Andrew Ramsay Knox

Maximum Power Point Tracking Converter Based on the Open-Circuit Voltage Method for Thermoelectric Generators

Thermoelectric generators (TEGs) convert heat energy into electricity in a quantity dependent on the temperature difference across them and the electrical load applied. It is critical to track the optimum electrical operating point through the use of power electronic converters controlled by a maximum power point tracking (MPPT) algorithm. The MPPT method based on the open-circuit voltage is arguably the most suitable for the linear electrical characteristic of TEGs. This paper presents an innovative way to perform the open-circuit voltage measure during the pseudonormal operation of the interfacing power electronic converter. The proposed MPPT technique is supported by theoretical analysis and used to control a synchronous Buck-Boost converter. The prototype MPPT converter is controlled by an inexpensive microcontroller, and a lead-acid battery is used to accumulate the harvested energy. Experimental results using commercial TEG devices prove that the converter accurately tracks the maximum power point during thermal transients. Precise measurements in the steady state show that the converter finds the maximum power point with a tracking efficiency of 99.85%.

Facile Surfactant‐Free Synthesis of p‐type SnSe Nanoplates with Exceptional Thermoelectric Power Factors

Abstract A surfactant‐free solution methodology, simply using water as a solvent, has been developed for the straightforward synthesis of single‐phase orthorhombic SnSe nanoplates in gram quantities. Individual nanoplates are composed of {100} surfaces with {011} edge facets. Hot‐pressed nanostructured compacts (E g≈0.85 eV) exhibit excellent electrical conductivity and thermoelectric power factors (S 2 σ) at 550 K. S 2 σ values are 8‐fold higher than equivalent materials prepared using citric acid as a structure‐directing agent, and electrical properties are comparable to the best‐performing, extrinsically doped p‐type polycrystalline tin selenides. The method offers an energy‐efficient, rapid route to p‐type SnSe nanostructures.

Simple, fast and accurate maximum power point tracking converter for thermoelectric generators

Thermoelectric generators (TEGs) can harvest thermal energy producing electrical power from a temperature gradient. They are often employed in dynamic thermal environments, therefore it is important to quickly and precisely track the best operating point to maximize the power production. This paper presents an innovative way to measure the open-circuit TEG voltage without disconnecting the load, to be used in a Maximum Power Point Tracking (MPPT) algorithm based on the open-circuit voltage method. The proposed system is composed of a buck converter with embedded microcontroller, which is used both to compute the MPPT algorithm and to control the charging of a lead-acid battery. The prototype converter is tested using a TEG system and it can accurately set the optimum operating point almost instantaneously and without significant computational power requirements.

Scalable solar thermoelectrics and photovoltaics (SUNTRAP)

This paper presents the design, manufacture and electrical test of a novel integrated III:V low concentrator photovoltaic and thermoelectric device for enhanced solar energy harvesting efficiency. The PCB-based platform is a highly reliable means of controlling CPV cell operational temperature under a range of irradiance conditions. The design enables reproducible data acquisition from CPV solar cells whilst minimizing transient time for solid state cooling capability.

Hardware Implementation of Maximum Power Point Tracking for Thermoelectric Generators

This work describes the practical implementation of two maximum power point tracking (MPPT) algorithms, namely those of perturb and observe, and extremum seeking control. The proprietary dSPACE system is used to perform hardware in the loop (HIL) simulation whereby the two control algorithms are implemented using the MATLAB/Simulink (Mathworks, Natick, MA) software environment in order to control a synchronous buck–boost converter connected to two commercial thermoelectric modules. The process of performing HIL simulation using dSPACE is discussed, and a comparison between experimental and simulated results is highlighted. The experimental results demonstrate the validity of the two MPPT algorithms, and in conclusion the benefits and limitations of real-time implementation of MPPT controllers using dSPACE are discussed.

Megawatt scale energy recovery in the Rankine cycle

It has, in recent times, become the focus of national and international political pressure to reduce the impact of climate change [1]. The amount of CO2 that is released to the atmosphere now has legislative and tax implications with CO2 emitters around the world in both developed and developing countries having to implement CO2 reducing technologies to reduce costs and maintain profitability [2]. We aim to exploit the Peltier effect exhibited in semiconductor devices to create an enthalpy capture device using the significant amount of energy rejected by such a power plant. A thermoelectric device applied in its heat pumping mode, enables the redirection of energy released in the condensation process. We aim to prove that using the thermoelectric device in a particular configuration enables the preheating of water returning to the boiler (feed water). Such an application of a heat pumping device will increase the net efficiency of the Rankine cycle.

Photovoltaic-thermoelectric modules: A feasibility study

In this paper a hybrid solar system made with photovoltaic cells and thermoelectric modules has been analyzed. The theoretical energy conversion and the performance parameters have been investigated and compared with respect to design and geographic location using a simulated model. In particular, the effects of the global radiance, of the ambient temperature and of the hours of sunshine on the power and energy production are assessed. The obtained results show that the advantages of the thermoelectric modules use are less significant when the locations considered are very distant from the equator.

An electron emission model for use with 3D electromagnetic finite element simulation

Abstract Using commercial 3D finite element (FE) simulation packages it is now possible to model the self-consistent behaviour of charged particle beams in electromagnetic fields within a complex problem geometry. However, in many cases the accuracy of the simulation is restricted by the accuracy of the particle emission models traditionally in use. Most such models date back to the time when problem complexity was limited by what could be solved. Artifacts of this early work in, for example, vacuum tubes, led to the development of simplified models like those by Child and Langmuir aiming to describe space charge limited electron emission from thermionic cathodes. Such models, which are still in use, have the twin disadvantages of their formulation being dependent on the problem geometry and their reliance on a “characteristic dimension” to specify the distance over which the space charge limited flow is to be computed. These disadvantages can make their application to general problem geometry in a FE simulation environment difficult and in some cases misleading. With the recent introduction of facilities to specify the initial particle dynamics in commercial space charge solvers there is no longer a need to rely on the above traditional but restricted emission models. This paper describes one method of implementing a completely general model for thermionic electron emission which utilizes the new facilities. The new methodology is applicable to any type of electron emission including thermionic, field and photoemission and depends only on the ability of the user to specify the starting conditions of the particle trajectories. The details of our approach are illustrated in the simulation of initial beam formation from a thermionic cathode in a thin CRT. In the example simulations, the use of a characteristic dimension is precluded. The emission characteristics are derived solely from the Maxwell–Boltzmann distribution which provides the electron velocities, and the Richardson–Dushman law which provides the saturation current density. Many problems require the solution to simultaneously include the total cathode emission current and yet cope with a large dynamic range of beam current. Methods developed to permit such solutions whilst keeping computation time within practical limits are discussed. The paper also discusses the effect the coupling of the particle beam to the model has on solution convergence.

Large-Scale Surfactant-Free Synthesis of p-Type SnTe Nanoparticles for Thermoelectric Applications

A facile one-pot aqueous solution method has been developed for the fast and straightforward synthesis of SnTe nanoparticles in more than ten gram quantities per batch. The synthesis involves boiling an alkaline Na2SnO2 solution and a NaHTe solution for short time scales, in which the NaOH concentration and reaction duration play vital roles in controlling the phase purity and particle size, respectively. Spark plasma sintering of the SnTe nanoparticles produces nanostructured compacts that have a comparable thermoelectric performance to bulk counterparts synthesised by more time- and energy-intensive methods. This approach, combining an energy-efficient, surfactant-free solution synthesis with spark plasma sintering, provides a simple, rapid, and inexpensive route to p-type SnTe nanostructured materials.

Outdoor performance of a reflective type 3D LCPV system under different climatic conditions

Concentrating sunlight and focusing on smaller solar cells increases the power output per unit solar cell area. In the present study, we highlight the design of a low concentrating photovoltaic (LCPV) system and its performance in different test conditions. The system essentially consists of a reflective type 3.6× cross compound parabolic concentrator (CCPC) designed for an acceptance angle of ± 30°, coupled with square shaped laser grooved buried contact (LGBC) silicon solar cells. A heat exchanger is also integrated with the PV system which extracts the thermal energy rejected by the solar cells whilst maintaining its temperature. Indoor characterization is carried out to evaluate the system performance under standard conditions. Results showed a power ratio of 3.12 and an optical efficiency of 73%. The system is placed under outdoor environment on a south facing roof at Penryn, UK with a fixed angular tilt of 50°. The high angular acceptance of the system allows collection of sunlight over a wider rang...