Combined heat and power: The key to dispatchable CSP?

CSP Today speaks with Luigi Crema, Scientific Coordinator of Digespo, from the Renewable Energies Environmental Technologies (REET) Unit at the Fondazione Bruno Kessler (FBK) in Italy, on where CHP can fit into utility-scale CSP.

By Rikki Stancich

Researchers from Italy’s Trentino-based Fondazione Bruno Kessler (FBK) will be presenting their research on a novel micro CSP-powered CHP unit at next week’s World Renewable Energy Congress in Abu Dhabi.

The aim of the project, which goes by the name of Digespo (Distributed CHP [combined heat and power] generation from small size concentrated solar power), is to create a modular 1-3 kWe, 3-9 kWth micro Combined Heat and Power (m-CHP) system based on concentrated solar power (CSP) and Stirling engine technology.

“The project involves the realisation of an integrated system that includes a number of 40cm x 2m parabolic trough, a receiver that has been specifically designed by the project partners, and a thermal fluid that flows in a hydraulic circuit at a temperature of around 350 degrees celcius, which comes into the Stirling engine for cogeneration of electric thermal power,” explains Luigi Crema, Scientific Coordinator of Digespo, and researcher at the Renewable Energies Environmental Technologies (REET) Unit at the Fondazione Bruno Kessler (FBK) in Italy.

“The m-CHP technology is able to provide a combination of electrical and thermal power, at 65 – 70% overall efficiency”, he adds.

Like any other CSP technology, the system relies on direct solar radiation. While this broadly rules out its use in Northern latitudes, Crema says that it could be used on buildings in the Mediterranean region and in other regional districts, such as the Northern Italian Alps with a southern exposition, given the high (70%-80%) of direct solar radiation.

Currently, Digespo is developing the base technologies, including the optics, the cermet layer, the evacuated solar tubes, and the Stirling engine, in cooperation with leading European developers and industries on the specific sectors. In this respect the project is open for collaboration with commercial players.  

According to Crema, the project is to be rolled out over three years. “The first half of the project will be completed by June 2011, when we will showcase the first prototype at the Hilton Hotel in Malta.”

The first prototype will be developed using more conventional technologies, while the second prototype, due for completion in 2012, will incorporate patented receiver, trough and Stirling engine technology. 

CHP for utility-scale CSP?

While Digespo is working on a micro-CHP unit, Crema says there is potential for scaling up the technology. “Such results may be extended over the limit of m-CHP,” he confirms.  

“Our intention is to work on market deployable technologies, provided of a full lifecycle analysis and of a low Levelized Energy Cost (LEC). It’s not yet clear what could be transferred at a big scale plant - for sure the optics, but not only,” says Crema. 

According to Crema, the efficiency of the m-CHP makes the CSP-CHP unit more competitive than standard standalone PV and CSP technology.

“ [Compared to standard PV] it has the same efficiency in the electrical fraction, but additional term on thermal, and [compared to] standard [Solar thermal] technology, the primary electrical energy values are more than only the thermal.”

Product innovation

The Digespo project, which was allocated €3.2 million in funding under the Energy Theme of the EU's Seventh Framework Programme (FP7) earlier this year, is one of several renewable energy pilots being rolled out by the Trentino-based research centre.

“Other notable pilot projects we are working on include biomass, geothermal and other renewable energy resources, as well as a thermal storage prototype using zeolites, or microporous crystalline solids,” says Crema.

Once the pilot projects are up and running independently of one another, the FBK will focus on how the projects can be integrated to deliver hybrid systems.

“The next step is to integrate the micro CSP and energy storage, or integrate the micro CSP and biomass units in a unique and compact co-generation system,” he explains. This next phase will likely take place from 2012.

“In the longer term we are looking at integrating these projects, at coupling solar and biomass, micro CSP and CHP. This could have added value in terms of reducing the cost of having coverage between sources and generated energy at the local level - and possibly even integrating with new forms of energy storage.”

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