On a sunny day, you can see the meters on the outside of the poultry house ticking as solar radiation is converted into electricity.

Inside, 60,000 hens go about their business, oblivious to the fact that their environment is being maintained without burning fossil fuel.

Or at least not nearly as much as a conventional poultry house would require.

Doug Wolgemuth of Wolgemuth's Farview Farms in Mount Joy had solar panels installed on the poultry house's south-facing roof three years ago.

He figured it was the right thing to do.

"It was convenient and it didn't interfere with any of my business," Wolgemuth said.

Back then, he had reason to believe the system could pay for itself in about seven years.

Federal and state grants paid $303,000 of the $544,000 total cost of installation.

And for every 1,000 kilowatt-hours generated by the system, Wolgemuth would get a renewable energy credit to sell for a sizable payment.

(Utility companies purchase the credits in order to fulfill state requirements that promote renewable energy.)

Lots of other farmers and businesspeople in the county and state came to the same conclusion as Wolgemuth did.

Livestock and poultry producers in particular took advantage of their long rooflines to have solar panels installed without using any land.

Wolgemuth, for instance, capitalized on the 380-foot-long layer house on the 2914 Homestead Road farm he works with his father, John.

"I could tell you a dozen places within two miles of here," Wolgemuth said.

They include farms, small businesses and even a private school.

Unfortunately, in one way it was too much of a good thing.

All those solar panels installed in the past few years created an oversupply of solar renewable energy credits.

As a result, Wolgemuth said he saw the $300 per credit he was receiving in 2010 drop to less than $50 last year.

At that point, "I looked at it and wondered why I did it," he said.

The price rebounded to $260 per credit recently, but it remains to be seen how future demand and other factors will affect prices.

And that uncertainty makes it hard for Wolgemuth to predict how long it will take for the system to pay for itself.

His best estimate now is eight to 10 years, compared to the seven years he originally calculated.

"I have to look at the whole picture to know if I'd do it again," he said.

The weather itself is another source of uncertainty.

A sunny day in winter can produce more electricity than on a typical summer day when haze blocks a lot of the sun's rays, Wolgemuth said.

But there have been an unusual number of cloudy days so far this winter.

The Wolgemuths keep a total of 90,000 laying hens in two houses.

The smaller house has no solar panels because it isn't situated as ideally as the larger house to catch the sun's rays.

The 10,000 square feet of solar panels atop the larger house generate about two-thirds of the operation's electrical needs.

The greatest electrical demands are from ventilation fans, especially in summer, and lighting inside the house.

The Wolgemuths, whose family has had the farm for 115 years, also use electricity to grind all their own feed.

For poultry farmers here, solar energy is the leading choice to replace fossil fuels, said Gregory Martin, Penn State Extension poultry specialist.

And despite the fluctuation in credit prices, the farmers who've gone solar have expressed little, if any, regret to him.

"Almost to a man, they feel like this was the right move," Martin said.

It's not known have many of the county's 5,462 farms have installed solar panels.

But many poultry farmers, whether they have solar panels or not, are using a host of other energy-saving techniques.

Some have installed new fluorescent lighting. Others have gone with more efficient direct-drive ventilation fans.

Some are looking at burning poultry litter for power.

"There's a lot of energy management going on," Martin said.