Enel Moves Hybrid Renewables Forward Again with World’s First Biomass and Geothermal Project

Italy’s Enel Green Power is entrenching itself as a global leader in hybrid renewables engineering and construction with another announcement of a global first. In November, the company revealed that it would build a €15 million, 5-MW biomass plant to boost the Cornia 2 geothermal plant’s 13-MW capacity in Castelnuovo Val di Cecina, Tuscany, as “the first plant in the world to use biomass to heat geothermal steam and boost the energy efficiency and output of the geothermal cycle.”

Francesco Venturini, CEO of Enel Green Power, commented at the announcement that “Hybrid technologies are the new frontier of renewable energy in our efforts to optimize performance, and this facility, which offers an innovative approach to integrating biomass and geothermal energy, is a replicable model that can open new prospects for the development of energy, the economy and employment for local communities.”

This project marks the second global first for Enel Green Power, which racked up its initial hybrid goal in May 2012, when it started up the world’s first solar-geothermal hybrid project near Fallon, Nev., at its Stillwater complex. A $70 million, 26-MW solar addition was built to complement its existing 33-MW binary-cycle, medium-enthalpy geothermal plant. The geothermal plant uses electric submersible pumps in the wells to pressurize and extract geothermal water, and the pump energy usage is partially offset by the 81,000 fixed polycrystalline-silicon solar photovoltaic panels in the solar farm.

Not resting on its laurels, Enel Green Power announced plans in August of this year to build a 2-MW concentrated solar power (CSP) unit at Stillwater. The company suggests that “This is the first hybrid plant in the world able to bring together at the same site the continuous generating capacity of binary-cycle, medium-enthalpy geothermal power with solar photovoltaic and solar thermodynamic.” SkyFuel, of Arvada, Colo., is the technology provider for the parabolic trough solar field being integrated into plant. 

The company has signed a Cooperative Research and Development Agreement (CRADA) with the National Renewable Energy Laboratory (NREL) and Idaho National Laboratory (INL), under the oversight of the U.S. Department of Energy Geothermal Technologies Office (GTO), “to model the combination of geothermal and CSP systems, validating simulated results with real-world data from the Stillwater facility. The fruits of this work will be used to explore and quantify the potential benefits of different operating strategies and integration schemes, with the goal of opening doors for the development of future hybrid renewable energy facilities.”

In hybrid combinations, naturally-occurring low to moderately-heated geothermal water — with a temperature below 400°F — and a secondary or binary fluid, with a much lower boiling point than water, move through a heat exchanger, causing heat from the geothermal water to flash the secondary fluid to vapor, used to drive turbines and generators. MIT in 2006 estimated that the United States has extractable, low temperature, enhanced (needing production enhancement) geothermal resources (EGS) that would generate some 200 zettajoules. One ZJ is equal to one sextillion (1021) joules. Annual global energy consumption is approximately 0.5 ZJ, according to Wikipedia.

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Charles W. Thurston is a journalist who specializes in renewable energy, from finance to technological processes. He has been active in the industry for over 25 years, living and working in locations ranging from Brazil to Papua New Guinea.

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