Surprising and not-so-surprising discoveries from the OG&E Mustang Solar Farm

OKLAHOMA CITY - It's been three months since OG&E President Sean Trauschke and Gov. Mary Fallin 'flipped the switch' on Oklahoma's first community solar farm located at the site of OG&E's Mustang Power Plant. Since then, the company has learned a great deal about solar.

'As we discover how solar operates within our system, we're learning how it can align with our commitment to maintaining a diverse generation portfolio that balances affordability, reliability, safety and environmental responsibility,' said Keith Mitchell, Chief Operating Officer for OG&E.

Scott Milanowski, director of engineering innovation and technology at OG&E and project manager for the Mustang solar energy pilot, monitors the farm's output daily.

'The biggest eye opener for me has been the way solar energy fluctuates continually,' Milanowski said. 'If a cloud moves between the sun and the panels, the farm's capacity drops about 80 percent within seconds. Once the cloud moves, the farm operates at full capacity again.'

However, although cloud cover can be detrimental to solar output, sometimes a few clouds in the sky are a good thing for solar operations, according to Milanowski.

'On a partly cloudy day, when there is blue sky with scattered cumulus clouds, the sun's rays actually bounce off the clouds, and the indirect sunlight, in addition to the direct sunlight, helps the farm produce more energy. This is referred to as the 'edge of cloud effect,'' he said.

Another factor affecting solar farm operations is the temperature. Extremely hot days have reduced the efficiency of the solar farm.

'You might expect the farms to be more efficient on hot days, when the sun is higher in the sky, but extreme heat negatively affects the output of our solar panels,' Milanowski said. 'The farms actually can operate better on cooler summer days.'

As winter nears, with the sun lower in the sky, OG&E expects energy from the solar farm to be reduced as well.

'The winter also is a time when demand on our system is lower, since there will be no air conditioners running in colder weather,' he said. 'In addition, as we 'fall back' from Daylight Saving Time to Central Standard Time, the peak time for solar has shifted as well, from 12:30 p.m. to 2 p.m. to 11:30 a.m. to 1 p.m.'

He added that, with customer peak demand during the summer being at 5 p.m., the need for diverse generation is important to help supplement solar customers' needs.

'At our farms, solar energy output is highest at times when our customer demand during the summer is just ramping up. So, having a solar system tied to and supported by the grid, with a diverse generation portfolio, is important to maintaining a continuous, reliable flow of electricity, whether customers install rooftop solar or eventually purchase solar power from us.'

The smaller of OG&E's two solar farms has the panels installed on stationary racks, while the larger farm is using a tracking system that follows the sun.

'It's interesting to see how the tracking system can extend the time that the solar panels can produce at nearly full output. At 5 p.m., when the output of the fixed system is dropping off significantly, the tracking panels are still nearly at full output, better serving our peak demand times in the summer.'

There is still much to learn. OG&E will continue to monitor the 10,000 panels at its solar farms as well as the rooftop installations at two of its facilities to determine the best and most reliable use for this technology.

'I believe all our customers will benefit from what we're learning through our study,' Milanowski said.

OG&E currently is developing a solar power product, similar to its wind offering, and is exploring possibilities for adding more solar to its system. Those interested can learn more about renewable energy options in Oklahoma at http://oklahomasenergyfuture.com.

OG&E, a subsidiary of Oklahoma City-based OGE Energy Corp. (NYSE: OGE), serves approximately 819,000 customers in Oklahoma and western Arkansas. OG&E, with about 6,900 megawatts of capacity, generates electricity from natural gas, western coal, wind and solar.

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