INNOVATION & TECHNOLOGY

Disruptive Frontiers of Solar Energy

Solar energy can be considered the primary energy source by excellence. Its exploitation can be obtained through the direct conversion of light into electric power (photovoltaic technology).
The basic components of photovoltaic systems are solar cells made by a wafer a few tenths of millimeter thick or by a thin layer of semiconductor material (e.g. silicon) only a few microns thick, suitably treated. Presently, the cost of power generation from photovoltaic plants is still high (0.2-0.5 €/kWh).
In order to overcome the current limits of solar energy exploitation, it is crucial to introduce technologies that can reduce the quantity of silicon used, while producing the same amount of energy, and in the longer term to substitute silicon with polymer or organic materials whose production costs are significantly lower, with performances comparable to those of present commercial technologies.
Eni has launched several research activities in both new and emerging solar technologies that can potentially generate significant discontinuity. In particular, the activities involve solar cells based on organic materials and nanocomposites, the most promising given the potentially very low costs and highly scalable production processes. Eni also launched R&D activities that can lead to technical innovations in the Concentrated Solar Power field. For more details see Along with Petroleum Program

Eni signed a strategic alliance with MIT in Boston for research in energy-related fields. The core of the collaboration is the Eni-MIT Solar Frontiers Center, founded in July 2008 with the aim to produce and accelerate the development of advanced solar technologies, in which Eni will allocate 25 million dollars in five years. The research activities of the Center are focused on several areas: nanotechnologies and solar energy; Solar Energy and bio-mimetic approaches; artificial photosynthesis; new materials for Solar energy; new approaches to solar concentration; paper-thin photovoltaics.

PHOTOACTIVE MATERIALS
HYDROGEN PHOTO-PRODUCTION
csp

Scheme of photoactive material In 2008 in the laboratories of the Eni Donegani Institute, materials capable of working as spectrum converters were identified: they are able to increase the amount of solar energy that a photovoltaic device can convert into electric energy. The materials and the relative preparations are original and on these basis some patent applications are have been filed.
The photoactive plates were obtained trough low-cost deposition of a thin layer of acrylic material containing dyes onto commercial Plexiglas™. If illuminated with ultraviolet light, not visible by human eyes, these plates emit visible light, blue or red depending on the type of component used hence, working as a spectrum converter. The device increases the fraction of solar energy that can be transformed into electricity by a photovoltaic system.

Scheme of photo-production of hydrogen The production of hydrogen by means of solar energy (photo-production) is the other great frontier of advanced solar energy. This technology can represent a system for solar energy storage – intermittent by nature.
At the Eni Donegani Institute some materials including titanium dioxide and tungsten dioxide were synthesized in nanotube form, to convert light into chemical energy in the cycle of water-splitting into hydrogen and oxygen. Such procedure is original and a patent application has been filed. The components (photo-anode) of the photo-electrochemical cell (PEC cell) have been prepared in-house. This cell has been used to split water in oxygen and hydrogen in the gaseous state, by means of light irradiation.

CSP Scheme 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.