What Solar and Offshore Wind Can Do Together; When cities are running at full speed, a combined approach to renewables might be needed.

What Solar and Offshore Wind Can Do Together; When cities are running at full speed, a combined approach to renewables might be needed.

Herman K. Trabish, June 15, 2012 (Greentech Media)

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For cities along the coast, where the price of electricity is highest and demand, especially at peaking periods, is greatest, researchers are exploring the idea of combining solar and wind to offer a new solution to meeting peak demand.

“I assumed offshore wind is going to happen,” explained State University of New York atmospheric sciences researcher Richard Perez, whose previous research has been in the use of photovoltaic (PV) solar to meet peak demand.

Perez also assumed the Google-backed Atlantic Wind Connection, the offshore windtransmission backbone being developed along the Eastern seaboard, will provide adequate interconnection. “There is more and more serious talk that it is going to happen, so I just assumed a wind farm off the coast of New York City could plug into it.”

Pioneering projects that combine solar and wind are being developed around the world and researchers are beginning to quantify the synergistic value of such an approach. Because of his “study of the capability of dispersed PV to do peak shaving,” Perez was approached by co-researchers Jeff Freedman of AWS Truepower and Thomas E. Hoff of Clean Power Research to consider the potential of offshore wind.

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“The sun creates the heat wave that creates the peak demand and at the same time the sun can supply the power for PV. It’s a natural match,” Perez explained. Offshore wind, Freedman pointed out to him, works similarly. “When heat builds up on land along the coast with the cold ocean next to it, there is a natural updraft and a down draft at sea,” Perez said. “The wind comes in. Inland a few miles, there will be no wind but on the coast and immediately offshore there will be. If you have been on the beach on a hot afternoon, you will know this.”

The wind comes up a after the sun gets hot and lasts longer. “The sun will peak at noon,” Perez said. “Offshore wind will peak at 7 p.m. or 8 p.m., and the load peaks at 3 p.m. or 4 p.m. in big cities like New York, Baltimore, and Washington, D.C., so the wind and solar are really complementary.”

One of the key obstacles for offshore wind in the U.S. has been cost. But peak shaving -- this is called capacity value -- has the highest value of all electricity generation.

“If I were to do customer-side economics in New York City, where I get my peaking value from peaking reduction, I would say forget about offshore wind, because I’m better off using all PV,” Perez acknowledged. “However, if I see a bigger picture and I’m a regulator or a utility concerned with stability on the grid, I will pay a little more attention to what my options are for that later part of the peak.”

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The options, he said, are backup generation, demand side management or storage technology. “I have not done the optimization of cost between those options,” he conceded. “We just looked at the physical match.”

The synergy between offshore wind and PV is potentially valuable, Perez speculated, because so much of coastal cities’ peak demand is from commercial consumers. “If you put a PV system on top of a commercial office building, you will have a probability to cut demand by about 60 percent of your total capacity,” Perez said. In the New York City Con Ed and LIPA utility regions, “demand is worth about $25 per kilowatt per month in the peak summer months. That is a good chunk of cash flow.”

Whereas “PV’s economics are calculated on the customer side of the meter, wind’s are on the supply side,” Perez said. “But in the end, it is about putting electrons on the grid, and the meter is just a piece of regulatory equipment.” Ultimately, he said, “you have to care about what you bring to the grid in terms of value.”

By combining offshore wind and PV, there is much more than an increase in energy supply to be gained. There is also, Perez said, “grid capacity, transmission and distribution risk of outage minimization, and fuel price mitigation value.” The benefit to the grid at peak demand could very well exceed the cost of adding wind and PV generation and the capacity value of both combined would be higher than each individually.

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“What we found out,” Perez said, is that “the more you put those two technologies on the grid, the bigger the synergy effect. At very low penetration, like 1 percent or 2 percent, PV does very well alone; it doesn’t need wind. But as you gradually penetrate from 2 percent all the way to 40 percent, the synergy between them grows. When you reach that 30 percent or 40 percent penetration, you see that solar absolutely needs wind, because you need to address that later part of the peak in the day.”

The researchers’ modeling showed, as other modeling has, that there is “almost twice the capacity value with wind and solar than you would get with solar alone at 30 percent penetration. And compared to wind alone, it is huge, maybe five or six times.”

The economics of offshore wind in the U.S. is still largely speculation. Cape Wind was accused of having too high a cost for rate payers. But regulators found the price reasonable, given its wide range of as-yet unquantified values. Adding its potential capacity value to that calculation could make offshore wind an even more interesting proposition.

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