|M.Sc Student||Kruger Nimrod|
|Subject||Frequency Conversion of Solar Radiation for Energy|
|Department||Department of Energy||Supervisor||Professor Carmel Rotschild|
|Full Thesis text|
Solar energy, in all its forms, is essentially the cleanest and most renewable source at our disposal. Sunlight as the source of energy in photovoltaic cells or bio-diesel crop is inexhaustible, but lacks in continuity and flux density. We also note that no single energy conversion system can efficiently convert a broadband source such as solar radiation, meaning that an inherent mismatch exists between the solar spectrum to the energy harvesting system. This leads to loss in absorption of the harvesting system or inefficient energy conversion of major parts of the solar band.
Here we present three projects aiming to tackle this problem. By using a combination of fluorescent materials and energy transfer between them we alter the incoming solar spectrum, better fitting it to the system in question.
Algae grown under adequate illumination, and with steady CO2 supply, show great potential in applications of bio-diesel production, but are not as yet cost effective. We propose increasing algae energy absorption, by sunlight manipulation, increasing growth rates and reducing production costs. In collaboration with Prof. Zvy Dubinsky of Bar-Ilan University we present a novel device concept able to efficiently convert the inefficient sunlight to energy better utilized by the algae.
The second project aims to increase photovoltaic efficiency by photon-splitting. Any photons with energy twice that of the PV’s band-gap can potentially contribute double the current, but up to the closing of this work attempts to utilize this wasted energy were fruitless. We present our progress in broadband photon-splitting using the frequency conversion scheme described early in this work.
The third project, as the counter part of the second projects, aims to increase photovoltaic efficiency by photon fusion. Many of the incident solar photons are mid infra-red to far infra-red photons, with energy that is too low to be absorbed and converted to practical energy. Here we present a novel method of harvesting this energy by “Entropy-Driven Up-Conversion”, where very low frequency photons (10.6um wavelength) are efficiently converted to near infra-red photons (1um wavelength). We present the experimental work done to identify this phenomenon.
The work presented here on algae light treatment, down-conversion and up-conversion, are the initial steps and lay the foundation to future progress in each of one of these fields.