The way your plant controller is programmed to manage curtailment events can have a significant impact on your bottom line, especially during periods with variable cloud conditions
Grid interconnection agreements for utility PV projects are becoming more complex. As grid penetration for renewable assets grows in the US, more and more utilities are imposing curtailments for utility PV, including limits to real power output and ramp constraints. This creates a new bottom-line performance concern for owners: the behavior of the plant controller implementing these curtailments. The way your plant controller is programmed to manage curtailment events can have a significant impact on your bottom line, especially during periods with variable cloud conditions.
To illustrate the difficulty of this challenge, look at some real data from a plant in Hawaii with 5 central inverters:
Real site data from a plant in Hawaii showing effects of variable cloud cover on inverter production
When you add in constraints like interconnect limits and ramp rate constraints and you see how fast the dynamics of cloud cover impact a site like this, it becomes clear that optimizing energy harvest under all conditions can be a real challenge
Before 10AM you can see a pair of cloud coverage events that affect all parts of the array equally. After 10AM, however, you can see that some inverters are operating near capacity, while other inverters are seeing big drop-offs. This indicates variable spatial irradiance, meaning that there is different cloud coverage, and therefore fuel availability, over different parts of the array. Since most PV plants are built with excess DC capacity, other inverters are able to ramp up to compensate when one or more inverters exhibit diminished production. However, when you add in constraints like interconnect limits and ramp rate constraints, and you see how fast the dynamics of cloud cover impact a site like this, it becomes clear that optimizing energy harvest under all conditions can be a real challenge. SCADA system design at the plant controller level governs how the system reacts to this complex challenge.
This can be a particularly difficult issue for owners because control system procurement is typically managed by the EPC. EPCs are not financially incentivized to invest extra time or effort to ensure that the system optimizes performance; on the contrary, because they must satisfy the utility that the project will meet control and curtailment requirements in order to pass the commissioning process, they may be inclined to err on the side of caution, restricting production more than necessary.
How your plant controller addresses this challenge can have a significant impact on ROI. We constantly advise owners that they must get involved early and advocate for their long-term operational interests during the SCADA system design process. Choice of who provides the control system, and how they design it, can have a big impact on energy harvest and overall project returns.