Government incentives, high utility bills enhance solar electricity’s draw

By Vicky Boyd


Since the 1970s, Markus Bokisch has dreamed about farming the sun. With the completion of the first phase of a two-part rooftop solar energy system in 2003, the Victor, Calif.-area winegrape grower realized those dreams.

“This is a long-term, economical and political solution to the oil situation,” Bokisch says. “We try to farm with conservation and sustainability, not only in relationship to our inputs into the vineyard but also energy.”

He completed the second phase in 2004 and currently has 3,000 square feet of photovoltaic panels on his farm shop roof producing 22.5 kilowatts of electricity.

In addition to reducing his operating costs, the solar generation system also lessens Bokisch’s contribution to the San Joaquin Valley’s air pollution problems.

The total number of California growers who use solar generation to provide electricity on their farms is unknown.

“It’s becoming more common in vineyards as the time goes by, but currently it’s more common with wineries,” says Joe Browde, Petalume, Calif.-based project manager for the California Sustainable Winegrowing Alliance.“Bottom line, it’s starting to grow, and we as an organization would like to see it pick up a lot more.”

Pacific Gas and Electric Co., which serves California north of Bakersfield, provides incentives for solar generators that are hooked into its electricity distribution grid. So far, most of the agricultural interest in solar generation has come from wineries, packinghouses, cold storage and food processors, says Patsy Dugger, PG&E program manager for agriculture and food processing in San Francisco.

“If you include wineries, there’s a lot going on in solar right now,” Dugger says.

Currently 85 agricultural generators feed solar-produced electricity into PG&E’s grid, but the utility doesn’t differentiate between size or type of operation.

Nationwide, determining photovoltaic generation by agriculture is difficult.

The U.S. Department of Energy in Washington, D.C., tracks photovoltaic shipments from manufacturers, but it doesn’t break down recipients by industries, says spokesman Jonathan Kogan.

In the Midwest, small-scale agricultural solar energy generation is common, but feeding excess energy into a power distribution grid is rare, says Don Jones, a Purdue University agricultural engineering professor in West Lafayette, Ind.

At least half of the Indiana producers with cow-calf operations use 7- to 10-watt photovoltaic systems to generate power for electric fences. Some producers also use solar energy to power small livestock watering systems.

They typically store the excess electricity in batteries for use on cloudy days.

“They use it where they don’t have 120 [volt AC] power, so it would be fairly common,” Jones says. “It’s used for convenience in Indiana and mostly every place east of the Mississippi. Because of all of the cloud cover, you won’t find any major energy production.”

Go figure

Bokisch’s goal was to generate about 80 percent of the electricity needed for the ranch foreman’s house, a 25-horsepower well that irrigates 109 acres of winegrapes and the farm’s machine shop, which includes lighting and power tools.

To determine what size solar system he needed, Bokisch studied utility bills from the previous three years to calculate his average monthly electrical use. He also had a consultant conduct a pump test on his well to identify any inefficiencies and suggest ways to improve them.

Then he studied how much daily sunlight he could expect to receive each season, discounting for weather, such as rainstorms and the thick winter tule fog.

He figured he could count on an average of 5.5 hours of daily solar generation. Each Shell solar module comprising the panel was rated under laboratory conditions to produce 140 or 150 watts, depending on the model. Under field conditions, Bokisch says the modules produce only about 90 percent of the rated value.

In the end, he decided he needed about 3,000 square feet of photovoltaic panels to produce 22.5 kilowatts of electricity.

The roof of his machine shop—with some modifications—was an obvious location for the solar installation, Bokisch says. Although the panels weigh only 5 pounds per kilowatt, they nonetheless were too heavy for the building’s original support structure. So Boskich had to add another “I” beam in the middle to handle the added load.

Farm shop roofs typically have little slope to them. But the panels needed to be at a 27-degree angle for the most efficient generation.

He used supports to raise the panels to the prescribed angle and built a false back on the north side of the shop to prevent winds from ripping away the panels.

Utility bills reflect solar production

The solar panels and installation cost about $10,000 per kilowatt. With state and federal energy generation incentives and accelerated depreciation, the net price was about $5,000 per kilowatt.

All of the electricity Bokisch generates flows past a meter and into the PG&E power grid.

Electicity Bokisch uses for the pump, the foreman’s house or shop tools comes from the grid and is metered as any other agricultural user.

Bokisch subscribes to a time-of-use metering program, which charges more during peak periods and less during off-peak periods.

The same is true for what he generates. He receives 13 cents per kilowatt-hour during peak periods and only 7 cents per kilowawtt-hour during off-peak hours.

“Farming is a very elegant application of solar,” Bokisch says. “You use most of the electricity in the off-peak hours, yet you produce most of the electricity during on-peak hours. You sell that energy into the grid when they need it the most.”

At the end of the year, PG&E trues up his bill. If the price of the electricity he used exceeds the price he received for generation, he pays the difference. But if the price of the electricity he generated exceeds what he used, he receives no payment under California Public Utility Commission rules.

“We produce about 80 percent of what we use, but dollar for dollar, PG&E gets free energy from us,” Bokisch says. “It’s not a lot—about 1 to 5 percent of all the energy we produce is excess in terms of dollars.”

Originally, Bokisch figured the system would pay for itself in about seven and a half years. With rising electrical costs, he says the payback period should be slightly shorter.