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Advanced Inverters Are Critical for a Smart Solar Solution

Solar energy has the potential to deliver cost savings, a healthier climate, and improved public health. While solar power holds great promise as a clean energy source, its use up to this point has been limited by shortcomings in the technology. But the technology is evolving, and new advances are making solar power “smart” enough to overcome those constraints, and turning solar power owners into grid contributors.

Overcoming Obstacles

Some of the issues with solar include the inability to adapt to minor disturbances, exchange electricity with the larger distribution system, or stagger the timing of restarting following a power outage to avoid contributing to another disturbance. According to a paper by the National Renewable Energy Laboratory (NREL), advanced inverters resolve these issues with the following capabilities: 

  • Ability to “ride through” minor disturbances to frequency or voltage. “These functions…direct the distributed system to stay online and respond accordingly to relatively short-term, minor events. In some cases, this function can actually help the grid to self-heal from a disturbance.”
  • Ability to inject or absorb electricity into or from the grid. “Inverters can [change] the level of real power output from the system…by controlling the rate at which real power is fed into the grid…or by injecting or absorbing reactive power into or from the grid.”
  • Ability to provide a “soft start” after power outages. “This technique avoids spikes in the active power being fed onto the grid as it returns to normal functioning, limiting the risk of triggering another grid disturbance.”

Connecting to the Grid

Otherwise known as “smart inverters,” this technology is so effective that it became required by the state of California in late 2017. Rule 21 ensures that inverters include features that contribute to the overall functioning of the grid. Industry experts agree that such measures will become increasingly common to bring the use of solar energy to its fullest potential.

According to Jennifer Runyon, writing for Renewable Energy World, the assumption is that smart inverters have “technology installed that will give utilities the ability to communicate with them, should they wish.” Further, “With communications protocols embedded in four-quadrant inverters, solar + battery systems could theoretically provide volt/var support and serve as both energy sinks and energy generators depending on what the grid needs moment by moment.”

Runyon quotes Chris Chen, Strategy Development Manager for San Diego Gas & Electric, who “sees a future in which all ratepayers have a greater awareness of the grid itself and each person with a grid connection…has a real stake in keeping the grid healthy.” According to Runyon, Chen states, “We’re engaging customers in their role and helping them recognize that everything they do — they turn a light on, they turn a light off, they put a battery in — everything they do impacts the grid.”  

Updating Legislation

Additional regulations to allow the use of advanced inverters have been suggested by industry experts. Benjamin Mow at NREL recommends three factors for decision makers to consider:

  • Requirements and compensation for grid stability services. That is, whether owners must contribute to frequency/voltage control, when they would do so, and whether they would be compensated for doing so.
  • Standards that allow for advanced inverter functionality. This factor concerns developing new ranges for grid frequency and voltage requirements as well as staggered ramping of PV systems following outages.
  • Alternative ownership structures. There is a possibility for alternative ownership arrangements such as utility-owned inverters.

Mow notes that Hawaii and Arizona are following the lead of California in weighing the costs and benefits of such legislation.

The next few years will likely see additional growth of a more complete smart solar solution with a continued focus on technology and legislation.

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