Solar power | EPFL Graph Search

Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic effect. Concentrated solar power systems use lenses or mirrors and solar tracking systems to focus a large area of sunlight to a hot spot, often to drive a steam turbine. Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s. Since then, as the cost of solar electricity has fallen, grid-connected solar PV systems have grown more or less exponentially. Millions of installations and gigawatt-scale photovoltaic power stations continue to be built, with half of new generation capacity being solar in 2021. In 2022 so

THERMOECONOMIC ANALYSIS AND OPTIMISATION OF AIR-BASED BOTTOMING CYCLES FOR WATER-FREE HYBRID SOLAR GAS-TURBINE POWER PLANTS

Raphaël Michel Adrien Marie Sandoz

Among the plethora of alternatives available, concentrated solar power (CSP) appears as one of the most favourable options. The stability and dispatchability of production achievable by the integration of storage and fuel-solar hybridisation are amidst the major advantages of this technology. Nevertheless, conventional CSP plants are based on stream-turbine cycles which consume large amounts of water. In addition to the low thermodynamic efficiency of this type of cycle, the installation of such plants in water-scarce areas is complicated by their reliance on water resources. Thus, the study of new concepts that overcome these drawbacks is necessary for the future of this technology. The availability of high temperature solar receivers for solar tower systems opens the way for the use of gas-turbines in hybrid solar- natural gas configurations. In order to increase the efficiency of the cycle while keeping the water consumption as low as possible, a promising alternative to the recovery of the waste heat in steam-turbines is to use a low-temperature intercooled-recuperated gas-turbine cycle. This work focuses on the analysis and optimisation of the performance of an innovative hybrid solar gas-turbine power plant with an air-based bottoming cycle (ABHSGT). The evaluation considers thermodynamic performance, economic viability and environmental impact as interrelated concerns. With this in mind, detailed steady-state and dynamic models of the power plant have been developed and validated by comparison with existing components. A second model without bottoming cycle has been built for comparison. A multi-objective optimisation using an evolutionary algorithm has then been performed, optimising both capital cost and specific CO2 emissions and resulting in a Pareto-optimal set of possible designs. The analysis of the trade-off curves resulting from the optimisation reveals promising outcomes. The global minimum for the levelised cost of electricity, found at relatively high solar shares, proves the economic potential of the technology. The integration of the bottoming cycle decreases significantly the levelised cost of electricity and the CO2 emissions of the system compared to the reference plant, and higher efficiencies are achieved. The optimal design selected for an in-depth thermoeconomic and environmental analysis exhibits a levelised cost of electricity of 109 [USD/MWhe] for a solar share of 20% and an overall exergetic efficiency 38.5%. The specific CO2 emissions are reduced by 33% compared to those of a simple gas-fired power plant. The water consumption is kept at very low levels compared to other CSP plants, making the system suitable for the deployment in water-scarce areas. In addition, the environmental impact induced by the land use requirements is considerably lower than that of other renewable energy technologies. The sensitivity analysis performed to assess the consequence of changes in varying financial conditions on the levelised cost of electricity and the net present value reveals that the system studied represents a profitable investment in the presence of feed-in tariffs. In the light of the performance obtained in the three aspects considered (thermodynamic, economic and environmental), it can be concluded that the ABHSGT represents a promising alternative to other renewable energy technologies, especially in water-scarce areas.

2012

Aspects of the energy transition and their effects on power systems

Laurent Vincent Pagnier

Most European countries are committed to an energy transition which consists in the substitution of conventional CO2 emitting energy sources by new renewable energy sources (RES), in particular wind and solar power. As opposed to conventional energy sources, new RES are distributed, non-dispatchable, fluctuating and inertialess and have negligible marginal costs. In this thesis, we investigate the impact of the energy transition on the electricity sector in Europe. In the first part of this thesis, we investigate the future electricity production and prices in Europe. We develop a dispatch algorithm on an aggregated model of the pan-European power grid with which we study the future European productions. We show that, as the penetration of new RES increases, the transmission grids are more strongly used and that more flexibility is required from conventional generators. The existing infrastructures seem to able to absorb, through increased international power exchanges and usage of the existing pumped-storage hydroelectricity, the variations of new RES productions even for high penetrations. Then we investigate the effects of new RES on electricity prices. We explain why, due to their negligible marginal cost and their lack of dispatchability, they tend to drag electricity prices down and can be considered as a reduction of the load in the electricity pricing. In particular, photovoltaics decreases the volatility of electricity prices. We show that, in most European countries, the day-ahead electricity price is strongly correlated with the residual load, which is obtained by subtracting the non-dispatchable productions, in particular those of the new RES, from the load. From this observation, we build an effective price model based solely on the residual load with which the revenues of different electricity producers are evaluated. The second part of this thesis deals with disturbances in large transmission grids. The substitution of conventional generators by inertialess RES reduces the amount of inertia connected to power systems which might affect their reliability. To examine the propagation of disturbances in large transmission grids, we develop a dynamical model of the continental European transmission grid. We observe that the magnitude of the disturbance following a power loss depends on the fault location. We show that when inertia and primary control are uniformly distributed, the faults exciting the slowest eigenmodes of the network Laplacian are followed by the strongest disturbances. Reducing inertia on those eigenmodes, which are mostly located in the periphery of the grid, affects more its resilience than when the reduction occurs in its center. Finally, we use perturbation theory to derive algorithms for optimal placement of inertia and primary control when some mild inhomogeneities are present in their distributions. We show that,when the vulnerability of the whole grid is taken into account, a uniform distribution of inertia is optimal and the primary control is best placed in the periphery of the grid.

EPFL2019

Novel concepts of compressed air energy storage and thermo-electric energy storage

Young Min Kim

The interest in energy storage is currently increasing, especially from the perspectives of matching intermittent sources of renewable energy with customer demand and storing excess nuclear or thermal power during the daily cycle. Technologies to be considered for load leveling for large-scale energy systems, typically in the range of hours to days of discharge time, include pumped-storage hydroelectricity, compressed air energy storage (CAES), sodium sulfur (NaS) batteries, advanced absorbent glass mat lead acid batteries, and flow batteries. CAES is a promising technology because of significant advantages such as its high reliability, economic feasibility, and low environmental impact. Thermo-electric energy storage (TEES), which was recently proposed as a method for large-scale energy storage, is another mechanical storage method based on thermodynamic cycles. This thesis presents a guide to precisely understand each system along with energy and exergy analyses to characterize the key parameters for achieving high efficiency for each of the systems. In addition, some novel concepts for the systems are proposed in order to address some of the current drawbacks and to widen the scope of their applications. Conventional CAES systems are most commonly operated under constant volume conditions with a fixed, rigid reservoir and compressors and turbines that can operate over an appropriate pressure range. These varying pressure ratios can degrade the efficiencies of compression and power generation owing to deviations from design points. Although it is possible to increase the storage volume to reduce the operating pressure range, doing so results in reduced energy density and high construction costs. Therefore, in order to resolve such problems, a novel constant-pressure CAES system combined with pumped hydro storage is proposed. An energy and exergy analysis of the novel CAES system was performed in order to understand the operating characteristics of the system according to several different compression and expansion processes. The effects of the height of the storage cavern and heat transfer between two media (air and water) and the cavern on the performance of the novel CAES system were also examined. Although the large-scale CAES systems are dependent on the right combination of site-dependent geological factors for air storage, a micro-CAES system with man-made air vessels can be a very effective system for distributed power networks, because it provides energy storage, generates electric power using various heat sources, and incorporates an air cycle heating and cooling system. This thesis presents the results of energy and exergy analyses of different types of micro-CAES systems, as well as some innovative ideas for achieving high efficiency of these systems. Recently, another type of mechanical storage, namely, thermo-electric energy storage (TEES) systems, which use heat pumps and heat engines with thermal storage, have been proposed. The advantages of TEES systems are their higher energy densities and independence from geological formations. In particular, a TEES system with transcritical CO2 cycles is considered to be a promising method for large-scale energy storage. This thesis reviews current TEES systems and proposes a novel isothermal TEES system with transcritical CO2 cycles. It is shown that in the case of TEES systems with transcritical CO2 cycles, the roundtrip efficiency and energy density can be increased by isothermal compression/expansion. In addition, novel transcritical or supercritical CO2 cycles using both low-temperature (LT) and high-temperature (HT) heat sources are proposed to maximize the power output of the CO2 power cycle with the given HT heat sources for use in applications such as nuclear power, concentrated solar power, and combustion. Moreover, the previous TEES system with transcritical CO2 cycles can be combined with the proposed transcritical CO2 cycle using both LT and HT heat sources.

EPFL2012