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How to size a solar trailer for a NZ dairy farm

Most NZ dairy operations sizing solar power trailers fall into two camps: replace a noisy backup genset on the comms shed, or take an entire pump or calf-shed off diesel. This guide walks through the load profiles, the peak vs continuous trap, and how to pick between Tier 1 and Tier 2 for typical NZ farm duty.

Published 2026-04-26 · Read time ~7 minutes · For NZ dairy and lifestyle-block operators sizing off-grid power

What dairy farms actually run on backup or off-grid power

Real NZ dairy use cases we see most often, with typical electrical profiles:

"Peak" is what the load asks for at any single moment — your inverter must deliver that. "Continuous" is what the load averages over time — that drives daily kWh and battery sizing.

The peak-vs-continuous trap

Where most farm sizing goes wrong: looking at the kWh number alone and missing the peak draw. A 1.5 kW continuous load with a 4 kW startup spike (centrifugal pumps, compressors, welders) needs a 4 kW inverter, not a 2 kW one. Tier 1 — Solo's 3 kW pure sine-wave inverter handles most farm pumps and tools but trips on a high-startup load like a deep-bore well pump.

Always size by peak draw first, then verify daily kWh fits your tier's battery storage. Get one wrong and the system either trips on startup or runs out of charge by 4pm.

Bad-weather contingency: the 2-day rule

Every Solar Trailer Co tier ships with battery storage sized for 1.5–2 days of typical site load with zero solar input. That covers a normal NZ winter cold front. For longer outages — a week of overcast in deep July — you have three options:

• Hybrid LPG module rental. A small LPG generator that mounts on the trailer and tops the battery overnight when solar regen is below threshold. Most farm clients choose this if they're risk-averse on critical loads (vat alarm, milking).
• Pair two trailers. Common at festivals; less common at dairy. Doubles capex, also doubles peak inverter capacity.
• Accept a 2-day blackout window on non-critical loads. If your only load is irrigation, who cares — irrigate when you have charge.

For dairy with real-time critical loads (vat-alarm sensors, security comms, milking systems), choose option 1.

Tier 1 — Solo: the typical dairy fit

Most single-shed or single-pump dairy use cases fit cleanly inside Tier 1 — Solo:

• 2.5–3.0 kW folding solar — covers ~12–18 kWh/day in NZ summer, ~5–8 kWh/day in deep winter
• 5 kWh LiFePO₄ (expandable to 15 kWh) — 1.5–2 days of comms-cabinet draw with no sun
• 3 kW pure sine-wave inverter — handles most farm pumps and tool benches
• Tows on a 1-tonne ute on a normal car licence
• NZ$19,500 capex

This is what one Taranaki dairy operator chose: a Tier 1 + comms cabinet replaced their old diesel backup gen and saved ~NZ$4,200/year in diesel. It's also what one Manawatū lifestyle block uses with the EV charger module.

Tier 2 — Crew: when you need it

Tier 2 — Crew is the right call when:

• Your peak inverter draw exceeds 3 kW (deep-bore pumps, welder, large EV charger)
• Your daily kWh is consistently above 18 kWh (multi-shed, simultaneous loads)
• You need split-phase output (some 3-phase shed systems ask for it)
• You want headroom for adding modules later

Tier 2 ships 5.0 kW bifold solar, 20 kWh LiFePO₄ (expandable to 40 kWh), 5 kW split-phase inverter, 2.4 m³ insulated storage. NZ$36,500.

Modules that pair well with dairy

The five mountable modules and how they fit dairy:

• Irrigation pump module — 1.5 kW marine-grade pump, self-cleaning 200 µm filter, 100 m layflat hose. Pulls from creek, tank or bore. Runs all day on solar in summer.
• Tool & charging module — 6× Milwaukee/DeWalt/Makita fast chargers, 4× 240 V outlets, lockable tool wall, overnight battery rotation. Perfect for fence-and-tools workshops.
• Insulated chiller module — chest + chiller for catering and field crews (also handy for vaccine cold-chain on remote calf-rearing).
• PA & lighting rig — usually overkill for dairy unless you're hosting field days or open days.
• Espresso & hospitality module — same — open-day specific.

The 60-second sizing decision

1. List every load (continuous + peak) you want the trailer to cover.
2. Sum peak draws for any loads that might run simultaneously. If the total exceeds 3 kW → Tier 2.
3. Sum daily kWh across the loads, average across summer and winter. If it exceeds 18 kWh consistently → Tier 2.
4. If you have critical real-time loads (vat alarm, milking systems) → add a hybrid LPG module rental for winter contingency.
5. Run your numbers through the sizing calculator on the homepage to confirm.