Electrical costs and power reliability are critical elements in sustaining agriculture’s operations. But the state’s high cost of electricity is putting these industries at a disadvantage in a competitive global economy.

By Lyn Corum

Three California businesses operating in the agricultural food processing industry have installed the state’s largest privately-owned solar systems. Each system is different and we will take a look at tracking versus stationery solar panels. But on a larger scale, taken together these projects raise questions about what the impacts will be on local distribution grids after large numbers of distributed energy resources are added and what their influence might be on power quality.

California’s agricultural economy is the largest in the US and accounts for 7% of the state’s economy. It produces more than half of the nations fruits, nuts, and vegetables, making it highly dependent on electricity for irrigation and post-harvest processing, according to the California Energy Commission.

A packaging plant and two agricultural food processing companies in California’s food belt, the San Joaquin Valley, have each installed 1.1-MW solar systems to reduce their dependence on utility power, not only to save money but, in one case, to deal with power quality problems. Peninsula Packaging makes containers for fruits and vegetables, Paramount Farms, grows and processes pistachios and almonds, and P-R Farms grows and processes peaches, plums, apricots, nectarines, oranges, and apples.

Most agricultural operations have focused on reducing energy use through energy efficiency, as evidenced by the research and funding supplied by the CEC and the Department of Energy. Furthermore, distributed generation on farms has usually been installed to run irrigation pumps and reduce utility electricity purchases. So the large solar installations at the agricultural food processing plants profiled here are unusual.

Solar applications in the San Joaquin Valley have a particular environmental advantage. The valley suffers from considerable air pollution, second only to that of the Los Angeles basin. The pollution is due to industrial activities and regional weather patterns. Field burning, once very popular, is highly controlled, and the state has worked to keep local biomass power plants operating when market economics threatened to shut them down.

Peninsula Packaging
It’s fitting that a manufacturer transforming recycled materials into packaging for fruits and vegetables would install one of California’s three largest privately owned solar systems—1.1 MW of photovoltaic panels on a tracking trough system. The company bought land next door to its Exeter plant to lay out the array. But the company is not beating its chest about the tie-in, according to Ed Byrne, general manager at Peninsula Packaging.

At the time Peninsula Packaging started up in 2002, the owners were already discussing alternative energy sources, Byrne says. It took two years to settle on solar. The area is not windy, so a wind turbine was out. With the cost of natural gas at the time, cogeneration and microturbines were not appealing. “We felt the link; in terms of sustainability the benefits of solar outweighed the other options,” he says. Sometime in the future a gas-fired fuel cell may make sense, Byrne says, to allow the company to use the waste heat for process cooling in addition to supplementing the power generated by the solar system.

That solar system is a virtual solar farm. PowerLight Corp., a subsidiary of SunPower, installed the 4,000 Schott photovoltaic (PV) panels spread out over 10 acres in about six months in 2006. A tracking system allows the panels to follow the sun as it moves across the sky, thereby maximizing the amount of sunlight that is converted to electricity. An online energy management system allows Byrne to track solar power production daily and monthly.

Even though the system had been operating for seven months—since November 2006—it was hard to judge changes in the company’s electricity bills, which were still unacceptably large, owing to the fact that the business has been growing, Byrne explains. The real test for the solar system will be summer months, Byrne says, in terms of operational security when production is increased.

Peninsula Packaging operates 24 hours a day, seven days a week, and the solar system contributes about 30% of the electrical load during the hottest part of the day, “when the grid is in most jeopardy and when the most polluting generation is operating between 3:30 and 6 p.m., and most particularly when temperatures increase rapidly,” says Byrne.

During these periods, it is crisis time for plant operations. The equipment is voltage sensitive, Byrne explains, and if the voltage dips one-tenth of a second, it spells disaster. “Dirty power is our enemy,” he says. That slight dip will shut down major equipment, and it might be down for three hours. Tens of thousands of dollars of products might be ditched, devastating the company’s bottom line.

Operational security, therefore, is of prime importance. “When customers want a product, they have to have packaging right this minute,” says Byrne. Consequently, the solar system’s power is directly fed to the most important pieces of equipment. The extruder takes the raw material—plastic cornflakes produced by grinding up used water bottles—and melts it, then extrudes it into sheets of film. The second major piece of equipment, known as a thermalformer, heats the sheets and shapes them into the forms the customers have ordered.

The solar system cost $7.8 million, and the company borrowed $4.4 million to pay for it. It paid another $300,000 for the land next door, on which the system was installed. Southern California Gas Co. awarded the project $3.4 million in state rebates, which went to PowerLight so that Peninsula’s cash outlay would be less. Savings on electricity bills will pay off the loan, Byrne says. A $1 million federal tax credit will reduce the cost further, and the company will enjoy $1 million in accelerated depreciation. He says $500,000 will be deducted from taxes in the first year.

PowerLight’s Tracker System
Jeff Shingleton, of Shingleton Design LLP, designed the tracking system that was installed in Peninsula’s solar system. Now licensed to PowerLight, the tracker involves a limited number of moving parts. He describes the system, explaining that a computerized microprocessor controls the motors that drive the panels.

There are six tracker gear motors on Peninsula’s system, and each, with its own controller, drives 200 kW of panels independently of other trackers. The tracker gear motor is attached to an industrial screw jack, and the linear motion translates to rotary motion. Each controller has a global positioning satellite (GPS) device which determines the latitude and longitude of its location along with the time of year. It then calculates where the sun is in relation to the horizon, and tells the motor when to move. If the GPS screws up, Shingleton says, the controller will put out an alarm.

Shingleton says it could be possible to create a fiber optic network on a similar system to control the trackers from a remote computer. Currently, in order to monitor performance, all energy production information is downloaded every morning. “We’ve made predictions of what the optimum performance should be and collected weather data, and if the system is not doing that, it indicates a problem,” Shingleton said. A technician also walks through the system to regularly check status lights and make sure the motors are operating.

Scheduled maintenance occurs once a year and includes injecting grease into the screw jacks. Large bearings also need to be greased. Shingleton says the tracker gear motors are lubricated at the factory and sealed for the lifetime of the motor.

Shingleton argues that tracker systems are cost-effective on smaller systems down to 50 kW. However, they become more cost-effective with the larger solar systems.

Paramount Farms
Paramount Farms started operating its $7.5 million solar system located on eight acres of flat land near its processing plant in May 2007. SolarCraft built and installed the 8,208, 136-watt amorphous thin-film panels manufactured by United Solar Ovonic. Located in Lost Hills, CA, Paramount is a vertically integrated farming business. It grows almonds and pistachios on 110,000 acres of orchards and sells them nationwide.

Paramount declined to be interviewed for this story, but instead referred us to Chris Bunas, SolarCraft vice president. Bunas says Paramount invested in the solar system because of its commitment to sustainable business practices. Its Web site, www.paramountfarms.com, bears this out. The system will avoid about 2,600 tons of greenhouse gases annually.

Bunas says the fixed-mount system took six to seven months of planning and preparation and four to five months to install. The amorphous thin film technology used in the panels is new and has a high heat production rate in dusty environments that reduce sunlight, such as in the San Joaquin Valley, where Paramount Farms’ system is located. He says temperatures there reach 110°F, and a silicon panel will not work well at temperatures above 95°F, whereas the inherent characteristics of the amorphous thin film produce more power at higher temperatures—as much as 10% more. He added that this type technology is much less affected by the tilt of panels.

Bunas says the system has real-time computer monitoring and he is already seeing 10% more energy output than a typical silicon-based system provides.

The number of solar DG systems currently operating in parallel with the grid is small.

Tracking, or Fixed-Mount?
Bunas says the hot discussion item emerging in the solar industry is solar tracking systems versus fixed-mount systems. “Nobody knows if more energy will be produced with a tracking system,” he says. “Some claim a 40% benefit with tracking, but there’s no science proving it.”

To evaluate the claims, SolarCraft is installing two 50-kW systems side by side at Jacuzzi Winery in Sonoma to monitor performance and maintenance of the two types of systems. SolarCraft is eating the increased research and development costs for the project, Bunas says.

SolarCraft will install a single axis tracking system on one of the Jacuzzi Winery systems. It will have one actuator motor moving up to 300 kW on heavy-duty bearings. For safety, the system goes flat if heavy winds start blowing. Bunas adds that if you have a 50-mile-per-hour wind all day, you should have a fixed system.

The systems will be monitored from SolarCraft’s office, where it can receive e-mail error messages, Bunas says.

Bunas cautions that a tracking system will require more maintenance, since any time there are moving parts there will be breakage. Bushings and bearings need to be maintained, he adds, whereas maintenance of a fixed system is limited to washing the dirt and dust off once a year.

P-R Farms
PowerLight completed installing the 1.1-MW roof-integrated solar system at P-R Farms in July 2005. The lightweight building-integrated PV system cost $6.4 million. Rebates reduced the price for P-R Farms to $3.2 million, according to owner Pat Ricchiuti. The roofing assembly, which holds 7,744 solar tiles, was installed on 98,100 square feet of an existing roof membrane covering the farm’s packing house.

The solar cells are made of solid-state semiconductors converting sunlight into direct current. As with all systems, the DC output is converted into alternating current by inverters, then stepped up to three-phase electricity by isolation transformers and fed into the building’s electrical distribution system.

The system supplies 50% of the power for the packing facility, which processes about 1.5 million boxes of the farm’s fruit production annually. Ricchiuti says PowerLight’s analysis in 2006 revealed the solar system is producing 20% more electricity than it was projected to provide. He expects the system to be paid off in eight years. It will reduce carbon-dioxide emissions by 10,000 tons over 30 years.

Ricchiuti said his electricity bills are now about 20% to 30% of what they were before the system was installed. His monthly electricity bills for the packing house are running from $2,500 to $3,500 a month, down from $12,000 to $15,000 per month. The cold storage unit is on a separate meter, although under the same roof. Its electricity bills are now from $6,500 to $8,500 per month, down from $25,000 to $35,000 per month. He financed the farm’s portion of the system cost and makes six $65,000 payments a year for five years.

Ricchiuti’s reasons for buying the system: Environmentally it is the right thing to do, saving energy allows others to use it, and it had a reasonable payback. He says he experienced only occasional power quality problems before the solar system was installed, and it did not contribute to his decision to install the system.

Ricchiuti does acknowledge that his system goes down when the grid goes black. He will be investigating installing a switch to disconnect from the grid when that happens so that some critical portions of his packing process can continue to operate.

DG’s Impacts on Grid
A great deal of work has gone into developing equipment and standards to allow California’s utility distribution grids and customers’ distributed generation (DG) systems to operate together. Mike Gravely, a research program manager in the Public Interest Energy Research (PIER) group at the California Energy Commission (CEC), says interface requirements have been developed at the California Public Utilities Commission. Now interconnections between a customer’s solar system, microturbines, fuel cells, or wind turbines and the utility’s grid are routine. Furthermore, as new technologies are developed, standards will continue to be updated, Gravely says.

Roger Dugan, a senior technical executive at the Electric Power Research Institute (EPRI) in Knoxville, TN, is an acknowledged expert on distribution systems. He has studied the impacts of solar installations on the distribution system in Sacramento Municipal Utility District’s (SMUD’s) service territory, and he says research is continuing.

The number of installed DG systems, including solar, currently operating in parallel with the grid is small. “There will be a substantial increase in distributed generation connected to utility distribution systems over the next decade,” Dugan says. However, as the numbers increase, especially with the expansion of the California Solar program, issues may develop. California’s goal is to have 3,000 MW of new solar systems
installed by 2017.

Problems may occur as the numbers of DG systems increase, and Dugan addresses some of these in a paper he coauthored entitled, “Distributed Generation,” published in the March/April 2002 issue of IEEE Industry Applications Magazine. Instead of repeating the engineering details here, let it be said that Dugan and his coauthor describe how DG systems operating in parallel to a distribution line can negatively impact overcurrent protection, instantaneous reclose, ferroresonance, reduced insulation, transformer connections, and ground faults.

In a recent conversation, Dugan explains that the best a 1.1-MW solar system can do is add 40%—or 440 kW—of effective capacity to a distribution system. Given a typical distribution feeder rated to handle 8 MW, an effective capacity of 2 MW contributed by solar or other DG systems may create voltage regulation issues for anywhere from 10% to 40% of the neighborhood customers tied to that distribution line. It depends on the length of the distribution line, Dugan says. If the 1-MW system is at the end of a 10-mile distribution line, customers could probably sense when the system comes online. But if the DG system is close to the substation, customers won’t be affected. Dugan also found in his SMUD study that customers who had installed solar were upset that it would not serve as backup during blackouts. Since they operate in parallel to the grid, the solar systems will likewise be affected by the blackout. If it is to continue operating during the blackout or brownout, the solar system needs a battery backup. But the cost for the backup will double the cost of the solar system, Dugan says.

Power Quality Issues
The agricultural food-processing industry is undergoing a transition to a highly automated production process at the same time it is competing in a global marketplace. Two-thirds to three-fourths of the industry is now automated, according to the CEC. The high degree of precision in manufacturing processes due to automation has increased agricultural productivity. However, the advances in the use of digital controls, advanced sensors and integration of electronics make operations susceptible to power quality problems such as voltage sags and harmonics, causing severe economic losses.

Can a large solar system solve Peninsula Packaging’s voltage sag problems? The EPRI’s Dugan says there are cheaper ways to handle power quality. He suggests equipment that borrows reactive power from other sources like DVAR or American Super Conductor, or Statcom.

The CEC’s Gravely says that power quality in general is a big deal in industrial environments. Since electricity has become one of the most critical elements of successful agricultural food processing–plant operations, the industry is just as affected by power quality as is the semiconductor industry, Gravely says.

Apparently in agreement with Dugan, Gravely says the processing plant has to have equipment and a backup system to deal with voltage sags, which can be caused by an accident as basic as that of a car hitting a distribution pole. Harmonics and interference from several pieces of equipment may also cause power interruptions lasting only milliseconds. Voltage sag occurrences are equally brief in nature—capacitor or resister failures account for 80%–90%—and equipment is available to ride through these voltage sags, Gravely concludes.

The CEC sponsored research by the EPRI, which monitored the food processing equipment in 2003 at Del Monte’s plant in Modesto, CA. It recommended such equipment solutions as the dynamic sag corrector, the dip-proofing inverter, or a constant voltage transformer. The study estimated the cost to implement such solutions on all production processes at the Del Monte plant to be about $74,000.

Gravely also recommends that when automated equipment is to be purchased, plant managers should specify that the equipment must be able to ride through voltage sags. Making designers design more robustly will save money in the long run, he concludes. Equipment that doesn’t respond appropriately to sags will eventually disappear from the market.

California-based writer Lyn Corum specializes in energy topics.

DE - November/December 2007