Sustainability Toolkit

Solar panels or photovoltaic collectors are comprised of photovoltaic modules which convert energy from the sun into direct current (DC) electricity. The majority of solar panel systems are equipped with power inverters that convert the DC electricity into alternating current (AC) electricity that allows us to utilize the energy for common uses such as lighting or motors. Basic systems in the Northern Hemisphere are most effective when orientated due south and the opposite is true in the Southern Hemisphere in order to collect the most amount of the sun’s energy as possible.

Figure 1. Solar panels at March AFB

Solar panel systems utilized to supply partial or full power to a facility can produce a substantial financial return as a long-term investment. The benefits of solar panels will vary depending on the location of the Air Force Base. For instance, it may not be a cost effective energy source in climates that receive little sunlight due to frequent cloud cover or areas that receive a great deal of shade due to adjacent topography. The amount of direct or peak sunlight a site receives on a daily basis will be one of the largest factors affecting the rate of investment return. The specific design and size of a photovoltaic system depends on two fundamental variables.

First and foremost, the amount of peak sunlight the area receives on a daily basis since this directly affects the output capability of solar panels.

Figure 1. Solar panels at March AFB

The second factor influencing the system magnitude is the desired output from the system. Once these two variables have been determined the solar panel system design and cost can be determined. As a general guideline the formula below may be used to establish the payback period for a solar panel system in the United States:

Z / (Y * W) = X

Where:
Z = Cost of installed solar panel system.
Y = Annual usage of kilowatthours.
W = Average national price per kilowatthour in 2006 per the Energy Information Administration. See below for application guidelines:

● Residential   $0.104
● Commercial   $0.0946
● Industrial   $0.0616
● Transportation   $0.0954

X = Number of years to payback solar panel system cost.

If solar power is deemed a preferred energy source, select a system with a lifespan exceeding the X value.

Figure 2. Tracking solar panels at Nellis AFB

LEED EA Credit 2 offers three possible points for “On-site Renewable Energy” based on net metering of energy production.

The angle of sunlight changes with the seasons. To maximize the system output the solar panels should be adjusted as the sun changes position.

The following can be used as a rough guide for adjustment:

Early February: set the solar panel at the same angle as the latitude.
Early May: set the solar panels at the angle of latitude minus 15 degrees.
Early August: set the solar panel at the same angle as the latitude.
Early November: set the solar panel at the angle of latitude plus 15 degrees.

An automatic solar tracker can be used for a more meticulously efficient solar energy system. These are solar "pathfinders" that follow the sun's daily path to collect maximum power from the sun.

Benefits of Solar Panels

In addition to the financial rewards mentioned above, solar energy is also a viable method to reduce carbon based pollution. Regulations limiting the amount of greenhouse gases an installation may emit are steadily becoming more stringent. Pollution related to our facilities will undoubtedly need to be minimized in order to allow activities, such as aircraft flight, to continue unaffected in support of mission objectives.