On October 13, 2016, MA-50's Erik Haukdal gave the Sustainability Performance Office (SPO) a tour of Forrestal’s rooftop solar array. 

The main array was installed so DOE Headquarters could lead by example implementing renewable energy in their buildings. Several smaller arrays demonstrate solar technologies, serving awareness and education purposes.  Since 2008, about 100 tours have been given to high school groups, college groups, boy/girl scouts, members of Congress, local government officials, foreign dignitaries, and even president Obama!

When the main array was installed in September 2008, it was the largest in DC clocking in at 205 kW, enough to power 40-50 homes.  The crystalline silicon panels were manufactured by Sun Power, yielding 18% efficiency.  The panels are durable with the ability to withstand hurricane winds and golf-sized hail stones. 

The cost of solar is falling dramatically.  In September 2008, all 891 panels cost about one million dollars, not including the cost of labor.  Today, the same array would cost around four hundred thousand dollars.  Solar energy is becoming much more affordable and the technologies themselves have also improved, making them more efficient.

In 2008, it was estimated that the breakeven period would be 70 years. The panels themselves need to be replaced every 30-40 years depending on the level of wear. However, due to rising conventional energy prices, the breakeven point may be much sooner than 70 years.  In fact, it is projected that DOE could break even before they would need to replace the panels in a few decades.

In addition to the main array, Forrestal also has its “technology showcase” consisting of four other types of solar panels.  These are swapped out as newer technologies emerge for educational and research purposes.  They include:

1. Crystalline silicon panels also manufactured by Sun Power.  These cells were built into the frames, which are tilted and interlock to hold the entire array down without having to drill through and build a support system.  They offer a 5% tilt, which can increase efficiency.
2. Crystalline silicon panels manufactured by Suniva that are 20% efficient.  What makes these cells interesting however is that their manufacturing process has eliminated certain steps, making their cells cheaper to purchase.
3. Thin-film cadmium telluride cells produced by First Solar that can be purchased at a lower cost but yield lower efficiency.
4. Global Solar manufactured cells that are printed onto a flexible medium, making the cells bendable under the tempered glass.  These are also not as efficient as some of the other products on the market, yielding only 10-12% efficiency, however they are more versatile due to their malleable nature.

SPO is thankful to Erik Haukdal and MA-50 for allowing us the opportunity to learn more about efficiency at Forrestal, have an up-close look at the solar array, and even take in the gorgeous DC sights from up high.