By Teresa Hansen, Editor in Chief
For more than 100 years, most electricity in the developed world was generated at utility-owned central station power plants and sent to customers via transmission and distribution systems. This 100-year-old process is changing, however, as distributed energy resources like solar photovoltaic (PV) are added to the generation mix.
Distributed solar PV is important for developing a cleaner, more sustainable energy future, however, because it is available only when the sun shines, its addition to the grid creates challenges for distribution utilities. Experts and leaders from the electricity industry in the Western U.S., including utility CEOs, believe smart inverters are central to overcoming some of those challenges.
|University of California at San Diego (UCSD) has become a state leader in the deployment of solar power. A rooftop installation at UCSD’s Revelle College, pictured here, is one of the university’s many solar installations. Courtesy SDG&E.|
GTM Research, the research arm of Greentech Media, reported that in 2012 solar production accounted for 49 percent of all new electricity generation added in the U.S. In its “Distributed Solar Energy Generation” report, Navigant Research predicts that from 2013 to 2018, 220 GW of distributed solar PV will be installed worldwide. It credits feed-in-tariffs, commoditization of PV modules and innovative leasing programs for residential solar installations as the drivers of this growth. Navigant predicts that some countries could see triple digit growth over the next five years.
Navigant’s report said that as solar PV has become a commodity, the technology costs have steadily declined and will continue to do so. Navigant expects that by the end of the decade, solar PV will be cost competitive, without subsidies, with retail electricity prices in “a significant portion of the world.”
California is a part of the world where Navigant’s prediction likely will hold true. A July 2013 report from the California Public Utility Commission (CPUC) said that 1,629 MW of solar capacity has been installed at 167,878 customer sites in the service territories of the state’s three investor-owned utilities (IOUs)—Pacific Gas and Electric Co. (PG&E), Southern California Edison (SCE) and San Diego Gas & Electric (SDG&E). The CPUC also reported that a record 391 MW were installed statewide in 2012, which is a growth of 26 percent from 2011.
This tremendous growth began when the California Senate passed a bill in 2006, creating the California Solar Initiative (CSI). CSI combined the CPUC’s efforts to advance solar energy with then Governor Arnold Schwarzenegger’s million solar roofs vision. The CSI program budgeted $2.167 billion over 10 years with a goal of reaching 1,940 MW of installed solar capacity in California’s IOU’s service territories by the end of 2016. If installations continue at the current rate, the budgeted funds will be depleted and the capacity goal will be met long before the end of 2016. Many experts believe that depleted incentives will not impact solar’s growth in California. They believe solar energy will continue to be installed well beyond 2016, even without incentives.
Grid Challenges and Smart Inverters
|According to WEIL, smart inverters, like the one pictured here, are necessary to ensure grid reliability and safety for the region’s millions of customers.|
The addition of clean, sustainable solar energy aids California in meeting its clean energy goals. The CPUC claims that the 1,629 MW installed so far is enough to power approximately 150,000 homes and avoid building three new power plants. Integrating this intermittent energy into the grid is not problem free for the state’s distribution utilities, however.
In early August, the Western Electric Industry Leaders (WEIL) Group released a report detailing the immediate need for smart inverters to be required on all new solar energy installations. WEIL members, which include chief executive officers and executive leaders from IOUs, municipalities, government agencies, regional transmission operators and others in the western U.S. responsible for delivering electricity to wholesale and retail customers, are sending a letter to relevant state PUCs and legislators urging them to act on the issue of smart inverters. WEIL said the devices are necessary to ensure grid reliability and safety for the region’s millions of customers.
WEIL said in a press release that the inverters are key to seamlessly integrating solar energy into the grid without sacrificing reliability and power quality during unpredicted fluctuations. The devices, WEIL said, are a low-cost way to mitigate the voltage changes caused by the fluctuating solar generation, and thus prevent potential power quality problems. If smart inverters are not installed, voltage swings can potentially damage utility equipment and residents’ home appliances, increase grid maintenance costs, require installation of larger, more expensive alternatives and even contribute to distributed outages.
“As more and more solar generators are placed on the regional electric grid, we need to work together to smoothly bring these clean resources onto our system by fitting them with smart inverters to counter the voltage fluctuations that occur with these intermittent renewable resources,” Mike Niggli, president and chief operating officer of SDG&E and a member of WEIL, said in the press release.
San Diego Gas & Electric Challenges
Niggli knows as well as anyone how solar PV can impact the distribution grid. In an exclusive interview with POWERGRID International, Niggli and Mike Turner, principal engineer at SDG&E, talked about the addition of solar energy in SDG&E’s service territory.
“We’re currently adding about 800 systems per month,” Niggli said. “Last year that number was somewhere around 300 to 400 per month.”
The number has been increasing for the past two or three years and SDG&E expects it to continue for several years, he said.
The total number of solar installations in SDG&E’s service territory is around 26,000, or only 2 percent of SDG&E’s customer base. This small percentage, if evenly dispersed throughout the service territory, would be easy to integrate; however, it is not evenly dispersed and in many cases the installations are clustered into certain geographic areas.
“Because the systems are not spread out evenly, there are places on the grid where we are already experiencing problems,” Niggli said. “If the installations were spread out, the problems would be eliminated, or at least mitigated.
“When PV systems are operating at high capacity, parts of our distribution system are meeting or even exceeding voltage limits. When a cloud comes over, the voltage drops off quickly and dramatically, causing voltage fluctuations and problems. This problem will continue and get worse if smart inverters aren’t installed and required going forward,” he said.
The solar PV systems are clustered in certain areas due to economic reasons—higher socioeconomic areas have more PV—as well as geographical locations. Some locations in the service territory, especially along the coast, are less conducive to solar PV generation.
Germany has already experienced problems with voltage fluctuations and system reliability due to consumer PV systems. Germany’s government has ordered a mass retrofit of smart inverters on solar installations. WEIL has said this retrofit, which is already underway, will cost hundreds of millions of dollars.
SDG&E and WEIL are trying to be proactive and move the requirement for inverters forward before major problems occur, Niggli said.
They want to avoid a scenario similar to Germany’s. WEIL said the cost to consumers will be small—about $150 more than the current inverter that is used on a $12,000 PV installation.
WEIL identified smart inverter functionalities needed, which include:
- Communications capabilities,
- Real and reactive power support,
- Dynamic volt-amperes reactive injection,
- Expanded frequency trip point,
- Low-voltage ride through, and
- Randomization of timing for trip and reconnection.
Smart inverters with some of these features are already available in the United States, and they are commonly available and in use in Europe.
“Because smart inverters cost more, most installers don’t use them. But, if they become required, we’re confident manufacturers will make them available in the U.S. and installers will use them,” Niggli said. “In fact, some PV system inverters installed already have some of the functionality required of smart inverters, that functionality is just disabled.”
WEIL’s letter and report can be viewed at http://www.sdge.com/weil.
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