Technical Proposal for a Photovoltaic Energy Storage System at a Hotel in Portugal

Portuguese hotels are commercial buildings that operate continuously throughout the year; guest room air conditioning, hot water systems, kitchen and bathroom facilities, and wastewater treatment equipment all consume electricity on an ongoing basis. In addition to conventional grid-connected operation, this project also supports independent power supply through a combination of photovoltaic (PV) systems and energy storage when the mains supply is unavailable, thereby reducing the hotel’s electricity procurement costs. The configuration of the PV strings and the wiring of the energy storage system must be compatible with the interfaces of the integrated inverter-controller unit to ensure stable power generation and system operation. Based on the hotel’s actual electricity requirements, this project combines photovoltaic systems, integrated inverter-controller units and energy storage equipment, balancing the economic efficiency of day-to-day operations with the reliability of backup power supply during power cuts.

📌I. Main System Equipment Configuration

System Configuration Diagram

1.☀Photovoltaic modules

Solar panel installation diagram

Each module has a power output of 630W; with a total of 396 modules, the total installed capacity is: 396 × 0.63 = 248.28 kWp. The modules’ STC electrical parameters are: Voc = 48.8V, Vmp = 42.0V, Voc temperature coefficient −0.24%/°C; the modules have an IP68 protection rating and are suitable for use in outdoor environments across Europe. String configuration: 18 strings of 20 modules each, and 2 strings of 18 modules each, totalling 20 strings; 2 strings are connected in parallel to a single MPPT interface.

2.⚡All-in-one photovoltaic-storage inverter-controller unit

Rated AC output: 125 kW; MPPT operating voltage range: 150–950 Vdc; maximum DC input voltage: 1,000 Vdc; features two independent battery DC interfaces, with a maximum charge/discharge current of 100 A per channel; rated grid-connected output: 125 kW; rated output in standby mode: 125 kW; supports seamless switching between grid-connected and off-grid modes, and supports bidirectional battery charging and discharging.

3.🔋Energy storage batteries

Four 241 kWh high-voltage energy storage cabinets, each with a battery operating voltage range of 300–950 Vdc. The four cabinets are divided into two groups, with each group comprising two cabinets connected in parallel to form a single battery cluster; the two battery clusters are connected to the inverter’s two battery DC interfaces respectively, with a total energy storage capacity of 964 kWh. After the BMS of each energy storage cabinet is configured in a daisy-chain network, the communication signals from the two groups of battery clusters are connected to the corresponding battery communication ports on the inverter, enabling the inverter to manage the charging and discharging, monitor the status and provide protection control for all four energy storage cabinets. Each energy storage cabinet is equipped with an independent DC protection switch, facilitating maintenance or disconnection of individual units from the system without affecting the operation of the remaining energy storage units.

4.✅ System design parameters: 

average daily power generation of 1,247 kWh; daily energy storage charging of 964 kWh. Photovoltaic power is prioritised for supplying the hotel’s on-site loads, with surplus electricity stored in the energy storage batteries. When photovoltaic output is insufficient, the energy storage system discharges electricity to supplement the load, enabling fully independent operation powered solely by solar and energy storage without the need for the mains grid.

II. Voltage Matching Verification for Photovoltaic Arrays

This project comprises a total of 20 strings, of which 18 consist of 20 modules each and 2 consist of 18 modules each; two strings are connected in parallel to a single MPPT interface. The open-circuit voltage of the 20-panel strings is 976 V, with a maximum power point voltage of 840 V; the open-circuit voltage of the 18-panel strings is 878.4 V, with a maximum power point voltage of 756 V. The voltages of both sets of strings fall within the inverter’s MPPT operating voltage range and DC withstand voltage limits, enabling normal maximum power point tracking and meeting the operational requirements of the equipment.

III. Statistics on the hotel’s electrical load, system load capacity and backup duration

The hotel’s load comprises guest rooms, multi-purpose rooms, sewage treatment and reserved ancillary facilities; the breakdown of equipment power is as follows:

In the table above, 95 kW represents the theoretical maximum load when all equipment is switched on simultaneously; in the hotel’s actual operations, the probability of all equipment running at full load simultaneously is very low, and the actual daily load is lower than this figure. The rated output power of the integrated inverter-controller unit in backup mode is 125 kW, which exceeds the hotel’s total calculated load.

The total energy storage capacity is 964 kWh; assuming a comprehensive system discharge efficiency of 90 per cent, the effective usable energy storage capacity is approximately 867.6 kWh.

Operating condition 1: Power supplied by energy storage only (no photovoltaic input)

Operating condition 2: No mains supply; standalone power supply via solar PV and energy storage only

Video: Diagram showing the direction of current flow in the system

The system operates completely off the mains grid; during the day, the hotel’s loads are powered directly by the photovoltaic system, with surplus electricity stored in the energy storage system; at night, the hotel’s electricity supply is entirely maintained by discharging energy from the storage batteries. The system generates an average of 1,247 kWh of photovoltaic power per day and can store 964 kWh of electricity daily. During the day, when photovoltaic output is sufficient, it can support the hotel’s full load of 95 kW; at night, the load is maintained by the energy storage system. Due to the limitations of the storage capacity, prolonged operation at the full load of 95 kW is not advisable; it is recommended that the load be limited to 60 kW or below during normal night-time operations to ensure continuous power supply throughout the night. In the event of prolonged overcast or rainy weather resulting in insufficient solar irradiance, non-essential high-power loads should be reduced appropriately to ensure the uninterrupted supply of the base load.

Note: In standalone solar-plus-storage mode, the maximum output of the inverter remains at 125 kW; this power limit must not be exceeded.

IV. System Operating Modes

System Topology Diagram

This project is a purely off-grid system with no connection to the mains electricity supply; it relies entirely on the combined output of photovoltaic (PV) panels and energy storage to power the hotel’s entire load.

1. Daytime (ample sunlight) mode: Electricity generated by the PV array is prioritised to supply all electrical loads in the hotel, including guest room air conditioning, water heaters, sewage treatment and multi-purpose rooms; when PV output exceeds the hotel’s real-time electricity consumption, the surplus energy is used to charge the energy storage batteries, achieving a daily charge of 964 kWh; Once the batteries are fully charged, the system implements power limiting.

2. Night-time / Low-light operation mode: With no photovoltaic output, all hotel loads are powered by discharge from the energy storage batteries; when the battery charge level drops to a preset protection threshold, the system issues an alert and disconnects non-high-power loads such as electric water heaters and air conditioning, prioritising power supply to critical equipment such as lighting and sewage treatment systems.

3. Emergency mode for insufficient sunlight: In the event of consecutive overcast days or low irradiance conditions, where photovoltaic generation is insufficient, the system actively restricts the operation of non-essential high-power equipment based on the battery’s State of Charge (SOC) to prevent excessive discharge and maintain the continuous operation of the hotel’s basic loads.

V. Analysis of Power Generation, Energy Storage and Load Matching

The photovoltaic installation has a capacity of 248.28 kWp, with a designed average daily power generation of 1,247 kWh and equivalent daily sunshine hours of 5.02 hours, matching the local solar radiation levels in Portugal.

The system’s daily energy storage charging capacity is 964 kWh, with an effective usable energy storage capacity of 867.6 kWh. During the day, photovoltaic generation directly supplies the hotel’s load, with surplus electricity stored in the energy storage system; at night, the hotel’s electricity requirements are met by discharging the energy storage system.

In a standalone photovoltaic-and-storage operation scenario, the system’s power generation and energy storage capacity can meet the hotel’s electricity requirements for the majority of the time; during prolonged periods of overcast weather, load management is required. The inverter has a rated AC power of 125 kW, with a DC installed PV capacity of 248.28 kWp and a DC over-design factor of approximately 1.99, representing a well-established configuration for commercial and industrial solar-storage systems; in low-light conditions, PV output is utilised to the full, whilst in high-light conditions the inverter limits power output to maximise the system’s total lifetime energy yield.

VI. System Protection and Operations and Maintenance

The system is equipped with a comprehensive suite of hardware protection functions, including DC-side surge protection, AC-side surge protection, insulation monitoring, and protection against overvoltage, overcurrent and reverse polarity. The equipment supports remote monitoring via a cloud platform, enabling the viewing of power generation data for each MPPT branch, battery SOC status, charge and discharge power, and real-time load data for the hotel, thereby facilitating O&M personnel in monitoring the system’s operational status.

The hardware protection rating of the equipment meets the requirements for outdoor use and is suitable for coastal environmental conditions in Portugal. When operating in a standalone photovoltaic-storage configuration, O&M personnel can monitor the remaining battery charge via the monitoring platform and adjust the load in a timely manner to prevent over-discharge of the batteries; the energy storage cabinet is equipped with an independent protection switch, allowing a single unit to be isolated for maintenance in the event of a fault, whilst the remaining equipment continues to maintain system operation.

VII. Summary

This project involves the design of a photovoltaic and energy storage system solution based on the hotel’s total calculated load of 95 kW. The photovoltaic array comprises 20 strings: 18 strings of 20 modules each and 2 strings of 18 modules each, with the string voltages matched to the inverter’s MPPT range; Four 241 kWh energy storage cabinets are connected in parallel in pairs to form two battery clusters, each connected to one of the inverter’s two battery interfaces, thereby enabling the full energy storage capacity to be integrated and managed, ensuring stable system operation.

The system’s effective usable energy storage capacity is 867.6 kWh; in the event of a grid failure, this can support the hotel’s entire 95 kW load for approximately 9.1 hours. In addition to conventional grid-connected operation, the system supports standalone power supply via photovoltaic and energy storage alone when the mains supply is unavailable. By combining on-site photovoltaic generation for self-consumption with energy storage to smooth out peak and off-peak loads, the system reduces the hotel’s electricity costs whilst providing emergency power backup in the event of a power cut.