Case Study Frogs Leap, Rutherford, California

Originally founded on a spot along Mill Creek known as the frog farm, John Williams started frog’s leap in 1981 at the site of the historical Adamson Winery,

Fig. 5.51 The new 30 kW Satcon inverter

originally built in 1884. One of the key features of the property was the historical red barn which John and his team restored to its original state in 1994 using many of the original timbers. Frog’s Leap is set amongst 130 acres of vineyards in Rutherford. Using the best of Napa Valley’s organically grown grapes and the most traditional winemaking techniques, frog’s leap strives to produce wines that deeply reflect the soils and climate from which they emanate. Preserving the environment and stewardship of the land are core values for frog’s leap. Some of the practices that demonstrate frog’s leap’s commitment include the use of com­post and planting of cover crops to organically enrich the soil and dry farming to conserve water and reduce soil erosion. But it was not until 2004 that solar PV came to the fore (Fig. 5.52).

The 178 kWp DC photovoltaic installation uses 1,020 sharp (175 W mono­crystalline) modules facing southeast tilted at 5° angles. Covering 1/2 acre of the winery’s septic leeching field, the system does not use any valuable vine growing area but yet offers a suitable site with full solar access (Fig. 5.53). The high performance modules (16.2% cell conversion efficiency), are mounted on a GroundTrac™ ground mount racking system, which was supported on 328 con­crete piers (300-600 mm deep). Each panel weighs approximately 16.5 kg and has tempered, anti-reflective glass with a rust-proof aluminium frame. The installation is connected to a 225 kW Xantrex PV-225 inverter, located adjacent to the col­lector field (Fig. 5.54).

The annual output of frog’s leap’s photovoltaic system is typically 260,000 kWh, which is about 85% of the winery’s requirement. John Williams believes that 85% is beneficial in that it offers an incentive to reduce the winery’s electrical consumption through changing to more efficient lighting and altering the cycle times of some of the higher-use equipment, without breeching the PG&E imposed 100% ceiling. Good monitoring is essential to measure the energy dynamics. The PV system at frog’s leap is monitored using the Fat Spaniel’s monitoring solution. Real-time online monitoring with multiple views, SMS-based

alerts and web based triggers for automated module washing and cooling gives management live feedback of the system performance.

The system went live on February 2005, with the installation being completed in 11 weeks, which was within the 12 week estimate. At a cost of US $1.2 million, the overall cost to frog’s Leap was much less. With a 50% rebate from pacific gas and electric’s self generation incentive programme worth US $600,000 and with other available tax credits and deductions, frog’s leap’s investment in solar power will take less than 6 years to payback.

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