Energy management system to combine residential PV with gravity storage

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A group of researchers from the International University of Rabat in Morocco has developed a smart house energy management system (SHEMS) to optimize electricity production in residential PV systems combined with gravity energy storage (GES).

“The SHEMS supports two-way communication between smart home users and grid utilities,” the research’s corresponding author, Asmae Berrada, told pv magazine. “SHEMS is flexible in managing and controlling smart home appliances, renewable energy resources, and energy storage systems in order to participate in electricity conservation and demand response.”

In the paper “Intelligent Energy Management System for Smart Home with Grid-Connected Hybrid Photovoltaic/Gravity Energy Storage System,” published in the Journal of Energy Storage, Berrada and her colleagues explained that the proposed system is based on a novel one-week dynamic forecasting model that considers PV power generation, the state of charge of the GES system, the electricity price, and the scheduled load on the horizon for one week.

“In addition, it enables the user to perform intelligent household energy allocation, optimize household load allocation in the time dimension, achieve customer demand response, relieve grid pressure during peak hours, and improve grid stability,” they stated, adding that the system’s hardware consists of a SHEMS center, smart meters, communication and networking systems, and other unspecified smart devices that connect all home appliances.

The SHEMS usually uses PV power generation from the solar array to power the house’s loads. When excess electricity is produced, the system uses it to energize the GES system or injects it into the grid. When PV power is insufficient to meet all the household’s electricity needs, the GES system is activated by the SHEMS. “In situations where neither the PV power nor the GES power is sufficient to cover the entire energy demand of the loads, the system draws power from the electrical grid,” the Moroccan group said. “The grid acts as a backup source of electricity to ensure that all the loads in the house receive the required power.”

The researchers validated their model through a case study considering a household with a maximum power consumption of 6 kW, a 5 kW PV system, and a 0.5 kWh GES system with a water tank volume of 28.63 m3. The house is assumed to also use heating, ventilation, and air conditioning (HVAC) systems and to host EV recharging, with the EV battery being programmed to charge during the period between 1 am and 5 am.

“This time window takes advantage of the low energy prices and ensures that the vehicle is fully charged by the morning,” the research team explained. “Other loads are scheduled to operate when there is available PV production, except for the refrigerator, lighting, TV, computer, and fans. However, a portion of the energy consumption for these appliances can be supplied by the energy storage system (GES).”

Through their modeling, the academics found that the PV-GES unit can cover the household’s power demand for approximately 8 h each day, with discharging of the GES system occurring usually between 4 pm and 5 pm. “This leads to significant reductions in the house’s energy costs and its adverse environmental footprint,” it emphasized.

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