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Off-grid energy storage systemdesign

Photovoltaic power generation systems are usually divided into on-gridsystem, on-grid&off-grid system and off-grid system. This article will introduce the designelements of an off-grid energy storage system.

The common off-grid energy storage system is a standby power supply system(UPS), whichis widely used in areas with frequent power outages and unstable power grids, or in loadswithhigh requirements for power supply guarantee rate. Its core component is an integratedall-in-one machine with dual functions of charging and inverting. When the grid is normal, theinverter can directly connect the grid to supply power to the load, and at the same time, it cancharge the storage battery, and ensure that the charging of the battery will automaticallystopwhen there is an outage or the battery is fully charged. When there is a blackout, the inverter will automatically cut off the connection between the grid and the load, start the inverter instantlyusing battery to provide power for the load.

Diagram of Off-grid System connected to the grid

Off-grid energy storage system is a PV energy storage off-grid system composed of PVpower generation system, energy storage system and inverter system, etc. It can directlyusePVpanels to charge the battery to meet the demand of electricity.Off-grid systemis mainly suitablefor power loads far from the grid, and has great market demand space in some communication, border guard posts, islands or field operations, especially in less developed countries andregions such as Africa.

Case Study of South Africa’s 15KW Off-grid Household Energy Storage Project
Related Product: SPF 5000TL HVM

Off-grid energy storage power stations can also be installed in places where power isoftencut off or power supply is unstable. The battery system can be charged not only by PVsystem, but also by conventional power to ensure power supply.

Case Study of Colombia’s 15KW Off-grid Household Energy Storage Project
Related Product:SPF 3000 ES
Off-grid photovoltaic energy storage power station

Issues to consider in the design process

1. Leave enough margin for the inverter.

Usually, off-grid photovoltaic power generation is a power supply systemfor specific loads. Inthe design process, the rated power of the load connected to the system should be calculatedandchecked, and the output power of the inverter should be determined according to the total powerof the load. The surge current, starting power and reactive power required by some special loadsshould be fully considered, and the possible impact and demand on the inverter shouldbeleft enough margin. Once the capacity of the inverter is determined, the capacity of the connectedload cannot be expanded or increased at will, so the off-grid photovoltaic power generationsystem should leave enough margin for the inverter.

2. Fully consider the matching of various loads and Growatt inverters.

The off-grid photovoltaic power generation system should fully consider the matchingof various loads and Growatt inverters, especially if there are inductive loads such as washing machines, refrigerators, air conditioners, etc., sine wave or quasi-sine wave inverters must be selectedandequipped to meet the demand of inductive loads for inverter output waveforms.

3. Calculate the daily average working hours and power consumption of each load

Design the capacity of photovoltaic array and storage battery based on customer demand, soas to meet the demand of users and control the overall investment cost.

4. Take the solar radiation in the worst month of the year as the design basis

Off-grid system should ensure the least radiation month, and photovoltaic systemcanstill guarantee power supply (usually the worst month of the year is in winter. This is different fromon-grid system, and the design basis of on-grid power station is the total solar radiationinthewhole year. Therefore, off-grid photovoltaic power generation systems usually designtheinclination of photovoltaic arrays according to the best inclination of the worst month. That istosay, the array inclination angle of off-grid system is usually 2 ~ 8 larger than thelocal geographical latitude angle to take into account the weak solar radiation in winter.

5. The capacity Qp of photovoltaic array can be calculated by the following formula.

Pi: load power hi: load working time h: worst monthly solar radiation daily peak hour ηb: batterycharging and discharging efficiency ηc: controller efficiency ηi: inverter efficiency.

6. The battery capacity Qb can be calculated by the following formula

Summary: Only by well designing the system can the maximum power generationof thepower station be realized. In specific projects, it is suggested to refer to and applyflexibly, and not to design blindly.

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