According to the Solar Energy Industries Association (SEIA), more than 114 GW dc of utility-scale solar projects are currently either under construction or development in the United States (that’s enough new generation to power more than 85 million homes!) These costly infrastructure developments are driven9 by economics and are growing in size and frequency as the cost of materials goes down and the demand for renewable energy goes up. As the project size and number of projects concentrated in one area rises, so does the complexity of integrating these projects reliably into existing networks.
An important aspect of utility-scale solar projects, and one that solidifies its economic viability, is the power purchase agreement (PPA). Many utility-scale power plants are only built once sufficient power PPAs have been secured, guaranteeing off-takers (and revenue) for the power that the plant will produce. But an interesting quirk of the business is that the developers who build the plants are not necessarily in it for the power generation revenue.
The utility-scale solar developer handover
In a frequent scenario, a developer will build a utility-scale solar plant and secure the PPAs that guarantee buyers for the generated power. Once built, the developer will sell the site to an owner/operator who may not have participated in the plant’s original build and design decisions. Buyers apply their due diligence when purchasing the plant, checking the validity and stability of the PPAs and the site’s production capabilities, but it’s impossible to predict the impact of a constantly evolving energy market landscape influenced by regulations at federal, state, and local utility levels. These regulations influence energy pricing, production levels allowed onto the grid, and how the site is maintained and operated. In addition to regulations, the influx of new utility-scale solar PV projects coming online within the same vicinity can also impact production settings.
As these conditions shift, so too can the anticipated ROI of the plant, leading the plant operators to make modifications to ensure the plant remains profitable and compliant with all regulations. Original equipment such as inverters, transformers, and other control mechanisms have capability limits which might not easily accommodate the new conditions, especially if they’re already stretched to the maximum of their capability range when installed.
As the grid evolves and market conditions shift, the new owner will want to make updates to the plant such as including more generating assets, including battery energy storage, or upgrading the software to improve the plant’s revenue opportunities. In these cases, it can be easier to replace legacy systems and configure a new system from scratch than to attempt to patch an original system which was not designed with the new components in mind.
Owner/operator plant upgrades
A customary practice for renewable energy plants is to replace the SCADA system every five years. This may be necessary due to the equipment upgrades, expansions, or can be related to outdated systems and hardware causing increased downtime, maintenance, and missing data. In effect, this amounts to several changeovers during the lifetime of the solar PV panels and PPAs. These system retrofits and replacements cause disruptions to power production as the new system is installed and configured. Once the learning curve for staff to become familiar with the new system is factored into the upgrade expenses, the costs related to a SCADA upgrade add up quickly.
One way to reduce these costs is to leverage the capabilities of a sophisticated power plant controller (PPC) that relies on software rather than hardware solutions to manage the plant’s assets and equipment. Such a renewable power plant controller can integrate power plant control, SCADA, and energy management system functions within a single platform, simultaneously consolidating the HMI, alarm functions and plant data history. In addition to reducing the burden on staff to learn and manage multiple systems, a sophisticated PPC can extend the life of capacitors, inverters, relays, and gears through its ability to precisely manage power flow, thereby reducing the wear and tear caused by extreme power flow variations.
Plus, a high-end, software-based controller eliminates the need for PLCs, which can be time-consuming and expensive to re-configure whenever equipment adjustments are made. The PPC can also maximize the performance of capacitors, reducing the quantity needed to manage power quality.
Case study: Slate utility-scale solar PV + storage facility
An example of a successful equipment and SCADA system retrofit is the Slate Solar + Storage facility in Lemoore, CA. Sited on 2,490 acres, it is comprised of five solar PV plants, each ranging between 26–93 MW. Four of the plants have battery storage amounting to 47 battery energy storage system (BESS) inverters for a combined capacity of 140.25 MW AC / 561 MWh (megawatt hours). The massive plant serves five separate PPAs through a single point of interconnection (POI) at a Pacific Gas & Electric (PG&E) switching station under the jurisdiction of the California Independent System Operator (CAISO). The site requires a solution where the five individual plants work in unison, ensuring they collectively meet the voltage schedule in the interconnection agreement.
The site was originally developed without storage and included a SCADA solution that could not manage the added complexity of integrating energy storage. PXiSE Energy Solutions stepped in to provide its Renewable PPC to consolidate power plant and SCADA control for both the PV and battery assets. Under the PXiSE configuration, each of the five solar PV plants is equipped with its own PXiSE PPC. These are aggregated under a primary PXiSE PPC that oversees the entire system. The primary/secondary controller configuration allows precise control at the POI without losing the ability to control the assets independently at each plant level. This enables precise fulfillment of the individual PPAs (with independent maintenance and scheduling functions) while simultaneously complying with CAISO requirements and dispatches in less than one second.
The PXiSE solution offers the typical PPC advantages including PV smoothing/ramp control and energy shifting while also handling the more complex calculations required to satisfy the PPA and CAISO requirements. Plus, managing everything with the same software platform offers scalability and flexibility to easily adapt to any future site or ISO changes—so no need to replace the system every five years.
You can learn more by downloading the Slate Solar Farm Storage Addition case study.
