For fleet managers making the switch to natural gas vehicles, one of the most important considerations is how they will fuel the fleet. Here are several options to consider.
On-site or offsite
One of the first decisions is whether or not the vehicles will be fueled on-site or at an off-site location.
Offsite fueling: Making the switch to natural gas vehicles often is made easier when there is public access fueling nearby, including stations operated by the local gas company, a retail fuel provider or another public or private fleet. When evaluating this option, it’s important that to check with the station owner to make the station’s equipment is capable of accommodating the additional vehicles.
Here are the considerations:
Fleet fueling patterns: Will all your vehicles be fueling at the same time or at different times during the day? This impacts compressor size and capability
Proximity to your business: Fleet managers need to consider the convenience and cost of driver time spent traveling to and from an offsite.
On-site fueling: If use of existing fueling infrastructure is not practical, fleet manager may consider building a new station on-site or nearby. This may be accomplished several ways.
Operate your own site: One option is to contract design and construction of a station and then retain ownership, operations and maintenance responsibility. While this option may offer the promise of greatest savings, it also incurs the greatest risk. For low volume applications, this is likely the only option available if existing fueling infrastructure is not available.
Contract with an outside company to run the operation for you fuel: Another option is to completely delegate station development, ownership, operations and maintenance to an experienced natural gas fueling provider. This option tends to be available to fleets using large volumes of fuel and typically entails entering into multi-year contracts for fuel and services. The minimum contract volume requirement likely will be influenced by the number of other stations that provider operates in the area, whether the contract allows for “outside the fence” retail or contract sales to others, and the number of other existing and potential NGV customers in the area.
Contract maintenance and operations of your site: Another option is to build and retain ownership but contract operations to a third party with expertise. This option also tends to be available only to larger volume customers and usually is charged on a monthly fee, fee-per-gasoline gallon equivalent assessment or some combination of the two. By retaining locally-based skilled NGV station technicians on staff and stocking critical components in inventory, independent natural gas fuel providers and operations and maintenance companies are positioned to handle this task.
Fast-fill Versus Time-fill
Fast-fill stations offer the convenience and flexibility of fueling as quickly as with liquid fuels like gasoline or diesel, and all public stations are fast-fill.
Fast-fill stations employ a combination of compressors coupled with stationary high-pressure steel storage vessels. Using multi-stage compressors, natural gas is boosted from the lower pressure delivered by the local gas utility up to 4000-5000psi. When the fuel hose is connected to the vehicle and the ANSI Weights & Measures-approved dispenser is activated, gas flows from the higher pressure storage vessels to the vehicle’s onboard cylinders. The rate of dispensing and the total amount of available fuel is a function of the pressure differential, the number of vehicles fueling at one time from the same storage bank and the control sequencing of the compressor. Your design consultant will work with you to come up with the right combination of compression and storage.
Time-fill fueling is the most economical, but it is works only for fleets that return to their own central fueling facility for an extended time—such as refuse trucks. These systems, which refuel vehicles’ onboard storage cylinders at slower rates, are considered the most efficient and economical because they do not require as much compression capacity as a fast-fill system, nor do they require on-site CNG storage nor ANSI-approved dispensers. The rate of fuel transfer will depend on the size of the compressor and number of vehicles fueling at any one time, but may be as little as one gasoline gallon equivalent (gge)/hour to as much as five or six GGE/hour. In time-fill applications, drivers connect their vehicle to the automated system. The fueling apparatus automatically shuts off when the vehicle’s fuel cylinders are full, so there is no need to monitor the dispensing. The automated nature of time-fill fueling reduces as much as 15 minutes of labor time per driver per day.
Fleets that opt for on-site fueling work with experienced CNG station design consultants who can help them identify their requirements, assess options to modify existing fueling operations and then select the best option that meets their needs and their budgets. These services may be contracted through an independent CNG station design engineering consultant who may handle the process from design through station commissioning or they may be provided by the engineering staff of a CNG equipment packager.
Regardless of the station development process a fleet chooses, fleet managers will need to have this information available:
Vehicle Fueling Requirements
- How many vehicles need to fuel each day and what is the average and maximum amount of fuel used by each vehicle?
- What are the available fueling windows of each vehicle and is this able to be managed?
- Will there be full- or limited-public access by other fleets and what is the projected transient use by these additional vehicles?
- Is there back-up fueling capability nearby in case of planned or unplanned equipment downtime and how does this affect equipment redundancy requirements?
With this information, you and your design consultant can calculate projected total daily fuel requirements and maximum hourly flow rates, which will determine the type of station required, the amount of compression needed, whether storage is required and –if so - how much, how many and what type of dispensers will be required.
Fueling Site Information
- What is the volume and pressure of gas available to my site and what are the minimum and maximum inlet pressures I may expect delivered to my compression equipment?
- What is the moisture content of the gas?
- What is the available electric service on site and will I need to upgrade it to meet my compressor motor needs?
- Where are my utility services located on site and is my site plan up to date?
- Which building and construction codes apply in this area and what permits and/or approvals will I need?
- What is the amount of space and the optimum footprint for my equipment and fueling island(s)?
- What are the vehicle ingress/egress issues – if any? How will future expansion of this site potentially affect my plan?