CSP-biomass hybrids: Utility-scale projects take root

Power providers hesitating to explore CSP have a new way to ensure the solar option won't abandon them during peak hours – by pairing it with a biomass boiler. CSP-biomass hybrid projects are now under development in China, the Mediterranean and northern Brazil.

By Bob Moser, Americas correspondent

Last month, US-based parabolic trough maker SkyFuel, announced its decision to partner with Brazilian energy developer BraxEnergy to build CSP-biomass hybrid plants in northeast Brazil.

SkyFuel will design and supply the solar concentrators, while BraxEnergy will coordinate and develop the project, which it has done for more than 3 GW of small hydro, biomass and biogas projects in Brazil.

When considering environments conducive to CSP, developers say key variables include annual humidity, rainfall, altitude and solar radiation intensity. With flexibility and creative thinking, cheap waste biomass can be found near almost any CSP hot-spot.

“We're convinced there are areas in northeast Brazil that are desolate, forgotten and non-productive agriculturally that can be taken advantage of for high radiation indexes, which makes sense for CSP,” said Fred Jordan, chief project development and procurement officer with BraxEnergy. “If you have coconut growers nearby, the partnership makes great sense.”

Discounted grid access for RE

Currently more than 75% of Brazil's electric supply is generated from hydropower. In a bid to diversify the nation’s energy matrix, the National Agency for Electric Energy is offering transmission discounts to other renewable sources.

BraxEnergy has already obtained licenses to begin construction on three CSP-biomass plants. The plans are on hold at the moment while the company pursues PPAs through a national energy auction planned for late this year. Jordan says the first CSP-biomass plant will be operational by 2013.

Waste biomass is available in almost any environment for CSP. The key is situating a plant close enough to the source to make it economical. BraxEnergy has done that in northeastern Brazil, planning its first CSP plant in the town of Coremas, Paraiba state, within 30 miles of multiple coconut farms that have few secondary markets for their shells.

Burgeoning biomass waste streams

Brazil passed a law in 2010 prohibiting the expansion of landfills around the country. This law has made coconut shells a sudden burden on farmers, which have few secondary markets for the shells.

BraxEnergy will sign coco farmers up for 20-to-30-year contracts, and install machinery on the farm to crush coco waste and press it into briquettes with high calorific rates, which farmers will then sell to the CSP plant. The coco briquettes have a calorific rate on par with sugarcane bagasse, Jordan says, the latter being a well-established biomass in Brazil that cane mills have burned for energy for decades.

The 50 MW hybrid power plant will run on CSP during the day, up until 7 pm. From 7-10:30 pm, power turbines will run on steam from boilers processing shell biomass.

In Brazil, government-contracted PPAs often only require a power provider to operate during peak hours, which ends after 10 pm. While BraxEnergy will be able to turn off production during late-night hours, it will demonstrate to the Brazilian government that it can deliver power on-demand, 24 hours a day if needed.

BraxEnergy will also capture CO2 from the power plant for transfer to greenhouses situated between rows of solar collectors. The gas will help grow a variety of produce for a population that, until now, experienced very little diversity in local fruits and vegetables.

Solar Euromed, a solar developer focusing on projects in South Europe, North Africa, India and the Middle East, is currently building a 12 MW CSP-biomass demonstration plant on the Mediterranean island of Corsica.

Officials there asked Solar Euromed to help solve the island's problems with power inconsistency. After realizing the island had great solar potential and a forest so overgrown that the biomass waste was posing a wildfire hazard, a CSP-biomass hybrid plant appeared to be a perfect solution, said Marc Benmarraze, CEO of Solar Euromed.

The company is building a hybrid power plant using Fresnel reflectors and a 9 MW biomass boiler. The island's annual forestry waste has been estimated at 250,000 tonnes, but Benmarraze says the power plant will only need 90,000 tonnes per year.

Solar Euromed has had to overcome some technological speed bumps to combine the use of two different boilers. Steam produced by solar boilers and biomass boilers have different response times, Benmarraze said. To harmonize the two, a small buffer of either pressurized water or steam storage is introduced in between, providing an answer for cloud variation.

“We have solved it and other engineers in power plants can solve it,” Benmarraze said. “It's nice to be able to combine two renewables and to ensure 24-hour (power) service.”

The Corsica plant is expected to produce 25 Gwh via sunlight and up to 50 Gwh from biomass. It's a modest amount, Benmarraze said, but helpful for Corsica and a potential example of success for others in the industry.  

China's Penglai Electric has partnered with eSolar for its CSP power tower technology, and is awaiting final approval from a national oversight commission for its first CSP-biomass hybrid plant. The commission’s decision on the 92 MW plant at the Yulin Energy Park in Shaanxi province, is expected by the end of 2011 northwest China, said Eric T. Wang, Penglai's executive vice president.

The Penglai hybrid plant will harvest the local sand willow tree for biomass, planted there decades ago by the government to prevent desertification. The company is already developing more sites in western China; with the understanding its first project will ultimately be approved.

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