Solar thermal power

Solar thermal power and cooling are primary candidates for fulfilling the Abu Dhabi government’s commitment to renewable energy sources. Solar thermal technologies have emerged as a promising candidate for large scale power generation due to their capability to supply power constantly during day and night. This is a clear advantage compared to wind and solar photovoltaic. Furthermore power generation cost from solar thermal technologies is expected to decline while generation capacity increases. Continued progress in solar thermal technologies will move the levelised electricity cost (LEC) towards parity with alternative carbon free electricity generation from nuclear power and power from coal or gas with carbon capture and storage.

Solar thermal power generation cost/resource tradeoffs are site specific and for this reason local expertise needs to be provided for the industry to flourish. The mandate of LENS is to fill this expertise gap by educating a generation of young researchers who can contribute to the deployment of solar thermal energy applications. In this context the Masdar Solar Platform is a unique shared facility operated by the Masdar Institute. The main objective is to promote and contribute to the development of solar radiation concentrating systems in the UAE and more generally in the MENA (Middle East and North Africa) region. The Masdar Research Platform builds around a set of unique experiments such as the Beam Down Concentrating Tower and the Fresnel and Parabolic concentrator arrays connected to double effect absorption chillers. A broad solar research program that includes activities within power generation and industrial/commercial application i.e. solar cooling will be carried out within the Masdar Research Platform.

The Masdar Solar Platform will be an open facility where researchers and universities from the whole region and the world are encouraged to carry out R&D activities and to showcase their technologies. The philosophy of the Masdar Solar Platform is to facilitate open collaboration between local industry and scientific institutions in the region driving research, development and demonstration of solar thermal technologies. This objective is in line with the Masdar vision of making Abu Dhabi the preeminent source of renewable energy knowledge, development, implementation and a world benchmark for sustainable development.

The Beam Down plant and vertical cross sectional view of the plant.

Solar photovoltaics

Solar photovoltaics, while being considered a promising solution for environmentally sustainable energy production, must address some key issues to unlock this potential and be widely accepted at power plant scale level.

Besides the well known cost issue there are more subtle, and possibly more problematic, aspects related to availability of raw materials, to the refinement cost of those available, to the large area required for power generation by current low efficiency photovoltaic systems and to the necessity to build up a completely new supply chain for this technology to access the Terawatt scale.
Solar photovoltaic concentration has long been proposed as a realistic alternative to flat plane technologies since it allows to substitute large surfaces of materials that are expensive, like in the case of solar grade silicon or rare, like the case of Indium in CuInGaSe2, or dangerous, like in the case of CdTe cells, with large area reflective of refractive plastic elements. Still, silicon based photovoltaic concentration is unable to achieve the high efficiency necessary for this technology to solve the large area requirement for solar power generation.

Given the inherent limits of a single bandgap photoactive element, related to the widespread spectral distribution of solar radiation, research is attempting to use simultaneously different semiconductors to convert the concentrated radiation beam. This is currently done either by the stacking of multijunction III/V solar cells or by splitting the solar concentrated beam, by the use of dichroic mirrors, in different spectral regions sent and, in turn, converted by specifically selected single bandgap elements.

The long wavelength region of the useful solar radiation from 700 to 1050 nm can be efficiently converted by single junction silicon concentrator solar cells, following a classical approach, with conversion efficiencies approaching 30%.The shorter wavelength region, from 400 to 700 nm, is more problematic since it requires a high bandgap (>1,5 eV) device that can withstand concentrated solar radiation.
While III/V InGaP devices are a promising approach their development requires high quality Ge substrates, raising cost and availability issues.

Alternative approaches can be based on the interesting physics of quantum confinement based devices, where the bandgap can, to certain extent, be tailored at will. On the other side reconsideration of CuInxGa1-xSe2 (CIGS) technology or similar II-VI compounds (that do not require lattice matching) can provide elegant and efficient solutions.

The approach of Pulsed Electron Deposition, starting from sintered targets having highly controlled stoichiometry, allows to obtain devices having the desired composition and electrical properties. Since low cost is, moreover, not an issue (to certain extents) for components aimed at concentration, the use of specialized substrates for CIGS deposition will be considered to improve the device electrical properties and thermal management. To handle the high level of current produced in the cell, it will be necessary to develop, photographically, a high density front contact grid minimizing the contact shading. This will be carried out by the use of fractal contact pattern as, successfully, demonstrated in previous experiments.

Another interesting subject where recent technologies may offer valuable contribution is the one of the optics used for beam steering, splitting and concentration. While this is usually done by prisms, mirrors and lenses, new horizons are opened by the development (by e-beam lithography and nano-imprinting techniques) of periodic sub-wavelength structures to “mold” the flow of light.

Surface treatment to reduce H2O needs during cleaning