Are Hybrid Systems the Next Big Trend in Power Generation?

In 1999, hybrid gas-electric vehicles (HEV) were introduced to the U.S. market. HEVs combined the power of a combustion engine with the purity of an electric powertrain to meet consumer demands for balance between performance and fuel efficiency.

The concept, by all accounts, struck a deep chord with consumers. Today, HEVs are expected to account for a third of passenger vehicle sales in North America by 2025.

Is the power generation market headed down a similar path?

Hybrid power plants offer solutions to many problems and concerns faced by power producers, grid managers and consumers. In a hybrid system, clean but intermittent solar power can be paired with a reliable generator fueled with low-priced natural gas. Waste wood from timbering can be co-fired with waste coal to lower emissions. Wind power can be coupled with compressed air to create a reliable source of power for remote areas with limited transmission. Some hybrid projects combine diesel generator sets with solar PV technology.

Hybrid power generation systems provide a source of power that is both clean and consistent. They can provide power on demand. What’s more, they can be an effective tool in integrating more renewable resources into the grid while providing firm capacity to back up those variable resources.

But hybrid systems are either panned or praised in the world of power generation. Despite the obvious benefits, there are several drawbacks that create a concerning level of risk for hybrid power projects.

The benefits of renewable systems coupled with either a generator or energy storage depends greatly on the value of the firm capacity. If renewable power represents a small percentage of a system’s load, other generators in the system can easily make up the difference when the wind doesn’t blow or the sun doesn’t shine. Under this scenario, the firm capacity provided by the hybrid system is usually poorly valued.

Also, in remote locations, the power cannot be easily sold due to a limited number of potential buyers.

In this issue of Power Engineering, our cover story examines several combinations of technologies used in hybrid power plants and specific projects that have captured the industry’s attention with innovative systems that work in cooperation to provide clean and consistent power.

Nevada’s Stillwater hybrid plant is the world’s first power plant using geothermal power and two types of solar power – solar PV and solar thermal – to produce electricity. The project, which was officially inaugurated in March, is a cooperative system integrating a 33-MW geothermal plant, a 26-MW solar PV system and a 2-MW solar thermal facility.

Coupling the solar thermal facility with the geothermal plant boosted the output at Stillwater by 3.6 percent versus output from the geothermal plant by itself. The finding was confirmed by researchers at the U.S. Department of Energy.

“The lessons we are learning at the advanced geothermal-solar facility will be key to the development of other hybrid plants throughout the world,” said Francesco Starace, chief executive officer of Enel, the plant’s owner.

Meanwhile, researchers are developing new hybrid systems designed to unify power generation technologies you might not think about marrying.

Researchers at the Massachusetts Institute of Technology have developed a concept that combines two well-known power generation technologies: Coal gasification and fuel cells. The hybrid system could be twice as fuel efficient as a conventional coal-fired power plant, according to an article posted by MIT.

The syngas produced from the coal would be used in a fuel cell, where it would react with oxygen to produce electricity, the article stated. “Both processes operate at similarly high temperatures of 800 degrees Celsius or more. Combining them in a single plant would thus allow the two components to exchange heat with minimal energy losses.”

Comparing the market for hybrid power plants to the market for hybrid cars may not be perfect, but it’s a simple analogy full of good old-fashioned horse sense.