Abstract
The Earth receives around 1000 W.m−2 of power from the Sun and only a fraction of this light energy is able to be converted to biomass (chemical energy) via the process of photosynthesis. Out of all photosynthetic organisms, microalgae, due to their fast growth rates and their ability to grow on non-arable land using saline water, have been identified as potential source of raw material for chemical energy production. Electrical energy can also be produced from this same solar resource via the use of photovoltaic modules. In this work we propose a novel method of combining both of these energy production processes to make full utilisation of the solar spectrum and increase the productivity of light-limited microalgae systems. These two methods of energy production would appear to compete for use of the same energy resource (sunlight) to produce either chemical or electrical energy. However, some groups of microalgae (i.e. Chlorophyta) only require the blue and red portions of the spectrum whereas photovoltaic devices can absorb strongly over the full range of visible light. This suggests that a combination of the two energy production systems would allow for a full utilization of the solar spectrum allowing both the production of chemical and electrical energy from the one facility making efficient use of available land and solar energy. In this work we propose to introduce a filter above the algae culture to modify the spectrum of light received by the algae and redirect parts of the spectrum to generate electricity. The electrical energy generated by this approach can then be directed to running ancillary systems or producing extra illumination for the growth of microalgae. We have modelled an approach whereby the productivity of light-limited microalgae systems can be improved by at least 4% through using an LED array to increase the total amount of illumination on the microalgae culture.
Highlights
Light The irradiance from the sun varies widely with wavelength and has been well characterised [1]
The spectrum of light passing through three different filters has been modelled as outlined above
This is in the range of what can be absorbed efficiently be algae and can be generated efficiently by Light emitting diodes (LEDs)
Summary
Light The irradiance from the sun varies widely with wavelength and has been well characterised [1]. There are two standard terrestrial solar spectral irradiance distributions [2] used in the testing of photovoltaic modules. There are two standard spectra defined in the standards [3] The first of these is the direct normal spectrum, which is ‘the direct component contributed to the total hemispherical (or ‘global’) radiation on a 37°-tilted surface’ [3]. The latter is a reasonable average for photovoltaics panels tilted towards the equator, in the United States of America and regions of Australia and applies to Sun facing 37°-tilted surfaces [3]. The standard defined in ASTM G-173-03 takes into account average values for the atmospheric composition, aerosols, water vapour and ozone content [2]
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