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Case Study: Frog's Leap Winery, Rutherford, CA

Case Study: Frog's Leap Winery, Rutherford, CA

Leeching Field
Aerial photo of Frog's Leap before

John Williams started Frog's Leap in 1981 at the site of the historic Adamson Winery, originally built in 1884. One of the key features of the property was the historic Red Barn, which John and his team restored to its original state in 1994, using many of the original timbers.

Preserving the environment and stewardship of the land are core values for Frog's Leap. "We think good ecology is good business," says Williams. Some of the practices that demonstrate Frog's Leap's commitment include use of compost and planting of cover crops to organically enrich the soil and dry farming to conserve water and reduces soil erosion. But until 2004, the idea of generating clean solar power for the vineyard was something that remained elusive, as Williams notes, "it always sounded good, but there was a lot of mystery around it."

Situation Summary

When Sunlight Electric first met the team at Frog's Leap, the winery was spending nearly $50,000 annually for electricity. The prospect of reducing consumption of fossil fuel-generated electricity was appealing, but the Frog's Leap team still had two big questions. First, "Could a compelling business case be made for solar?" and if so, "Could the system be installed over their leeching field?" – the only land unsuitable for growing Frog's Leap's organic grapes. The roof of the historic Red Barn was out of the question as was the Barrel Chai, which had hidden wires and conduit in it's 6" thick insulated roof.

Our Solution

In their first meeting in March 2004, Sunlight Electric demonstrated how, with available subsidies, an investment in solar power could offer a compelling return. With a rebate from Pacific Gas & Electric's Self-Generation Incentive Program and with other available tax credits and deductions, Frog's Leap's investment in solar power would take less than 6 years to payback.

With the business case proven, Sunlight Electric filed a reservation for a $592,000 PG&E rebate for Frog's Leap. While the rebate request was being processed, Sunlight Electric began to work up basic designs as well as worked with the County of Napa's Department of the Environment and with the designers of the leech field, Summit Engineering of Santa Rosa, to overcome any concerns about installing a photovoltaic system over a septic field.

Major Components

Solar's GroundTrac™
Solar's GroundTrac™ groundmount racking system

The heart of Frog's Leap's system designed is 1,020 Sharp 175-watt single-crystal silicon modules. These ISO9000-certified high-performance modules operate at 16.2% cell conversion efficiency, weigh ~37 pounds each, have tempered, anti-reflective glass and a rust-proof aluminum frame, and carry a 25-year warranty.

The inverter selected for this application is the Xantrex PV-225, one of the most reliable and efficient models on the market.


To fit the area over the leeching field – approximately 250' x 75' – and straddle the leeching lines without interfering with their operation, Sunlight Electric selected Professional Solar's GroundTrac™ ground-mount racking system, which only required 2' deep concrete piers that could be placed between individual leech lines.

The Result

Photo after installation
Photo after installation


In September 2004, Sunlight Electric's preferred installer - Power Independence Electric of Stockton - began the installation by laying, digging, and pouring 328 1' x 2' deep concrete piers to support the GroundTrac™ racks.

A worldwide shortage of PV modules caused a brief delay in the installation process, but Power Independence used that time to install the racking, inverter, transformer, and dig trenches for underground conduit.

In December, when the modules were delivered, Power Independence began installing them and completed installation and the system went live on February 9, 2005. All told, excluding the delay for the modules, the installation was completed in 11 weeks, on target with our 10-12 week estimate, and on budget.


The annual output of Frog's Leap's photovoltaic system will be 260,000 kilowatt-hours, about 85% of site usage, which presented Frog's Leap with a challenge. "We're using this opportunity to push ourselves to reduce our consumption through changing to more efficient lighting and altering the cycle times of some of our higher-use equipment," says Williams.


Like all Sunlight Electric systems, Frog's Leap's system carries a 5-year warranty on the entire system, a 10-year warranty on the inverter, and a 25-year warranty on module performance.

Performance Monitoring for Management and Marketing

While PG&E sends monthly statements on power purchased and power "sold" back to the grid, we wanted to give Frog's Leap's management a more real-time way to monitor the performance of their system as well as merchandise their investment in solar on site and online.

Using Fat Spaniel's monitoring solution, we deployed real-time online monitoring with multiple views, SMS-based alerts, and web-based triggers for automated module washing and cooling.

For more information about how Sunlight Electric can help your business be more sustainable, contact us at or 866-GET-SOLAR.

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Situation Summary
The Result