Mads Pagh Nielsen

Modeling of CO Influence in PBI Electrolyte PEM Fuel Cells

In most PEM fuel cell MEA’s Nafion is used as electrolyte material due to its excellent proton conductivity at low temperatures. However, Nafion needs to be fully hydrated in order to conduct protons. This means that the cell temperature cannot surpass the boiling temperature of water and further this poses great challenges regarding water management in the cells. When operating fuel cell stacks on reformate gas, carbon monoxide (CO) content in the gas is unavoidable. The highest tolerable amount of CO is between 50–100 ppm with CO-tolerant catalysts. To achieve such low CO-concentration, extensive gas purification is necessary; typically shift reactors and preferential oxidation. The surface adsorption and desorption is strongly dependent upon the cell temperature. Higher temperature operation favors the CO-desorption and increases cell performance due to faster kinetics. High temperature polymer electrolyte fuel cells with PBI polymer electrolytes rather than Nafion can be operated at temperatures between 120–200°C. At such conditions, several percent CO in the gas is tolerable depending on the cell temperature. System complexity in the case of reformate operation is greatly reduced increasing the overall system performance since shift reactors and preferential oxidation can be left out. PBI-based MEA’s have proven long durability. The manufacturer PEMEAS have verified lifetimes above 25,000 hours. They are thus serious contenders to Nafion based fuel cell MEA’s. This paper provides a novel experimentally verified model of the CO sorption processes in PEM fuel cells with PBI membranes. The model uses a mechanistic approach to characterize the CO adsorption and desorption kinetics. A simplified model, describing cathode overpotential, was included to model the overall cell potential. Experimental tests were performed with CO-levels ranging from 0.1% to 10% and temperatures from 160–200°C. Both pure hydrogen as well as a reformate gas models were derived and the modeling results are in excellent agreement with the experiments.© 2006 ASME

Modeling and Implementation of a 1 kW, Air Cooled HTPEM Fuel Cell in a Hybrid Electrical Vehicle

This work is a preliminary study of using the PBI-based, HTPEM fuel cell technology in automotive applications. This issue was investigated through computational modeling and an experimental investigation. A hybrid fuel cell system, consisting of a 1 kW stack and lead acid batteries, was implemented in a small electrical vehicle. A dynamic model was developed using Matlab-Simulink to describe the system characteristics, select operating conditions and to size system components. Pre-heating of the fuel cell stack with electrical resistors was investigated and found to be an unrealistic approach for automotive applications. A simple and reliable approach to temperature management in the stack was using the unpressurized, cathode air stream as coolant.

Feasibility Study and Techno-economic Optimization Model for Battery Thermal Management System

The paper investigates the feasibility of employing a battery thermal management system (BTMS) in different applications based on a techno economic analysis considering the battery lifetime and application profile, i.e. current requirement. The preliminary objective is to set the decision criteria of employing a BTMS and if the outcome of the decision is positive, to determine the type of the employed BTMS. However, employing a BTMS needs to meet a number of application requirements and different BTMS associates a different amount of capital cost to ensure the battery performance over its lifetime. Hence, the objective of this paper is to develop and detail the method of the feasibility for commissioning BTMS called “The decision tool framework” (DTF) and to investigate its sensitivity to major factors (e.g. lifetime and application requirement) which are well-known to influence the battery pack thermal performance, battery pack performance and ultimately the performance as well as utility of the desired application. This DTF is designed to provide a common framework of a BTMS manufacturer and designer to evaluate the options of different BTMS applicable for different applications and operating conditions. The results provide insight into the feasibility and the required specification and configuration of a BTMS.

Operation strategy for solid oxide fuel cell systems for small-scale stationary applications

Solid oxide fuel cell micro-cogeneration systems have the potential to reduce domestic energy consumption by providing both heat and power onsite without transmission losses. The high-grade heat produced during the operation of the power causes high thermal transients during the startup/shutdown phases and degrades the fuel cells. To counteract the degradation, the system should not be stressed with rapid load variation during the operation. The analysis will consider an average profile for heat and power demand of a family house. Finally data analysis and power system limitations will be used to develop a viable strategy of operation.

Choosing the Right Technology: Optimized Design of Renewable Supply Systems for Residential Houses

The use of renewable energy sources (RES) has continuously increased throughout the last decade. In the residential building sector the trend goes towards energy supply systems based on multiple RES. This is mainly due to political requirements, governmental subsidies and fuel price development. These systems not only require an optimal design with respect to the installed capacities but also the right choice in combining the available technologies assuring a cost-effective solution.

Experimental Evaluation of a Pt-based Heat Exchanger Methanol Reformer for a HTPEM Fuel Cell Stack

Fuel cell systems running on pure hydrogen can efficiently produce electricity and heat for various applications, stationary and mobile. Storage volume can be problematic for stationary fuel cell systems with high run-time demands, but it is especially a challenge when dealing with mobile and automotive applications. Using a liquid hydrocarbon as e.g. methanol as the hydrogen carrier and reforming it to a hydrogen rich gas can solve some of these storage issues. The work presented here examines the use of a heat exchanger methanol reformer for use with a HTPEM fuel cell stack. Initial experimental results and conclusions are presented for this reformer.

Local versus national: designing supply systems for individual net zero energy buildings with flexible electricity prices

The building sector has obtained increased awareness throughout the last decades due to its notable contribution to global greenhouse gas (GHG) emissions. One approach to decrease these emissions is the concept of net zero energy buildings (Net ZEB), which produce as much energy out of renewable sources as they consume through public grid connections on an annual balance. A global design solution for these buildings does not exist, since the energy resource availability is different everywhere. In earlier publications a methodology was presented which allows for the cost optimal design of individual energy supply systems based on on-site weather and building conditions, as well as considering the expected energy consumption profile. However, local planning processes are problematic if they do not take regional or national impacts into account. Given the grid connection, the local building solution also has an impact on a national scale by exchanging electricity. Therefore it is important to implement respective grid loads into the planning process in order to avoid technology choices, which might counteract grid stability or cost inefficiencies at other sites. The aim of this paper is to adapt the earlier proposed methodology by integrating flexible national electricity prices and thus taking account for the aforementioned effects. The methodology is applied in a case study for a single family house under Danish conditions. The results show that the system configuration might not necessarily be changed but an adaptation in the mode of operation is important and could even lead to cost reductions when allowing for flexible tariffs.

Performance of a reversible heat pump/organic Rankine cycle unit coupled with a passive house to get a positive energy building

This paper presents an innovative technology that can be used to deliver more renewable electricity production than the total electrical consumption of a building while covering the heat demand on a yearly basis. The technology concept uses a heat pump (HP), slightly modified to revert its cycle and generate electricity, coupled to a solar thermal collector roof. This reversible HP/organic Rankine cycle unit presents three operating modes: direct heating, HP and organic Rankine cycle. This work focuses on describing the dynamic model of the multi-component system followed by a techno-economic analysis of the system under different operational conditions. Sensitivity studies include: building envelope, climate, appliances, lighting and heat demand profiles. It is concluded that the HP/ORC unit can turn a single-family house into a PEB under certain weather conditions (electrical production of 3012 kWh/year and total electrical consumption of 2318 kWh/year) with a 138.8 m2 solar roof in Denmark.