Power Factor Penalties and Cannabis Facility Equipment Loads

What power factor actually measures

Every AC load draws two kinds of power. Working power, in kilowatts, is the part that becomes light, heat, and motion and is what your energy meter registers. Reactive power, in kilovolt-amperes reactive (kVAR), does no useful work but is needed to sustain the magnetic fields inside motors, transformers, and similar equipment, and it takes up room in the distribution lines [dte-power-factor-explainer]. Apparent power, in kVA, is the vector total of the two, and it is what generators, transformers, and wires have to be sized for [dte-power-factor-explainer].

Power factor is the ratio of working power to apparent power, kW divided by kVA [dte-power-factor-explainer]. A facility with a power factor of 1.0 is pulling only working power. A facility at 0.80 is making the utility deliver 1.25 kVA for every kW it uses. Typical values run from 0.80 to 0.98 [dte-power-factor-explainer].

The napkin version: kVA = kW divided by PF, and kVAR = the square root of (kVA squared minus kW squared). A 400 kW load at 0.85 PF is 471 kVA and about 248 kVAR of reactive draw. The same 400 kW at 0.95 PF is 421 kVA and 131 kVAR. The kilowatt-hours are identical; the strain on the wires is not.

Which grow equipment drags power factor down

Inductive loads are the problem. DTE's guidance names motors and transformers as the main sources, and calls a lightly loaded induction motor one of the worst offenders, because motors are sized for the heaviest load they will ever see and then spend most of their life running below it [dte-power-factor-explainer]. That description fits a cultivation facility well.

Equipment	Why it hurts power factor	Typical share of grow load
HVAC compressors, condenser fans, air handlers	Induction motors, often oversized for the design-day peak and lightly loaded the rest of the year	Cooling alone was 15 percent of electricity use in the Northwest Council's producer survey, with ventilation another 12 percent [nwpcc-cannabis]
Dehumidifier compressors	Same motor issue, and they cycle constantly	Dehumidification was 4 percent of surveyed use, but a larger share in sealed rooms [nwpcc-cannabis]
Circulation and exhaust fans	Dozens of small single-phase motors, each at a poor individual power factor	Included in the ventilation share above
Magnetic HID ballasts	Older core-and-coil ballasts are transformers; uncorrected units can sit well below 0.90	Lighting was 66 percent of surveyed use, mostly HID at the time [nwpcc-cannabis]
Low-cost LED drivers	Switch-mode supplies without power factor correction pull distorted current; harmonics show up as a low "true" power factor	Growing share as facilities retrofit
Well pumps, irrigation pumps, RO systems	Motors again, often started across-the-line	Small in kWh, but they add kVAR at the same moment as everything else

Lighting deserves a note because it is the largest load. DLC's horticultural technical requirements, the list most utility rebate programs key off, require a measured power factor of at least 0.90 at any reported input voltage at full output, and current total harmonic distortion no greater than 20 percent [dlc-hort-v4]. A DLC-listed LED retrofit therefore tends to raise a facility's power factor compared with magnetic ballasts. Fixtures that are not on the list have no such floor, and a 0.7 PF driver bought by the pallet can drag the whole service down. The tradeoffs in LED vs. HPS lighting include this.

Timing matters too. Utilities that bill power factor usually measure it at your peak interval, and a grow's peak is lights-on plus HVAC catching the heat. That is exactly when the compressors are all running. See demand charges explained for how that interval is set.

How utilities bill for it

There is no single method. Four real tariffs show the range.

Inflated billing demand (Austin Energy, Xcel Energy Minnesota). Austin Energy applies an adjustment when the power factor is below 90 percent during the interval of greatest monthly use: billed kW equals measured kW times 0.90, divided by actual power factor, and the adjusted kW feeds the delivery, demand, and regulatory charges [austin-energy-pf]. Xcel's Minnesota General Service schedule works the same way in principle: billing demand is adjusted upward if the power factor shown on the bill is below 90 percent, on top of a ratchet at half of the highest billing kW in the preceding 11 months [xcel-mn-ci-rate-card]. On that 2019 price sheet the secondary-voltage demand charge was 14.79 dollars per kW in June through September and 10.49 dollars in other months [xcel-mn-ci-rate-card], so every kW of adjustment costs real money.

A separate reactive charge (DTE Electric). DTE's primary supply schedule states that rates are based on the customer maintaining a power factor of not less than 85 percent lagging, that anything below 70 percent is not permitted and must be corrected at the customer's expense, and that for retail access (choice) customers, excess reactive demand from operations below 80 percent power factor is billed at 3.50 dollars per kVAR per month, measured at the location's single highest 30-minute on-peak kW interval [dte-d11-primary-supply]. Excess kVAR is the difference between the coincident kVAR reading and the kVAR that would exist at 80 percent power factor [dte-power-factor-explainer].

A per-kWh adjustment in both directions (PG&E). Schedule B-19, the medium general demand-metered TOU schedule, computes an average monthly power factor from the ratio of lagging reactive kilovolt-ampere-hours to kilowatt-hours. Rates are based on 85 percent; the bill goes down by the power factor rate times kWh for each percentage point above 85, and up by the same amount for each point below [pge-schedule-b-19]. The current adjustment rate is 0.00005 dollars per kWh per percentage point [pge-schedule-b-19]. Small per unit, but it applies to every kWh, and a grow uses a lot of them.

Billing on kVA instead of kW. Some utilities skip the arithmetic and simply bill demand per kVA. On a kVA tariff, a 0.85 power factor costs you 18 percent more demand than a 1.0 power factor, with no threshold at all. Check the demand line's unit on your bill; understanding your commercial utility bill walks through where to look.

Utility and schedule	Threshold	Mechanism
Austin Energy, commercial	Below 90 percent at the peak interval	Billed kW = kW x 0.90 / PF [austin-energy-pf]
Xcel Energy MN, General Service	Below 90 percent	Billing demand adjusted upward [xcel-mn-ci-rate-card]
DTE Electric, D11 primary (retail access)	Below 80 percent for the kVAR charge; 85 percent basis; 70 percent floor	3.50 dollars per excess kVAR per month [dte-d11-primary-supply]
PG&E, B-19	85 percent basis, adjustment either direction	0.00005 dollars per kWh per percentage point [pge-schedule-b-19]

A worked example

Every number here is an input we chose so you can follow the arithmetic. Substitute your own.

Assume an indoor facility with a 500 kW coincident peak at lights-on, 300,000 kWh per month, a measured power factor of 0.82 at the peak interval, and a delivery demand charge of 14 dollars per kW. Then work it three ways.

1. Austin-style demand inflation. Billed kW = 500 x 0.90 / 0.82 = 549 kW. The penalty is 49 kW x 14 dollars = 686 dollars per month, about 8,200 dollars a year, for reactive power the energy meter never counted.

2. DTE-style reactive charge. At 500 kW and 0.82 PF, apparent power is 610 kVA and reactive draw is about 349 kVAR. The kVAR allowed at 0.80 PF for 500 kW is 375 kVAR, so in this case there is no excess and no charge. Drop the facility to 0.75 PF and reactive draw is 441 kVAR; excess is 66 kVAR x 3.50 dollars = 231 dollars per month. This structure is gentler until you cross its line, then it is not.

3. PG&E-style per-kWh adjustment. Three points below 85: 300,000 kWh x 0.00005 x 3 = 45 dollars per month. Raise power factor to 0.95 instead and the same formula pays you a credit of 300,000 x 0.00005 x 10 = 150 dollars per month.

The spread between 45 dollars and 686 dollars a month for the same facility is the point: the penalty depends far more on which tariff you are on than on how bad your equipment is. Utility rate classes explained covers how you end up on one schedule versus another.

Correction capacitors and what they cost

Reactive power for inductive loads can be supplied locally by capacitors instead of by the utility. A capacitor bank installed at the service entrance, or at individual large motors, supplies the kVAR the motors need so the utility meter sees a higher power factor. DTE lists the benefits of improving power factor as reduced energy and distribution costs, lower losses in your own wiring, steadier voltage, more usable capacity in your existing service, and reduction or elimination of power factor charges [dte-power-factor-explainer].

Sizing follows from the numbers above. To move the assumed 500 kW facility from 0.82 to 0.95 PF, you need to cancel the difference in reactive draw: 349 kVAR (at 0.82) minus 164 kVAR (at 0.95) equals about 185 kVAR of capacitance. Installed capacitor pricing varies with voltage, enclosure, switching (fixed versus automatic stages), and harmonic filtering, and we are not going to quote a national number. What we can say is that in the Austin-style example the penalty was roughly 8,200 dollars a year, and an electrician's quote for a 185 kVAR automatic bank is the number to compare that against.

Three cautions:

1. Do not over-correct. A leading power factor (too much capacitance) can raise voltage and is penalized by some tariffs just like lagging. Automatic banks that switch stages in and out as load changes avoid this, and matter in a grow where load steps by hundreds of kW twice a day.
2. Harmonics are a different problem. Capacitors fix displacement power factor from motors. They do not fix distortion from switch-mode LED drivers, and in some cases they resonate with it. If a large share of your load is LED, ask for a harmonic study before installing a plain capacitor bank, and buy drivers that already meet the 0.90 PF and 20 percent THD floor [dlc-hort-v4].
3. Fix the motors first where you can. Variable frequency drives on air handlers and condenser fans, and right-sized motors instead of oversized ones, raise power factor at the source and cut kWh at the same time. HVAC sizing for grow rooms explains why grows so often end up with oversized equipment.

How to check your own facility

1. Pull twelve months of bills and look for kVAR, kVA, reactive, or power factor lines, and for a power factor percentage in the meter detail.
2. If your meter records reactive energy, download the interval data and find the power factor at your peak interval each month. That is the number most tariffs bill on. See interval data and AMI meters.
3. Read your delivery tariff's power factor clause and note the threshold (90, 85, or 80 percent), the basis (peak interval or monthly average), and the mechanism (demand inflation, per-kVAR, per-kWh, or kVA billing).
4. Run the arithmetic above with your numbers, get a capacitor quote, and compare.