Most California producers have already invested in standby generators, but with power outages increasing in frequency and length, some may be wondering if their emergency plans and equipment are sufficient.

Highlights: What you need to know about emergency power on California dairies

  • While existing standby generators may service the milking parlor they may be inadequate to power other critical equipment. Planning ahead can help minimize problems during a prolonged outage.
  • If extended power outages are immanent, producers should test their generators under load, ensure they have adequate fuel supplies for several days and make sure their utility company can provide detailed updates directly to their phones.
  • Air quality regulations allow you to run standby generators for unlimited hours during an emergency, but there are annual limits of use hours for repair and maintenance.
  • Good maintenance can keep a standby generator running for decades. Repairing an existing generator may be less expensive than replacement with newer one required to have a higher EPA/ARB Tier certification.
  • While portable generators from 10 kW to more than 4,000 kW can be rented, generator availability may be nonexistent one to two days into a public safety power shutdown.
  • Utility companies may offer free energy audits and financial incentives to upgrade equipment. Almost $6 ½ million of incentives have been made to California dairy farms to improve efficiency in pumps, refrigeration and lighting.

More than any other type of agricultural facility, dairies are dependent on electricity to power critical systems including milking and refrigeration equipment, vacuum and well pumps, fans and feed equipment. Producers are familiar with short-term power failures resulting from wind events, road accidents or animal intrusions. Squirrels alone cause an estimated 240,000 power outages in the U.S. every year. Because rural power outages occur every year, most dairy producers have invested in standby generators. In the fall of 2019 however, California experienced the most geographically widespread and longest duration Public Safety Power Shutoffs (PSPS) in the state’s history. In an effort to prevent wildfires during extreme wind events, some 800,000 residential and commercial customers in 34 counties lost power, sometimes for more than four days. While most of the state’s dairies were unaffected by the shutoffs, some producers were. This article links to resources for producers considering expanding or replacing their emergency power generating capacity, as well addressing regulatory issues, equipment rental and standby generator maintenance.

Preparing for a Power Outage

A Public Safety Power Shutoff (PSPS) impacting a dairy can be a logistical challenge. Perhaps the only advantage of PSPS events over an unexpected power outages is that there may be some time for producers to prepare. In June of 2019 utility companies warned of potential PSPS events and in October most customers had at least 24 to 48 hours’ notice of imminent power loss. In the window between receiving a warning of a potential outage to the actual loss of power there are several useful actions producers can take:

Perform Final Generator Check: The most destructive and costly fires in California typically occur from June to December, most frequently in the last three months of the year. Prior to that time producers will want to perform a comprehensive annual or semi-annual maintenance on their standby generator. Immediately before a planned power outage the generator should be run under load as a final check.

Ensure Adequate Fuel Supply: A 400 kilowatt generator can consume 16 gallons of diesel fuel an hour and a 2 megawatt generator can burn through 72 gallons an hour. During widespread power outages availability of some types of fuel may be limited. Particularly if potential exists for road closures from fires or flooding, producers will want to ensure they have adequate fuel supplies on hand for at least several days or have confidence that those supplies can be replenished.

Sign Up for Notification: It seems counter-intuitive but sometimes the only customer contact information a utility company may possess is a service and/or billing address. By updating your contact information, utilities like Pacific Gas and Electric or Southern California Edison can send outage information to you by voicemail, text or email. This information is typically more current and specific than outage maps located on internet sites, websites which may also be crashing due to intense traffic. Having narrower time frame for power loss can be useful in planning for outages but also to know when power has been restored and a generator can be turned off.

Identify Rental Equipment Early: Besides the milking parlor there may be other critical systems requiring power during and extended outage. During or immediately prior to a PSPS however, there may be no appropriate generators available. The earlier a producer engages a rental company the more likely they will be able to identify rental units.

Pacific Gas and Electric has its comprehensive Power Resilience Playbook focusing on businesses and commercial facilities. The company also has a quick one-page checklist on preparing your facility for potential power outages.

The Basics of Standby (Emergency) Power Generators

Most often engines for large standby generators are driven by diesel or but may also be powered by propane, natural gas, gasoline or even renewable energy sources such as solar, wind or methane from lagoon digesters. Most renewable energy sources (such as solar) are directly connected to the utility power grid, precluding use during power outages unless costly infrastructure, including battery storage, has been added. Generators must provide the same type of power at the same voltage and frequency as supplied by the utility lines. A properly used and maintained generator should last 20 to 30 years. An excellent introduction to standby electric generators is available from the University of Kentucky.

Types of Standby Generators

Standby generators for farms can be generally divided into those driven by dedicated engines and those using Power Take-Off (PTO) drives.

Engine-Driven Generators

In order to furnish sufficient wattage to power critical operations on larger dairy farms, standby generators for typical larger California dairies are typically permanent and pad-mounted with a dedicated engine, usually diesel. Dairy standby generators range greatly in size depending on how much load (equipment) it is servicing. Besides milking and cooling equipment and a well pump, the system may also be running housing fans, feed mixing equipment and irrigation wells. Depending on the size of a dairy and its emergency load, standby generator capacity may range from less than 100 kilowatts to more than 1,000 kilowatts (one megawatt). Motors using more than about 10 horsepower (about 7.5 kilowatts) require a three-phase system.

 PTO-Driven Generators

Without the added cost of a dedicated engine, Power Take-Off (PTO) driven units may be half the cost of similarly-sized permanent engine-operated units. They can be transported to remote locations when mounted on a trailer or attached to 3-point hitch. Most commercially available PTO-driven generators are limited in output to about 10 to 100 kilowatts, although the largest units may approach the 150 – 160 kilowatts range. This smaller size usually precludes use of PTO-driven units to power large western milking parlors, but some PTO-driven units may still be useful to operate modest sized irrigation pumps, feeding equipment etc. An excellent fact sheet addressing PTO-driven generators is available from the Ontario Ministry of Agriculture.

Replacing or Expanding Electrical Systems on Dairies     

Planning for Expansion Wiring systems on dairies can be enormously complex and the process of adding to or replacing a permanent standby generator can be daunting. Fortunately an outstanding guide to Planning Electrical Systems for Dairy Expansions is available from the Wisconsin Farm Electric Council. The reference addresses numerous issues for expanding electrical systems including developing an “electrical planning team”, selecting service location and type of service, temporary service, equipment protection and safety considerations.

Limiting Costs There are currently no state or federal programs available to support replacement of older generators with newer, cleaner ones. Similarly, while some commercial utility companies may offer no-interest farm loans to upgrade to more efficient electrical equipment, these loans typically can’t be used to upgrade standby generators. Because newer tier standby engines can be costly to purchase and install, if feasible producers will want to consider repairing rather than replacing an existing generator. If additional capacity is needed because some limited dairy expansion has occurred, producers may also consider curtailing some non-critical systems during emergency operations. Critical Load Sizing is described below.

Energy audits, often available for free, may reveal options for more cost efficient equipment that could potentially decrease power costs or decrease load on a standby generator. Pacific Gas and Electric (PG&E) agricultural customers can request an onsite energy audit by calling 877-311-3276. PG&E has also partnered with California dairy farms providing almost $6 ½ million of incentives and rebates to improve efficiency in pumps, refrigeration and lighting. A catalog of rebates for farms and dairies available from PG&E is available.

Capacity & Sizing

Generator capacity is typically measured in kilowatts, with one kilowatt being equivalent to about one and one third horsepower. The amount of power required to start equipment moving (vacuum pumps, feed augers) can be 2 to 12 times the amount of power necessary to continuously run it. Therefore a standby generator’s corrosion-resistant nameplate should specify both its continuous output rating as well its short-term output rating which variously referred to as surge, over-load or peak capacity. The over-load capacity is typically used only for short periods such as when the motor is starting. One rule of thumb it to have at least four times as much surge capacity as operating output.

Standby generators are available to provide either single or three phase power but the more efficient, more reliable three phase motors are preferred. In particular three phase power should be considered if motors of 10 horsepower or greater are used. Single phase can be converted to three phase on the farm. Consult your local power supplier when considering purchase of standby power to get its recommendations and requirements for installation.

How much standby generator capacity a facility will invest in varies with how much equipment will need be operated at the same time. Critical-Load Sizing ensures that just equipment critical to operation (milking and milk cooling, fans and well pumps, etc.) is powered. Under a critical (or partial) load system, initially all electrical equipment is turned off or disconnected. After the generator is in operation equipment is turned on with the load limited to the capacity of the generator. Some producers will elect to use Total Load Sizing where a standby generator completely replaces utility grid power. An example of sizing calculations for a dairy standby generator are available in an Iowa State reference.

Dairy Employee and First Responder Safety

Improperly installed or maintained electrical systems have caused injury and death to livestock, employees and utility linemen working to reestablish power. Faulty electrical equipment is also one of the most common causes of barn fires. Installation or upgrades to standby generator sets should be performed by licensed, bonded electricians experienced with livestock facilities. All work should be in compliance with the California Electrical Code, in particular Chapter 7, Article 700 dealing with emergency systems.

Transfer Switches One of the most important state and federal requirements for standby generators is a manual or automatic transfer switch preventing the standby generator from inadvertently being connected to the utility grid. This is typically accomplished by a “double pole, double throw” isolation switch. This prevents power from your standby generator feeding into the grid and potentially electrocuting lineman working to reestablish power. In addition, a standby generator connected to the grid can become overloaded as it attempts to provide electrical power to neighboring farms on the same utility grid distribution line. Similarly, a code-compliant switch prevents damage to your equipment when the utility lines are reenergized. Finally, most standby equipment warranties are void if code-compliant transfer switch is not in place.  Attempting to install standby generators without an adequate transfer switch is both dangerous and illegal. The University of Nebraska provides an excellent guide on recommended practices for electrical systems for agricultural buildings.

Carbon Monoxide Generator exhaust creates carbon monoxide gas that is odorless, colorless and toxic to both humans and livestock. Generators must be positioned outside and in well ventilated areas, or if permanently located in a shelter, must have exhaust gasses removed by a sealed exhaust system.  Do not use generators indoors such as parlors, sheds, or barns. Do not place generators near air intakes such as windows to prevent pumping fumes into the building. Install and check carbon monoxide detectors in areas near standby generators.

PTO-Driven Generators Never operate a generator that is not securely mounted. The torque necessary to spin a generator is potentially great enough to spin the entire generator, causing damage to the unit or bodily injury. It may be helpful to provide a guide for backing the tractor so that it is properly positioned to the generator. PTO drive shaft should be rated for the horsepower being used and equipped with a free-rotating shield. The PTO drive shaft should be stored with the generator to avoid using the wrong one. Ensure that generator is running at its recommended RPM, often 540 or 1000 RPM. Operating the generator faster will not produce more power, but may alter the frequency or phase it is putting out. Operating a generator at an RPM not recommended by the manufacturer may damage it.

Regulatory Compliance and Standby Generators       

State Regulations California’s minimum requirements for diesel-fueled emergency standby engines are dictated by the state’s Air Toxic Control Measure (ATCM), part of the California Code of Regulations. While standby engines can be used for an unlimited number of hours during emergencies and unplanned power outages, the following requirements still apply:

  • Engines must be used solely to provide electrical power or mechanical work during electrical power service failures, fires, or floods beyond the control of the operator.
  • Statewide, hours of non-emergency operation (maintenance and testing) is limited to no more than 100 hours per year. Some local jurisdictions may require lower limits, for example 20-50 hours per year, depending on the age of the engine.
  • Each diesel-fueled emergency standby engine will be equipped with a non-resettable hour meter, used to keep a record of annual hours of operation, including hours of testing and maintenance, hours of emergency operation and the type of fuel used.
  • Diesel engines must use of low-sulfur diesel fuel (<0015% sulfur by weight) which has been certified by the California Air Resources Board (CARB). This is typically the only diesel fuel commercially available in California.
  • If a diesel-fueled emergency standby engine is replaced, or a new one added to increase capacity, the new or newly-installed engine needs to meet the latest EPA/ARB Tier certification level not requiring add-on controls. The current emission requirements are shown in the ATCM, Table 1 and are equivalent to:
    • 50 – 74 horse power (bHP): Interim Tier 4
    • 75 – 749 horse power (bHP): Tier 3
    • ≥ 750 horse power (bHP): Tier 2
  • Existing emergency standby engines are not required to be replaced with newer Tier certified engines, but just must comply with any hour of operation limitations.
  • Tier requirements apply only to diesel engines, not those driven by natural gas or propane. Some Air Districts however may require a catalyst for natural gas or propane engines.

Local Regulations While the Air Toxic Control Measure (ATCM) regulatory requirements apply statewide, the local air pollution control/air quality management districts may have stricter requirements. Therefore, before making purchase and installation decisions, the local air district where the affected engine is located should be consulted for specific information. Contact information for the 35 California air districts are available on the ARB website. Finally, local jurisdictions may have additional requirements unrelated to air quality, such as construction requirements or noise abatement ordinances.


Because diesel generators may sit idle for extended periods, without diligent, continuous maintenance they face a high risk of start-up failures. During Hurricane Sandy 16% of emergency medical service diesel generators did not perform as expected. Maintenance also protects the financial investment. Standby generators may only operate for 30 minutes a week for maintenance or as much as several hundred hours per year depending on the number and duration of power outages. In either case a properly used and maintained standby generator should last 20 to 30 years.

Penn-State Extension has an introductory reference on Meaningful Maintenance for Generators. A more comprehensive checklist for standby generator maintenance is available from Authorized Services of New England, an authorized Generac dealer.

Scheduling Maintenance Preventive maintenance and service can be based on either a calendar schedule or on hours of engine use. Depending on the size and fuel type (gasoline, diesel, or propane) the maintenance program and frequency of service of the generator may vary. It’s always prudent to consult your owner’s manual or service technician for specific requirements and service intervals for your generator.

Weekly or Monthly Check Before completing any maintenance, make sure the power to the generator is locked out and tagged out to prevent any unintentional start-ups. At a bare minimum the generator should be inspected on a monthly basis. The examination will reveal if combustible materials are collecting near its exhaust port, if there is dirt or dust accumulation, or if rodents are taking up residence. The engine coolant, oil and battery should be checked and the engine examined for fluid leaks. On a weekly or monthly basis the generator should be exercised. This is typically done under not under load and is often performed by a timer attached to an automatic transfer switch. Verify that the unit has run there are no alarms or warnings.

Annual or semi-annual maintenance These can be performed by a certified technician or experienced employee and includes a closer inspection of cables, connections, belts, coolant lines and check or replacement of air, fuel & oil filters. Load banks can be tested and diesel fuel can be tested and reconditioned. Fuel stabilizing additives may be helpful in preventing fuel degradation over a prolonged storage period.

Generator Rental

Aside from the milking parlor, there may be other critical equipment needing power including irrigation pumps, feed mixers or housing fans. If the main standby generator doesn’t supply this equipment, or the main generator fails, a producer may be forced to consider generator rental. Numerous companies provide generator sales, service and rental.

Availability During the 2019 PSPS events generator service & rental companies reported equipment “flying of the shelves” with their inventory exhausted in just a couple days. Large companies such as Costco and municipal water services have been renting large generator sets for the entirety of the state’s fire season, roughly August to November. The farther in advance a producer can anticipate the need for generator and engage a rental company the more likely they will be able to identify rental units.

Cost Portable generators are available with engines driven by diesel, propane and natural gas, with outputs ranging from 10 kW to more than 4,000 kW. For a standard rental of a mid-sized 100 kW generator, producers can expect to pay $2,000 to $3,000 per month. This basic rental may not include additional equipment needed such as cables, transfer switches and containers for extended fuel storage. In addition there may be operational charges of $2 to $3 for every hour the generator is used.

Contributors & Reviewers

The CDQAP gratefully acknowledges the following experts who contributed to or reviewed this webpage:

Ramon Norman, Air Quality Engineer, San Joaquin Valley Unified Air Pollution Control District

Justin Witte, Senior Customer Relationship Manager, AG/Food Processing / Business Energy Solutions, Pacific Gas & Electric Company

James McMullen, California State Fire Marshal (retired), President, The McMullen Company

Darrin Ogletree, Federal Equipment Coordinator, Agriculture & Natural Resources, University of California