Researchers Explore Hybrid Concentrated Solar Energy System

Scientists from the Australian National University (ANU), Tianjin University in China and Chromasun, a Silicon Valley company with strong Australian connections, will join forces to create roof-mounted solar trough concentrator systems that they believe will be more cost-effective and efficient than previous models. The aim is to make the systems ideal for take-up in emerging economies like China and by budget and environmentally conscious consumers in developed nations.

According to ANU professor Dr. Andrew Blakers and Dr. Igor Skryabin, Business Development Manager for the Centre for Sustainable Energy Systems (CSES)  at ANU , the university has been actively engaged in the development of PV linear concentrator technology since 1995, developing its first major system — a 160 m² PV/trough concentrator — in 2000.

The system, which is grid-connected, uses a 2-axis collector that is 80 meters long and has 80 mirrors. Blakers explained that each mirror focuses sunlight on a strip of highly efficient solar cells. The cells are mounted on air-cooled receivers.  The system has a rated capacity of 20 kilowatts (kW).

Once that system was in place and working properly, Blakers said that the next step for the university was to use the "naturally produced heat in the photovoltaic linear concentrators by developing hybrid photovoltaic thermal technology."

To that end, a 300 m² Combined Heat and Power Solar (CHAPS) system was installed on a residential dorm that houses 98 students at ANU in 2005. Blakers said that the "two-in-one" heat and power system is comprised of eight collectors, hot water storage, hydronic in-slab floor heating and gas-fired boosters with a 40-kW inverter that interfaces the system with the grid.

Recognizing the potential market for much smaller devices, together with engineers from Chromasun Inc. and researchers from Tianjin University, ANU researchers are working on developing a cost effective version of a hybrid "microconcentrator" and a protoype has been developed.

The prototype measures 1.7 x 1.5 x 0.2 meters and incorporates seven mirrors that focus sunlight onto receiver tubes. Blakers said that crystalline Si micro PV cells — with an efficiency of about 20% under concentrated sunlight — will be fitted to the receivers to operate under concentrated x20 - x30 sunlight with water cooling being used to deliver heat to the hot-water tank.

He said that heat power output of such a system is typically 3 times larger than its electrical power output.

They are keeping costs low by using off-the-shelf products. "Traditionally, these kinds of systems have been built with expensive, specialist concentrator cells. We'll be modifying and upgrading commercially available non-concentrator solar cells, which should result in major savings," he said.

"We'll also be developing more efficient techniques to reduce the influence of moving shadows, which have the potential to eat into the amount of energy being generated," said Blakers.

International Partnership Key To Developing the Technology

There are huge advantages to working with research teams from across the globe, according to Skryabin, with each team bringing its own expertise to the table. While ANU has pioneered the system, "researchers from Tianjin University are strong in thermal and chemical engineering, which will assist development of the thermal part of a receiver," he said.

And for manufacturing expertise, "industrial engineers from Chromasun are developing cost-effective manufacturing processes."

Additional advantages of international collaboration also relate to market adoption of the technology. China is potentially the largest market for the system and has manufacturing expertise. Skrabin explained that since many roofs in Chinese cities are flat, it would be easy to install and maintain linear concentrators.

"Further, studies at Tianjin University identified price targets acceptable for the Chinese market. We believe that these targets will be met when the microconcentrator system are finally mass manufactured in China," he said.

It is too early in the development phase to give a final price for the system, but Skrabin indicated that he feels the price will be "competitive."

The project partners will also be identifying market opportunities in other APP nations (Australia, Canada, China, India, Japan, Republic of Korea and the United States) and countries where the cost of more expensive forms of solar-power technology presents a barrier to adoption.

Finally, the international collaborations provides access to a broader funds base. The Australian government has provided AUS $1.8M to fund the participation of the Australian team under Asia-Pacific partnership (AP6). The Chinese government will independently fund Tianjin researchers under its own AP6 program.