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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

Typical NZ dairy use cases, with representative 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.

Put those daily-kWh numbers next to what a trailer actually generates before you go any further. Across a New Zealand year, budget roughly 3.2 kWh per day for each kW of array — so about 4–5 kWh/day from Solo's 1.43 kW, 9 kWh/day from Crew's 2.85 kW, and 18 kWh/day from Command's 5.7 kW. Midsummer runs meaningfully above those figures and deep winter well below them. That is the number most farm sizing gets wrong.

The peak-vs-continuous trap

Where farm sizing goes wrong in both directions: looking at the kWh number alone and missing the peak draw, or buying for peak and forgetting the energy budget. A 1.5 kW continuous load with a 4 kW startup spike (centrifugal pumps, compressors, welders) needs an inverter that can deliver that spike, not just the 1.5 kW average.

Every tier ships the same 6 kW inverter, which covers the startup spike on most farm pumps and tool benches — check a deep-bore well pump's surge rating against it before you commit. What separates the tiers on a farm is energy, not peak: array size and battery capacity. Solo's inverter is fixed at 6 kW; Crew expands to 12 kW and Command to 24 kW if you genuinely need simultaneous heavy loads.

Size by peak draw first so nothing trips on startup — then check that your daily kWh fits inside what the array generates and the battery stores. Get the second one wrong and the system runs out of charge by mid-afternoon.

Bad-weather contingency: the 2-day rule

Every Solar Trailer Co tier ships with battery storage sized for roughly 1.5–2 days of typical site load with no solar input — based on an assumed typical daily consumption for the site; actual runtime varies with load. 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

Low-energy, single-shed dairy use cases — a comms cabinet, a vat alarm, security, a modest tool bench — fit cleanly inside Tier 1 — Solo:

• Mount — 2.4 m trailer, or skids (static, non-towable, lower cost)
• Solar — 1.43 kW included (3 × 475 W panels), expandable to 2.85 kW with up to three floor-mounted panels. Budget ~4–5 kWh/day as an annual NZ average: roughly 6–7 kWh on a good midsummer day, 2–3 kWh in deep winter
• Battery — 5 kWh LiFePO₄ included, expandable to 10 kWh (max 2 units) — roughly 1.5–2 days of comms-cabinet draw with no sun (actual runtime varies with load)
• Inverter — 6 kW, not expandable on this model
• Switchboard — 16 A
• Cargo bay — not available on Solo
• Build time — 30 days
• On the trailer mount, tows behind a light ute on a standard Class 1 (car) licence
• From NZ$19,123 ex-GST on a trailer, or NZ$15,223 ex-GST on skids

Be realistic about what that array carries. A Solo comfortably runs a ~3 kWh/day comms cabinet year-round; it will not carry a calf shed, an irrigation pump and a tool bench at the same time. As an illustrative example, a Solo covering a comms cabinet in place of an old diesel backup gen could displace on the order of 700–800 L of diesel a year — roughly NZ$1,600–1,800 at ~NZ$2.25/L, assuming the genset previously ran about 130 days a year. Illustrative only, and dependent on runtime, load and fuel price.

Tier 2 — Crew: when you need it

Tier 2 — Crew is the right call when:

• Your daily energy use sits consistently above what Solo's array and battery carry — call it more than ~5 kWh/day averaged across the year
• You need a 32 A outlet as well as 16 A
• You need inverter headroom past 6 kW for simultaneous heavy loads — Crew takes a second inverter to 12 kW, Solo doesn't expand
• You want room to grow: the array to 5.7 kW and the battery to 20 kWh
• You want the optional enclosed 2 m × 2 m cargo bay for tools and spares

Tier 2 — Crew ships on a 3.4 m trailer (or skids), with 2.85 kW of solar (6 × 475 W panels, expandable to 5.7 kW), 10 kWh of LiFePO₄ (expandable to 20 kWh), a 6 kW inverter (expandable to 12 kW), a 16 A / 32 A switchboard and an optional enclosed 2 m × 2 m cargo bay. Build time 40 days. From NZ$30,186 ex-GST on a trailer, or NZ$23,686 ex-GST on skids.

Budget roughly 9 kWh/day from the base array as an annual average — around 12 kWh midsummer, 4 kWh in deep winter. If your combined dairy load runs past that year-round, expand Crew's array and battery or step up to Tier 3 — Command (5.7 kW solar, 20 kWh battery, ~18 kWh/day annual average, from NZ$53,742 ex-GST on a trailer).

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. Think in pumping windows rather than continuous duty: on a Solo in good summer conditions that's roughly 3–4 hours a day, on a Crew closer to 7–8. Runtime depends on load, sunlight and battery size.
• 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 6 kW → you need Crew or Command, where the inverter expands.
3. Sum daily kWh across the loads and average it across summer and winter. Under ~5 kWh/day → Solo. Up to ~9 kWh/day → Crew. Up to ~18 kWh/day → Command. Above that, expand the array and battery or run a second unit.
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.