Journal · 2026.09 · 12 min

How Much Power Does a Greenhouse Need? Reading Contract Capacity, Supply Type and Wiring Cost from the Equipment List

The previous article asked whether power can be connected; this one asks how much. Greenhouse demand cannot be estimated from floor area alone. It depends on the crop, the equipment installed, and which items run at the same time. Only once those conditions are written down can contract capacity, supply type, connection budget and outage backup be judged, so that equipment is not bought before anyone has checked whether the site can power it.

Two greenhouses of roughly 0.1 hectare can have very different demand: one with only roll-up motors and circulation fans, the other adding pad-and-fan cooling, pressurised irrigation, high-pressure fogging, supplemental lighting or cold storage.

Area is a starting point for estimating how many units you need, but it does not convert directly into the capacity you apply for. For a farm operator, power planning starts with three questions: which equipment runs together, how many hours a day, and which items must not stop during an outage?

The kW on an equipment label is power; the kWh (“units”) on the electricity bill is accumulated energy. They are related, but not interchangeable.

For example, suppose a group of equipment has an actual combined input power of 10 kW, running at full load 8 hours a day for 30 days a month: 10 kW × 8 h × 30 days = 2,400 kWh.

That is an energy estimate for this group of equipment. It is not the farm’s electricity bill, and it does not mean the contract capacity should be 10 kW. Other equipment running at the same time, and the hours of use, still have to be added.

If a breaker trips the moment a motor starts, check starting current, voltage drop on the line, breaker settings and the condition of the equipment separately. Do not assume the contract capacity is too small.

Before applying for power, the most useful document is an equipment schedule. Beyond names and quantities, record at least the following:

• Model number and a photo of the nameplate.
• Rated voltage, single- or three-phase, frequency.
• Input power and rated current of the complete unit.
• Hours of operation per day, and which items run together.
• Starting method, and whether expansion is planned.

The table below demonstrates the method with a hypothetical set of equipment. All figures are assumed, confirmed input powers of complete units. The quantities are not a recommended configuration per 0.1 hectare, nor a sizing standard for ventilation or irrigation.

The table says only this: if the equipment above runs simultaneously at the listed powers, the total is 14.45 kW. Roll-up and shade drives, lighting, sockets, cold storage and anything else not yet listed must be added.

Rather than applying a rule of thumb for kW per 0.1 hectare, complete the list first. Leaving out a set of grow lights or a cold room does far more damage to the plan than an imprecise decimal.

The sum of the equipment is not necessarily the contract capacity. Roll-up motors may run for only a few minutes and irrigation pumps may cycle by zone, while exhaust fans and the pad pump may run continuously through the hot hours.

Plan around the farm’s actual operation by listing a few scenarios:

Taipower’s demand contract is based on 15-minute average demand, not the instantaneous peak current when a motor starts. Contract capacity is therefore estimated from operating scenarios; the effect of motor starting on the supply and protective devices is checked separately.

Leaving room for expansion is reasonable, but a blanket 20–25% margin is not a universal answer. Equipment that will definitely be added belongs in the phased plan; for needs still undecided, judge how much to reserve case by case.

Where several motors start together, staged delayed starting can be considered; for larger pumps, soft starters or variable-frequency drives depending on the equipment. These measures must fit the motor and system design. Raising the contract capacity alone does not solve starting problems.

As contract capacity approaches 100 kW, confirm the supply arrangement with Taipower early. Do not assume you must build your own high-voltage receiving equipment.

Under Taipower’s rules, in areas served at 11.4 kV or 22.8 kV, a case of 100 kW or more but under 500 kW may still be supplied at three-phase four-wire 220/380 V low voltage where technically feasible, billed under a demand contract at time-of-use rates. Whether this applies is confirmed by Taipower against local line and supply conditions.

Only once high-voltage supply is confirmed do you evaluate your own transformer, HV switchgear, the space they need and ongoing maintenance. These costs cannot be summarised in one lump figure; capacity and scope of work come first.

Phased construction does not mean applying for the final capacity in phase one. A sounder approach: plan the final demand, apply for what phase one actually needs, then decide which conduits, panel space and equipment positions are worth reserving.

Reserving space reduces the chance of rebuilding later, but it does not mean Taipower has reserved future capacity for you, nor can anyone promise that a later increase will not require new lines.

When a farm says “add lights”, it may mean different things:

Photoperiod lighting and photosynthetic supplemental lighting need very different intensities. One W/m² figure cannot be applied to all agricultural lighting.

Lighting design depends on crop, growth stage, season, natural light, hours of lighting and fixture layout. If PPFD is used to express light intensity at the crop, the full unit is μmol/m²/s, and it cannot be converted into a fixed wattage without knowing fixture efficacy and layout.

Power estimates should go back to the actual input power of the chosen fixtures. For arithmetic only, suppose the lighting design averages 60 W/m² of input power:

• Over a 200 m² nursery area, that totals 12 kW.
• Over a 1,000 m² area, it totals 60 kW.

60 W/m² is not a recommendation for any crop. The point is that the lit area changes the power demand dramatically.

For the operator, first identify the production problem lighting is meant to solve, then compare equipment cost, electricity cost and expected benefit. If only the nursery needs improving, there is no need to light the whole greenhouse.

With several fans, pumps or larger motor loads, three-phase supply is usually worth evaluating first, but “over 1 HP” is not a hard rule. Taipower’s business rules do cap single-phase appliances: 110 V motors at 1 HP each and 220 V motors at 3 HP each; above that, three-phase is required.

Before purchasing, have suppliers state voltage, phase and frequency in writing. For imported equipment especially, confirming “380 V” is not enough; confirm it is rated for Taiwan’s 60 Hz.

Three-phase three-wire 220 V and three-phase four-wire 220/380 V are also different:

• Three-phase three-wire 220 V: equipment must match this supply type and voltage.
• Three-phase four-wire 220/380 V: 380 V between lines, 220 V line to neutral; 110 V is not directly available.

If the site has 110 V equipment, a compatible supply must be arranged separately. The neutral must never be used as an earth.

Some motors can be reconnected per the nameplate, but the controller, power supply and other components of the complete unit may not follow. Have the supplier confirm the whole-unit specification before purchase.

The meter is installed to match the approved supply and metering arrangement. Fitting a larger meter does not mean the existing cables, main breaker and distribution board can carry a larger load.

When viewing land, noting pole positions, pole numbers and possible connection routes is useful. But the nearest pole is not necessarily a usable source, and spare capacity cannot be judged by eye.

When estimating, separate the costs:

For ordinary new or increased regular supply, Taipower’s line-installation charge comprises a “supply capacity charge” and, where applicable, a “new line length charge”. The length charge in principle applies only to the portion of the calculated line length beyond 1,000 m; special conditions follow the relevant rules.

Under the tariff effective 1 January 2026, the listed low-voltage supply capacity charge is NT$3,300 per kW including business tax. A new 30 kW connection, for this item alone, is NT$99,000. Agricultural power is exempt from business tax by law, so the amount payable is the listed figure divided by 1.05. This is neither the total connection cost nor a monthly bill.

Distance still matters, especially for long customer-side runs. Line length, current, conductor and installation method all affect voltage drop and cost, so a single price per metre cannot be applied to every site.

Three-phase is a supply type; the agricultural power certificate concerns recognition of agricultural use and tariff relief. The two are related but not the same.

Lighting and temperature control for protected horticulture, where compliant and supported by the required certificate from the competent authority, qualify for agricultural power relief. Lawful use of land and facilities and other documents must still be confirmed against the actual use and local requirements.

Once eligible and registered, the demand charge may be reduced according to load factor, and months with zero load factor are exempt under the rules. When estimating electricity costs, confirm eligibility and the applicable billing method alongside contract capacity and kWh.

Relief does not mean capacity can be inflated freely. Initial installation charges, demand charges in operating months, and charges when actual demand exceeds contract all have to be weighed together.

Greenhouses contain irrigation, fogging, pad walls, fertilisers and chemicals; equipment positions and wiring methods must suit the environment. Rather than simply specifying a “waterproof panel”, carry out the following:

• Place distribution boards in drier, accessible locations, away from flooding and direct spray.
• Choose enclosure protection and corrosion resistance for the exposure, and deal with heat dissipation and condensation.
• Configure earth-leakage, earthing and overcurrent protection per circuit and equipment characteristics.
• Plan surge protection for power and communications together with earthing and equipment interfaces.
• Separate power from control and sensor wiring; route conduit away from drips, abrasion and rodents.
• Label circuits clearly and keep the equipment schedule, drawings and maintenance records.

Earth-leakage protection for irrigation and similar equipment is already regulated; it should be handled by qualified electrical professionals according to the equipment and location.

Expansion is a separate check: spare ways in a panel do not mean the feeder, busbars and main breaker have capacity. Reserved items should be written down at the planning stage.

A greenhouse relying on mechanical ventilation and cooling can heat up quickly in an outage. How fast depends on weather, shading, vent openings, crop condition and layout; no fixed “degrees in minutes” figure applies.

Backup has two layers. The first is safe operation after power is lost: which vents can be opened by hand, whether the controls are easy to reach, who is responsible, and where the shade system should be parked. The shade screen need not be fully retracted; decide by ventilation and shading needs, and rehearse it.

The second layer is backup power: of exhaust, pad wall, irrigation, climate control and communications, which must keep running and which can pause or start in batches.

Generators cannot be sized by kVA per 0.1 hectare. Beyond the continuous load, consider motor starting, starting sequence, supply voltage and permissible voltage drop. kVA and kW are not the same number; confirm against the unit’s rating data.

An automatic transfer switch (ATS) switches the source, but it is not uninterruptible power. If the climate computer, alarms and communications cannot tolerate the switching gap, consider a UPS. After installation, arrange load testing, fuel management and regular exercising to confirm the system behaves as intended in an outage.

The earlier the equipment list is organised, the easier it is to confirm supply type and budget. If you already have the site, the main equipment models and the planned expansion, you can start preparing the application now rather than waiting for the greenhouse to be finished.

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