sits alongside the load-based one, useful specifically because state-of-charge data from a separate Cyrix Marine battery monitor isn’t yet integrated with the Victron system. If battery voltage drops below 24.5 volts — signalling the battery bank itself is getting low, even if instantaneous load looks modest — shore power connects regardless of the load threshold. A second safety condition disconnects shore power entirely if the battery bank reaches a full 27 volts, deliberately letting the battery discharge slightly before shore power engages again, rather than needlessly topping up a pack that’s already full.
Watching it actually work
Testing came down to something simple: switching on a vacuum cleaner drawing roughly 900 watts, set against an 800-watt threshold. Watching the display in real time, the ten-second countdown ran, the current draw crossed the threshold, and shore power connected automatically — visible both on the Victron Connect screen and directly on the inverter’s own physical display, confirming mains power flowing in while the battery sat neutral rather than discharging to cover the tool’s draw. Switch the vacuum off, and the system disconnected shore power again just as automatically, reverting to battery inversion without any manual intervention needed either way.
Why this actually matters, beyond the electricity bill
Genuine flexibility is the real payoff here — the system adapts to actual daily conditions rather than running on a fixed rule regardless of circumstances. A bright, sunny day with strong solar input means running power tools straight off the boat’s own generation with no shore power involved at all. A cold, overcast day, or working later into the evening after the sun’s dropped, still has shore power available as a real backup rather than leaving the battery bank to run down with no support.
There’s a genuine environmental angle too, worth being honest about the local context: Spain’s grid isn’t heavily coal-dependent, which softens the argument somewhat while docked here specifically. Back home in Australia or New Zealand, plugging into shore power draws far more directly on coal-fired generation — making this same setup considerably more meaningful wherever the boat eventually returns to those grids.
For more on Paikeas’s electrical system set up see Adding a 24-Volt System to a 30-Year-Old Catamaran