Grid stability is one of the biggest challenges in renewable integration. Onshore wind and solar farms generate clean electricity, but the variability of their output causes voltage fluctuations that can compromise reliability. Reactive power is one of the fundamental mechanisms for controlling such instabilities.
In this article, we explore why reactive power is essential, the technologies used in onshore renewable projects, and how they help improve grid stability.
Understanding Reactive Power (RP) and its Importance
Reactive power balance is essential for maintaining voltage levels, ensuring the efficient transmission of electricity, and preventing voltage instability in the grid. Unlike active power (measured in watts), reactive power (measured in volt-amperes reactive, or VARs) impacts voltage levels. Without adequate RP, power grids face the risk of voltage collapse, power losses, transmission congestion, and system inefficiencies. Having proper compensation in place ensures that electricity from renewable assets can be delivered efficiently with the reduced likelihood of voltage instability and system constraints.
Reactive Power Compensation Technologies for Onshore Renewables
Onshore renewable plants rely on reactive power compensation to meet grid code requirements and maintain stability. Different technologies are applied depending on the network’s strength, variability, and compliance obligations.
1. Static Synchronous Compensation (STATCOMs)
STATCOMs are the most dynamic solution. Using voltage-source converters, they can inject or absorb reactive current within milliseconds, making them highly effective for wind and solar farms where operating conditions change rapidly. Their ability to stabilise voltage in weak or remote grids, combined with a smaller physical footprint than traditional systems, has made them a leading choice for modern renewable integration. Crucially, STATCOMs also improve fault ride-through (FRT), allowing generation to remain online during short-term disturbances rather than disconnecting from the grid.
2. Static VAR Compensators (SVCs)
SVCs provide a more cost-effective but slightly less flexible option. They regulate reactive power through thyristor-controlled reactors and capacitors, offering smooth voltage control under varying conditions. In some cases, as well as stabilising voltage, static VAR compensators can help mitigate the user’s harmonics to improve power quality. They are also built to last; their service life can be measured in decades, along with minimal maintenance requirements.
3. Shunt Capacitor Banks
Shunt capacitor banks are the simplest and most financially friendly way to provide leading reactive power. While they lack the dynamic response of STATCOMs or SVCs, they are an effective tool for steady-state voltage control and power factor correction. Their straightforward installation and ability to reduce transmission losses make them attractive where budget and speed of deployment are priorities.
4. Synchronous Condensers
These technologies are seeing renewed use in areas with weak grid strength and high renewable penetration. Unlike purely electronic systems, these rotating machines supply both reactive power and mechanical inertia, helping regulate frequency and improve fault ride-through. Their proven track record over decades of service makes them a dependable choice, particularly where additional short-circuit strength is required to support grid stability.
The Benefits of Reactive Power Compensation in Onshore Renewables
Grid Voltage Control
Reactive power technologies dynamically adjust voltage, keeping it within safe operating limits and reducing the risk of dips or overvoltages. This is critical for renewable integration, where variable wind speeds and solar irradiance can otherwise cause destabilising voltage swings.
System Stability
By mitigating power oscillations and improving fault ride-through, reactive power compensation strengthens overall grid resilience. This prevents cascading failures and allows renewable plants to stay connected during disturbances.
Caption: DIgSILENT simulation results of a three-phase fault demonstrating full compliance with ENA G99 fault ride-through requirements, confirming system stability during severe disturbances.
Enabling Renewable Integration
Effective reactive power management allows wind and solar farms to connect seamlessly, reducing curtailment and ensuring maximum clean energy output. Without it, renewable projects risk inefficiencies, forced output limits, and reduced profitability.
Commercial Value
Reactive power compensation reduces transmission losses, avoids non-compliance penalties, and ensures more generated electricity is delivered to the grid. The result is stronger project revenues and a more reliable return on investment.
Power Factor Correction and Efficiency
Power factor optimisation can minimise the transmission losses and maximise its energy transfer capability, while also ensuring compliance with grid operator requirements. Compensation reduces the risk of financial penalties and improves the cost efficiency of renewable generation.
Regulatory Requirements and Grid Code Compliance
Caption: Simulation confirming full compliance with ENA G99 falling frequency requirements. The system maintains active power output within the required range, ensuring stability under frequency dips.
Grid operators impose strict reactive power requirements to keep networks stable. In the UK, NESO requires medium-to-large scale generators to operate within a power factor range of 0.95 lagging to 0.95 leading at the connection point. This ensures renewable projects support voltage levels rather than destabilising the grid.
To connect, developers must demonstrate:
- Voltage support capability – delivering dynamic voltage control using solutions such as STATCOMs or SVCs (If needed).
- Reactive power verification – proving that the plant can both supply and absorb reactive power before connection approval.
- Compliance with penalties in mind – non-compliance can result in grid access restrictions or significant financial penalties.
Internationally, the same principles apply. ENTSO-E network codes in Europe and FERC Order 661-A in the United States both require renewable generators to provide dynamic voltage support. Countries such as Germany and Australia enforce equally stringent policies to safeguard grid stability.
How EPS Delivers Reactive Power Solutions
EPS has supported a wide range of renewable energy projects across the UK where reactive power compensation was critical to successful grid integration. Our role typically focuses on the studies, modelling, and compliance engineering that underpin technology deployment.
Notable projects include:
- Comprehensive grid connection studies, aligning projects with UK NESO, ENTSO-E, ENA G99 Recommendations, and other international standards to secure grid connection approvals.
- Power system studies and specifications for STATCOM and SVC deployment on large-scale wind and solar farms, ensuring voltage stability and compliance with NESO requirements.
- System strength and feasibility assessments for synchronous condensers in weak grid areas, providing the justification for reactive power compensation, additional inertia and short-circuit support.
- Design studies for capacitor bank integration in industrial renewable applications, delivering cost-effective power factor correction and reduced system losses.
EPS Projects: Ensuring Reactive Power Compliance for UK Solar Farms
Client: Undisclosed, 10.5 MW Solar PV Farm
Background: Onshore Renewables
Location: Kent, UK
Date: August 2025
EPS was engaged to carry out a full G99 Grid Compliance Study for a new generation project. A critical part of this assessment focused on the project’s reactive power capability and its role in supporting voltage stability at the connection point.
Caption: DIgSILENT PowerFactory simulation showing full compliance with ENA G99 V–Q reactive power requirements, confirming the system’s ability to support grid voltage.
Our engineers conducted detailed simulations in line with ENA G99 Clauses 13.5.5 and 13.5.6, covering both V–Q (voltage-reactive power) and P–Q (active-reactive power) capability. The model was tested across the full operating range and under conditions below registered capacity.
Caption: Simulation confirming full compliance with ENA G99 P–Q reactive power requirements. Results show the system can supply and absorb reactive power effectively at both full and part-load operation
The output from our simulations using DIgSILENT confirmed that the system could provide adequate voltage support and maintain stability under varying network conditions and that no additional mitigation or corrective measures were required to meet regulatory standards.
By validating reactive power performance early in the connection process, EPS ensured the project achieved regulatory approval and was ready for safe and reliable integration into the grid. This work highlights our capability to deliver precise compliance studies that help clients reduce risk and accelerate project delivery.
Final Thoughts
Reactive power is not a secondary consideration; it’s a foundation of modern power systems. As adoption of renewable power generation continues to grow, effective compensation plays an essential part in safeguarding network stability, optimising operational efficiency, and ensuring compliance with increasingly stringent grid codes.
At EPS, we help clients navigate this complexity through detailed power system studies and design support for advanced reactive power compensation technologies.
