Disruptive Frontiers of Solar Energy

Some new materials have been synthesized recently at the Research Centre for Non Conventional Energies – Donegani Institute, which are able to work as spectrum converters. Besides being useful for a better fitting of solar spectrum to the absorption profile of photovoltaic cells, thus enhancing their energy production, they can be used in devices called "luminescent solar concentrators" (or LSCs). LCSs are thin sheets of transparent materials doped during the production phase with spectrum converting molecules. Thanks to these molecules, part of the light incident on the sheets can be converted and kept inside them to be fed at their edges to conventional solar cells, whose better exploitation implies more favourable economics. As part of the light can pass through, this kind of devices can be easily integrated in buildings, thus deploying "photovoltaic windows".
Materials and the relevant preparation routes are original and on this basis a number of patents have been filed.

The production of hydrogen by making use of solar energy (or hydrogen photoproduction) is another challenge of advanced solar. As a matter of fact, it would allow to circumvent one of the biggest drawbacks of solar energy, its intermittence, thus increasing the possibilities for its exploitation and diffusion. At the Research Centre for Non Conventional Energies – Donegani Institute, some materials have been synthesized, among which titanium dioxide and tungsten oxide nanotubes, which are used to build advanced components (photoanodes) of electrochemical cells, devices able to split water into hydrogen and oxygen with light. Starting from laboratory studies and results, a demonstrator of this technology at a remarkable scale has been recently built, which is able to work outdoor using the sunlight. The originality of the research activities has led to the filing of a number of patents.

Solar energy can also be exploited to fuel power conventional thermodynamic cycles: it is called Concentrated Solar Power or CSP. In this case vast fields of mirrors are used (taking up to 2-5 hectares for every MW installed) by positioning them so as to focus the reflected light on special receiving elements containing thermovector fluids inside (typically diathermic oil but also molten salts, like in the Enea's Archimede project), that consequently warm up. The fluid releases its thermal energy and is used to produce steam that, in turn, powers a classic steam cycle.
Parabolic mirrors with single axis tracking systems concentrate solar rays on a line where the receiving pipes are located; dish-like mirrors with double tracking focus rays on a spot where an external combustion engine is placed (e.g. Stirling engine). The concentration in this case is higher.
In both cases, the use of mirrors allows a high degree of concentration of the incoming radiation (from several tens of times to several hundreds of times) and reaching temperatures required for power generation (several hundred of degrees).These systems require high investments to be set up but relatively low operating costs as they do not involve any use of fuel and produce small amounts of greenhouse gases during operations.