Solar-powered hydrogen refuelling station for unmanned aerial vehicles: Design and initial AC test results

Fuel cell technology can offer environmental benefits (low noise and emissions) and also a competitive advantage over conventional power sources (better performance, low thermal signature, less vibration issues, etc) in small manned and unmanned electric air vehicles (UAVs). To develop an environmentally acceptable solution, the hydrogen fuel source must be produced on-site from renewable energy sources. This paper describes the development and testing of a fully operational small-scale demonstrator to generate and supply hydrogen for 2 to 3 daily fuel cell-powered UAV operations. The purity of the hydrogen delivered to the air platforms is >= 99.99%. Solar irradiation data and daily hydrogen demand across the year for the location selected (Ocana, Spain) were employed as the primary input to a spreadsheet-based model to calculate a recommended the optimum sizing solution. Simulations were then performed to assess the expected operation of the system. Additional practical issues were then considered, including project budget, available space, size and availability of commercial components, safety standards and regulatory compliance. The design selected comprises a concentrated photovoltaic array (CPV), an alkaline electrolyser, a hydrogen buffer tank and a diaphragm hydrogen compressor. Four small composite tanks rated at 3000 barg are included to ensure enough endurance and fast refuelling of the UAVs at any time during the year. These tanks are recharged and installed on-board the UAV at the beginning of each flying mission. For the system to operate effectively the recommended design has 10 kW of CPV capacity and over 34 Nm(3) of total hydrogen storage capacity to accumulate hydrogen generation during sunny periods and guarantee performance across winter months. Once the detailed design was completed, all components were installed and assembled, including a bespoke control system for self-governing off-grid operation. Grid-connected tests were then carried out to assess the components integration and acceptance prior to any unsupervised off-grid operation. It is expected that the system will provide enough field data to act as a test-bed towards a fully autonomous refuelling solution for UAVs. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.