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Integrated solar energy harvesting and storage devices

University of British Columbia

Large scale storage of electricity is a vital requirement for the realization of a carbon-neutral electricity grid. This thesis provides a study of integrated solar energy conversion and storage systems in order to increase the efficiency and reduce the utilization cost of solar energy. The efficient performance of photogalvanic cells relies on high dye solubility and selective electrodes with fast electron transfer kinetics. A new configuration is proposed for photogalvanic cells that removes these impractical requirements. Instead of illuminating the device through the electrode a new vertical configuration is employed with light coming between the two electrodes. This way, the light absorption and hence electron generation is spread through the depth of the device which can be adjusted according to the concentration of the dyes to absorb all the incoming photons even with low solubility dyes and slow electrode kinetics. The proposed configuration is mathematically studied and a numerical model is built for detailed analysis that gives practical guidelines for working towards device parameters with high power conversion efficiency. The analysis suggests that upon the realization of highly selective electrodes and an improved dye/mediator couple, an efficiency higher than 13 % should be achievable from the new configuration compared to 3.7 % at best using the conventional approach. Storage however in this system will be challenging due to the characteristic recombination times of dyes and mediators in the same phase. For significant and long-lived storage we designed and demonstrated an integrated solar-battery structure based on two relatively well established technologies of the redox flow battery and the dye-sensitized solar cell. The cell consists of a sensitized electrode in a redox flow battery structure. The design enables independent scaling of power and energy rating of the system thus it is applicable for large scale storage purposes. An areal energy capacity of 52 μWhcm−², charge capacity of 1.2 mAhL−¹, energy efficiency of 78 % and almost perfect Coulombic efficiency are observed for the integrated cell. These values show a 35 times increase in charge capacity and 13 times improvement in areal energy density compared to similar devices.

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2015-04-20

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52899

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/