Diesel is the most common fuel used by emergency and standby generators in New York City, but natural gas generators are a promising alternative. Unfortunately, the current NYC Building Code hinders their use, since there are only two cases where natural gas is allowed as the only fuel supply for a generator.

• Emergency power systems in buildings classified as occupancy Group R-2. This occupancy group includes high-rise multifamily buildings.
• Standby power systems, as long as they are isolated from other gas services in the building with an outside cut-off valve. In addition, this valve must meet the requirements of the NYC Fuel Gas Code.

This article will provide an overview of natural gas generators, and their advantages and disadvantages.

Advantages of Natural Gas Generators

Natural gas is the only fuel delivered as a utility service in New York City, immediately giving it a logistical advantage over diesel, gasoline, heating oil and propane. With any fuel other than natural gas, a local storage tank becomes necessary, taking up space. In addition, it is necessary to keep track of fuel level and schedule deliveries accordingly. To summarize, all fuels other than natural gas require ongoing attention to ensure availability.

Natural gas does not require a storage tank and is delivered through a pipe, immediately making it easier to manage: a natural gas generator will always be ready for operation as long as it remains connected to the gas service entrance. In addition, natural gas generators can normally achieve a lower generation cost per kilowatt-hour compared with diesel units.

Another advantage of natural gas is service reliability under emergency conditions, and this was evident in the year 2012 during Hurricane Sandy. While one-fifth of New York City was left without electricity, gas supply interruptions were very rare. This way, properties with natural gas generators could remain powered even when a significant portion of the power grid was compromised. Of course, for this approach to be viable, the natural gas generator must be installed out of the reach of floodwaters.

Lithium-ion batteries are another promising backup power source for buildings, and they can be a cleaner alternative than natural gas generators if combined with a renewable generation system, such as a solar photovoltaic array or a wind turbine. In fact, lithium batteries can be charged with the power grid itself during off-peak hours, when the lowest electricity rates apply. Unfortunately, batteries are less resilient that natural gas generators during an extended power outage:

• If there is no renewable energy system, the power supply is lost as soon as the lithium battery bank is depleted.
• Even if there is a renewable energy system, power availability may be intermittent. For example, the cloudy weather that comes with a hurricane hinders solar energy generation, and wind turbine owners may have to dismount them temporarily to protect them from harsh winds.

Natural gas generators would be deployed in more NYC buildings if allowed as the main emergency power system in more occupancy classifications. Unfortunately, this only applies for R-2 occupancies and standby power systems. In addition, an on-site fuel supply for 6 hours of use is required in all other occupancies, favoring diesel generators over natural gas generators.

Other than in emergency situations, natural gas generators could be deployed by energy consumers subject to time-of-day rates. Some customers with time-of-day rates pay above 30 cents per kilowatt-hour during peak hours; a natural gas generator can be configured to run when peak electricity rates apply, sparing its owner from using expensive peak-hour electricity.

If a natural gas generator is equipped with a heat recovery system, it can also be used to preheat water before sending it to a boiler. This improves overall fuel efficiency for the building in question.

Disadvantages of Natural Gas Generators

When compared with diesel generators, the most evident drawback of natural gas generators is their higher upfront cost. For a given nameplate capacity, a natural gas generator can be up to 20% more expensive. It is also important to note that a gaseous and highly flammable fuel is being used, which means proper maintenance is extremely important to prevent gas leaks and accidents.

It is also important to note that natural gas is a fossil fuel, therefore it is a non-renewable energy source and it produces greenhouse gas emissions, although in much lower quantities than coal and oil. New York City has set the ambitious target of reducing its emissions by 80% by the year 2050, compared with 2005 levels. Future legislation and incentives can be expected to favor renewable energy systems over natural gas and other fossil fuels.

The fact that the NYC Building Code only allows natural gas generators as primary backup power in some occupancies is also a limitation: they become an additional building system in all other occupancy groups, and thus an extra capital expenditure. The prospect of installing two separate generators may not be financially attractive for many property owners.

Conclusion

Natural gas generators are a promising alternative to diesel generators,with increased reliability under emergency conditions and a lower running cost. They can be very valuable in a high-rise residential building during an emergency, since they provide an electric power supply when the utility grid and nearby gas stations stop operating due to a harsh weather. Consider that New York City has a very high population density and evacuating a large portion of the city can be very difficult. Natural gas generators can turn high-rise residential buildings into reliable shelters for extended periods of time.

The Building Resiliency Task Force was created in the aftermath of Hurricane Sandy in 2012, with the goal of providing suggestions to make NYC more resistant to extreme weather events. One of their main recommendations was to eliminate code restrictions on natural gas generators, allowing them to serve as primary emergency power in more occupancy groups beyond R-2. Many buildings started using diesel generators after the storm, but fuel tanks were quickly depleted and deliveries became very difficult or even impossible in the presence of floodwater.