Originally designed and constructed in 1989 to 1991, the Schatz Solar Hydrogen System (SSHS) is a stand-alone renewable energy system that uses hydrogen as the energy storage medium for the output of a photovoltaic (PV) array and a PEM fuel cell to convert the hydrogen back to electricity. The SSHS is located at Humboldt State University's Telonicher Marine Laboratory in Trinidad, California, and the load for the system is the marine lab's air compressor. After 16 years of system operation, we are currently completing work to implement major design changes in the system that will improve overall efficiency and modernize the equipment.

In the original system, the PV array was divided into 12 discrete 24 V sub-arrays. The power from each sub-array was independently directed via relays either to an inverter to power the load or to an electrolyzer to produce hydrogen for later use. Since the power demand by the inverter never exactly equals the output from an integer number of sub-arrays, a battery buffer was added to either absorb the extra power or make up the deficit. When there is insufficient solar radiation, the PEM fuel cell system takes over the load without interruption, consuming the stored hydrogen until it is all used or the sun returns. When hydrogen storage is exhausted, grid power serves as back-up for the compressor, a critical load for the lab.

In the new system, the PV array has been re-wired into 6 discrete 48 V sub-arrays, thereby reducing the resistive power losses within the sub-arrays and associated transmission lines. Each sub-array is connected to a maximum power point tracker, which maximizes sub-array power output and efficiency. Each of the sub-arrays is connected in common to a 48 V power bus; the inverter and a small battery bank are also connected to this bus. The electrolyzer is connected via a high efficiency step-down dc-to-dc converter and the fuel cell is connected via a high efficiency step-up dc-to-dc converter. Using dc-to-dc converters permits the direct and smooth control of the power output to the electrolyzer as well as the power input from the fuel cell and makes it possible to utilize a fuel cell stack with fewer cells. The entire system is automated using LabView® software written in-house.

In this paper, we will discuss the design issues and technical challenges encountered in this conversion, present some preliminary operational tests, and compare the new vs. original system performance.