Case Studies of Wind Hydrogen System (part 2)

During 2004 and 2005, four major wind-hydrogen projects have been launched in Europe: the Utsira project in Norway; the HARI project at Loughborough; the promoting unst renewable energy project in Unst, UK; and the RES2H2 project in Greece and Spain.

On the Utsira Island, a wind-hydrogen system was installed to serve 10 households with a peak demand of 45 kW in an autonomous mode. The existing grid connection was kept for emergency situations to avoid the high costs of redundancy. The hydrogen plant consists of a 48 kW alkaline electrolyzer producing 10 Nm3/h H2, a hydrogen compressor for the filling of a 12 m3 storage tank at 200 bars with a 2400 Nm3 H2 capacity, a hydrogen generation set of 55 kW, and a PEM fuel cell of 10 kW nominal power. A 600 kW wind turbine supplies a varying portion of its power to the system feeding the rest of its power to the grid. At maximum load, the electrolyzer and compressor need approximately 54 kW of electrical power.

In the “PURE” project on the Shetland Islands, the wind-hydrogen system is composed of two wind generators of 15 kW power each, a 15 kW advanced alkaline electrolyzer operating

at 55 bars, a 16-cylinder stack of 44 Nm3 H2 capacity at the same pressure, and a 5 kW PEM fuel cell.

A hydrogen plant was integrated to an existing infrastructure of renewables, which included two 25 kW wind turbines, photovoltaics, and two microhydroelectric turbines in the HARI project. The wind turbines are two-bladed, stall-regulated, and pitch overspeed. The hydrogen plant is composed of a 36 kW alkaline electrolyzer, a hydrogen compressor, 48 pressurized hydrogen cylinders of 2856 Nm3 capacity at 13.7 MPa, and two

different fuel cells of 2 and 5 kW nominal power.

The alkaline electrolyzer with a 46-cell stack produces 8 Nm3/h H2 at 2.5 MPa and operates in a 20–100% range of its nominal power. The 3.75 kW single-stage hydrogen compressor has a capacity of 11 Nm3/h for an inlet pressure of 2.5 MPa and an 8:1 compression rate. To reduce the on/off switching cycles of the electrolyzer, which affect its long-term stability and performance, a 20 kWh battery was incorporated. The battery helped to moderate the power supply variations to the electrolyzer.

The mean electrolyzer stack efficiency measured was 75%, whereas the average conversion efficiency of the electrolyzer–battery–compressor system was 49%, including the balance of plant losses. The performance of the electrolyzer decreased gradually over 2 years of operation, with the stack power requirement increasing from 36 to 39 kW and the total power requirement, including the hydrogen purification section and auxiliaries, from a maximum of 43 to 45 kW.

In the frame of the RES2H2 project, a wind-hydrogen system was installed and tested in a wind park near Athens, Greece. The hydrogen system consists of a 25 kW alkaline electrolyzer

producing 5 Nm3/h H2, a hydrogen compressor for filling high-pressure cylinders at 220 bars and metal hydride tanks. The plant and all the auxiliaries are connected to a 500 kW wind turbine, which feeds the rest of its power to the grid. Under variable power input, the electrolyzer rarely reaches its nominal operating temperature of 80°C, and its efficiency varies from 70% to 85% for an electrolysis temperature in the range 45–70°C.

source: (2009) Hydrogen Fuel, Production, Storage & Transportation by Ram B Gupta (ed)

Case Studies of Wind Hydrogen System (part 1)

Water electrolyzers have been designed in the past for continuous or discontinuous operation with grid current converted to DC current. Most of the case studies reported in the literature refer to stand-alone systems. In fact, several of these stand-alone systems have part of their auxiliaries connected to the grid, or use the electrical grid as backup power.

A wind-hydrogen system of 20 kW installed power has been developed, constructed, and optimized at the Fachhochschule Wiesbaden in Germany since 1985. A 20 kW wind energy converter, designed for stand-alone operation, feeds DC to a pressurized alkaline electrolyzer of 20 kW, and the produced hydrogen is used in two gas motor generators of 8 and 4 kW electrical output. The overall energy effi ciency from wind electricity to gas generator electricity is around 15%.

At the University of Stralsund in Germany, a 100 kW wind turbine and a 20 kW alkaline electrolyzer supplying hydrogen at 25 bars to a storage tank of 8 m3 have been in operation for several years. According to the wind speed, the asynchronous wind generator can be operated at 1000 or 1500 rpm producing 20 or 100 kW of electricity, respectively. Both the static and the dynamic behaviors of the wind-hydrogen system were investigated, and an electrolyzer efficiency of approximately 65% with respect to the HHV has been reported.

The Hydrogen Research Institute in Canada has developed and tested a stand-alone renewable energy system composed of a 10 kW wind turbine, a 1 kWpeak photovoltaic array, a 5 kW alkaline electrolyzer, and a 5 kW PEM fuel cell. The components of the system are electrically integrated on a 48 V DC bus.

A small stand-alone, wind-powered hydrogen production plant was designed, constructed, and tested in Italy, at the National Agency for New Technologies, Energy and the Environment. The main aim of the project was to study the control of a wind turbine to produce a smooth power output, the tolerance of an electrolyzer to fluctuating power inputs, and the overall economics of a wind-hydrogen system.

The system was composed of a 5.2 kW wind turbine with a synchronous generator at variable speed, a 2.25 kW electrolyzer, and a 330 Ah battery bank. The variable frequency AC power output from the turbine was rectified and supplied to the electrolyzer. Hydrogen purity remained satisfactory even at low-capacity factors, with oxygen content in hydrogen in the range 0.15–0.35 vol%, although the efficiency of the electrolyzer stack (50%) was lower than state-of-the-art electrolyzers (70%).