Academic studies show the theoretical value of co-located wind and solarwhen characteristics like resource intensity are complementary. Pilot projects in the U.S. and other countries have validated the research. Power purchase agreements (PPAs) for utility-scale hybrid projects are in place in Oregon and Arizona. But the concept may not become a marketplace reality until regulatory and policy barriers are overcome.

In theory

Hybrid projects are defined as two or more fuel sources that share a point of interconnection and are dispatched “as a single generation entity,” according to Peters. Theoretically, such projects could allow renewables to participate in capacity markets and be stored for use during peak demand periods that would otherwise require natural gas peaker plant generation.

“Wind and solar are the two cheapest options for new generation, but their production is variable and they don’t always generate when the grid needs it most,” Rice University Associate Professor of Civil and Environmental Engineering Daniel Cohan told Utility Dive.

Wind’s nighttime generation and solar’s daytime output can address some of those limitations, Cohan’s research on the Texas grid showed.

Co-located wind-solar projects, sited at or near the same substation, are also technically feasible and can be economically viable, he said. But sites needs adequate wind and solar resources, suitable land and available transmission capacity, and those three conditions “won’t be everywhere,” he added.

Adding low priced solar to wind projects in places with high wind capacity like West Texas and Iowa makes sense because transmission capacity is likely to be available for solar during the day, he said.

Wind-solar-storage would also likely be economically viable in those places, because those projects would require less storage, which is still not as cheap as wind and solar.

Though there are not many co-located hybrid projects in service, such projects do exist at different levels of development and operation across the U.S., Asia and Australia, Global Wind Energy Council (GWEC) Director of Market Intelligence Karin Ohlenforst told Utility Dive.

A key to growth will be demonstrating that the unique values of hybrid projects, like delivering capacity when it is most needed, are not just theoretical, she added.

Utilities and developers are beginning to move those values from theory to practice, starting with solar-storage hybrids.

In practice – utilities

“Utilities from coast to coast, in places that would never be expected to be interested in solar-storage hybrids, are going after” hybrid projects, Invenergy VP of Storage Derek Price told Utility Dive. “The solar-storage hybrid is going to explode in the marketplace.”

“We have a large number [of hybrid projects] under development for 2020 to 2023 delivery,” Price said at the conference. “As the cost of solar drops, greater acceptance of the technology by utilities will follow quickly.”

Invenergy expects almost all of its installed solar to be retrofitted with storage, he added. Arizona Public Service (APS) “calls it ‘solar after sunset’ and sees it as having a big impact on its cost curve.”

APS announced a groundbreaking 65 MW solar plus 50 MW battery storage hybrid project in February 2018, which is scheduled to come online in 2021, replacing natural gas peaker generation. The price remains undisclosed, but came out of a competitive all-source solicitation.

The utility doubled down on solar-storage hybrids in its February 2019 Clean Energy Initiative, which will add 850 MW of battery storage at new and existing solar projects by 2025, APS spokesperson Jenna Rowell emailed Utility Dive. And another APS solar-storage solicitation was issued April 3 for 100 MW of solar and 100 MW of storage, the next stage of a build-out toward 1 GW of solar-storage capacity by 2025.

In Oregon, Portland General Electric (PGE) announced an even bigger breakthrough in February. Wheatridge, the first co-located U.S utility-scale wind-solar-storage hybrid project, will include 300 MW of wind, 50 MW of solar and 30 MW of 4-hour duration battery storage, and is expected to be fully online by 2021, PGE spokesperson Steven Corson told Utility Dive.

PGE will pay $160 million to own 100 MW of the wind. NextEra Energy Resources will build and operate Wheatridge, own the balance of the project, and sell the output to PGE under a 30-year PPA. Offers, including NextEra’s undisclosed winning bid in the all-renewables solicitation, came in at prices “competitive with conventional resources,” Corson said.

“The levelized cost of energy (LCOE) from new wind resources is expected to be below the LCOE of a combined cycle combustion turbine,” PGE’s draft 2019 integrated resource plan reported. And “in futures with low technology costs and high renewable development across the West, batteries may be cost competitive with traditional thermal resources.”

To maximize the return on the federal investment tax credit, the PGE project’s solar generation will charge the batteries, Corson said. “That will allow the solar-storage component to smooth the wind’s variability. The draft plan may lead to another all-renewables solicitation for non-emitting capacity resources.”

With both the APS and PGE flagship U.S. hybrid plants yet to come online, they do not take the hybrid concept far beyond theory. But developers are making big plans.

In practice – developers

GE has built and tested two hybrid projects over the past five year as part of subsidiary GE Renewables’ focus on integrated hybrid projects. The companyrecently estimated the global market for hybrid power to be at least $1.47 billion by 2024.

In Minnesota, it paired a 2.3 MW turbine with 500 kW of solar and in India, paired a 1.6 kW turbine with 223 kW of solar.

Efficiency is key to development. Each project had an approximately 5% energy production improvement over projections for individual resources. “Even a small increase warrants the investment,” Jean-Claude Robert, GE’s hybrid solutions lead, told Utility Dive.

To further drive hybrid project efficiency, GE also developed a “hybrid plant control solution.” The digitally-based technology enables the hybrid system to produce “renewable MWhs” rather than “wind MWhs or solar MWhs,” Robert said.

La Plana, a comparable Siemens Gamesa hybrid pilot built in Spain, combines an 850-kW wind turbine with 245 kW of solar, the company’s head of hybrid systems for the Americas Christine Grey told the Windpower session. Batteries were added to further test Siemens’ Hybrid Plant Controller.

Hybrids are attracting worldwide interest, with India leading, Robert said. A January 3 solicitation from the Indian state of Andhra Prahdesh would procure 5,000 MW of wind-solar hybrids through 2023. The solicitation specified the resources must “be configured to operate at the same point of grid connection.”

“Large, grid connected wind-solar PV systems” increase the “optimal and efficient utilization of transmission infrastructure and land,” the solicitation said. They also create “better grid stability” by reducing “the variability in renewable power generation.”

Countries “leading the charge on hybrids have less technically advanced systems [and] want as much renewable energy as they can get to meet their growing demand, but need steadier delivery,” Robert said. “GE is working with customers around the world to develop scale projects in real time, as we speak. In the U.S., the emergence is likely to be in solar-storage hybrids in California to address solar over-generation.”

U.S. developer Enel Green Power expects wind-storage growth in Texas to similarly address over-generation from wind, Enel Business Development Director Chris Hickey told Utility Dive.

The developer is also considering where it may be practical to add solar at existing wind sites, “especially in Texas and other high wind production areas in the Midwest,” Hickey said. It is “an emerging solar market” because “grid operators dealing with transmission congestion when wind production rises have ample transmission capacity at times of high solar production.”

Both Enel’s 497 MW High Lonesome wind project and its 450 MWRoadrunner solar project, now under construction in Texas, are candidates for storage additions, he said. “And every new Enel project is being evaluated for storage, whatever the renewable technology, because utilities looking for renewables plus storage is a growing trend.”

It is clear “this can be done technically and there is value in it,” GE’s Robert said. “A hybrid wave is coming. The only missing piece is regulations to drive development by rewarding project developers for delivering that value.”

Barriers

Barriers such as interconnection, dispatch and compensation are “the big issue,” but there are “paths forward,” InterTran’s Peters said at the Windpower conference.

“Many places do not have an interconnection process for hybrids,” she said. And the grid operator needs a model for dispatch in real-time operations, “which often does not exist or, if it does, may not be optimized.”

Additionally, “most systems do not have a hybrid project capacity accreditation,” Peters said. “They have accreditation for solar and wind and many operators are developing a capacity accreditation for battery storage, but it is nonexistent for hybrid projects.”

Some system operators are more progressive than others, she said. The MidContinent Independent System Operator (MISO) “has good rules on hybrid interconnection” and on “additions to existing projects.” In contrast, PJM’s rule requires any fuel source change to “go back through a years-long queue process,” even if “it will not require a modification to the interconnection.”

MISO’s generator replacement policy and surplus interconnection policy, both under review by the Federal Energy Regulatory Commission, also represent current best practices, Peters said.

The surplus policy allows a project not using its full interconnection capacity to add more nameplate generation without going through the queue process again, she said. Its generator replacement policy can allow “a new resource to replace an existing one” without a burdensome re-application delay.

Session speakers Jack Kiroff, the Enel Green Energy VP of Regulatory Affairs, and Siemens’ Grey endorsed Peters’ assessment.

Hybrid-specific revisions of federal tax credits for wind and solar are also needed, Kiroff said. And “the Clean Peak Standard, which provides compensation for generation delivered to the grid during peak demand periods, should be implemented more broadly to recognize the value of clean electricity delivered when it is needed most.”

“I can’t do any projects until the policy and regulatory issues are settled,” Grey said. “But if we can overcome at least some of these challenges, there will be more hybrid projects built.”

If obstacles to “a more unified national policy on hybrids” are resolved, wind-solar-storage hybrids “can be built in six months and the shift to low-cost, zero-carbon resources can happen much faster,” Peters