Everything a Solar EPC Should Know About BESS for Power Plants
Everything a Solar EPC Should Know About BESS for Power Plants
As a solar developer or EPC, increasing solar energy penetration at your power plants is likely a top priority. However, the mismatch between solar production curves and load consumption patterns can make this difficult. One of the most effective and increasingly popular solutions is integrating Battery Energy Storage Systems (BESS) with your solar PV installation.
But when exactly is BESS used in solar power plants, and how does it work in practice, and why should the power plant controller be part of the conversation from day one of system design rather than an afterthought? In this article, we explore the key benefits of integrating battery storage with solar energy systems, the role of the power plant controller in making that integration work in the field, and how Elum Energy’s Energy Management System (EMS) helps capture this value.
1. BESS Terms: Definitions and Explanations
- Battery racks: Racks composed of different cells that convert electrical energy to chemical energy. Different technologies exist, the most popular being Lead-Acid or Lithium-Ion.
- BESS: Battery Energy Storage Systems are composed of a Power Conversion System (PCS) and batteries.
- EMS: An Energy Management System is a controller able to execute a high-level strategy decided by the final user.
- Solar power plants: In this article, the term refers to large-scale solar installations with a capacity greater than 1 MWp, including grid-tied systems, off-grid cities and remote islands, and isolated industrial sites such as off-grid mines.
Broadly, these installations fall into two categories: grid-tied and off-grid solar power plants.
In grid-tied applications, national Distribution System Operators (DSOs) aim to reduce the intermittency of solar energy production. Batteries can help address this issue by stabilising energy output and enhancing grid reliability.
In off-grid applications, such as remote cities, islands, or mining operations, electricity is primarily generated by thermal power plants. However, fuel costs are high and volatile due to fluctuations in global oil prices and logistical or security costs.
To reduce this dependence on fossil fuels, energy suppliers are increasingly integrating local energy provisions, such as PV plus storage, with their existing diesel gensets. This hybrid approach lowers fuel consumption, enhances energy reliability, and reduces operating costs.
2. Advantages of Energy Storage Systems for Power Plants
BESS systems, when combined with other power sources, can serve a variety of applications depending on the sizing of PV, batteries, and genset, but also on the load curve and specific client requirements.
Within the context of power plants, BESS provides the following features:
Increased Reliability
Storage can be used for backup purposes. When the grid is down, storage can respond instantaneously and take over supplying energy. This is an essential feature for industries where constant production is crucial, as electrical blackouts can damage expensive equipment, such as in the mining industry. For this reason, it is important to select a Power Conversion System with an uninterruptible power supply (UPS) function for your BESS.
Reduced Fuel Consumption
BESS stores excess solar energy generated during the day and delivers it during peak demand periods, often during the night in remote cities, villages, and tourist resorts. This means they don’t need to rely on diesel generators to produce power when stored energy is available. In many countries and remote locations, PV plus storage is now more cost-effective than using fuel alone.
Increased Solar Penetration
When PV production is higher than load consumption, BESS can store the excess production during the day to use it for other services. The right sizing between PV, batteries, and gensets is mandatory to maximise PV penetration.
Behind-the-Meter Services
In some countries, utility pricing structures make BESS installations financially attractive:
- Load shifting: When utilities apply time-of-use tariffs, such as peak and off-peak rates, BESS in combination with an EMS can charge during low-cost periods and discharge during high-cost periods to reduce energy bills.
- Peak shaving: For industrial consumers with high demand charges, BESS can discharge strategically during peak usage periods, helping maintain power consumption below the utility’s maximum demand threshold and avoiding costly peak penalties.
In-Front-of-the-Meter Services
For grid-tied applications, some countries have utility services markets that may allow a BESS to be profitable:
- Utilities can purchase solar and BESS energy during the evening with a bonus fee. This avoids running peak plants that can be expensive and polluting. This pricing model is used, for example, in France in non-connected islands (ZNI) where solar and BESS systems have been installed in recent years.
- Utilities can pay for frequency regulation services. When the grid’s frequency is low or high, BESS can be discharged or charged accordingly to stabilise the overall frequency of the national grid.
These services can be combined and customised to meet specific client requirements. Implementing an EMS is essential to ensure the project’s profitability, efficiency, and long-term viability.
3. Characteristics and Limitations of Energy Management Systems
As mentioned above, energy management systems are key to the profitability of a project. The EMS is the central factor that:
- Actively monitors the system’s performance at the device level, including PV inverters, battery PCS, genset controllers, meters, and weather stations.
- Displays operating information via various interfaces using industrial protocols such as Modbus.
- Offers multiple automated modes of operation to meet client requirements.
Different EMS providers exist. Some companies offer Battery Energy Storage Systems with a built-in EMS, while others, like Elum Energy, provide a standalone EMS that is compatible with most leading BESS solutions.
Compatibility
Ensuring EMS compatibility with BESS systems, PV inverters, and genset controllers is crucial for the success of any hybrid energy project. In many cases, gensets are existing, brownfield assets that must be seamlessly integrated into the new system.
For solar developers and EPCs, having a flexible EMS that supports a wide range of equipment allows for optimal system design. This flexibility enables teams to select the best-performing and most cost-effective PV inverters and battery storage systems based on project-specific requirements such as location, budget, and energy demand.
Conformity with Client Requirements
In sectors like utilities and mining, client requirements often come with strict technical constraints that can make or break a project. Choosing an EMS that can be customised to specific site configurations is a major advantage when bidding for microgrid or hybrid energy projects.
Key considerations include:
- Control of relays and loads: The EMS must be capable of managing breaker operations, opening or closing relays based on the system’s operating mode, to ensure safe and efficient load control.
- Support for non-standard site architectures: Many sites have existing, brownfield electrical infrastructure. The EMS must adapt to these unique configurations, taking into account pre-installed equipment and ensuring full interoperability with legacy systems.
4. Why the Power Plant Controller Belongs in the Design Phase
One of the most common mistakes EPCs make when scoping a BESS project is treating the power plant controller as a downstream integration task, something to be sorted out once the PV array, battery racks, and genset have already been specified. In practice, the PPC is the system that determines whether the rest of the equipment can actually deliver the value the project was sized for. Bringing it into the conversation at the design phase, rather than at commissioning, is what separates a BESS project that performs as modelled from one that underdelivers against its business case.
Why Design-Phase Integration Matters
A solar plus BESS plus genset system is only as effective as its control architecture. Depending on the project scale and grid requirements, this role can be handled by an EMS or a PPC. For BESS-based C&I and hybrid projects, the EMS coordinates PV production, battery charge/discharge, genset operation, load behavior, and grid interaction according to the site’s operating strategy. For utility-scale or grid-code-driven projects, the PPC manages plant-level active and reactive power control, ramp-rate limits, frequency response, and grid-code-related setpoints. Defining the right controller layer during the design phase helps ensure that the selected PV inverters, battery PCS, genset controllers, and communication protocols are compatible with the intended control strategy
Designing with the PPC in mind from the outset allows the EPC to verify three things before committing to a bill of materials: that the intended value streams, whether peak shaving, load shifting, or frequency regulation, are technically achievable with the proposed equipment combination; that the sizing of PV, batteries, and genset capacity is coherent with the control strategy that will actually be deployed; and that the selected hardware is compatible with the controller’s supported protocols.
Protocol Compatibility: A Design-Phase Checklist
Protocol compatibility is one of the most frequent sources of late-stage integration delays in BESS projects. EPCs should confirm the following during the design phase, not during commissioning:
- Communication protocols: Most PV inverters, battery PCS units, and genset controllers communicate via Modbus TCP or RTU, but some legacy or brownfield equipment may rely on proprietary protocols, CAN bus, or older serial interfaces that require additional gateway hardware.
- Data point mapping: Confirming that the specific data points the EMS needs, such as state of charge, inverter active and reactive power setpoints, and genset run status, are actually exposed by the selected equipment’s communication interface.
- Brownfield genset integration: Where an existing genset is being retrofitted into a hybrid system, the EPC must verify whether the genset controller supports remote start and stop commands and load-following setpoints, or whether a retrofit controller is required.
- Response time requirements: Confirming that the communication architecture can support the response times required for the intended application; frequency regulation, for example, typically demands sub-second response, which is a materially different requirement from load shifting.
A flexible EMS that supports a wide range of equipment, like Elum Energy's ePowerControl, gives EPCs the freedom to select the best-performing and most cost-effective components for each project, rather than being locked into a single BESS or inverter vendor's proprietary control ecosystem.
Grid-Code Compliance Considerations for BESS Projects
For grid-tied BESS installations, the power plant controller is also the system responsible for grid-code compliance, a dimension that becomes considerably more complex once a battery is added to the equation. Beyond the active power, reactive power, and frequency regulation requirements that apply to a PV-only plant, a hybrid system must also satisfy requirements around how quickly the battery can ramp output up or down, how the system behaves during a grid fault when both PV and battery are contributing to plant output, and how the controller arbitrates between grid-code compliance obligations and the commercial dispatch strategy, such as peak shaving or spot market participation, that the BESS was installed to deliver.
EPCs bidding on grid-tied hybrid projects should confirm early in the design phase which grid code applies at the point of connection, what reactive power capability curve the combined PV and BESS system must support, and whether the relevant grid operator requires the battery to contribute to fault ride-through performance alongside the PV inverters. These requirements directly inform battery PCS sizing and the control architecture the PPC must implement, which is why they cannot be resolved as an afterthought once the system has already been procured.
For a complete technical breakdown of how a power plant controller manages active and reactive power, frequency regulation, and grid-code compliance for both grid-tied and off-grid hybrid plants, see Elum Energy’s dedicated ePowerControl PPC page.
5. Benefits of ePowerControl Technology for Energy Storage Systems
Elum Energy’s ePowerControl technology is purpose-built to enhance the performance, reliability, and scalability of energy storage systems across C&I and utility-scale applications.
Solar Controllers - Integration and Management of Power Sources
To improve a solar power plant’s reliability and efficiency, an energy storage controller is essential.
Elum Energy solar controllers connect to PV inverters, battery PCS, and genset controllers to seamlessly integrate and manage multiple power sources.
Utility Scale Power Plant Control and Optimization
Elum Energy’s advanced EMS will automatically control the output power of PV and battery inverters according to client requirements and respect the thermal plant’s constraints.
The PPC controller can manage the spinning reserve and battery sets, manage the reactive active power, and regulate the frequency adapted to the final client needs. Elum is compatible with most of the inverters, PCS, and genset controllers available in the market.
Remote Monitoring & Customizable Alerts
Through a web platform, ePowerMonitor, Elum Energy provides remote monitoring. The interface displays all key performance indicators across various power sources, giving users complete system visibility.
6. Resource: Learn More About BESS
Battery Energy Storage Systems (BESS), when integrated with a smart Energy Management System like the ePowerControl range, offer significant value across both grid-tied and off-grid power applications. From improving reliability and reducing fuel consumption to enabling load shifting and peak shaving, the benefits are both technical and financial.
For those looking to explore these systems in greater depth, you can deep dive into our Ultimate Guide to Battery Energy Storage Systems, a comprehensive resource for solar professionals looking to stay ahead in a rapidly evolving energy landscape.
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