Your daily dose of Photovoltaic Technology Developments and Solar News

News Feeds | Newsletter | Advertise | About Us | Subscriptions

Order your copy of Photovoltaics International Edition 1#

Photosynthesis meets photovoltaics: Perpetual Power installs ‘solar orchard’ at Limoneira

29 October 2008 | By Tom Cheyney | Chip Shots

One of nature's metabolic processes, photosynthesis, has been a crucial solar-sourced element of Limoneira's fruit and nut growing business, giving life to the 115-year-old company's thousands of acres of citrus, avocado, pistachio, and cherry groves in California. Now the Santa Paula, CA-based firm has put the sun to work in another way, taking advantage of the photovoltaic effect.

A 1.2-MW "solar orchard," comprised of 6400 Mitsubishi Electric PV-UD 185MF5 (185-watt-peak, rated at 13.4% conversion efficiency) ground-mounted modules, has been designed and installed by Perpetual Power (P2) on 5.5 acres of prime Limoneira real estate at its bucolic Ventura County location, north of the Los Angeles megalopolis.

The aerial view of the site (see below) reveals the PV system divided into four sections. If one assumes a relatively equal portion of modules per quarter-plot, that's about 1600 panels, or on a cell basis (with 50 156 mm² slabs of silicon per box), some 80,000 polycrystalline pieces turning photons into electrons (part of the 320,000 cells comprising the entire system). Since each 65 x 33-inch module weighs 17 kg, the total weight of the glass/aluminum/silicon units comes in at 108.8 metric tons--plus the additional heft of the racks, inverters, and other miscellaneous components.

No information is available on the ratio of fruit and nut trees in the arboreal orchards to the number of modules or cells in the solar orchard. Also missing are the numbers for expected PV electricity generated per bushel of harvested lemons.

A pair of 500-KW Satcon inverters help turn the PV electrical juice from direct to alternating current. The P2 Oasis mounting rig, which has an optional feature that permits the array's tilt to be adjusted seasonally to maximize power output, is one internally developed by the system integrators, according to P2 founder, Mark Palamountain.

Once fully operational, the solar electric system will produce about 2 million kilowatt-hours, covering about a third of Limoneira's annual energy needs. Palamountain said in an email that regional utility Southern California Edison "has fully connected the system, and it is producing energy to the grid as we speak."

He also noted that the project, which took four months to build, "was the first of its kind [to be] built to LEED (Leadership in Energy and Environmental Design) specifications and is awaiting certification." In a Mitsubishi case study, details of other PV-related aspects of the LEED work emerge.

"Underneath the solar array," the document says, "Limoneira has planted native vegetation as a cover crop to minimize dust on the modules that could affect the system's performance. The native vegetation allows the company to avoid spraying weed killer on the soil, and miniature sheep graze the vegetation to control the height of the plants."

Data on the industrywide use of miniature sheep or other livestock in agricultural PV project maintenance programs remain sketchy.

limoneira_view

Unlike some other similar-scale projects in California, the Limoneira system is not part of a power purchase agreement, according to the P2 exec. His customer "decided to lease this system through bank financing," which still let it have the system installed with no upfront costs. P2 "guarantees system performance and provides system maintenance for the duration of lease period," according to the case study.

"By farming the sun, we're going to vastly reduce our energy costs," said Harold Edwards, Limoneira's president and CEO, in a statement. "That’s especially important given how fast the price of power is rising. Clearly, this investment will continue to pay off for decades. And, we found yet another way to demonstrate that there's no conflict between sound business decisions and being an environmentally conscious, sustainable enterprise."

The agricultural company must be pleased with P2's efforts to date, since Palamountain told me his firm is "currently working on another 1-MW Ag project for Limoneira in Ducor, CA (in Tulare County), which is targeted for their water pumping needs."

For native Southern Californians of a certain age, we have bittersweet memories of verdant orange, lemon, and avocado orchards once blanketing areas that now sprawl with suburban subdivisions and shopping malls.

The future holds a different vision, one of acres of PV power systems on everything from remaining agricultural lands to warehouse and residential rooftops to utility substations, making sage use of the area's most abundant source of sustainable energy--that world-class Southern California sunshine.