The US Military is sitting on a potential 7GW of untapped solar power capacity in the Mojave and Colorado Deserts, according to a recent Department of Defense report that analyzed the applicability of a variety of solar technologies across seven military installations.

Initially nine military installations were analyzed, seven in California and two in Nevada, taking in sites used by the Army, Navy, and Air Force as well as the Marine Corps. By comparing competing solar energy technologies on such a large scale, the report (titled Solar Energy Development on Department of Defense Installations in the Mojave and Colorado Deserts, available in PDF on the ESTCP website) gives insight as to the commercial viability of solar power in the US today.

Though building roofs and car park shades were identified as potential homes for solar collectors, ground sites make up the vast majority of the potential solar sites analyzed in the study. These areas were subject to GIS analysis, overlaying up to 40 variables per location. Suitable sites were assessed for their technical and economic feasibility; six solar electricity-generating technologies were examined, including crystalline photovoltaics, thin-film photovoltaics, and concentrating solar thermal systems.

Due to the lack of "significant solar development potential" in the Nevada bases, they do not contribute to the 7GW of potential solar capacity identified by the study. Additionally, the report found that, for the seven bases in California, 96 percent of the land was also unsuitable—excessive slopes, environmental conflicts and the presence of exploding things being among the reasons for exclusion. That left 125,000 acres of land, of which 100,000 were deemed either "likely" or "questionably" suitable for solar, and 25,000 "suitable."

The seven California military installations analyzed were the Marine Corps Air Ground Combat Center (Twentynine Palms), Marine Corps Logistics Base Barstow, Naval Air Weapons Station China Lake, Chocolate Mountain Aerial Gunnery Range, Naval Air Facility El Centro, Edwards Air Force Base, and Fort Irwin.

The 7GW of potential solar capacity relies upon two assumptions. The first is that all of the suitable land would be put to use for solar generation; the second is that 25 percent of the likely and questionable land would also be utilized. The report characterizes 7GW of capacity as the "maximum" potential for solar development across the sites. Note that the capacity of a solar power plant is, as for any power plant, the theoretical maximum output under ideal conditions. A capacity factor is used to describe the actual output of a facility over time, as a proportion of the capacity. Capacity factors for solar technologies are typically cited at around 20 percent for areas with high levels of solar radiation, such as California.

To contextualize 7GW of potential solar power, the largest solar facility of any kind is currently the 354MW-capacity Solar Energy Generating System, also in California's Mojave Desert. To tap the solar potential identified in this report would require infrastructure equivalent to roughly 20 times this facility, albeit distributed across several sites.

The report finds that development of the 125,000 acres is economically feasible, though only to private investors able to benefit from current tax incentives at both the Federal and State level. Direct DoD funding of solar projects "would be financially unattractive in all cases," the report suggests. More positive was the finding that the government could receive a potential $100 million per year through rental payments and reduced power costs as the result of solar development across the bases.

In the unlikely—if not implausible—event that all 125,000 acres were to be developed, the report says that the potential electricity generated would be equivalent two thirds of the DoD's nationwide demand. Less than half of that land would need to be developed to meet all of the DoD's NDAA 2010 renewable energy targets, namely that 25 percent of facilities energy use be supplied by renewable sources. Development of a mere six percent of the identified land would cover its EPAct 2005 goals.

The report gives an interesting insight into the commercial viability of current solar technologies. Fixed-mount crystalline-silicon PV was identified as the technology with the greatest capacity across all bases, but single-axis tracking PV (i.e. panels that turn to follow the sun) was projected to yield the greatest returns on investment. The 7GW solar capacity identified by the report is based on tracking systems being used—resulting in a calculated capacity of 7,147MW across the seven bases. The installed capacity of a fixed system was found to be 51 percent higher, at 10,811MW. But this is not to say a fixed system would generate more electricity. Tracking systems have a lower capacity than fixed systems because fewer cells fit into a given area, but thanks to their ability to track the sun, they will operate nearer their capacity more of the time.

The significant majority of the potential 7,147MW of solar capacity was confined to Edwards Air Force Base (3,481MW) and Fort Irwin (2,629MW), with NAWS China Lake trailing behind (960MW). Twentynine Palms offers a little better than nothing (77MW), which was more than could be said for Chocolate Mountain and El Centro (zeroes for all solar technologies, both).

Meanwhile, concentrating solar thermal systems were judged economically non-viable due to higher installation costs, though the report concedes there is some doubt due to a lack of such projects in the US in recent times.

The report highlights the "increasingly important" contribution of solar power to backup power systems, potentially reducing DoD reliance on diesel generators to power essential systems in the event of power cuts. It recommends that initial solar expansion on military installations (most of those analyzed already have 1 to 2MW of solar capacity) should be specifically targeted at backup systems.