Hydrogen Energy Case Study

The “Hydrogen Office building (HO)” presents a wind–hydrogen energy system, located in Fife/Scotland, which has been set-up to demonstrate the role of hydrogen in reducing the impact of wind intermittency in a grid-tied microgrid. The main components of the system are a wind turbine, alkaline electrolyser, hydrogen storage and a PEM fuel cell. The building demand is met by the wind turbine, while the fuel cell provides back-up power to the ground floor when wind power is unable to meet the demand.

Accurate modelling of wind–hydrogen systems allows their successful implementation and operation, however, most of the currently available simulation tools do not provide consistent methods to represent the dynamic behaviour of such systems which is essential for their precise design, control, performance optimisation and economic study. Previous research lacks global methodologies for a whole-system scope simulation. Moreover, experimental validation is missing in most of these models and no guidelines are given for parameter estimation, which are essential for replicability.

This paper presents a comprehensive methodology for the modelling, simulation and performance evaluation of wind–hydrogen systems, while including experimental validation and guidelines for parameters estimation. The developed model encompasses usability, adaptability, dominant dynamics accuracy and reliability that makes it able to assess different systems prior and after their installation. The proposed model has succeeded to depict the HO dynamic behaviour accurately with an error of less than 2% in average.

The model has also been successfully utilised to evaluate the HO system performance. Evaluation criteria includes: average energy production, stand-alone operation and round-trip efficiency among others. Quantitative analysis has showed how this methodology can contribute to improve the design and performance of such systems.

In the normal operation mode of the vehicle, the power for the electric motor comes from the battery pack. When required, the fuel cell operates on the most efficient part of its cycle to charge the battery pack. This can occur whilst the vehicle is in motion or stationary waiting on a taxi rank.

The system is sized for operating speeds up to the vehicles normal cruising speed of 60mph. To achieve the target maximum speed of 75 mph, the system combines the power output from the fuel cell with the battery. Computer aided vehicle simulation work has been conducted to size the propulsion components and this has determined the amount of hydrogen storage required to enable the vehicle to achieve its target range.

The fuel cell system is a development of two Intelligent Energy single stack evaporatively cooled modules which together provide an output of 30 kW. A single air delivery subsystem reduces system losses and is mounted remotely from the main fuel cell power module to aid packaging. A bespoke liquid/liquid plate heat exchanger enables the heat generated to be used in conjunction with waste heat from other electrical components to heat the vehicle cabin. This is then coupled to a conventional radiator located at the front of the vehicle to remove excess heat. The stacks are housed within the fuel cell power module which is positioned in a modified vehicle transmission tunnel.

Careful packaging has been necessary to maintain the current forward luggage storage compartment and preserve the existing passenger space, providing capacity for five occupants and wheel chair use. The fuel cell module and heat exchanger are chassis mounted and installed from underneath the vehicle. Packaged into the front of the vehicle is the hydrogen storage tank. At this stage a 350 bar system has been chosen, with a tank capacity of 3.7kg. This pressure rating is compatible with the existing UK hydrogen refuelling facilities and the size of tank sufficient to exceed the 150 mile target range. The installation design has protected for a 700 bar tank, which could be used with higher pressure refuelling stations and would give the vehicle a greater range.

The 400 V, 14k Wh battery back is constructed from lithium polymer cells with a battery management system to monitor the charge and discharge and control the balancing of the cells. Its modular construction allows it to be packaged into the chassis beneath the passenger compartment without raising the floor or causing any reduction in ground clearance.

The drive system is a DC brushless electric motor, with a peak power of 100 kW and a continuous power of 50 kW. This drives the rear wheels through a single speed transmission. Front wheel drive was considered but rejected because of the wheel angle dictated by the turning circle requirements. Direct drive hub motors just on the rear were also considered but without the multiplication factor that gearing gives, hub motors currently on the market could not provide the required torque to enable the taxi to meet its performance targets.

The electric motor and gearbox are housed under the rear floor of the taxi, where the live rear axle is normally located and are mounted on their own subframe. The new powertrain located at the rear of the vehicle has resulted in the development of a new rear suspension for the vehicle and rear brakes.

A fully independent trailing arm and lateral link system has been designed to fit in the package space available without any modifications to the vehicle structure.

Apart from minor revisions to the centre console in the driver's compartment, the interior of the taxi remains unchanged from the standard vehicle. Two in-car displays will be incorporated into the vehicle, one to give the driver information about the electrical systems and a more pictorial display in the passenger compartment informing them of the way the vehicle is operating and displaying the energy it is using.

SPECIFICATION

Overall Length: 4,580 mm

Overall Width: 2,036 mm



Overall Height: 1,834 mm

Weight: 2,180 kg

Motor: 3-phase brushless permanent magnet (100 kw)

Fuel Cell: PEMFC (Intelligent Energy)



Fuel Storage: Pressurised hydrogen tank (350 bar)

Battery: Li-polymer battery 14 kWh

Range: 160 miles (257 km)

Top speed: 80 mph (128 km/h)

Acceleration 0-60 mph (0-100 km/h): 15.5 seconds

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