By Judah Moseson, Special To Solar Power World
Photovoltaic (PV) solar-farm technology improvements, as well as the size and number of installations, have increased dramatically in the past five years. This has created an increase in potential generation and revenue—which means traditional power-plant issues and considerations have become more prevalent in the solar energy sector.
One example of an emerging need— and, in some cases, requirement for solar plants,— is the use of 24/7 monitoring and control. Round-the-clock coverage for traditional power plants (and even renewable resources such as wind and hydro) are commonplace. Such monitoring and control of industrial and aggregated commercial solar farms is now becoming a requirement of owners and operators, as well as NERC regional entities, independent system operators (ISOs) and local utilities.
Solar farms rely on complex electronic control systems, i.e. supervisory control and data acquisition (SCADA) systems. Advanced systems can provide uniform platforms for multi-plant sites. These controls provide feedback, control and performance measurements; when coupled with 24/7 monitoring and control, they can provide critical response that enables solar farms to meet their estimated annual energy production (AEP).
Why Solar Farms Require 24/7 Coverage
Photovoltaic based solar farms only produce power during daylight hours. The issue that is causing concern among stakeholders is not the PV cells themselves, but the BOS components— including combiner boxes, inverters, step-up transformers and the accompanying medium/high voltage substations that are on line and in service around the clock. The presence of this associated equipment and the opportunity for alarm or even failure during non-daylight hours has given rise to requirements from North American Electric Reliability Corp. (NERC), ISOs and local utilities. Additionally, environmental events such as inclement weather causing fouling by snow, sleet, ice or even mud can become issues in non-daylight hours.
When an issue occurs during hours when the PV is not producing electricity, the common practice is to wait until sunrise to address it, possibly dispatching resources to the field to resolve the issue. This practice creates production and revenue losses, because at sunrise, NERC, ISOs and local utilities expect electricity production and not phone calls explaining why the solar farm is out of service.
For NERC, ISOs and local utilities, this is a reliability issue for which procedures have been in place for all other generation assets, both traditional and renewable (wind and hydro) power plants. It is a sign of the maturity of the solar industry and its impact on system capacity and reliability that is driving this requirement across the United States electrical regional grids.
24/7 Monitoring and Control Center
Real-time monitoring and control are commonplace in most electric power generation companies and traditional utilities. But the use of such control centers, staffed by NERC certified operators, has not been common among solar generation facilities. As the number of solar farms continues to increase, the industry is rising to the challenge of integrating solar power into the larger power grids and recognized the value of around the clock monitoring. Without 24/7 monitoring, solar farms miss the simple and most effective way to ensure production is maximized.
The 24/7 monitoring and control center provides NERC-qualified operators who have undergone extensive training and testing. As a result, they are accepted as industry experts by NERC regional entities, ISOs and local utilities. These operators are trained in the use of the SCADA systems, which maximizes the benefits of early-warning systems, trending and performance reporting as a part of their routine of monitoring. In addition, they use systems for monitoring news, weather and spot-market pricing to ensure all issues are included in the monitoring process.
Control center operators can remotely reset most systems as soon as the event occurs, which returns the solar farm to full potential and makes the PV cells available at sunrise for all potential energy generation. This results in revenue that would otherwise be deprived.
For issues such as grid outages or curtailments, control center operators respond according to approved protocols with the grid managers. Control centers typically use voice-recording systems to capture all verbal communications from grid operators as a reference, should post incident resolution be required.
With the emergence of nodal-based electrical-grid-reliability systems, ISOs are requiring advanced energy projections for the day-ahead market. When issues arise that result in lower production, these same entities are requiring hour-ahead projections, another task easily handled by the 24/7 control center.
Additionally, the operators can record all incidents and actions within the SCADA system or another external workflow system as a log to be used as a historical and analytic record.
Finally, a critical benefit is the enhanced safety for personnel as a result of having 24/7 monitor and control centers available to them. When a control center is in use, each service provider is required to check in with the center prior to performing any maintenance. The center can participate in the safety protocols such as “lock out and tag out,”using remote operations and document the personnel entering the area and the activity being performed. When the work is complete, the service provider contacts the center and gives the “all clear”signal. The control center helps close out the “lock out and tag out”process and then documents the completion of work. Upon the safe exit of all personnel, the control center operators restart the equipment and systems remotely. This makes the process—and the service providers—safer by creating a protocol for verification prior to action.
As the solar industry continues to mature and the MW levels increase, you can expect solar farms to adopt the same controls and protocols the traditional power plants use across the United States. This change is a welcome sign that the PV solar farms are finally considered mainstream.
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