Installing PNNL’s system in front of natural gas power plants turns them into hybrid solar-gas facilities. The system uses solar heat to convert natural gas into syngas, a fuel containing hydrogen and carbon monoxide. Because syngas has a higher energy content, a power plant equipped with the system can consume about 20 percent less natural gas while producing the same amount of electricity.
This decreased fuel usage is made possible with concentrating solar power, which uses a reflecting surface to concentrate the sun’s rays like a magnifying glass (pictured). PNNL’s system uses a mirrored parabolic dish to direct sunbeams to a central point, where a PNNL-developed device absorbs the solar heat to make syngas.
About four feet long and two feet wide, the device contains a chemical reactor and several heat exchangers. The reactor has narrow channels that are as wide as six dimes stacked on top of each other. Concentrated sunlight heats up the natural gas flowing through the reactor’s channels, which hold a catalyst that helps turn natural gas into syngas.
The heat exchanger features narrower channels that are a couple times thicker than a strand of human hair. The exchanger’s channels help recycle heat left over from the chemical reaction gas. By reusing the heat, solar energy is used more efficiently to convert natural gas into syngas. Tests on an earlier prototype of the device showed more than 60 percent of the solar energy that hit the system’s mirrored dish was converted into chemical energy contained in the syngas.
With the US increasingly relying on inexpensive natural gas for energy, this system can reduce the carbon footprint of power generation. The US Energy Information Administration estimates natural gas will make up 27 percent of the nation’s electricity by 2020. PNNL says that its system is best suited for power plants located in sunshine-drenched areas such as the American Southwest.
The amount of natural gas used to generate electricity this year is significantly lower than last year at this time, when low natural gas prices led to significant displacement of coal by natural gas for power generation, according to figures released earlier this month by the US Energy Information Administration.
By late March, wholesale natural gas prices at the Henry Hub trading center were back to $4 per million British thermal units, a dollar or so higher than a year ago. In response, electricity generators used 16 percent less natural gas this March compared with March 2012. Coal recovered some market share as as result of the natural gas price rise, the EIA said.