The number of grid-connected solar photovoltaic (PV) systems is expected to increase dramatically over the coming decades. This increase in the number of PV units leads to an increased focus by utilities and other solar generating firms on achieving the highest level of performance and reliability from the solar asset. In addition to the typical focus of thinking about up -front costs of a solar plant, determining a plan and budget for operations and maintenance (O & M) is essential in assessing the business case for a PV facility. As in the case of conventional generating plants there are various types of maintenance strategies that can be used for a PV plant. This document provides the reader with insights into developing a solar PV operating model from a variety of choices. Regardless of what monitoring system or maintenance strategy a firm chooses, the operational support model defines how the new plant will be run on a daily basis including who will perform system monitoring, plant repairs, and scheduled maintenance. The model addresses the mechanical and electrical needs of the plant as well as maintaining the grounds and communication systems.
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- Solar Photovoltaic Plant Operating and Maintenance Costs
- September 2010
- Solar Photovoltaic Plant Types and Components
- Solar cells can be classified into three generations which indicate the order in which each became prominent. Currently, research is being conducted on all three types of cells. The first generation technologies accounted for 89.6% of 2009 production First Generation Photovoltaic (PV) Cells consist of large area, high quality, single junction devices. First generation technologies involve high energy and labor outputs, preventing any significant progress in reducing production costs Second Generation PV Cells have been developed to address energy requirements and production costs of solar cells. The manufacturing costs are lower than first generation, but due to inherent defects, the efficiency is lower Third Generation PV Cells or advanced thin-film photovoltaic cells are a range of various alternatives to the first and second generations A utility-scale solar PV plant is made up of the following*: Photovoltaic panels The PV panels are composed of solar cells that convert the suns rays or photons into DC electric power Panel trackers are mechanisms used on some PV systems allowing the solar panels to track the sun throughout the day for optimal power production Trackers can enable the system to produce more power but also require more maintenance than stationary systems The balance of system (BOS) components The BOS components include such things as wires, combiners, junction boxes, mounting equipment, conduit runs, and communications equipment** The inverter The inverter is the unit that conditions or converts the DC electricity produced by the solar cells into AC electric power
- *U.S. Department of Energy, 2010, www.doe.gov **Banke, Bryan. Solar Electric Facility O&M: Now Comes the Hard Part three-part series, Oct-Dec 2009, www.renewableenergyworld.com
- Estimating Solar Photovoltaic O&M Costs
- The number of grid-connected solar PV systems is expected to increase dramatically over the coming decades. This increase in the number of PV units leads to an increased focus by utilities and other solar generating firms on achieving the highest level of performance and reliability from the solar asset. In addition to thinking about up front costs of the solar plant, determining a plan and budget for ongoing operations and maintenance (O&M) expenses is essential in assessing the business case for a PV facility Government incentives and regulations are leading utilities to think about ownership of solar-based generation plants A shift from the current power purchase agreement (PPA) approach to obtaining solar energy assets outright creates a need for utilities to come up with a plan for regular maintenance on these PV plants As a new solar plant nears completion, operation and maintenance (O&M) assumptions must be revisited to ensure that adequate funding is set aside for the reliable operation of the asset Deriving O&M costs of a new solar photovoltaic (PV) plant in the absence of data is a challenge. Working through each cost item will also address many of the operational needs that require attention when bringing a new plant online. Projecting costs should be as much the result of careful process planning as it is an exercise in budgeting To estimate O&M costs, it is helpful to first have an understanding of the following items: Solar PV plant components The various levels of maintenance and typical maintenance needs The different monitoring types available The plant operational support model Additional considerations for PV O&M costs
- Utility-Scale PV Plant O&M Cost Estimates
- Source: Electric Power Research Institute, Engineering and Economic Evaluation of Central-Station Solar Photovoltaic Power Plants, 2010
- Fixed-Tilt c-Si is defined as polycrystalline modules mounted at a fixed 30 degree tilt facing south Fixed-Tilt CdTe is defined as cadmium telluride modules mounted at a fixed 30 degree tilt facing south Fixed-Tilt a-Si is defined as amorphous silicon modules mounted at a fixed 30 degree tilt facing south Fixed-Tilt c-Si is defined as monocrystalline modules on a north-south axis tracker tilted south at 20 degrees with backtracking Single-Axis tracking c-Si is defined as monocrystalline modules on a north-south axis tracker with backtracking
- The table below provides a breakdown of costs across four categories - scheduled maintenance; unscheduled maintenance; inverter/equipment replacement; and insurance, property taxes, and owners costs for five conceptual 10 MW PV plants
- PV System Failure Areas and Relative Frequencies
- Source: Electric Power Research Institute, Engineering and Economic Evaluation of Central-Station Solar Photovoltaic Power Plants, 2010
- The figure below provides the relative frequency of photovoltaic system component failures along with their corresponding outage impacts
- Maintenance Strategies and Needs
- The various types of maintenance strategies for a PV plant include: Preventative Maintenance includes routine inspection and servicing of equipment to prevent breakdowns and production losses Corrective or reactive maintenance addresses equipment breakdowns after the occurrence. This break and fix method has low upfront costs, but bears the risk of unplanned downtime and higher costs on the back end. This is the current industry standard Condition based maintenance (CBM) uses real-time data to prioritize and optimize maintenance and resources More than one of these maintenance strategies is needed, but a proper strategy can limit the amount of surprises and will decrease the amount of unplanned downtime When establishing a preventative maintenance schedule, it is important to do so based upon each component and system manufacturers recommendations. Corrective maintenance procedures should also be established to address items that require immediate repairs and items that can be repaired with routine maintenance visits. Some typical maintenance needs at PV plants include: Over the course of time, dust collects on the PV panels significantly affecting system efficiency. Panels must be cleaned regularly to minimize efficiency loss PV operators and suppliers have found that one to two cleanings per year will adequately serve most plants needs System components must go through a thorough maintenance checklist at least once or twice per year. The checklist should include such items as: Checking connections of wires Testing voltage / current through wires and PV modules Inspecting components for moisture Greasing actuator gears and topping off hydraulic fluid on tracker components, if applicable Testing of SCADA and meteorological systems communications Confirming settings on the inverter Resealing of system components Additional maintenance needs include the removal of snow, ice, grass, and vegetation to ensure effective system operation
- Source: Electric Power Research Institute, Addressing Solar Photovoltaic Operations and Maintenance Challenges, July 2010.
- Typical Maintenance Needs
- This illustration highlights some of the plant maintenance needs that must be factored into an O&M budget
- Clean panels Grease tracker gears and actuators Check hydraulics Calibrate controllers and sensors Remove vegetation, snow, and ice from blocking panels
- Test inverter functionality and settings Perform thermal imaging to test electrical connections Inspect for loose connections, rust/moisture, or pest infestation
- Perform thermal imaging to test electrical connections Inspect for loose connections, rust/moisture, or pest infestation Test string current
- Other items: Inspect SCADA and meteorological systems communication connection and test signal strength
- String Combiner
- Inverter
- Grid Interconnect
- DC Disconnect Switch
- AC Disconnect Switch
- Sub Combiner
- Line from additional arrays
- PV Panels
- * Advanced Energy Global Systems, 2010. ** Banke, Bryan, Solar Electric Facility O&M: Now Comes the Hard Part three-part series, Oct-Dec 2009, www.renewableenergyworld.com.
- PV Plant Monitoring
- PV system monitoring capabilities have advanced significantly over the last decade. Monitoring systems can now offer data at a more granular level. This monitoring capability is especially important given the majority of PV plants are unmanned and supervised off site Traditional PV monitoring and a method widely used simply compares actual energy generation with forecasted generation. If actual compares favorably with predicted, then there is not a problem with the asset. This is a simple and affordable approach. This approach is also fairly reliable, but is more reactive than proactive and a lag often exists between detection and repair. Several new monitoring techniques are currently in the market:
- Source: Electric Power Research Institute, Addressing Solar Photovoltaic Operations and Maintenance Challenges, July 2010.
- The Plant Operational Support Model
- Regardless of what monitoring system or maintenance strategy a firm chooses, the operational support model defines how the new plant will be run on a daily basis -- including who will perform system monitoring, plant repairs, and scheduled maintenance. The model addresses the mechanical and electrical needs of the plant as well as maintaining the grounds and communication systems In House Staff: Existing staff may be leveraged when the plant is adjacent to existing generation facilities For example: System monitoring and plant operation may be performed by fossil operators throughout the course of their shift Mechanical engineering not included in the warranty may be handled by onsite fossil maintenance staff Site electrical maintenance may be supported by plant operations crews or transmission maintenance crews The advantages of this system include: better visibility on personnel and equipment issues, greater quality control, ability to use existing personnel and assets, and it will lead to a standard PV O&M process The disadvantages of this system include higher upfront costs, increased risks, and the need to develop an expertise quickly in your work force EPC Contractor: The utility may opt to use the Engineering, Procurement, and Construction (EPC) contractor that sold and built the system to oversee an O&M contract This limits the use of multiple contracts and simplifies dealing with warranty-related repairs versus maintenance Third Party Provider: Another option for O&M services not covered under the warranty is to use a third party provider which may support multiple PV sites Use of a third party for an organizations first PV plant helps instill best management practices for maintenance schedules and for system repairs One variation of this model is to contract some functions (i.e., mechanical engineering, grounds maintenance, and panel cleaning) to a third party while keeping some tasks (i.e., communication and monitoring, electrical engineering) in-house Advantages of both the EPC and third party option include lower upfront costs and greater flexibility, lower upfront risk, less drain on the current labor force, and potentially greater expertise Disadvantages of the EPC and third party option include less understanding of the O&M process, higher back end cost potential, and that it requires dependence on an outsourced contractor
- Source: Electric Power Research Institute, Addressing Solar Photovoltaic Operations and Maintenance Challenges, July 2010.
- The Solar PV Plant Operational Support Model
- Where tasks are performed internally, cost estimates should be as close as reasonably possible. To derive a total labor cost and to ensure that each support need is addressed, a matrix of tasks can be developed capturing each variable As illustrated below, an analysis of support costs might include a task description, the organization performing the work, org WBS to which the work is charged, hours for the task, frequency of the task, hourly labor cost, yearly hours, and total yearly cost
- Illustrative
- Additional Considerations for PV O&M Costs*
- As more utility-scale PV plants come online, more is being learned about system performance and capacity. This includes a better understanding of what to expect with regard to system operation and maintenance, as illustrated in the following lessons learned: Preventative Maintenance: Focus on design, engineering, and the initial build of the PV plant Target a downtime of 1 percent (3.7 days/year) and prepare for 10 percent downtime (36.5 days/year) Measure system degradation over time and clean panels when the cost of lost power approaches the cost of cleaning Mitigate risk by using multiple smaller inverters rather than one large inverter Perform site visits at least 1-2 times/year Consider transitioning outsourced O&M to in-house staff Monitoring: Consider monitoring the system at the string level for plants between 250kW to 2 MW and use the data to address maintenance needs Note: larger plants may not see the cost benefit from this level of detail Automate system monitoring and supplement by reviewing system reports multiple times throughout the day Assure good access to historical data Perform simple site analytics once per month Identify core factors that determine the economic tradeoffs of monitoring resolution Warranty: Make sure warranty terms are clear; avoid vague clauses Perform due diligence before agreeing to a construction contract
- Source: Electric Power Research Institute, Addressing Solar Photovoltaic Operations and Maintenance Challenges, July 2010. * Banke, Bryan, Solar Electric Facility O&M: Now Comes the Hard Part three-part series, Oct-Dec 2009, www.renewableenergyworld.com.
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