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Let the Sunshine In: Efficient Solar Power Management in the Grid

Aug 20, 2020
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The rapid growth of solar photovoltaic (PV) installations is a positive development for green energy providers, consumers, and investors. However, as more and more of these renewable energy resources, are integrated into existing power grids, grid operators must work closely with solar power plant operators to efficiently manage power resources. This way, they can balance power generation with demand to deliver the same reliable power they have provided in the past.

The Right Balance—Meeting Modern Power Demands

In many countries, renewable-energy power plants are facing increasingly stringent regulations. GreenPowerMonitor, a DNV GL company’s Global Head of Project Execution and Grid Integration, Luis Serrano explains, “In the past, plants could produce as much power as they wanted without being concerned about the amount they injected into the grid. But when renewable energy accounts for up to 20% of power generation, its effect on the grid becomes more noticeable.” As a result, grid operators now have new demands, such as needing to know how many renewable-energy plants are supplying power to the grid and how much power each one of them is capable of contributing.

Grid operators now enforce grid codes that the renewable-energy plant operators must agree and adhere to if they want to continue to supply power to the grid. In addition, these grid codes allow grid operators to remotely monitor the renewable-energy sources integrated into the grid and make adjustments when the supply and demand don't match.

A Greener Grid—Tools to Drive Efficient Solar Power Integration

As countries around the world are promoting power generation from renewable energy sources, the ability to monitor and control the amount of such power flowing into the grid has become a top priority. One solution is to deploy a power plant controller (PPC). When a PPC receives control commands on new set points from grid operators, it can quickly and accurately deliver the new set points to PV assets (e.g., inverters). This will enable the inverters to quickly switch to the new set points resulting in an adjustment in the amount of solar power integrated into the grid without requiring human intervention on site.

Under some grid codes, PPCs need to ensure speedy adjustment of set points, as fast as 200 ms. The speed at which power equipment can comply with new requirements is dependent on how quickly and reliably information on the new set points is delivered to the inverters. The two main challenges are: (1) Network disconnections that cause inverters to not receive the control commands (2) Limitations of traditional communication protocols than can cause delays in adjusting the set points. As a long-term partner of Moxa and a leading provider of solar PV monitoring and control systems, GreenPowerMonitor, a DNV GL company, has integrated its PPC with Moxa's network solutions to successfully solve these challenges in over 3GW solar power plants.

1. Ensuring On-time Delivery of New Set-point Information

To prevent data loss and ensure data caught within a potentially congested network always arrives at its destination on time, a backup network should be in place. When one network is unavailable, data can be transmitted via the backup, ensuring uninterrupted data flow. Moxa and GPM has developed a mechanism to prevent network disconnection and guarantee a 20-ms recovery time, which is faster than the 1,000-ms solutions available in the industry.

2. Ensuring Power Devices Implement the New Set Points Without Delay

Another consideration is how to ensure timely delivery of information on new set points to inverters so that they can adjust to the new requirements. Typically, in utility-scale solar plants that incorporate hundreds of inverters, most of the inverters are serial-based. Here the traditional Modbus polling cycle isn’t fast enough because it only allows communication with one inverter at a time and data transfers usually take about 100 ms. This means, if more than two inverters need to communicate, it will take longer than 200 ms. However, by leveraging edge computing and local control functions, communication can be decentralized and parallel communications enabled so that inverters can adjust their set points, as required by grid operators, in a timely manner.

In the past, the variability of the energy from renewable resources has prevented consistent power delivery. But now, grid operators can overcome this challenge by using PPCs installed at power plants and take advantage of the higher reliability of plant networks to remotely control grid-connected renewable energy resources. With this, Serrano observes, "Power plants can provide the same reliability they’ve always delivered—just greener.”

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