arXiv subjects

Colin C. Kelsall

Publications and source records attributed to Colin C. Kelsall.

3 recordsLinked to original sources

arXiv2023

Power Availability of PV plus Thermal Batteries in real-world electric power grids

As variable renewable energy sources comprise a growing share of total electricity generation, energy storage technologies are becoming increasingly critical for balancing energy generation and demand. In this study, we modeled an existing thermal energy storage unit with estimated capital costs that are sufficiently low to enable large-scale deployment in the electric power system. Our analysis emphasizes the value of using such units to cost-effectively improve renewable energy dispatchability. This study modeled an existing real-world grid rather than simulating hypothetical future electric power systems. The storage unit coupled with a photovoltaic (PV) system was modeled with different storage capacities, whereas each storage unit size had various discharge capacities. The modeling was performed under a baseline case with no emission constraints and under hypothetical scenarios in which CO$_2$ emissions were reduced. The results show that power availability increases with increasing storage size and vastly increases in the hypothetical CO$_2$ reduction scenarios, as the storage unit is utilized differently. When CO$_2$ emissions are reduced, the power system must be less dependent on fossil fuel technologies that currently serve the grid, and thus rely more on the power that is served from the PV + storage unit. The proposed approach can provide increased knowledge to power system planners regarding how adding PV + storage systems to existing grids can contribute to the efficient stepwise decarbonization of electric power systems.

math.DS↗

arXiv2021

Thermophotovoltaic Efficiency of 40%

We report the fabrication and measurement of thermophotovoltaic (TPV) cells with efficiencies of >40%, which is a record high TPV efficiency and the first experimental demonstration of the efficiency of high-bandgap tandem TPV cells. TPV efficiency was determined by simultaneous measurement of electric power output and heat dissipation from the device via calorimetry. The TPV cells are two-junction devices comprising high-quality III-V materials with band gaps between 1.0 and 1.4 eV that are optimized for high emitter temperatures of 1900-2400°C. The cells exploit the concept of band-edge spectral filtering to obtain high efficiency, using high-reflectivity back surface reflectors to reject unusable sub-bandgap radiation back to the emitter. A 1.4/1.2 eV device reached a maximum efficiency of (41.1 +/- 1)% operating at a power density of 2.39 W/cm2 under an irradiance of 30.4 W/cm2 and emitter temperature of 2400°C. A 1.2/1.0 device reached a maximum efficiency of (39.3 +/- 1)% operating at a power density of 1.8 W/cm2 under an irradiance of 20.1 W/cm2 and emitter temperature of 2127°C. These cells can be integrated into a TPV system for thermal energy grid storage (TEGS) to enable dispatchable renewable energy. These new TPV cells enable a pathway for TEGS to reach sufficiently high efficiency and sufficiently low cost to enable full decarbonization of the grid. Furthermore, the high demonstrated efficiency also gives TPV the potential to compete with turbine-based heat engines for large-scale power production with respect to both cost and performance, thereby enabling possible usage in natural gas or hydrogen-fueled electricity production.

physics.app-ph↗

arXiv2021

Technoeconomic Analysis of Thermal Energy Grid Storage Using Graphite and Tin

Energy storage is needed to enable dispatchable renewable energy supply and thereby full decarbonization of the grid. However, this can only occur with drastic cost reductions compared to current battery technology, with predicted targets for the cost per unit energy (CPE) below $20/kWh. Notably, for full decarbonization, long duration storage up to 100 hrs will be needed at such low costs, and prior analyses have shown that in such high renewable penetration scenarios, CPE is more critical than other parameters such as round trip efficiency or cost per unit power when comparing the costs of different technologies. Here, we introduce an electricity storage concept that stores electricity as sensible heat in graphite storage blocks and uses multi-junction thermophotovoltaics (TPV) as a heat engine to convert it back to electricity on demand. This design is an outgrowth of the system proposed by Amy et al. in 2019, which has been modified here to use a solid graphite medium and molten tin as a heat transfer fluid rather than silicon as both. The reason for this is two-fold: (1) the CPE of graphite is almost 10X lower than that of silicon, which derives from the lower cost per unit mass (i.e., $0.5/kg vs. $1.5/kg) and the higher heat capacity per unit mass (2000 J/kg-K vs. 950 J/kg-K); and (2) the melting point tin and solubility of tin in graphite are much lower than that of silicon, which lessens the number of issues that have to overcome along the research and development pathway. The usage of graphite also eliminates the need for a second tank, but the main disadvantage of using a solid medium is that one cannot easily provide a steady discharge rate, as the power output from the storage will change with time, as the graphite cools during discharge. Thus, the objective of this work is to examine how these changes in the system design effect the overall technoeconomics.

physics.app-ph↗