Review of energy balance in raceway ponds for microalgae cultivation: Re-thinking a traditional system is possible David Chiaramonti a,⇑ , Matteo Prussi a , David Casini a , Mario R. Tredici b , Liliana Rodolfi b , Niccolò Bassi c , Graziella Chini Zittelli d , Paolo Bondioli e a RE-CORD and CREAR, University of Florence, Florence, Italy b Dipartimento di Biotecnologie Agrarie, University of Florence, Florence, Italy c Fotosintetica & Microbiologica S.r.l., Florence, Italy d Istituto per lo Studio degli Ecosistemi, CNR, Florence, Italy e INNOVHUB – Stazioni Sperimentali per l’Industria – SSOG Division, Milan, Italy highlights " Review of energy consumption in raceway ponds (RWPs). " Theoretical/CFD and experimental analysis of RWP in pilot plants. " Distributed and concentrated head losses evaluated and compared to literature. " An innovative low-energy consuming RWP design was developed. " Results validated by experiments: scale-up from pilot to demo considered. article info Article history: Received 8 February 2012 Received in revised form 3 June 2012 Accepted 18 July 2012 Available online 11 September 2012 Keywords: Microalgae Biofuel Raceway ponds Head losses Energy Mixing abstract The present work addresses energy consumption in raceway ponds (RWPs). This kind of systems are today the most utilized industrial plant for outdoor algae cultivation. The problem has been addressed combining theoretical correlations and experimental data. Head losses for conventional raceway ponds were evaluated, and the results were compared with data available in literature. Computational fluid dynamics was used to support the theoretical analysis. This study suggested possible improvements to the traditional RWP design: an Innovative Raceway Pond (IRP II) was therefore designed, built and oper- ated in parallel with a reference pilot RWP in a test site. Several modifications to traditional RWP design were implemented in the IRP II: the paddle wheel was substituted by a propeller, the water head was reduced and baffle boards were installed in the curves. To validate the new design, head losses and there- fore energy consumption in the different systems were evaluated, during cultivation experiments, with two microalgae strains. The theoretical and experimental study allowed a validated calculation, which showed the importance of concentrated head losses towards distributed ones. The analysis highlighted how these losses weight at different pond scales, suggesting possible improvements of the RWP energy performance – as achieved in the IRP II – through revised design for optimized mixing. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Mass cultivation of microalgae is considered as a possible mean for large scale advanced generation biofuel production. Microalgae for biofuels can be extremely efficient in terms of land-use, as the potential oil productivity per hectare is considerably higher than traditional seed crops [1]. Comparing algae to terrestrial crops, large differences in terms of biomass and oil production can be ob- served [9]: this potential has already been investigated in many experimental facilities [1,7]. These figures have been demonstrated by various authors and research groups; for instance, within the Acquatic Species Program a 10 g m 2 d 1 long term productivity and 15% lipid content were demonstrated at Roswell, NM (USA) [11]. These figures are however still well below the theoretical maximum based on the photosynthetic efficiency. Differently from chemical and other high-added value non-en- ergy products, biofuels define very precise constraints to the mic- roalgae cultivation system: in particular, biofuels must be 0306-2619/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2012.07.040 ⇑ Corresponding author. Address: RE-CORD and CREAR, c/o Department of Energy Engineering ‘‘S.Stecco’’, University of Florence, via Santa Marta 3, 50139 Florence, Italy. Tel.: +39 055 4796436; fax: +39 055 4796342. E-mail address: david.chiaramonti@unifi.it (D. Chiaramonti). Applied Energy 102 (2013) 101–111 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy