Conversations about renewable energy often come down to a comparison—solar versus wind, for example, or hydroelectric versus geothermal—as though one technology, alone, could provide the single answer to our need for safe, emissions-free electricity production. However, a new utility-scale approach to renewable-energy generation is turning this idea on its head, bringing together multiple solutions at the same generation site. As shown by several such projects now coming online in the United States and around the globe, pairing technologies on the same site can improve overall efficiency and, as a result, its bottom line.
Called “hybrid” power plants, these projects tend to take one of two shapes. In some cases, they house co-located installations that operate independently. In other situations, though, the two technologies may work in tandem to produce a single electricity output more efficiently than either approach could on its own.
Co-located projects can benefit by sharing transmission capacity and the connection equipment that ties them to the larger transmission system. This is important because renewable-energy resources often are located remotely, and building the transmission lines to reach them can be an expensive proposition. Using the same line to carry more power for longer periods of the day means line developers (often different companies than those running the wind and solar farms) can earn a better and faster return on their investments.
This advantage is boosting the bottom line for Invenergy, a Chicago-based energy company that flipped the switch on a new 22-megawatt (MW) solar farm—the Midwest’s largest—this past July. The farm is next to its 210 MW Grand Ridge wind farm in LaSalle County, Ill., which was put into service between 2008 and 2009. Additionally, the company announced in late December that it will be adding 1.5 MW of battery-based energy storage capacity to the wind facility to help balance intermittency issues.
Similarly, European developer EDF Renewable Energy recently added the 130 MW Catalina solar farm to its adjacent 140 MW Pacific Wind farm in Kern County, Calif. According to EDF figures, pairing wind and solar in this installation will put transmission lines to use up to 60 percent of the time, versus 35–40 percent of the time with wind alone. The company also is planning to add up to 100 MW of solar generation to its plans for the nearby Avalon wind project, which is now making its way through the permitting process. Both of these efforts are taking advantage of a new substation Southern California Edison has installed as part of its larger Tehachapi Renewable Transmission project, which has opened access to Southern California’s high desert and its vast wind and solar resources.
Depending on the future of the wind energy production tax credit (PTC) and investment tax credit (ITC), both of which survived the most recent legislative battle at the fiscal cliff and will remain in place for another year, such solar additions to existing wind farms could become more common. Wind developers still need the PTC to turn a profit with new installations, and without it, new project launches are expected to slow considerably. However, new solar projects will retain their own ITC until 2016, so more solar panels may be sprouting in the wide-open spaces surrounding wind turbines.
But wind isn’t the only partnering option for solar-power proponents. The technology also is being married to conventional fossil fuel plants in a team effort to create the steam that drives traditional turbine generators. In 2010, Florida-based FPL added this kind of solar capacity to its existing Indiantown Martin plant. At 3,705 MW, this is the nation’s largest fossil-fuel plant. The company installed 190,000 parabolic troughs across 500 acres adjacent to the main generating station. These troughs concentrate the sun’s heat onto oil-filled tubes running across their faces, warming the fluid to 748°F. This fluid is pumped to a steam generator attached to the plant’s existing turbines. FPL estimated this 75 MW system cost 20 percent less than a stand-alone version would have, thanks to the shared transmission line and steam generator.
GE is working with (and investing in) a Pasadena, Calif.-based startup called eSolar to create a new approach to utility-scale solar/natural gas generation. The two companies are building a hybrid plant in southern Turkey using a different kind of solar collection. Instead of heating up distributed tubing, the television-sized solar panels will focus their light toward the boiler topping a 250-foot-high tower. The panels, called heliostats, will be controlled by software to track the sun as a way to maximize the solar heat they deliver to the boiler. The resulting steam will be piped to the steam turbine, where it will supplement steam produced from the waste heat of an adjacent gas-fired jet-engine turbine. A 22-MW wind farm will power the plant’s operations and feed its own excess capacity into the grid.