Partial State-of-Charge Mitigation in Standalone Photovoltaic Hybrid Storage Systems

Abstract

Energy Storage in photovoltaic installations has increased in popularity in recent years due to the improvement in solar panel technology and energy storage systems. In several places where the grid is not available, in remote isolated rural locations or developing countries, isolated photovoltaic installations are one of the main options to power DC micro-grids. In these scenarios, energy storage elements are mandatory due to the natural day-night cycles and low irradiation periods. Traditionally, lead-acid batteries have been responsible for this task, due to their availability and low cost. However, the intermittent features of the solar irradiance patterns and load demand, generate multiple shallow charge–discharge cycles or high power pulses, which worsen the performance of these batteries. Some Hybrid Energy Storage Systems (HESSs) have been reported in the literature to enhance the lifetime and power capabilities of these storage elements, but they are not intended to overcome the Partial State of Charge (PSoC) issue caused by daily cycles, which has an effect on the short and mid-term performance of the system. This paper studies the impact of the already proposed HESSs on PSoC operation, establishing the optimal hybrid ratios, and implementing them in a real installation with a satisfactory outcome.

Energy Shortage Failure Prediction in Photovoltaic Standalone Installations by Using Machine Learning Techniques

“…To evaluate the two types of RNN, three metrics widely used in regression problems are chosen: Root Mean Squared Error (RMSE) (9), Mean Absolute Error (MAE) (10), and Mean Absolute Percentage Error (MAPE) (11).…”

“…However, these overcharges reduce battery life, thus it is interesting to only overcharge the battery packs when needed. Other more complex solutions have been studied as in [9], where a hybridization between two battery chemistries is used to improve the performance of the installation.…”

“…while (NOT (EarlyStopping condition) AND (number of epochs < max epochs)) (5) Propagate the input forward though the network. (6) Calculate the output for each neuron/cell(7) Calculate the error signal(8) Propagate the errors backward through the network(9) Update the weights of each neuron/cell(10) Calculate the global error based on the cost function(11) end while Prediction stage of the NN based system.…”

Investigations into the Charge Times of Lead–Acid Cells under Different Partial-State-of-Charge Regimes

“…However, emerging use cases for batteries include those of home energy storage, off-grid use, load levelling, and micro-grids [6][7][8][9]. In these scenarios, the battery is cycled far more frequently and is generally operated at intermediate states of charge in a partial-state-of-charge (PSOC) regime [5,[10][11][12]. Whether the battery fully charges can be dependent on weather, energy prices, and household loads [13], as such, the full charges are irregular.…”