Case Study Introduction

Selection of Simulation Software

In order to be able to analyse multiple scenarios where a hydrogen buffering system was implemented, simulation software had to be used.  With the limited time period that we had to conduct these simulations it was beneficial to opt for software that already had hydrogen system components programmed within it. 

The National Renewable Laboratory’s (NREL) HOMER software was the software chosen because it offered a low degree of complexity in system manipulation and inputting data.  It also offered the option to model a grid connection, which suited our needs.

Introduction to HOMER

HOMER is an optimisation software tool freely available to download from the NREL_website.  The optimisation algorithm ranks outputs in order of cost, more specifically Net Present Cost (NPC).  In order for HOMER to be able to do this component cost curves must be input for capital, replacement and O&M costs.  These costs can be input with linear relationships or Different component sizes can then be considered and an iterative process adopted to find the optimal configuration. 

HOMER also offers the ability to carry sensitivity analyses on numerous variables including costs, interest rates, wind speeds and component efficiencies.

HOMER works on hourly time steps therefore for the annual analysis done in the case studies all data is calculated in this manner.

Introduction

The first location, selected for the off grid scenario, was chosen to be Stornoway on the isle of Lewis.  This was chosen after studying the H2 Seed project currently based on the island in which biogas of a waste management facility on the island has been used to fuel an electrolyser and produce hydrogen.  This hydrogen was then to be stored in a filling station to fuel two hybrid Toyota Prius fitted with hydrogen ICE engines.

In the first case study the hydrogen infrastructure has been expanded to use the electricity produced from wind turbines to produce enough hydrogen to use in a hydrogen buffering system.  The aim of this system is to simulate a stand-alone system that can match the demand of Stornoway using purely renewable sources with the additional objective of supplying enough hydrogen to supply two hydrogen fuel cell buses with enough fuel to run all year round. 

The second case study investigated utilising a hydrogen buffering system in conjunction with a well established grid connection to sell firm power output provided by a fuel cell to sell back to the grid.  The production of firm power for fixed amounts of time is a valuable commodity because of its predictable nature that eradicates the inherent intermittency of supply usually associated with renewables.  The buffering system in this case study again uses wind power and the location was chosen as Glasgow because of its central location and resulting strong grid connection.