Article by Scott Rommel
SERC got its start in 1989 when we designed and built the Schatz Solar Hydrogen Project (SSHP), the first solar hydrogen energy system in the U.S. The system was installed at Humboldt State University’s Telonicher Marine Laboratory in Trinidad, CA, 15 miles north of the HSU campus. Our installation was completed in 1991.
The purpose of the SSHP is to demonstrate the use of hydrogen to store solar electricity. The system consists of a 7.5 kW photovoltaic (PV) array, a 6 kW alkaline electrolyzer, a 1 kW 120 VAC inverter, and a 1 kW PEM hydrogen fuel cell. During the day when the sun is out, the PV array powers the load, the marine lab’s 600 Watt aquarium air compressor, while simultaneously making hydrogen via electrolysis. At night or during very cloudy times, the fuel cell draws on stored hydrogen to provide power for the load. The system is stand-alone and runs automatically with our custom control software.
Now, after 15 years of operation we find ourselves in 2006 with the solar hydrogen project still running, though not as well. The PV array that once produced 7.5 kWp is now degraded by 16% and produces only 6.3 kWp. Worse still, the array is providing less than 4.5 kW to the electrolyzer due to the fact that the electrolyzer’s operating voltage is far from the array’s peak power point. We’re also in need of a new fuel cell. Given these factors and how our original motivations for doing the project, diminishing oil supplies, strife over energy, and global climate change, have only intensified over the last decade and a half, SERC decided to completely redesign and rebuild our landmark energy project. Demonstrating the use of clean and renewable energy is more important than ever.
We began by attacking the mismatch problem between the PV array and the electrolyzer. In the old design, depending on conditions some portion of the system’s 12 PV sub-arrays were directly connected to the electrolyzer. This caused that portion of the array to operate at about 22 Volts, while the maximum power point of the modules is about 28.4 Volts. At full power with a current of 250 Amps, we were wasting almost 1500 watts! One method would have been to simply replace the existing PV array with a new one. But this would do nothing to improve system efficiency and would be quite expensive. We decided to regain the power lost due to PV degradation by installing state-of-the-art maximum power point trackers and DC-to-DC converters. These allow the PV array to operate at maximum power while outputting a lower voltage and boosting current to the load and the electrolyzer. To take full advantage of the current boost capability of the converters, we’ve rewired the PV array from 24 Volts nominal to 48 Volts nominal, reducing the resistive wire losses by a factor of four. We’ve also installed a separate 6 kW DC-to-DC converter to control current to the electrolyzer and facilitate maximum hydrogen generation during low and changing sun conditions. These changes will increase system performance to make the system run almost like new and increase overall efficiency in the bargain.
Our rebuild is currently in progress. The new power control devices are installed and the PV array has been rewired. Software modifications and the new fuel cell will be installed and operating by spring 2007. We’re going to report on these changes at the National Hydrogen Association’s annual meeting next March, and we’ll tell you about the outcome of this refurbishment project in a future newsletter. Stay tuned.