Table of Contents
Retrofitting and upgrading existing turbines has become a strategic priority for energy companies worldwide as they seek to maximize the value of their existing infrastructure while meeting modern performance standards and environmental regulations. These modernization projects offer a cost-effective alternative to complete turbine replacement, enabling operators to extend equipment lifespan, improve efficiency, reduce operational costs, and integrate cutting-edge technologies without the massive capital expenditure required for new installations.
The practice of turbine retrofitting spans multiple energy sectors, from wind farms to hydropower facilities and gas turbine power plants. By retrofitting aging turbines with modern control systems, power generation companies are extending equipment lifespans, enhancing operational efficiency, and tapping into robust global support networks. This comprehensive approach to asset management has proven particularly valuable as global energy demand continues to rise while supply chains face constraints and new equipment costs escalate.
Understanding Turbine Retrofits and Their Strategic Value
A turbine retrofit involves systematically upgrading specific components or systems within an existing turbine installation to improve performance, reliability, or compliance with current standards. Unlike complete repowering, which replaces entire turbines, retrofitting focuses on targeted improvements that deliver significant benefits while preserving the core infrastructure and minimizing downtime.
The strategic value of retrofitting becomes evident when considering the age of existing energy infrastructure. A significant portion of the U.S. hydropower fleet is over 50 years old, with original turbines and generators designed with the technology and operational constraints of their time. Similar aging patterns exist across wind farms and thermal power plants globally, creating enormous opportunities for performance improvements through modernization.
Retrofit solutions provide comprehensive and cost-effective solutions for updating older turbines – a sustainable and profitable choice compared to investing in new turbines. This economic advantage stems from several factors: reduced capital expenditure, shorter implementation timelines, minimal civil engineering work, and the ability to maintain existing grid connections and regulatory approvals.
Key Drivers for Turbine Retrofitting
Several compelling factors drive energy companies to pursue retrofit projects:
- Economic Efficiency: Retrofits typically cost a fraction of new turbine installations while delivering substantial performance improvements
- Extended Asset Life: Modern components can add decades to the operational lifespan of existing turbines
- Regulatory Compliance: Upgrades enable older turbines to meet current environmental and grid code requirements
- Performance Optimization: Advanced control systems and components unlock efficiency gains previously unattainable
- Reduced Downtime: Targeted upgrades minimize operational interruptions compared to complete replacements
- Environmental Benefits: Upgrading a turbine makes great sense from a climate perspective: No resources are used building a new turbine, and extended service life means more low-emission energy from the same asset
Wind Turbine Retrofit Projects: Real-World Examples and Outcomes
The wind energy sector has embraced retrofitting as a critical strategy for maintaining competitiveness and extending the productive life of wind farms. As the first generation of commercial wind turbines reaches the end of their original design life, operators face critical decisions about whether to decommission, repower, or retrofit these assets.
Control System Retrofits in Wind Turbines
A team performing a wind turbine retrofit refits an existing turbine with new blades, as well as a new generator, converter, control system, and pitch system. However, many operators focus specifically on control system upgrades as a first step, given their relatively quick implementation and immediate benefits.
Highly experienced suppliers can perform a control system retrofit in one or two days for each turbine, using out-of-the-box solutions predesigned for the most common wind turbine models across nearly every original equipment manufacturer. This rapid deployment capability minimizes revenue loss from downtime while quickly delivering operational improvements.
With pre-engineered solutions, most retrofits can be completed in a day or two, making them highly attractive for operators managing large wind farms with diverse turbine portfolios. The plug-and-play nature of modern retrofit solutions means that existing cabinets and wiring can often remain in place, with new control modules connecting directly to legacy connectors through specialized adapters.
STATKRAFT Wind Turbine Retrofit Program
One of the most notable examples of large-scale wind turbine retrofitting comes from the Norwegian energy supplier STATKRAFT. STATKRAFT has retrofitted over 100 of its wind turbines with service lifts, demonstrating a commitment to improving operational safety and reducing maintenance costs across its fleet.
This project focused on access technology improvements rather than power generation components, highlighting how retrofits can address multiple operational challenges. By installing modern service lifts, STATKRAFT significantly reduced the time and physical demands required for technicians to access nacelle components, leading to faster maintenance cycles and improved worker safety.
Multi-Manufacturer Retrofit Solutions
Experience across more than 40 different wind turbine generator designs provides a safe and simple upgrade path for regaining the maximum performance within wind turbines. This breadth of experience enables retrofit providers to serve operators with mixed fleets containing turbines from various manufacturers and vintages.
Nordic Wind Technology is a trusted partner of Vestas, Siemens Gamesa, and other small and large players in the global wind industry, with more than 20+ years of controller expertise and 487+ installed solutions. Such extensive implementation experience demonstrates the maturity and reliability of modern retrofit technologies.
Benefits Realized from Wind Turbine Retrofits
Companies see at least four key benefits after a control system retrofit: improved service and longer lifetimes, more advanced operations, more effective failure modes and effect analysis, and global support. These benefits translate directly to improved financial performance through increased energy production, reduced maintenance costs, and extended asset life.
An Emerson retrofit includes advanced control algorithms and intelligent SCADA solutions to improve annual energy production, heighten turbine availability, and provide remote access. The remote access capability proves particularly valuable for operators managing geographically dispersed wind farms, enabling centralized monitoring and control that reduces the need for on-site personnel.
ROI is typically delivered in less than a year, making wind turbine control retrofits one of the most financially attractive improvement options available to operators. This rapid payback period results from the combination of increased energy production, reduced maintenance costs, and improved availability.
Addressing OEM Support Challenges
When long-term service agreements end, the owner takes control of the turbine, and support from OEMs is often limited and expensive, with turbines operating outside of LTSAs usually in the lowest priority group for help from the original manufacturer. This support gap creates significant operational risks and costs for wind farm operators.
Retrofitting with modern control systems from specialized providers addresses this challenge by establishing new support relationships with companies focused on the retrofit market. These providers typically offer more responsive service and competitive pricing compared to original manufacturers supporting legacy equipment.
Hydropower Turbine Modernization: Case Studies and Innovations
Hydropower facilities represent some of the oldest continuously operating power generation assets, with many installations dating back 50 to 100 years. Hydropower turbines have an unparalleled life span, however, at some point during the life of a hydro plant, there will undoubtedly come a time where plant modernization will be required. The longevity of hydropower infrastructure makes it an ideal candidate for retrofitting, as the civil works typically remain sound even as mechanical and electrical components age.
New Lanark Mills Francis Turbine Refurbishment
The World Heritage Site at New Lanark Mills, Scotland, commissioned Gilkes to refurbish a 1931 twin-runner Francis turbine originally installed by Boving, and despite being in an advanced state of decay, it was possible to scan enough of one runner to recreate the full hydraulic geometry. This project demonstrates the power of modern reverse engineering techniques to restore historical equipment.
The resulting 3D CAD model was used to validate the hydraulic and structural performance of the design before CNC milling replacement turbines. This approach combines historical preservation with modern manufacturing precision, enabling the facility to maintain its heritage character while achieving contemporary performance standards.
Turgo Turbine Upgrade with Modern Control Systems
Another compelling hydropower retrofit example involves upgrading control systems on Turgo turbines operating in sediment-laden water conditions. The mechanical aspects of the turbine were found to be operating in good condition despite constant attack from sediment laden water, with the Turgo turbine having a reputation for excellent abrasion resistance, and many parts that are in constant contact with the water still originals from when the turbine was supplied.
The original spear valve actuators had become unreliable and frequently needed maintenance; therefore, these were upgraded to modern modulating rotary actuators to provide reliable control of flow through the turbine. This targeted upgrade addressed the primary failure point without requiring replacement of the still-functional turbine runner and housing.
The new control system is fully automated, improving the annual energy production of the generator significantly, due to higher reliability and lower operator dependence. The automation eliminated the need for constant operator attention and enabled more precise optimization of turbine operation across varying flow conditions.
StreamDiver Retrofit Technology for Existing Dams
Retrofitting hydropower on existing dams and weirs requires the installation of a turbine, a generator that converts mechanical energy into electricity, and usually some construction work, while Voith’s all-in-one StreamDiver bulb-type turbine-generator is the manufacturer’s latest answer to the challenges faced by owners.
In the United States alone, only 3 percent of the 80,000 dams are equipped with the means to produce electricity, representing an enormous untapped potential for renewable energy generation through retrofitting. The StreamDiver technology addresses this opportunity with a simplified installation approach.
Six turbines are planned to be installed in Serayu, Indonesia (4,500kW), one turbine in Bela Visa, Brazil (488kW) and ten turbines in South Bend, Indiana (2,500kW), where the installation will help the University of Notre Dame eliminate the use of coal. These diverse international projects demonstrate the versatility of modern retrofit technologies across different scales and applications.
Efficiency Gains from Hydropower Modernization
Replacing older turbines with new, more efficient designs can often increase energy output by 5-15% without altering the dam structure or water usage. These efficiency improvements translate directly to increased revenue without requiring additional water resources or environmental permits.
Digitalization can improve efficiency by 1.2%, providing additional gains beyond mechanical upgrades. Digital twin technologies, advanced monitoring systems, and optimized control algorithms enable operators to fine-tune turbine performance in real-time based on actual operating conditions.
Modernization can improve the overall efficiency of a hydro plant, with increased generation and reduced downtime providing improved annual energy production due to higher reliability and lower operator dependence. The combination of mechanical and digital improvements creates synergistic benefits that exceed the sum of individual upgrades.
Environmental and Ecological Improvements
New sustainable practices and turbines with better ecological behavior can minimize environmental impacts, like the reduction of fish mortality, improvement of fish habitat availability, reduction of oil for lubrication purposes. Modern retrofit projects increasingly incorporate environmental considerations alongside performance improvements.
Innovative low head hydropower converters can exhibit good ecological behavior, with reduced costs (<5000 €/kW) especially when installed in existing weirs. These fish-friendly turbine designs enable hydropower facilities to meet stricter environmental regulations while maintaining or improving energy production.
Gas Turbine and Steam Turbine Retrofit Applications
While wind and hydropower retrofits receive significant attention, thermal power plants also benefit substantially from turbine modernization programs. Gas turbines and steam turbines in combined cycle plants, cogeneration facilities, and traditional thermal power stations undergo regular upgrades to maintain competitiveness and comply with emissions regulations.
Combined Cycle Plant Upgrades
Combined cycle gas turbine (CCGT) plants represent a significant portion of global power generation capacity. These facilities benefit from coordinated upgrades to both gas turbines and steam turbines, often including heat recovery steam generator (HRSG) improvements to maximize overall plant efficiency.
Modern gas turbine retrofits typically focus on hot gas path components, including combustion systems, turbine blades, and vanes. Advanced materials and coatings enable higher firing temperatures, which directly translate to improved efficiency and power output. Combustion system upgrades can also reduce emissions of nitrogen oxides (NOx) and carbon monoxide (CO), helping plants meet increasingly stringent air quality standards.
Digital Control System Integration
Similar to wind and hydropower applications, thermal power plants benefit enormously from digital control system retrofits. Modern distributed control systems (DCS) provide superior monitoring, diagnostics, and optimization capabilities compared to legacy analog or early digital systems.
These advanced control platforms enable predictive maintenance strategies, reducing unplanned outages and extending intervals between major overhauls. Real-time performance monitoring identifies degradation trends before they result in failures, allowing maintenance to be scheduled during planned outages rather than forcing emergency shutdowns.
Common Retrofit Components and Technologies
Across all turbine types and applications, certain components and systems are frequently targeted for retrofit projects due to their impact on performance, reliability, and operational costs.
Blade and Runner Replacements
Turbine blades and runners represent the primary interface between the working fluid (wind, water, or combustion gases) and the mechanical power generation system. Advances in aerodynamic design, materials science, and manufacturing techniques enable modern blades to extract more energy while withstanding harsh operating conditions.
For wind turbines, blade retrofits may involve complete replacement with longer, more aerodynamically efficient designs, or the addition of blade extensions and vortex generators to improve performance. Advanced composite materials provide superior strength-to-weight ratios while resisting fatigue and environmental degradation.
Hydropower runners benefit from computational fluid dynamics (CFD) optimization that was unavailable when older turbines were designed. Modern manufacturing techniques, including five-axis CNC machining and additive manufacturing for complex geometries, enable precise replication of optimized designs.
Control System and SCADA Upgrades
Leading-edge retrofit solutions provide advanced new control algorithms, open service tools, and interfaces to SCADA control systems, effectively optimizing the turbine’s annual energy production, increases availability, and provides intelligent remote access options.
Modern SCADA systems offer dramatically improved capabilities compared to systems installed even a decade ago. Cloud connectivity enables remote monitoring and control from anywhere with internet access, while advanced analytics provide insights into performance trends and optimization opportunities.
Analytical, predictive maintenance and forecasting tools effectively optimize the performance of the wind farm. These tools leverage machine learning algorithms trained on vast datasets to identify patterns that human operators might miss, enabling proactive interventions that prevent failures and optimize production.
Gearbox and Generator Modernization
Gearboxes represent one of the most common failure points in wind turbines, while generators in all turbine types benefit from advances in materials, cooling systems, and electrical design. Retrofit programs often address these components to improve reliability and efficiency.
Modern gearbox designs incorporate improved bearing systems, enhanced lubrication, and better load distribution to extend service life. Some retrofits replace traditional geared systems with direct-drive configurations, eliminating the gearbox entirely and its associated maintenance requirements.
Generator upgrades may include rewinding with improved insulation systems, installation of more efficient cooling systems, or complete replacement with higher-efficiency designs. Permanent magnet generators offer superior efficiency compared to traditional wound-rotor designs, making them attractive retrofit options where the additional cost can be justified by improved performance.
Sensor and Monitoring System Installations
As part of the retrofit, most companies will also opt to add a condition monitoring system, as it can be installed quickly and easily during construction to deliver even more benefits and faster ROI. Condition monitoring systems provide continuous surveillance of critical parameters including vibration, temperature, oil quality, and acoustic emissions.
Advanced sensor networks enable detailed analysis of turbine health and performance. Vibration sensors detect bearing wear, misalignment, and blade damage before they result in catastrophic failures. Temperature monitoring identifies cooling system problems and electrical issues. Oil analysis sensors track contamination and degradation in lubrication systems.
The data collected by these monitoring systems feeds into predictive maintenance algorithms that forecast component failures and optimize maintenance schedules. This data-driven approach reduces maintenance costs while improving reliability and availability.
Power Electronics and Converter Upgrades
Power electronic converters play critical roles in modern turbine systems, enabling variable-speed operation, grid compliance, and power quality management. Retrofitting older turbines with modern converter technology unlocks significant performance improvements.
Variable-speed operation enabled by advanced converters allows turbines to operate at optimal efficiency across a wider range of conditions. For wind turbines, this means capturing more energy during low and moderate wind speeds. For hydropower, variable-speed operation improves efficiency at partial loads and provides enhanced grid support capabilities.
Modern converters also provide superior grid support functions, including voltage regulation, frequency response, and fault ride-through capabilities. These features are increasingly required by grid codes worldwide as renewable energy penetration increases.
Implementation Strategies and Best Practices
Successful turbine retrofit projects require careful planning, experienced execution teams, and comprehensive testing and commissioning. Organizations that follow structured approaches achieve better outcomes with fewer complications and faster returns on investment.
Assessment and Planning Phase
Initial site survey and condition assessments identify required refurbishment and optimization work for both mechanical and electrical equipment. This assessment phase provides the foundation for all subsequent decisions about scope, budget, and timeline.
Comprehensive assessments include detailed inspections of existing equipment, performance testing under various operating conditions, and analysis of historical maintenance records and failure modes. Non-destructive testing techniques such as ultrasonic inspection, thermography, and vibration analysis reveal hidden defects and degradation.
The assessment phase should also include evaluation of regulatory requirements, grid code compliance, and environmental permits. Changes in regulations since the original installation may necessitate specific upgrades to maintain operating licenses.
Technology Selection and Engineering
Selecting appropriate retrofit technologies requires balancing performance improvements, costs, implementation complexity, and compatibility with existing systems. Organizations must consider both immediate benefits and long-term strategic objectives.
Retrofitting of grid-connected wind turbines with stall and pitch control technology increases efficiency, reliability and enables compliance with grid code while increasing the operational life of the turbines, with improved production and increased reliability leading to extended lifetime.
Engineering work for retrofits often proves more challenging than new installations due to the need to integrate modern components with legacy systems. Detailed documentation of existing equipment may be incomplete or inaccurate, requiring reverse engineering and field verification. Interface requirements between new and retained components must be carefully specified and validated.
Execution and Commissioning
Retrofit execution requires specialized skills and experience to minimize downtime and ensure successful integration. Many retrofit providers offer turnkey solutions that include all engineering, procurement, installation, and commissioning services.
Scheduling retrofit work during planned outages or low-production periods minimizes revenue impact. For wind farms, this typically means scheduling work during low-wind seasons. Hydropower retrofits are often timed to coincide with low-water periods or required maintenance outages.
Comprehensive testing and commissioning verify that retrofitted systems meet performance specifications and operate safely under all conditions. This includes factory acceptance testing of major components before shipment, site acceptance testing after installation, and performance testing under actual operating conditions.
Training and Knowledge Transfer
Retrofits often introduce new technologies and operating procedures that require training for operations and maintenance personnel. Effective knowledge transfer ensures that staff can fully utilize new capabilities and properly maintain upgraded systems.
Training programs should cover both normal operations and troubleshooting procedures. Hands-on training during commissioning provides valuable experience with actual equipment. Documentation including operating manuals, maintenance procedures, and spare parts lists must be comprehensive and accessible.
Financial Considerations and Return on Investment
The financial case for turbine retrofits typically proves compelling when compared to alternatives such as continued operation with degraded performance, complete turbine replacement, or facility decommissioning.
Capital Costs and Financing
A refurbished wind turbine offers improved performance at a lower price than a new asset: The CAPEX per MW is roughly half that of a new turbine. This substantial cost advantage makes retrofitting attractive even for operators with access to capital for new equipment.
Retrofit projects can often be financed through operating budgets or short-term loans rather than requiring long-term project financing. The shorter payback periods and lower risk profiles compared to new developments make retrofit financing more accessible and less expensive.
Revenue Enhancement and Cost Reduction
Retrofits generate financial returns through multiple mechanisms. Increased energy production from efficiency improvements directly increases revenue. Improved availability reduces lost production from outages. Extended asset life defers or eliminates replacement costs.
Maintenance cost reductions result from improved reliability, better diagnostic capabilities, and elimination of obsolete components with limited spare parts availability. Modern condition monitoring systems enable predictive maintenance that costs less than reactive or time-based approaches.
It is estimated that a total 42 TWh could be added to present hydropower energy production by implementing hydropower digitalisation, and such an increase could lead to annual operational savings of USD 5 billion. These figures demonstrate the enormous aggregate value available from systematic retrofit programs across the global hydropower fleet.
Risk Mitigation Value
Retrofits reduce several categories of operational risk. Technical obsolescence risk decreases as modern components replace aging systems with limited support. Regulatory compliance risk is addressed through upgrades that meet current standards. Catastrophic failure risk declines with improved monitoring and more reliable components.
The risk mitigation value of retrofits often justifies investment even when purely financial returns appear marginal. Avoiding a major unplanned outage or regulatory violation can save costs far exceeding the retrofit investment.
Regulatory and Environmental Drivers
Evolving regulations and environmental standards create both challenges and opportunities for turbine operators. Retrofits enable compliance with new requirements while often improving environmental performance beyond minimum standards.
Grid Code Compliance
DEIF controllers comply with the world’s major grid codes and are continuously updated, helping you trade wind energy and offer ancillary services to TSO/ISOs. Grid codes have evolved significantly as renewable energy penetration has increased, requiring capabilities that older turbines were never designed to provide.
Modern grid codes typically require fault ride-through capabilities, voltage and frequency support functions, and sophisticated power quality management. Retrofitting power electronics and control systems enables older turbines to meet these requirements and continue operating profitably.
Environmental Compliance and Performance
Environmental regulations affecting turbine operations include emissions limits for thermal plants, noise restrictions for wind turbines, and fish passage requirements for hydropower facilities. Retrofits can address these requirements while improving overall environmental performance.
For thermal plants, combustion system upgrades reduce emissions of criteria pollutants and greenhouse gases. Advanced control systems optimize combustion to minimize emissions while maintaining efficiency. Selective catalytic reduction (SCR) and other emissions control technologies can be integrated during major retrofits.
Hydropower retrofits increasingly incorporate fish-friendly turbine designs and operational strategies that minimize environmental impacts while maintaining or improving energy production. These environmental improvements often prove essential for license renewals and maintaining social license to operate.
Future Trends in Turbine Retrofitting
The turbine retrofit industry continues to evolve as new technologies emerge and operational requirements change. Several trends are shaping the future of turbine modernization.
Artificial Intelligence and Machine Learning
AI and machine learning technologies are transforming turbine operations and maintenance. Predictive algorithms trained on vast datasets can forecast failures, optimize operations, and identify improvement opportunities that traditional approaches miss.
Future retrofits will increasingly incorporate AI-powered control systems that continuously learn and adapt to changing conditions. These systems will optimize performance in real-time while predicting and preventing failures before they occur.
Digital Twin Technology
Digital twins—virtual replicas of physical turbines that update in real-time based on sensor data—enable sophisticated analysis and optimization. Operators can test operational strategies, predict component life, and optimize maintenance schedules using digital twins without risking actual equipment.
Retrofit projects increasingly include digital twin implementation as part of comprehensive modernization programs. The combination of enhanced sensors, advanced control systems, and digital twin analytics creates powerful capabilities for performance optimization.
Hybrid and Energy Storage Integration
With DEIF, you can integrate your wind assets in hybrid plants, for example to charge storage units from your turbines, and ensure uninterrupted power whilst replacing fossil fuels with renewables. Future retrofits will increasingly focus on enabling turbines to operate effectively within hybrid energy systems that combine multiple generation sources and energy storage.
This integration requires sophisticated control systems capable of coordinating with other generation assets and storage systems to optimize overall system performance. Retrofitting existing turbines with these capabilities extends their useful life and enhances their value within evolving energy systems.
Circular Economy and Sustainability
The circular economy concept emphasizes extending product life, reusing components, and recycling materials at end of life. Turbine retrofitting aligns perfectly with circular economy principles by maximizing the value extracted from existing assets.
Future retrofit programs will increasingly emphasize sustainability throughout the component lifecycle. This includes using recycled materials in replacement components, designing for future upgradability, and planning for eventual component recycling or reuse.
Challenges and Considerations
While turbine retrofitting offers substantial benefits, successful projects must address several challenges and considerations.
Technical Complexity and Integration
Integrating modern components with legacy systems requires deep technical expertise and careful engineering. Interface mismatches, unexpected incompatibilities, and inadequate documentation can complicate retrofit projects and extend timelines.
Organizations should engage experienced retrofit providers with proven track records on similar projects. Comprehensive engineering reviews and factory testing of critical interfaces reduce implementation risks.
Supply Chain and Obsolescence
Component obsolescence affects both the systems being replaced and the interfaces required for integration. Long lead times for specialized components can delay projects and increase costs.
Proactive planning and early procurement of long-lead items help mitigate supply chain risks. Maintaining relationships with multiple suppliers provides alternatives when primary sources face constraints.
Organizational Change Management
Retrofits often require changes to operating procedures, maintenance practices, and organizational structures. Resistance to change can undermine retrofit benefits if not properly addressed.
Effective change management includes early stakeholder engagement, comprehensive training, and clear communication about benefits and expectations. Involving operations and maintenance personnel in planning and implementation builds buy-in and ensures practical considerations are addressed.
Conclusion: The Strategic Imperative of Turbine Retrofitting
Real-world examples from wind, hydropower, and thermal power applications demonstrate that turbine retrofitting delivers substantial benefits across multiple dimensions. Improved performance, extended asset life, reduced costs, enhanced reliability, and better environmental performance combine to create compelling value propositions.
As global energy systems transition toward higher renewable penetration and stricter environmental standards, the importance of maximizing value from existing infrastructure will only increase. Turbine retrofitting represents a proven, cost-effective strategy for meeting these challenges while supporting broader sustainability objectives.
Organizations that embrace systematic retrofit programs position themselves to compete effectively in evolving energy markets. The combination of improved economics, reduced environmental impact, and enhanced operational capabilities creates sustainable competitive advantages that extend well beyond the immediate financial returns.
For energy companies evaluating their asset management strategies, the question is not whether to pursue retrofits, but rather how to prioritize opportunities and implement programs that maximize value. The extensive real-world examples and proven technologies available today provide a solid foundation for successful retrofit initiatives across all turbine types and applications.
To learn more about turbine technologies and energy system optimization, visit the U.S. Department of Energy or explore resources from the International Renewable Energy Agency. Industry organizations such as the American Clean Power Association and International Hydropower Association provide valuable insights into best practices and emerging trends in turbine retrofitting and renewable energy optimization.