A research team led by Japan’s Osaka University has proposed a novel ramp rate control method that utilizes PV module cooling.
Ramp rate refers to the speed at which the output of a PV system changes due to environmental conditions in a given time, and controlling it can enhance grid stability.
The traditional methods to manage short-term fluctuations use either a battery energy storage system (BESS), controllable power generation by fuel, and the dumping of loads. “The proposed method has a low system cost and environmental impact because it does not require the operation of a gas turbine or a large-capacity battery,” the group explained. “Also, the power saved during output power fluctuations is not dumped, but effectively utilized in the PV cooling unit.”
At the system's heart lies a control method that uses power demand, weather information, and PV generation forecasts from the relevant microgrid as inputs. This optimization problem is formulated mathematically, and optimal results can be obtained by a mathematical solver that can run online, utilizing platforms such as the Raspberry Pi.
The controller then decides to initiate one of four possible situations.
In situation 1, PV power matches demand, with no significant fluctuations in output and no cooling being activated. In situation 2, PV power exceeds demand and the cooling unit is activated, which prevents power surges to the grid as the modules produce more energy.
In situation 3, when a sudden increase in energy is required due to a sudden drop in solar irradiation or a sharp increase in demand, the cooling unit is turned off or its activity is reduced, and the power is sent to the grid. In situation 4, the panel temperature gradually rises due to the stop of the cooling unit, and the power boost is terminated.
To check the validity of the proposed method, the group tested it in a simulation. That includes a microgrid model located at Germany’s Oldenburg; a PV system consisting of 5,000 panels that add up to a maximum output of 1 MW; a cooling unit with a varying coefficient of performance (COP); and a small battery with charging capacities, used to assist the system.
The novel system was compared to a system using BESS over autumn, winter, spring, and summer. For each season it had a 15-minute measurement period in the morning, noon and evening.
“The effectiveness of our method was validated by simulation based on real-world data, which showed reductions in mean and maximum ramp rates of 43.5% and 76.2%, respectively, compared to traditional battery storage solutions,” the team said. “Notably, these improvements were achieved with a cooling unit having a coefficient of performance of less than ten and a minimal battery capacity of 20 kWh, highlighting the method's efficiency and its potential to significantly lower system costs and environmental impacts compared to traditional control strategies.”
The results also showed that a traditional system would require a 100 kWh battery to show the same mean and maximum ramp rate that the novel method achieved with a 20 kWh battery. “In other words, the proposed method reduced the required battery capacity by nearly 80%,” the team concluded.
The method and its demonstration were presented in “Enhancing grid stability in PV systems: A novel ramp rate control method utilizing PV cooling technology,” published in Applied Energy. The research was conducted by scientists from Japan’s Osaka University, as well as the Belgian research and development organization Interuniversity Microelectronics Centre (imec) and the Katholieke Universiteit Leuven (KU Leuven).
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