Harvesting the Sun’s Rays

Energy is the second largest airport operating expense, exceeded only by personnel, according to FAA’s Airport Cooperative Research Program report, published in December 2007. For this reason, airport facility managers and owners are looking for new and innovative ways to reduce their energy expenditure.

While many airports have already added tenant sub-metering, building automation systems (BAS), and computerized maintenance management systems (CMMS) to both monitor and control energy expenditure, operating on-site renewable power generation is next on the horizon.

In fact, research shows that employing a renewable energy like solar photovoltaics (PVs) can save as much as 5 to 15 percent of energy use during daytime hours when electricity costs are at their peak. PVs work by directly converting electromagnetic radiation from sunlight into electricity through a field of semiconductor technology.

PVs are low profile and come in the form of either thin, stand-alone solar panel modules or are integrated as part of the building structure itself. Some PV systems convert sunlight into energy for immediate use while others have the ability to store energy harvested during the day for use at night. The average output of a PV solar panel is between ten and 18 watts per square foot.

The benefits of PVs include minimizing operational energy expenditure, diversifying the energy supply, reducing the airport’s dependence on imported fuels, improving air quality, and offsetting greenhouse gas emissions by minimizing the need for the utility.

PVs for airport usage
There are a number of steps involved in designing PVs for airport use. From evaluating the site to performing load, shading and daylighting analysis, and assessing the PV’s potential impact on other trades and design options, airports have unique considerations when it comes to employing renewable energies.

Prior to the design stage, early confirmation that a PV is usable given an airport’s specific constraints and land availability is crucial. This will begin with site evaluation. Does the airport have the surface area for solar panels and is it in an appropriate location to ensure maximum sunlight? Searching the current site for available surface area or working together to plan new usable space, coordination of the building team during site evaluation is key. Reviewing an existing airport’s last 12 months of utility bills to determine electric load demands will take place during site evaluation as well. Once the evaluation has been completed, design engineers can determine how much solar power will be generated based on the selected surface area.

During the analysis phase of the project, climate is the first aspect evaluated to determine the viability of a PV system. Available sunlight during different times of the year is assessed along with shading and daylight modeling, which will forecast the sun’s rays. Second, a load analysis will help create a load profile for the airport. In an existing facility, this will involve utilizing the past 12 months of utility bills collected during the site evaluation phase to determine how much energy is needed at different times of the day. In new construction, this will be more challenging, but can be accomplished through modeling. Solar modeling determines the angle of the sun and weather patterns throughout the year.

Identifying the PV’s impact on other airport trades is an important aspect in determining viability as well. How will the new PV affect maintenance and general airport operations? This will be determined by: the type of structure needed to support the panels and how maintenance personnel will access, service, and operate them. When PV arrays are stationed on the ground, they are often larger in size and less obtrusive to the building itself, whereas rooftop applications typically have a finite amount of potential square footage.

Design/Build Options
Once the PV site evaluation and load analysis have been completed, two types of design/build options are available: Design-Bid-Build and Design-Build. In the Design-Bid-Build method, the full PV design is completed first and then put up for competitive bid. Many municipalities favor this option because it provides more of an opportunity to compete on price.

However, this delivery method requires a longer schedule time and limits the contractor from providing constructability input during design that can add value and flexibility to the project.

With the Design-Build method, the PV design is taken only to a schematic level identifying performance requirements and general parameters. Here, the contractor chosen will complete the design while building the PV on site, as the design engineer oversees the project for the owner. With this method, the overall schedule time is often reduced, as the contractor can start working sooner and make appropriate design decisions on the job. This can lead to reduced cost and more efficient ways of designing a PV because no one is restricted by a full design.

PV technology – the pros, the cons

While photovoltaics (PVs) help offset energy costs and simultaneously exhibit a strong environmental commitment, they are not appropriate for every airport.

1. Cost Effectiveness and ROI – Very often with city-owned airports, employing a PV can be a community-wide political issue. When this is the case, the airport may be willing to accept a longer payback period.

2. Maintenance – While maintaining PV panels are a consideration for any type of building, airport PVs have a unique air quality challenge as a direct result of the jet fumes, ground support equipment, and passenger vehicle traffic they are subject to on a regular basis. A maintenance program must be set in place to maintain the cleanliness of the solar panels in order to ensure they can operate at maximum efficiency.

3. Climate – Airport or office building, PVs are only going to make a real difference in harvesting usable energy in a year-round, sunny climate.

4. Carbon Footprint Reduction – In order to calculate how much carbon footprint reduction a PV array will lead to, projected energy savings must be calculated. Carbon reduction calculations need to include not only the energy saved from the operation of the PV system, but should also embody the energy and carbon required to manufacturer, transport, and install the PV or other related equipment.

5. Existing Airport vs. New Construction – When installing renewable energies at an existing airport, energy expenditure pre-installation can be compared to post-installation to determine real savings over time, as compared to new construction where the energy savings is assimilated. That being said, space constraints often plague PV instillations in existing airports, while new construction typically lends itself to more flexibility for PV installations.

6. Panel Angle and Direction – It is crucial that design engineers conduct studies on the angle of the sun versus the angle and direction of the panels to determine optimal PV panel orientation.

About the authors

Lalit N. Mehta, P.E.
A member of the Airport Consultants Council (ACC), the American Associations of Airport Executives (AAAE), and the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE).

Carl Newth, PE, LEED AP BD+C
An active member and serves on committees of the Airport Consultants Council (ACC), the American Associations of Airport Executives (AAAE), American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE), and the FAA’s NextGen Working Group.

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