In today’s guest post, Emerson’s Jim Cushman, a member of the Power & Water Solutions business, looks at the process control architecture requirements for solar photovoltaic-based power generation.

Early developers of solar photovoltaic (PV) did not consider the need to control the power generated from solar PV panels. In their minds, it was simply a matter of just connecting to the grid and monitoring the power flow that was being generated. These early systems were small, in the 1MW or less range and did not pose any problem to grid stability. As these small plants continue to multiply and the size of other plants increase from 20MW to over 100MW in many cases, there is a need to provide control.

There are two basic types of architectures that are being used today for control in solar PV. They are the typical PLC [programmable logic controller] and DCS [distributed control system] that are in so many plants today. Most people with controls experience tend to think that a PLC is a better fit for solar PV plants since it’s a simple process to control and would carry a lower cost. This is not necessarily the case and should be carefully studied by anyone considering controls for a solar PV generating facility.

PLCs tend to use more controllers and devices to establish their network and communications for control. Additionally, they most always have to integrate a human machine interface (HMI) for operator interface. This architecture adds complexity and cost especially in large solar PV plants.

DCSs are often thought of as very large and costly systems that would only have purpose in large-scale power generating plants. This is not the case for solar PV, since most of the cost in traditional power plants is the amount of hard-wired input and output devices to measure and control multiple processes in the plant. Additionally, traditional power plants have many operators to maintain and oversee the process of power generation, who require many workstations and supporting equipment to operate the plant.

In a solar PV plant, information is communicated over a fiber optic Ethernet bus, so there is little to no hard-wired input and output devices. Additionally, there is little to maintain and operate, so the amount of workstations and other supporting equipment is greatly reduced. Integration of other systems in the plant such as inverters, meteorological stations, revenue meters, switchgear, and protection systems is much easier when the development and implementation is being done on a DCS that has a common database platform.

Plan carefully and consider all the options!