Human Energy Harvesting in the Urban Environment

The overall aim of the thesis was to provide a holistic view of the potential for electrical energy generation from harvesting of human mechanical work in the urban environment. This required consideration of a broad range of topics including, energy in people, energy conversion technologies and the activity of people and focussed on floor and door integrated devices. The initial step was to consider the potential offered by an individual through consideration of the flow of energy within people and the potential available for harvesting from single actions on floor and door integrated devices. Secondly the process and technologies available for converting mechanical work into electrical energy were considered with a focus on the efficiency with which this could be achieved. Finally, computer based modelling was carried out to determine the expected energy outputs from a device or system of devices to both determine the maximum achievable values and for various assumption based location scenarios in the urban environment. In addition the economic value and displaced carbon dioxide emissions from the generated energy were considered in terms of replacing grid energy. It was concluded that although significant potential exists in the form of human activity, utilising this potential is problematic for a variety of reasons. Much of the energy expended by people is required to complete actions necessary for survival and everyday life, leaving only a small fraction available for energy harvesting. The efficiency with which mechanical work can be converted into electrical energy was found to vary greatly between technologies. In addition it was found that the energy potential is spread diffusely throughout the built environment, with even the most suitable locations returning only modest energy generation values. As a direct consequence it was highlighted that the cost and embodied emissions of devices must be low if human energy harvesting is to offer any benefits

An analysis of the energy flow and energy potential from human energy harvesting with a focus on walking

This paper aims to determine the limitations for electrical energy generation from harvesting mechanical work during walking. The assessment was considered from the point of chemical energy ingested in food, through the development of mechanical work, to the conversion into useful electrical energy from the perspective of the conversion efficiencies. An average person was considered, with four mechanical to electrical energy conversion technologies assessed. It was found that for an individual walking on level ground a potential of up to 5 J/step of electrical energy is available. Stair use impacts this, where stair ascent decreased and descent increased the potential. It was concluded that, although the energy outputs are small, they scale with the number of people, where an estimated potential of 900 MWh/day is calculated in the UK. Harvesting even a fraction of this available potential would appear worthwhile, however, it is unclear if this potential can be practically utilised

Fuel Economy of a Current Hybrid London Bus and Fuel Cell Bus Application Evaluation

London has over 8,500 buses in operation, carrying six million passengers on 700 routes each day. In central London the majority of the bus fleet has been replaced by diesel-electric hybrid buses. In this study, we will investigate the degree of energy efficiency via practical on-road bus performance recordings, forming a foundation for future improvements to diesel and fuel cell hybrid bus design. Research at UCL has investigated the design and performance of the ENVIRO 400H model bus on various different routes in London, obtaining a wide range of data for real world performance. This data includes information on routes, usage, energy consumption and passenger count profiling. Analysis has been conducted on the efficiency of the propulsion system over all the data sets. This knowledge can be used as the basis for developing computer modelling capabilities to in the future to optimize the system performance. The key components in the propulsion system are the diesel engine, generator, converter, battery bank, and traction motor. The energy management strategy has been analysed for different operating conditions and will be discussed in this paper. It was concluded that the system performance varied, with a number of patterns emerging with regards to the engine load and battery State of Charge for providing the propulsion power requirements. The operation strategies employed have been analysed to give a detailed understanding of the operation of the diesel-electric hybrid propulsion system under real-world operation

Impact of Coil Turns on Losses, Output power and Efficiency Performance of Flux-Pipe Resonant Coils

This paper presents a finite element analysis of five different sizes of flux-pipe resonant coil design with a different number of coils turns but having the identical length of litz copper wire and aluminum shield. The analysis was undertaken to establish the impact of the number of coil turns on the losses, magnetic flux distribution, power output, and power transfer efficiency of flux-pipe resonant coils. From the results presented, it was noted at a constant frequency, an increase in the excitation current causes a significant increase in the ohmic, core, and eddy current losses for each of the coil model designs. Similarly, at constant excitation current, it was observed that the eddy current losses increase significantly with an increase in resonant frequency. In contrast, the ohmic and core losses are relatively constant over the range of resonant frequencies used in the analysis. It was also noted that term k√Qps (where k is the coupling coefficient and Q ps is the product of the quality factor of the primary and secondary coils) has a significant influence on the input power, output power and coil-to-coil efficiency of a particular flux-pipe resonant coil design. Increasing the value of k√Qps increases the value of output power, input power, and coil-to-coil efficiency. Similarly, the lower the coupling coefficient, the higher the required optimum resonant frequency for optimum coil-to-coil efficiency and output power

Loss Performance Evaluation of Ferrite-Cored Wireless Power System with Conductive and Magnetic Shields

This paper presents a loss evaluation of ferrite-cored wireless power transfer (WPT) systems using conductive and magnetic shield materials. The modelling and analyses of the coil systems were implemented using the finite element method. Three coil systems were modelled-circular coils, rectangular coils and flux-pipe coil system using magnetic shields (Mumetal and electrical steel) and conductive shields (aluminum and copper). From the results presented in the analyses, it was noted that ohmic losses and core losses in the WPT system are independent of the type of conductive shield used. Similarly, it was noted that the self-inductance, coupling coefficient and losses in the system is affected by the type of magnetic shield used. For the flux-pipe resonant coil system, high power losses were recorded when a magnetic shield was used as the shielding topology while low power losses were recorded in the circular coil and rectangular coil resonant systems when the magnetic shield was used as the shielding material. For optimal WPT system requiring low eddy current losses, it was established that copper shield is the appropriate choice for flux-pipe resonant coils while electrical steel is the suitable shield material for the circular resonant coil and rectangular resonant coil systems

Development and Modelling of a Lab Scaled PEM Fuel Cell Drive System for City Driving Application

This paper details a study carried out by UCL to explore potential improvements to the Fuel Cell (FC) bus propulsion system specifically designed for the city driving environment. In this paper, a 1:10 scaled lab based FC bus drive train has been developed to study the performance of a FC directly driving an AC induction motor. The PEMFC is the main power source for the drive train while a boost converter will work as the power conditioning system to control the FC output voltage. The AC motor will work as the bus prime mover. The system has been built in the Electrical Laboratory to evaluate the performance of a FC driving a motor. MATLAB Simulink has been used to simulate the system and has been validated against the lab based system. A number of tests have been carried out in terms of efficiency and transit change response with both the lab and simulated models. The results showed that the FC is capable of directly powering the motor in general bus driving conditions, but it is not well suited for quick transient changes. This study provides an important contribution to further improve the FC bus with hybrid propulsion systems and validates the computer model to allow faster analysis of proposed system improvements. The next step of this study is to use an energy storage system to aid the FC to cover quick transient power demand and validate it against a representative load system

Stabilised control strategy for PEM fuel cell and supercapacitor propulsion system for a city bus

Fuel Cell (FC) buses have been developed as a long term zero emission solution for city transportation and have reached levels of maturity to supplement the coming London 2020 Ultra low emission zone implementation. This research developed a scaled laboratory Fuel Cell/Supercapacitor hybrid drivetrain implementing DC/DC converters to maintain the common busbar voltage and control the balance of power. A novel and simple hybrid control strategy based on balancing the currents on the common busbar whilst maintaining a stable FC output has been developed. It has been demonstrated that the FC power output can be controlled at a user defined value for both steady state and transient load conditions. The proposed control strategy holds the promise of extending FC life, downsizing power systems and improving the FC operating efficiency

Simulation of a stabilised control strategy for PEM fuel cell and supercapacitor hybrid propulsion system for a city bus

Fuel Cells (FC) are a clean energy source capable of powering a bus electrically with zero operating emissions. This research investigates the potential of FC and Supercapacitor (SC) hybrid buses for clean city transportation. To investigate the FC/SC hybridisation strategy, a scaled FC/SC hybrid drivetrain has been developed to provide the power system of a scaled bus model. The scaled model was developed as a MATLAB Simulink computer model and cross referenced against the constructed laboratory test rig for validation. A novel control strategy focusing on power balancing between the FC, the SC and the load has been developed and validated in the computer model. It has been demonstrated in both the test rig and computer simulation that the proposed control strategy is capable of maintaining a controlled and stable FC output while meeting different bus load regimes. The validated computer model can provide a reliably representative, convenient and low cost platform for further performance investigation and component optimisation of FC/SC hybrid drivetrains. The control strategy has also been demonstrated to be function as expected after scaling up the developed scaled model to a full scale model which can be used for simulation of practical bus performance

Catastrophic senescence and semelparity in the Penna aging model

The catastrophic senescence of the Pacific salmon is among the initial tests used to validate the Penna aging model. Based on the mutation accumulation theory, the sudden decrease in fitness following reproduction may be solely attributed to the semelparity of the species. In this work, we report other consequences of mutation accumulation. Contrary to earlier findings, such dramatic manifestation of aging depends not only on the choice of breeding strategy but also on the value of the reproduction age, R, and the mutation threshold, T. Senescence is catastrophic when $T \leq R$. As the organism's tolerance for harmful genetic mutations increases, the aging process becomes more gradual. We observe senescence that is threshold dependent whenever T>R. That is, the sudden drop in survival rate occurs at age equal to the mutation threshold value

Robust observational constraint of uncertain aerosol processes and emissions in a climate model and the effect on aerosol radiative forcing

The effect of observational constraint on the ranges of uncertain physical and chemical process parameters was explored in a global aerosol–climate model. The study uses 1 million variants of the Hadley Centre General Environment Model version 3 (HadGEM3) that sample 26 sources of uncertainty, together with over 9000 monthly aggregated grid-box measurements of aerosol optical depth, PM2.5, particle number concentrations, sulfate and organic mass concentrations. Despite many compensating effects in the model, the procedure constrains the probability distributions of parameters related to secondary organic aerosol, anthropogenic SO2 emissions, residential emissions, sea spray emissions, dry deposition rates of SO2 and aerosols, new particle formation, cloud droplet pH and the diameter of primary combustion particles. Observational constraint rules out nearly 98 % of the model variants. On constraint, the ±1σ (standard deviation) range of global annual mean direct radiative forcing (RFari) is reduced by 33 % to −0.14 to −0.26 W m−2, and the 95 % credible interval (CI) is reduced by 34 % to −0.1 to −0.32 W m−2. For the global annual mean aerosol–cloud radiative forcing, RFaci, the ±1σ range is reduced by 7 % to −1.66 to −2.48 W m−2, and the 95 % CI by 6 % to −1.28 to −2.88 W m−2. The tightness of the constraint is limited by parameter cancellation effects (model equifinality) as well as the large and poorly defined “representativeness error” associated with comparing point measurements with a global model. The constraint could also be narrowed if model structural errors that prevent simultaneous agreement with different measurement types in multiple locations and seasons could be improved. For example, constraints using either sulfate or PM2.5 measurements individually result in RFari±1σ ranges that only just overlap, which shows that emergent constraints based on one measurement type may be overconfident