Short Definition
A hybrid energy system combines multiple energy sources, storage systems, and, where applicable, controllable loads within a shared energy system. Typical combinations include photovoltaic (PV) systems and battery energy storage systems (BESS), PV and diesel generators, or PV, BESS, and generators. The system can be grid-connected, fully off-grid, or designed for temporary island operation.
Hybrid Energy Systems at a Glance
- A hybrid energy system coordinates generation, storage, and consumption at a technical level.
- A higher-level control system processes measurements and distributes setpoints according to defined priorities and operating limits.
- Possible objectives include increased self-consumption, reduced energy costs, improved security of supply, or greater energy independence.
- The hybrid energy system refers to the complete technical system. An EMS can be used within it as a higher-level control layer but is not the same as the hybrid system itself.
- Monitoring, active control, electrical grid-forming, and protection systems perform different functions.
How Does a Hybrid Energy System Work?
System operation is based on measurements from the integrated components and central electrical metering points. The grid connection point records how much power the site imports from or exports to the public grid. Other measurements may include PV generation, site load, the BESS state of charge and power limits, as well as the status, operational readiness, and available power of a generator.
A higher-level control system evaluates this information and distributes setpoints according to defined priorities, operating limits, and control objectives. In a typical grid-connected PV-BESS system, locally generated PV power is first balanced against the current site load. If there is a power surplus, the control system can charge the BESS. Any remaining power is exported to the public grid or reduced by limiting PV output. If there is a power deficit, the BESS can be discharged to reduce grid import or peak loads.
The actual energy flows result from the power balance at the electrical node. They depend on factors including the current measurements, the setpoints for the PV system and BESS, and the selected control strategy. Possible operating objectives include self-consumption optimisation, peak shaving, zero export, maintaining a fixed grid import or export setpoint, and maintaining an energy reserve.
Generator Control and Island Operation
In a system with a generator, the control system can start the generator when the state of charge is low, the load is high, or an energy deficit persists. Factors to be considered include minimum running times, start and stop thresholds, minimum load, power reserves, and, where applicable, warm-up, cool-down, and follow-on operating periods. Hysteresis and time delays prevent frequent switching and can help operate the generator within a suitable power range.
During island operation, at least one suitable component must provide the voltage and frequency reference and stabilise the local grid. A conventional grid-following PV inverter requires a grid reference and generally cannot establish a stable island grid on its own. Grid-forming capability, synchronisation, and protection functions must therefore be included in the electrical system architecture.
Available generation and storage capacity must also be continuously balanced against the site load. If the available power reserves are insufficient, prioritised load shedding, limitation of flexible loads, or generator start-up may be required. Depending on the application, black-start capability and controlled reconnection to the public grid must also be considered.
Where Are Hybrid Energy Systems Used?
- Commercial and industrial sites: PV and BESS are combined to increase self-consumption, limit peak loads, or shift grid import over time. Flexible loads or charging infrastructure can also be included in the operating strategy.
- Off-grid systems: At remote sites, PV, BESS, and often a generator jointly supply energy. The BESS balances short-term fluctuations, while the generator can cover longer periods of insufficient generation.
- Sites with an unstable grid supply: A hybrid energy system can support backup or island operation during grid outages or insufficient grid quality, provided that the components, switching equipment, and protection systems are designed accordingly.
- Microgrids: Multiple generators, storage systems, and loads are coordinated within a local electrical grid. The microgrid can operate permanently grid-connected, fully off-grid, or temporarily disconnected from the public grid.
Benefits, Limitations, and Technical Requirements
A coordinated hybrid energy system can improve the use of renewable energy, reduce generator fuel consumption, and increase security of supply. The achievable benefits depend on the load profile, energy generation, component sizing, operating objectives, and energy and fuel costs.
The components must be coordinated electrically, communicatively, and in terms of control engineering. Depending on the device, structured measurement, status, and control data can be exchanged via Modbus TCP, Modbus RTU, CAN, or manufacturer-specific APIs. Digital inputs and outputs are frequently used to transmit individual states, enable signals, or switching commands.
APIs can be provided locally or through the cloud. Because cloud-based connections may be subject to delays and interruptions, they are not suitable for every control task. The update rate, communication latency, communication reliability, and system behaviour during communication failures must be considered, particularly for time-critical functions.
The mere availability of an interface is not sufficient. The required measurements, operating states, and control commands must actually be available and transmitted with adequate quality. Limited communication capabilities, inaccurate measurements, or devices that cannot be controlled may restrict the functionality of the overall system.
A basic hybrid energy system can operate using the decentralised control functions of its individual components. However, coordinated optimisation of multiple generators, storage systems, and loads often requires a higher-level control layer. Monitoring makes energy flows and operating states visible but does not automatically coordinate the components actively. Grid-forming and electrical protection functions must, in turn, be performed by plant components designed for these purposes.
How Can EcoPhi Be Used to Implement a Hybrid Energy System?
EcoPhi can serve as a multi-vendor monitoring, communication, and EMS layer within a hybrid energy system. Measurements from PV inverters, BESS, generators, energy meters, and loads can be consolidated, visualised, and processed using project-specific control logic.
Depending on the system architecture and available device interfaces, the functional scope can include setting or limiting PV output, providing charging and discharging setpoints for the BESS, controlling generators, and regulating power at the grid connection point. The specific functionality is adapted to the integrated components, available data points, and operating objectives of the project.
EcoPhi does not perform electrical grid-forming or protection functions. These must be implemented using appropriately designed inverters, generator controllers, switchgear, and protection devices.
Hybrid Energy Systems in Summary
A hybrid energy system connects different energy sources, storage systems, and loads within a shared technical system. Coordinated operation requires a suitable electrical architecture, reliable measurements, available device interfaces, and clearly defined control strategies. The required control and protection functions depend on the energy supply task, grid conditions, and economic operating objectives.
Frequently Asked Questions About Hybrid Energy Systems
Is Every Hybrid Energy System an EMS?
No. The hybrid energy system refers to the complete technical system comprising generators, storage systems, loads, and other components. An EMS can be used within this system as a higher-level control layer.
Can a PV-BESS Hybrid Energy System Continue Operating During a Grid Outage?
Only if it is designed for island or backup power operation. At least one suitable component must provide the voltage and frequency reference. Appropriate switching equipment, protection systems, and continuous power balancing are also required.
Which Interfaces Are Used in Hybrid Energy Systems?
Structured measurement, status, and control data is frequently transmitted via Modbus TCP, Modbus RTU, CAN, or manufacturer-specific APIs. Digital inputs and outputs can additionally represent individual states, enable signals, or switching commands. The functions that can be implemented depend on the data points and control commands actually available.