10 Dec Solar Austin @ the Farm!

This past Monday afternoon, Solar Austin ventured forth on its first field trip with a posse of about 50 people. The destination was the Webberville Solar Farm several miles east of Austin. The solar installation is operated by True South and has a 25-year PPA (power purchase agreement) with Austin Energy.

Main Features – The Webberville project features around 127,200 panels with a capacity of 30 MW AC (alternating current), or about 35 MW DC (direct current). Over a year the array produces approximately 50,000 MWh of electricity which is about the amount required to power 5,000 Austin homes. Individual panel capacities range from 270 W to 280 W. The PV array occupies about 280 acres and is divided into 19 subsections each with an inverter that converts DC from the panels to AC for the electric grid. The panels are mounted on a rotating, single-axis system that allows them to follow the sun from east to west across the sky. As the gears engage, it sounds a little like a very large rattlesnake shaking its tail. All the panels go horizontal at night and during high-wind situations. The mounting system was built to withstand 100 mph winds.

Operation & Maintenance – This solar farm has been in operation for nearly three years and has truly been a learning experience for all concerned. Steve Webb with True South's operations team says they are literally writing the operating manuals because Webberville didn't come with instructions. Some of their most interesting challenges include mowing, panel washing and inverter failure.

Mowing – The solar panels at Webberville are mounted six feet off the ground. Since prairie grasses and wild sunflowers often grow to eight feet tall on the site, a regular mowing schedule must be maintained about 10 months out of the year. The installation’s California-based designers visited the site during the summer drought a few years ago and under-estimated the height and amount of vegetation during wetter times. 

Washing – All the many thousands of panels must be washed at least once a year. Soiling can lead to about 15% loss in power output. The cedar pollen and dust create a gunky coating on the panels that they scrub off manually with pushbroom-like brushes. The site operators have not yet found an automated wash system that they can customize for the Webberville array's configuration. Another complicating factor is the lack of water supply on-site. The 127,000 gallons needed for washing are hauled in 500 gallons at a time by truck. The process takes about six weeks!

Inverters – The operators have dealt with a number of inverter failures due to the extreme heat conditions out on the open plain in the summer. The inverter housings could be air-conditioned. However, they estimate that would require around two-thirds of their electricity output, so enduring the occasional inverter outage is worth the trouble.

The True South operators definitely have a list of recommendations for other photon farmers on how to improve the design and operation of utility scale solar in Central Texas. Hopefully they will shared their list with the folks developing Austin Energy's forthcoming community solar installation!

* Photos #1 by Griffin Gardner and #2 by Jeffrey Phillips, UT Webber Energy Group

* Photos #3 and #4 by Shannon Wisner, Austin Energy